A long life of excess: The interacting transient SN 2017hcc

A&A 669, A51 (2023) https://doi.org/10.1051/0004-6361/202244565 c The Authors 2023 Astronomy & Astrophysics A long life of excess: The interacting transient SN 2017hcc S. Moran1, M. Fraser2, R. Kotak1, A. Pastorello3, S. Benetti3, S. J. Brennan2, C. P. Gutiérrez1,4 , E. Kankare1, H. Kuncarayakti 1, S. Mattila1,5 , T. M. Reynolds1,6,7 , J. P. Anderson8, P. J. Brown9, S. Campana10 , K. C. Chambers11 , T.-W. Chen12, M. Della Valle13,14,15, M. Dennefeld16, N. Elias-Rosa3,17, L. Galbany17,18 , F. J. Galindo-Guil19 , M. Gromadzki20, D. Hiramatsu21,22,23 , C. Inserra24, G. Leloudas25 , T. E. Müller-Bravo17 , M. Nicholl26 , A. Reguitti27,28,3 , M. Shahbandeh29, S. J. Smartt30, L. Tartaglia3, and D. R. Young30 1Department of Physics and Astronomy, University of Turku, Vesilinnantie 5, 20500 Finland e-mail: [email protected] 2School of Physics, University College Dublin, Belfield, Dublin 4, Ireland 3INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy 4Finnish Centre for Astronomy with ESO (FINCA), University of Turku, 20014 Turku, Finland 5School of Sciences, European University Cyprus, Diogenes Street, Engomi, 1516 Nicosia, Cyprus 6Cosmic Dawn Center, DTU Space, Elektrovej 327, 2800 Kgs. Lyngby, Denmark 7Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 København N, Denmark 8European Southern Observatory, Alonso de Córdova, 3107 Casilla 19, Santiago, Chile 9George P. and Cynthia Woods Mitchell Institute for Fundamental Physics & Astronomy, Texas A. & M. University, Department of Physics and Astronomy, 4242 TAMU, College Station, TX 77843, USA 10 INAF – Osservatorio astronomico di Brera, Via Bianchi 46, 23807 Merate (LC), Italy 11 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA 12 The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 10691 Stockholm, Sweden 13 INAF – Capodimonte Astronomical Observatory, Salita Moiariello 16, 80131 Napoli, Italy 14 INFN – Napoli, Strada Comunale Cinthia, 80126 Napoli, Italy 15 ICRANet, Piazza della Repubblica 10, 65122 Pescara, Italy 16 Institut d’Astrophysique de Paris (IAP), CNRS & Sorbonne Université, 75014 Paris, France 17 Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Barcelona, Spain 18 Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain 19 Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Plaza San Juan 1, 44001 Teruel, Spain 20 Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland 21 Center for Astrophysics |Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138-1516, USA 22 Las Cumbres Observatory, 6740 Cortona Drive, Suite 102, Goleta, CA 93117-5575, USA 23 Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA 24 School of Physics and Astronomy, CardiffUniversity, Queens Buildings, The Parade, CardiffCF24 3AA, UK 25 DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, 2800 Kgs. Lyngby, Denmark 26 Birmingham Institute for Gravitational Wave Astronomy and School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK 27 Instituto de Astrofísica, Departamento de Ciencias Físicas – Universidad Andres Bello, Avda. República 252, 8320000 Santiago, Chile 28 Millennium Institute of Astrophysics, Nuncio Monsenor Sótero Sanz 100, Providencia 8320000, Santiago, Chile 29 Department of Physics, Florida State University, 77 Chieftan Way, Tallahassee, FL 32306, USA 30 Astrophysics Research Centre, School of Maths and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK Received 21 July 2022 /Accepted 22 October 2022 ABSTRACT In this study we present the results of a five-year follow-up campaign of the long-lived type IIn supernova SN 2017hcc, found in a spiral dwarf host of near-solar metallicity. The long rise time (57±2 days, ATLAS oband) and high luminosity (peaking at −20.78±0.01mag in the ATLAS oband) point towards an interaction of massive ejecta with massive and dense circumstellar material (CSM). The evolution of SN 2017hcc is slow, both spectroscopically and photometrically, reminiscent of the long-lived type IIn, SN 2010jl. An infrared (IR) excess was apparent soon after the peak, and blueshifts were noticeable in the Balmer lines starting from a few hundred days, but appeared to be fading by around +1200d. We posit that an IR light echo from pre-existing dust dominates at early times, with some possible condensation of new dust grains occurring at epochs &+800d. Key words. supernovae: general – supernovae: individual: SN 2017hcc – supernovae: individual: ATLAS17lsn – supernovae: individual: PS17fra Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This article is published in open access under the Subscribe-to-Open model.Subscribe to A&A to support open access publication. A51, page 1 of 22 A&A 669, A51 (2023) 1. Introduction Supernovae (SNe) are traditionally grouped into two types: type I (hydrogen-poor) and type II (hydrogen-rich; Minkowski 1941). There are subdivisions within both of these classes of SNe based on criteria such as spectral lines and light curve behaviour (Gal-Yam 2017). The type IIn designation was first introduced by Schlegel (1990) to describe SNe with narrow (FWHM .1000km s−1) hydrogen emission lines in their spectra. These narrow lines arise from dense circumstellar material ionised by an ongoing shock interaction (e.g., Chugai 1997). Most SNe IIn are expected to have progenitor stars with a high mass loss rate, providing the necessary circumstellar material (CSM) for later shock interactions post-explosion, and they have often been associated with luminous blue variable-like (LBVlike) stars (Kiewe et al. 2012;Smith 2017). Type IIn SNe are relatively rare, constituting about 9% of all core-collapse SNe in the local Universe (Li et al. 2011; Cappellaro et al. 2015); however, these estimates are uncertain, with Eldridge et al. (2013) finding a much lower rate of 2.4%, for example. Type IIn SNe show tremendous diversity in their light curves and spectra (e.g., Kiewe et al. 2012;Nyholm et al. 2020;Fraser 2020); this diversity likely reflects a large spread of CSM masses and density profiles, geometric configurations, wind velocities, chemical compositions, as well as properties of the progenitors and their environments. Some of the most extreme exemplars are characterised by long-lasting, slowly evolving light curves. SN 2010jl is an archetypal long-lived type IIn event, reaching an absolute magnitude of ∼−19.9mag in the Vband and remaining bright for several years (Stoll et al. 2011; Ofek et al. 2019). In this study we report on the long-lived, slowly evolving type IIn SN 2017hcc. As previously mentioned, SNe IIn are a heterogeneous group, so photometry and spectroscopy covering key epochs are a pre-requisite to deciphering the pre-explosion history of the progenitor. We present results from a comprehensive ultraviolet (UV) to mid-infrared (MIR) follow-up campaign conducted over a five year period. SN 2017hcc was discovered in the course of the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey (Tonry et al. 2018;Smith et al. 2020) on 2017 Oct. 2 (internal survey designation ATLAS17lsn, Tonry et al. 2017), and was classified by the All-Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014;Kochanek et al. 2017) as a type IIn SN (Dong et al. 2017). The SN is located at α= 00h03m50s.58, δ=−11◦2802800.78 J2000 (see Fig. 1). A number of surveys independently discovered SN 2017hcc. The Gaia Science Alerts (Hodgkin et al. 2021) project designated it Gaia17dcj; the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1; Huber et al. 2015) project called it PS17fra; and the Zwicky Transient Facility (ZTF; Bellm et al. 2019) called it ZTF18abtmgfn. Based on the measured wavelength of Hαin the +88d Nordic Optical Telescope (NOT) +ALFOSC gr17 spectrum, we adopted a heliocentric redshift of z=0.0168 ±0.0001 for SN 2017hcc, which is in line with the measurement obtained by Prieto et al. (2017). For a Hubble parameter of 70kms−1Mpc−1, taken as a compromise between inconsistent measured values (Freedman et al. 2019;Di Valentino et al. 2021), we calculated the luminosity distance to be 72.9±0.4 Mpc and the distance modulus to be µ=34.31 ±0.01mag. Unfortunately, there was no progenitor candidate observed for SN 2017hcc due to its distance. The explosion epoch has been set as MJD 58027.4 (2017 Oct. 1 09:36:00UTC, Sect. 3). 0h04m00s03m54s48s42s -11°26' 27' 28' 29' 30' 31' RA Dec N E 1' Fig. 1. SN 2017hcc (α=00h03m50s.58, δ=−11◦2802800.78 J2000), based on a Vband image taken with NOT+ALFOSC on 2018 Sept. 30 (+365d). The inset shows the region around the SN in more detail, with the faint nucleus of the host just visible to the west of the SN. All phases reported in this paper are with respect to this date. We take the foreground extinction towards SN 2017hcc to be AV=0.091 mag from Schlafly & Finkbeiner (2011, via the NASA Extragalactic Database, NED1), assuming an RVof 3.1 (Schultz & Wiemer 1975). The host galaxy of SN 2017hcc appears to be a dwarf spiral (Fig. 1). It has an apparent magnitude of rKron =17.8mag in the Pan-STARRS1 survey. For a distance of 72.9Mpc, this implies an absolute magnitude of −16.6 mag, taking Milky Way extinction into account, which is suggestive of a low mass host (Pskovskii 1965). The equivalent width of narrow sodium lines has frequently been used as a proxy for extinction (e.g., Poznanski et al. 2012). Whilst there are several concerns regarding the reliability of such methods (e.g., Poznanski et al. 2011), in the case of SN 2017hcc the presence of any significant sodium absorption in any of our spectra is unclear, which is at least qualitatively consistent with very little dust in the host line of sight. This is corroborated by Smith & Andrews (2020), who inferred an upper limit of E(B−V)=0.016 for the host extinction using echelle spectra. Additionally, the spectra of SN 2017hcc are quite blue when compared to other type IIn SNe, which gives a further indication of low extinction. As such, we regard extinction in the host galaxy to be negligible. The paper is organised as follows: in Sect. 2, we discuss the observational data acquisition and reduction. These data comprise ultraviolet, optical and near-infrared (NIR) imaging along with optical and NIR spectroscopy. The photometric and spectroscopic evolution is outlined in Sects. 3and 4, respectively. In Sect. 5we describe the calculation of the metallicity of the environment. Section 6contains a summary and our conclusions. All photometric data and logs of the optical and NIR spectroscopy are listed in tables in the appendix. We note that, alongside the previous works by Prieto et al. (2017), Kumar et al. (2019), and Smith & Andrews (2020), a detailed study by Chandra et al. (2022) concentrating on the X-ray, radio, and infrared (IR) 1http://ned.ipac.caltech.edu/ A51, page 2 of 22 S. Moran et al.: A long life of excess: The interacting transient SN 2017hcc properties of SN 2017hcc was posted to the arXiv preprint server whilst this work was under review. 2. Data acquisition and reduction 2.1. Optical imaging We have made use of optical imaging data from a number of telescopes and instruments for SN 2017hcc: the Las Cumbres Observatory (LCO) network of 1m telescopes, the NOT+ALFOSC, the Liverpool Telescope+IO:O, the 0.9 m Asiago Schmidt telescope+KAF-16803 CCD. We make use of observations taken in Sloan ugriz filters, as well as Johnson-Cousins Band V. In addition, photometry was obtained as part of routine operations of the ATLAS, Pan-STARRS1, and ASAS-SN surveys and the Gaia Alerts project. The Pan-STARRS1 imaging was taken in the wand ifilters, whilst for ATLAS cyan (c) and orange (o) filters were used, where cis comparable to g+rwhilst ois comparable to r+i. All Gaia photometry was taken in the Gaia G filter, a wide band filter that covers approximately g+r+i. The ASAS-SN photometry was taken in the Vand gfilters. Though there is ZTF photometry available for SN 2017hcc, we have not made use of it, since a template issue rendered the results unreliable. We reduced all optical images in a similar fashion. The images were bias and overscan subtracted before being flatfielded and trimmed. For the NOT+ALFOSC images, which were largely obtained via the NUTS and NUTS2 programmes2, and the Asiago images, we performed these steps with dedicated foscgui pipelines3for data reduction developed by E. Cappellaro. The data from the Liverpool Telescope were reduced automatically by the IO:O pipeline4, whilst the LCO data were reduced automatically by the banzai pipeline5. The ATLAS, ASAS-SN, and Pan-STARRS1 data were reduced automatically by their respective pipelines (Smith et al. 2020; Kochanek et al. 2017;Magnier et al. 2020) with Point-Spread Function (PSF) fitting being used to obtain photometry. From the start of the third observing season (&+600 d), the increasing contribution of the host galaxy became apparent. Since SN 2017hcc was still visible in our final observations, we were unable to obtain fresh SN-free template images in order to perform difference imaging, though shallow Pan-STARRS1 templates did exist for the field. As a result of this limitation, we used the autophot6code (Brennan & Fraser 2022) to measure the brightness of SN 2017hcc with PSF-fitting photometry. We calibrated the zeropoints for the Band Vbands against the APASS catalogue, whilst we calibrated those of the g,r,iand zbands against the Pan-STARRS1 catalogue. Full details of all optical photometric measurements determined with autophot are given in Table A.1. 2.2. Ultraviolet and X-ray imaging SN 2017hcc was also observed by the UltraViolet Optical Telescope (UVOT; Roming et al. 2005) on the Neil Gehrels Swift Observatory. Swift/UVOT data have been previously published by Prieto et al. (2017) and Kumar et al. (2019). We use photometry created by the pipeline for the Swift Optical Ultraviolet Supernova Archive (SOUSA; Brown et al. 2014), updated with 2https://nuts.sn.ie/ 3https://sngroup.oapd.inaf.it/foscgui.html 4https://telescope.livjm.ac.uk/TelInst/Pipelines/#ioo 5https://github.com/LCOGT/banzai 6https://github.com/Astro-Sean/autophot the zeropoints of Breeveld et al. (2010) and the updated sensitivity correction from CALDB 20200925. We did not perform host galaxy template subtraction. Full details of all Swift photometric measurements are given in Table A.2. Together with UVOT, Swift has a co-pointing X-ray instrument: the X-Ray Telescope (XRT, Burrows et al. 2005). We summed the 13 observations taken during the first 45 days, ending with 28.6ks of observing time. We do not detect any source at the location of SN 2017hcc. The 3σupper limit on the 0.3–10keV count rate is 8.4×10−4c s−1. Assuming a power law spectral model with a photon index Γ = 2 and a Galactic column density of 2.9×1020 cm−2(Willingale et al. 2013), one can translate this into an upper limit on the 0.3–10keV unabsorbed flux of <3.7×10−14 ergcm−2s−1, or on the X-ray luminosity of <2.5×1040 ergs−1. 2.3. Infrared imaging We used NOT+NOTCam, as part of the NUTS and NUTS2 programmes, and the New Technology Telescope (NTT) with the SOFI instrument for NIR imaging of SN 2017hcc, as part of the ePESSTO programme7(Smartt et al. 2015). We used the NOTCam QUICKLOOK8v2.5 reduction package, which is a set of IRAF scripts, with a few functional modifications (e.g., to increase the FOV of the reduced image), to reduce the NOTCam images. Bright and faint sky flats were taken and these were used to create a differential master flat. The flats were checked to make sure the count levels were linear. We masked out bad pixels (cold, hot, zero) during reduction and we used a model to account for the significant optical distortion of the NOTCam wide-field camera. We accounted for the dark current through the use of differential flats in the reduction process. For SOFI reductions, we used the pessto pipeline9 (Smartt et al. 2015). The raw frames were corrected for array crosstalk, and a sky image was created which was subtracted from the individual frames. The frames were flat-fielded with differential dome flats created by taking flats with the dome lamp on and off. An illumination correction was applied to account for the difference between sky and dome illumination patterns. The pipeline uses SExtractor to detect objects in the dithered images. The dithered images are aligned and combined using IRAF tasks based on a transformation between corresponding objects in the images. As in the case of the optical bands, we used the autophot code to measure the brightness of SN 2017hcc in NIR bands with PSF-fitting photometry. The zero points were calculated using the Two Micron All-Sky Survey (2MASS) catalogue10. As the 2MASS catalogue does not have Ks band photometry, we used the Kband measurements of the catalogue as a substitute. Full details of all NIR photometric measurements determined with autophot are given in Table A.3. TheW1 (3.4µm) andW2(4.6 µm)NEOWISE(Mainzer et al. 2011,2014) photometry was taken from the public NEOWISER Single Exposure (L1b) Source Table11 and can be found in Table A.4. We adopted the median value of the individual measurements at each observing visit as the magnitude after 7https://www.pessto.org/ 8http://www.not.iac.es/instruments/notcam/guide/ observe.html 9https://github.com/svalenti/pessto 10 https://irsa.ipac.caltech.edu/Missions/2mass.html 11 https://irsa.ipac.caltech.edu/cgi-bin/Gator/ nph-scan?mission=irsa&submit=Select&projshort=WISE A51, page 3 of 22 A&A 669, A51 (2023) removing data flagged as poor quality, or separated by more than 200 from the SN location. For the uncertainty, we adopted the standard error of mean of the individual measurements after 3 sigma-clipping outliers, with an additional uncertainty associated with the photometric calibration added in quadrature. We also include three epochs (393, 566, and 768 d) of Spitzer imaging at 3.6µm and 4.5 µm in our analysis, adopting the photometric measurements of Szalai et al. (2021). 2.4. Optical spectroscopy The bulk of the spectra were taken at the NOT using the ALFOSC instrument (23 out of the total of 52) as part of the NUTS and NUTS2 programmes, and at the NTT with the EFOSC2 instrument (13 of 52) as part of the ePESSTO and ePESSTO+programmes. Four spectra were taken at the Telescopio Nazionale Galileo (TNG) with the DOLORES instrument and two were taken at the Gran Telescopio Canarias (GTC) with the OSIRIS instrument. One was taken at the Very Large Telescope (VLT) using the Multi Unit Spectroscopic Explorer (MUSE) instrument. Two using the FLOYDS instrument at the FTS telescope as part of the LCO network of telescopes. One at the Asiago 1.82m telescope using the AFOSC instrument and five using the Asiago 1.22m and the B&C instrument. The complete log of optical spectral observations can be found in Table A.5. We reduced the NTT+EFOSC2 spectra using the pessto pipeline (Smartt et al. 2015). The raw two-dimensional spectra were overscan and bias subtracted, and divided by a normalised flat field before masking cosmic rays. The spectra were wavelength calibrated using an arc lamp to give the dispersion solution, together with an additional offset measured from bright sky emission lines in order to account for flexure within the instrument. Flux calibration was achieved using a master sensitivity function created from spectra of between three and seven spectro-photometric standard stars, observed at similar times to the science spectra. We combined gr11 and gr16 spectra taken on the same night into individual spectra using the scombine IRAF command. We reduced the NOT+ALFOSC, GTC+OSIRIS and TNG+DOLORES spectra in an analogous fashion. For the NOT+ALFOSC spectra, with the exception of the sole gr17 spectrum, we performed the reductions using the foscgui pipeline. In the case of the NOT+ALFOSC gr17 spectrum, the GTC+OSIRIS spectrum and the TNG+DOLORES spectra, we performed the reduction manually, using IRAF tasks. The DOLORES spectra have been shifted slightly (by a few Å) based on the position of the 6300.31Å skyline. We extracted the spectrum from already processed data cube taken with the MUSE instrument on VLT as part of the All-weather MUse Supernova Integral-field of Nearby Galaxies (AMUSING; Galbany et al. 2016). The extraction was performed using the qFitsView12 software package, by centring an annulus of radius one arc second on the location of SN 2017hcc. The FTS+FLOYDS spectra of which we make use were automatically reduced by the FLOYDS Pipeline13,14 at the LCO headquarters following the observation nights. 12 https://www.mpe.mpg.de/~ott/dpuser/qfitsview.html 13 https://github.com/griffin-h/floyds_pipeline 14 https://lco.global/documentation/data/ floyds-pipeline/ 2.5. Infrared spectroscopy Near-infrared spectra were taken with NTT+SOFI using an ABBA pattern of nodding along the slit. We reduced these data using the pessto pipeline (Smartt et al. 2015). The raw two-dimensional spectra were calibrated using an arc lamp and the frames were corrected for array crosstalk and flatfielded. Frames taken at position A were subtracted from those taken at position B (and vice-versa) to remove the varying sky background. Finally, the individual exposures were shifted and combined, before a one-dimensional spectrum was optimally extracted. A spectrum of a telluric standard was taken immediately after each science spectrum at a similar airmass, and this was used to correct for telluric absorption. The telluric standard was also used to achieve a flux calibration for each spectrum. We also obtained spectra from the NASA Infrared Telescope Facility (IRTF) using the SpeX instrument. These data were reduced using the IDL-based Spextool (Cushing et al. 2004) in an analogous fashion. The complete log of NIR spectral observations can be found in Table A.6. 3. Photometric evolution 3.1. Light curve and colour SN 2017hcc is an extremely long-lived SN, characterised by a slowly evolving and luminous light curve (see Fig. 2). The region of the sky where the SN exploded had been well-monitored by the ATLAS survey in the period immediately prior to the discovery epoch. Taking a midpoint between the first detection (MJD 58028.4, 17.44mag, ATLAS-o) and last non-detection (MJD 58026.4, ATLAS-o>19.04 mag)15, we estimate an explosion epoch of MJD 58027.4±1.0 for SN 2017hcc. SN 2017hcc has a slow rise to maximum, as can be seen in Fig. 2. To determine the peak of the light curve, we fitted a third order polynomial to the ATLAS oband light curve. We found the oband maximum to be at MJD 58084.1 at absolute magnitude −20.78±0.01 (apparent magnitude 13.53 ±0.01), which gives a rise time of 57±2 days. After maximum, the light curve begins a slow decline in the optical bands. In contrast to the optical, the UV light curve of SN 2017hcc declines from the first epoch in UVW2, and only shows a very small rise in UVW1. In season two (∼+230 to +460d), the Hand Ks light curves appear to flatten, with Ks perhaps even rising slightly and Jband behaving more similarly to the optical bands. At late times, from the third season onwards (&+600d), a further flattening in the light curve becomes evident, with a slight decline of about 0.1mag (100 d)−1in the Vband. We note here that at these later times there may be a significant host contribution to the photometry, that we are unable to remove given the poor depth of the available templates. However, the flattening is also evident in the Gaia light curve which is expected to be largely unaffected by background contamination, and so we regard it as a real effect. The decline rate is much slower than that expected from the decay of radioactive 56Co (0.98mag (100 d)−1,Miller et al. 2010), suggesting that circumstellar interaction remains the dominant mechanism powering the light curve. 15 The limiting magnitude determined by forced photometry on ATLAS images at the SN location is slightly deeper in the ATLAS-o (>19.69mag). We adopt the more conservative and shallower limit here, although either limit would imply an explosion epoch some time during the two day period between this epoch and discovery. A51, page 4 of 22 S. Moran et al.: A long life of excess: The interacting transient SN 2017hcc 0 250 500 750 1000 1250 1500 1750 Days from explosion in rest frame 5 10 15 20 25 Apparent magnitude 58000 58250 58500 58750 59000 59250 59500 59750 MJD ASAS-SN Asiago ATLAS Gaia LCO Liverpool ALFOSC Pan-STARRS TNG Swift NOTCam SOFI WISE Spitzer 30 25 20 15 10 Absolute magnitude w2 - 8 4.5 µm - 8 3.6 µm - 7.5 w1 - 7.5 Ks - 7 H - 6.5 J - 6 z - 5 i - 4 o - 2 w - 1 r + 0.5 G + 1.5 V + 3 c + 4 g + 5 B + 6 U + 9 UVW1 + 10 UVM2 + 11 UVW2 + 12 w2 - 8 4.5 µm - 8 3.6 µm - 7.5 w1 - 7.5 Ks - 7 H - 6.5 J - 6 z - 5 i - 4 o - 2 w - 1 r + 0.5 G + 1.5 V + 3 c + 4 g + 5 B + 6 U + 9 UVW1 + 10 UVM2 + 11 UVW2 + 12 Fig. 2. Full UV to MIR light curve of SN 2017hcc. The ATLAS points have been averaged to within 0.3 MJD. The ATLAS upper limits have been marked with inverted open triangles. A vertical line has been placed at the explosion epoch to guide the eye. We compare SN 2017hcc to the slowly evolving SNe IIn SN 2010jl (Stoll et al. 2011) and SN 2015da (Tartaglia et al. 2020), as well as to members of the class that are, at least initially, faster evolving, viz. SN 1998S (Fassia et al. 2000) and SN 2005ip (Stritzinger et al. 2012). These objects were chosen due to their diversity and their well-sampled data sets, however there are many other examples of comparable objects. The details of the comparison objects can be seen in Table A.7. Other long-lasting SNe IIn with long rise times include PTF12glz, HSC16aayt (SN 2016jiu), and SN 2015da. PTF12glz had a rise time of about 50days with photon diffusion through an aspherical CSM being offered as an explanation in that case (Soumagnac et al. 2019). HSC16aayt had an even slower rise, peaking at about −19.9mag after over 100days (Moriya et al. 2019). Similarly, SN 2015da had a rise time of 100 ±5days in the Rband, peaking at around −20.45±0.55 mag, and was observable for at least five years (Tartaglia et al. 2020). The peak rband magnitudes of our SN IIn comparison sample span the space from −18 to −21 mag and the light curves last a few hundred to over a thousand days (Fig. 3). A larger sample, such as that considered in Nyholm et al. (2020), shows that SN 2017hcc and SN 2010jl are exceptionally bright and long lived compared to more typical SNe IIn. Turning to the early colour evolution (Fig. 4), we see a reasonably steady transition towards the red for SN 2017hcc in the B−V,g−r,r−i, and V−Kscolours over the first observing season (the first ∼150days), consistent with the spectral evolution (Sect. 5). The B−Vevolution of SN 2005ip is not substantial, but SN 1998S behaves similarly to SN 2017hcc with its swift movement redwards. The B−Vevolution of SN 2015da is rather similar to that of SN 2017hcc, though it remains redder throughout. In g−rSN 2005ip and SN 2015da, like SN 2017hcc, are seen moving towards the red, though the shapes of the early evolution of SN 2005ip and SN 2015da differ from that of SN 2017hcc, with SN 2005ip quickly moving to a plateau before rising again and the evolution of SN 2015da being more gradual. The early evolution of SN 1998S in V−Ris very similar to that of SN 2017hcc in g−r. The early colour evolution of SN 2010jl contrasts with that of SN 2017hcc in that it steadily moves bluewards in r−i. Like SN 2017hcc in r−i, the SN 2015da and SN 1998S R−Icolours drift towards the red at early times before turning back towards the blue. SN 2017hcc has a strong shift towards the red in V−Ksin season one, but without any corresponding blueshifted spectral line evolution, which would often be seen in the case of dust formation in the ejecta. The V−Kscolour of SN 1998S has a similar redwards evolution to SN 2017hcc during the period corresponding to season one of the SN 2017hcc observations, but SN 2010jl is fairly flat at this time, as is SN 2015da. At early times SN 2015da is redder than SN 2017hcc in all colours and appears to evolve more slowly, though also in a redwards direction. The colour curves in season two (∼+230d to +460 d) are markedly different from those in the first season. Looking at the B−Vand g−rcolours (see Fig. 4), we see SN 2017hcc trending back towards the blue, though the scatter is large in the case of the B−Vcolour curve. SN 2015da has a similar trend towards the blue in B−Vduring an equivalent period, despite its consistently redder colour, but in g−rit is fairly A51, page 5 of 22 A&A 669, A51 (2023) 0 250 500 750 1000 1250 1500 1750 Days post discovery (rest frame) 21 20 19 18 17 16 15 14 Absolute magnitude SN 2017hcc (r) SN 2010jl (r) SN 2005ip (r) SN 2005ip (KAIT) SN 1998S (R) SN 2015da (r) Fig. 3. Comparison of the rband light curve of SN 2017hcc with that of SN 2010jl (Fransson et al. 2014) and SN 2005ip (Stritzinger et al. 2012), SN 2015da (Tartaglia et al. 2020) along with the Rband photometry of SN 1998S (Fassia et al. 2000). The open circles for SN 2005ip are unfiltered KAIT data (Smith et al. 2009), which are taken to be roughly equivalent to Rband. The error bars, where not visible, are smaller than the points. All light curves have been corrected for foreground extinction and time dilation. Phases are given against discovery date. Following (Tartaglia et al. 2020), we do not account for the host extinction of SN 2015da, but note that it could be significant (AR=2−3mag). stable at this time. The overall bluewards evolution of SN 2017hcc does not appear to be caused by an increase in photospheric temperature (see Fig. 5, and discussion of the bolometric light curve in Sect. 3.2). Rather, the colour evolution at this phase is likely due to changes in line emission which is affecting broadband photometry. In r−iit appears that SN 2017hcc remains at a roughly constant colour during the second season, whilst SN 2010jl and SN 2015da evolve towards the blue at equivalent times. Both SN 2010jl and SN 2015da show redwards evolution in V−Ksduring the period corresponding to the second season of SN 2017hcc. SN 2017hcc and SN 2015da appear to plateau in B−Vin season three (from ∼+600d to ∼+800 d), whilst SN 2010jl becomes bluer. In g−rSN 2017hcc shows a very slight trend towards the red with SN 2015da instead moving towards the blue, though it nevertheless remains far redder than SN 2017hcc. SN 2017hcc moves further redwards at this time in r−i, as does SN 2015da, whilst SN 2010jl instead continues on a trend of decreasing r−icolour. SN 2017hcc is also significantly further to the red in V−Ksin the third season than in the second, though later (∼+1000d) we see that there has been movement back towards the blue. The redwards evolution of SN 2017hcc, initially present in all bands, is only maintained in the colours containing redder bands as time goes on, reflecting the decreasing temperature of the continuum and the increasing prominence of the infrared black body component (Fig. 6). 3.2. Bolometric light curve We constructed both pseudo-bolometric and bolometric light curves (Fig. 7) using Superbol (Nicholl 2018), and including the following bands: UVW2, UVM2, UVW1 and UBgcVroizJHKs. We extrapolated and interpolated missing light curve data for a given filter assuming a constant colour relation with the nearest epochs; however, in the case of the Swift filters from Uto UVW2 we fitted a second order polynomial which we 0.0 0.5 1.0 1.5 B-V SN 2017hcc SN 1998S SN 2005ip SN 2010jl SN 2015da 0.0 0.5 1.0 1.5 2.0 2.5 g-r Days post explosion 2 1 0 1 r-i 0 250 500 750 1000 1250 1500 1750 Days post explosion 0 2 4 6 V-Ks Fig. 4. From top to bottom, B−V,g−r,r−i, and V−Kscolour curves for SN 2017hcc, compared to a selection of SNe IIn. The photometry has been averaged to one MJD (with errors added in quadrature), with colours then having been calculated with observations within one day of each other in the relevant bands, except in the case of the V−Ks observations where a larger window of seven days has been allowed, due to the paucity of observations. The errors bars, when not visible, are smaller than the points. Phases are given against discovery date, except in the case of SN 2017hcc, where the explosion epoch is used. No extinction corrections have been applied to the colours. In the second panel the SN 1998S data are actually V−Rrather than g−rand in the third panel both the SN 1998S data and the SN 2015da data are R−I rather than r−i. In the final panel the SN 2010jl and SN 1998S data are actually V−Krather than V−Ks. The dashed vertical lines mark the beginning of seasons one, two, three and four, five and six, respectively. used for the later evolution in season one (the first ∼150days), whilst we assumed that the colour was constant in the period before the first observations in those bands. We did not consider any contribution from the Uto UVW2 bands in later seasons (which were calculated separately), given the considerable A51, page 6 of 22 S. Moran et al.: A long life of excess: The interacting transient SN 2017hcc 4000 5000 6000 7000 8000 9000 10000 Rest frame wavelength (Å) Normalised F + constant +6d +32d +38d +44d +47d +56d +56d +63d +66d +69d +72d +80d +88d +89d +104d +230d +268d +272d +284d +295d +306d +310d +314d +330d +364d +381d +408d +429d +431d +453d +588d +619d +656d +666d +672d +687d +688d +777d +791d +1004d +1107d +1173d +1373d +1438d +1765d FLOYDS-FTS ALFOSC EFOSC2 B&C AFOSC MUSE OSIRIS DOLORES Balmer Series Na I D Ca II [Ca II] O I [O I] He I Telluric Fe II Fig. 5. Full sequence of optical spectra of SN 2017hcc, plotted in the SN rest frame. The wavelengths of some of the stronger SN lines are marked with coloured bands. The flux values for each spectrum have been normalised against the peak of Hα. A51, page 7 of 22 A&A 669, A51 (2023) 104 10 16 10 15 10 14 10 13 Phase: 45 d TBB 1: 12800 K RBB 1: 2.47e+15 cm 104 10 16 10 15 10 14 Phase: 92 d TBB 1: 9000 K RBB 1: 3.00e+15 cm TBB 2: 2500 K RBB 2: 1.96e+16 cm 104 10 17 10 16 Phase: 399 d TBB 1: 10600 K RBB 1: 4.22e+14 cm TBB 2: 1600 K RBB 2: 2.00e+16 cm 104 10 17 10 16 Phase: 773 d TBB 1: 10300 K RBB 1: 2.13e+14 cm TBB 2: 1200 K RBB 2: 2.77e+16 cm 104 Wavelength (Å) 10 18 10 17 Phase: 1020 d TBB 1: 9800 K RBB 1: 1.37e+14 cm TBB 2: 900 K RBB 2: 2.98e+16 cm Flux Density (erg s 1 cm 2 Å 1) Fig. 6. Black body fits to the spectral energy distribution. In the first two panels, representing early times, a single black body is sufficient to fit the SED, but in the final three panels, far later in the evolution of the SN, two black bodies are necessary. The rband data points were not included due to the influence of the strong Hαemission in this range. In each panel all points are from epochs within ten days of the listed phase, after interpolation. It should be noted that the second black body +92d SED fit had an upper limit of 2500K on the possible model temperatures and the model determined by the MCMC fitting is very close to this value. The horizontal bars on each point represent the bandwidths of the filters. The temperatures and radii of the black body fits used are given in each panel. This has been corrected for foreground extinction. drop-offin season one. After the initial peak there is a steady decline in the pseudo-bolometric light curve, as one would expect from the optical light curve. However, the temperature evolution panel in Fig. 7suggests an increase in temperature in the second season that begins a little after 200days post explosion, and which is matched by a faster decrease in the radius. Whilst this could potentially be explained by the CSM inter41.5 42.0 42.5 43.0 43.5 44.0 44.5 log 10 Lbol ( ergs 1) Observed flux Flux with BB correction SED black body 1 SED black body 2 2000 4000 6000 8000 10000 12000 14000 TBB ( K ) 0 100 200 300 400 500 Days post explosion (rest frame) 14.50 14.75 15.00 15.25 15.50 15.75 16.00 16.25 16.50 log 10 RBB ( cm ) Fig. 7. Plot of black body fit parameters. Top panel: Pseudo-bolometric light curve for SN 2017hcc, constructed from the UVW2, UVM2, UVW1, and UBgcVroizJHKs bands. In construction of the pseudobolometric light curve, we removed points obtained from Autophot with S/N<10. Middle panel: Corresponding temperature evolution of the black body. Bottom panel: Corresponding evolution of the black body radius. The cyan triangles and brown diamonds represent the black body fits shown in Fig. 6. action reheating the ejecta, this change does not appear to be reflected in the colour evolution, and it can be seen in Fig. 6 that a second black body becomes necessary to fit the spectral energy distribution (SED) at later times. It should be noted that the temperature of the first black body increases between +92 d and +399d. This can be explained by a forest of Fe ii lines, typical in SNe IIn, which affects the broadband photometry. We examined the SED evolution of SN 2017hcc over time by fitting it with black bodies (Fig. 6). At early times a single black body is sufficient to fit the SED. However, as time goes on, a clear IR excess becomes evident and a second black body is required to fit this component. We did not include the rband data in the SED, because the presence of the strong Hαemission within this wavelength range artificially boosts the flux, preventing the description of the SED with a black body. A51, page 8 of 22 S. Moran et al.: A long life of excess: The interacting transient SN 2017hcc SN 2005ip also displayed a growing IR excess with time, being fitted with two black bodies in Stritzinger et al. (2012) with the cooler black body becoming dominant by +100d. SN 2015da was another SN IIn showing such an excess; it required a second black body from +443d in order to reproduce the cooler component of the SED (Tartaglia et al. 2020). In order to explore the possible range of parameters that could generate the observed luminosity, we used the Pythonbased TigerFit16 code to fit models with a constant-density CSM shell to the bolometric light curve of SN 2017hcc. The TigerFit code makes use of semi-analytical light curve models described in Chatzopoulos et al. (2012,2013), Kasen & Bildsten (2010) and Dexter & Kasen (2013), based on the approaches outlined in Arnett (1980,1982). However, despite trialling models with an extremely broad range of parameters, we were unable to simultaneously describe the peak, early evolution and late evolution in a manner consistent with observations, suggesting more sophisticated modelling is required. 3.3. Infrared excess The development of an IR excess becomes evident from the V−Kscolour evolution soon after the peak (Fig. 4). We see that an IR excess is clearly apparent in the optical – IR SED by +92d from explosion. At this point we find it necessary to include a second black body component when fitting the SED (Fig. 6) and we estimate that the IR component contributes roughly 13% of the total luminosity obtained by summing the two black body components. By +399d the IR component is already very significant, contributing over 50% of the total luminosity and this increases to over 70% by +774d. We discuss this further in Sect. 6. There will naturally be a time delay between the arrival of optical photons which are emitted directly towards the Earth and those which are absorbed by dust and then re-emitted in the IR (Graham & Meikle 1986), however we do not expect the effect of this to be very significant given the very long time scale of our light curve, so we do not account for it. 4. Spectral evolution 4.1. Optical spectra The optical spectra of SN 2017hcc span a period of 1759 days (4.8yr): from six to 1765 d post-explosion (Fig. 5). The overall evolution is generally slow, in line with the photometric evolution. The spectra are initially characterised by a strong blue continuum and are dominated by strong Balmer emission, as is typical for a SN IIn. This can be seen clearly in our spectrum at +32d (Fig. 8), where the Hα, Hβ, and Hγlines are visible. Hα is well fitted by a single Lorentzian profile with a FWHM of 1170±20 kms−1. In addition, we see He iat λ5876 and λ7065 with a weak emission component and a P Cygni minimum at 4000km s−1. Fitting a black body to the +32d spectrum we find an effective temperature of 13.8±0.1 kK. However, this cools rapidly over the following week, dropping to 11.1 ±0.1kK at +38 d (we see a consistent trend in the evolution of the pseudo-bolometric light curve, see Sect. 3.2). The He iλ5876 emission also weakens, relatively, over the first two months. The Fe ii λ5018 line is apparent from at least the +32d spectrum in season one. 16 https://github.com/manolis07gr/TigerFit 3000 4000 5000 6000 7000 8000 9000 10000 Rest wavelength (Å) F (arbitrary units) Teff = 13840 K H H H He I 2500 0 2500 v (km s 1) Fig. 8. Early (+32d; 2017 Nov. 1) spectrum fitted with a black body. Identified emission lines are labelled, and an inset shows a zoom in on the Hαline in velocity space. In Fig. 9we show a medium-resolution (R∼5000) NOT+ALFOSC Gr#17 spectrum taken at +88d covering the Hα region. The spectrum clearly shows a narrow P Cygni absorption, indicative of absorption by slow moving optically thick CSM along the line of sight. In order to measure velocities of this feature, we fitted it with a four component model to describe the narrow and broad emission and the narrow absorption, as well as the continuum. The components were chosen purely due to their ability to reproduce the profiles seen in the data. These components are shown separately in Fig. 9, and the composite model does an excellent job of reproducing the observed Hαprofile, though there are a lot of parameters. The narrow Lorentzian has a FWHM of ∼63km s−1, whilst the P Cygni absorption has a minimum velocity of ∼−51kms−1with respect to the peak of the Lorentzian which we take as the pre-SN wind velocity of the progenitor. The FWHM of the broad Gaussian we fitted to the emission is ∼795km s−1. The aforementioned values have not been corrected for instrumental resolution and it is likely that the narrow emission feature that we fit with the narrow Lorentzian is not truly resolved. At approximately +120d, SN 2017hcc disappeared behind the Sun. When it re-emerged, at ∼+230d, the Hαemission had become broader, with a velocity of 1690±20 kms−1at ∼+270 d and the centre of the emission was clearly blueshifted with respect to the rest wavelength. The [Ca ii]λλ7291,7323 lines became visible in the +230d spectrum, with a velocity broadly similar to that of Hα. At some point between 104 and 230days post-explosion the Ca ii λλλ8498,8542,8662 triplet appears. The triplet grows in relative strength over the course of the next 200 days. The He iλ7065 line appears to have grown in relative prominence by +230d (the He iλ5876 line also appears to strengthen, but this is affected by blending with Na I D). It continues to be present throughout season two, though appears to weaken in relative prominence over the course of the season. After about +400d we see a pseudo-continuum beginning to form in the blue. Many emission lines, primarily iron, combine in raising the flux bluewards of about 5000Å. Similar behaviour has been seen in other SNe IIn (e.g., SN 1995N, Fransson et al. 2002; SN 2005ip, Stritzinger et al. 2012). We do not see a clear bluewards evolution in the B−Vcolours at late times, however there are relatively large uncertainties on our photometric A51, page 9 of 22 A&A 669, A51 (2023) 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogues from the survey area. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen’s University Belfast, the Space Telescope Science Institute, and the South African Astronomical Observatory. 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Optical photometry, apart from that of Swift. The Band Vfilters are in Vega magnitudes and the griz filters are in AB magnitudes. Date MJD Epoch B(err) V(err) g(err) r(err) i(err) z(err) Telescope (Instrument) (d) 2017-11-03 58060.9 33.5 13.85 (0.02) 13.75 (0.03) 14.04 (0.01) 13.81 (0.05) 14.05 (0.05) 14.34 (0.07) LT (IO:O) 2017-11-10 58067.0 39.6 - - - - - 14.30 (0.94) NOT (ALFOSC) 2017-11-14 58071.9 44.5 14.02 (0.05) 13.60 (0.03) 13.60 (0.06) 13.64 (0.04) 13.81 (0.05) 13.99 (0.04) LT (IO:O) 2017-11-16 58073.9 46.5 13.79 (0.06) 13.62 (0.04) 13.61 (0.03) 13.63 (0.04) 13.77 (0.05) 13.98 (0.06) LT (IO:O) 2017-11-17 58074.8 47.4 13.52 (0.09) 13.66 (0.08) 13.64 (0.06) 13.70 (0.07) 13.78 (0.05) - Asiago Schmidt (Moravian) 2017-11-18 58075.0 47.6 13.76 (0.03) 13.62 (0.06) 13.63 (0.05) 13.71 (0.04) 13.71 (0.05) 13.95 (0.05) NOT (ALFOSC) 2017-11-19 58076.9 49.5 - 13.60 (0.05) 13.60 (0.08) 13.56 (0.06) 13.82 (0.08) 13.95 (0.04) LT (IO:O) 2017-11-20 58077.9 50.5 13.85 (0.06) 13.63 (0.05) 13.63 (0.05) 12.46 (0.06) 13.72 (0.02) - NOT (ALFOSC) 2017-11-26 58083.8 56.4 13.80 (0.03) - - - - - Asiago Schmidt (Moravian) 2017-11-26 58083.9 56.5 - 13.65 (0.02) 13.64 (0.02) 13.64 (0.03) 13.74 (0.03) - Asiago Schmidt (Moravian) 2017-11-30 58087.9 60.5 13.91 (0.06) 13.67 (0.07) 13.70 (0.06) 13.68 (0.03) 13.66 (0.09) 13.87 (0.08) NOT (ALFOSC) 2017-12-03 58090.8 63.4 13.90 (0.04) 13.70 (0.05) 13.74 (0.03) 13.67 (0.03) 13.75 (0.03) - Asiago Schmidt (Moravian) 2017-12-05 58092.8 65.4 13.92 (0.03) 13.70 (0.03) 13.72 (0.02) 13.66 (0.02) 13.76 (0.03) - Asiago Schmidt (Moravian) 2017-12-07 58094.0 66.6 - - - 13.72 (0.02) 13.26 (0.01) - NOT (ALFOSC) 2017-12-09 58096.7 69.3 - 13.74 (0.03) 13.76 (0.02) 13.70 (0.02) 13.77 (0.03) - Asiago Schmidt (Moravian) 2017-12-09 58096.8 69.4 13.98 (0.03) - - - - - Asiago Schmidt (Moravian) 2017-12-18 58105.7 78.3 14.22 (0.06) - 13.97 (0.05) - - - Asiago Schmidt (Moravian) 2017-12-18 58105.8 78.4 - 13.90 (0.07) - 13.81 (0.06) 13.86 (0.05) - Asiago Schmidt (Moravian) 2017-12-23 58110.9 83.5 14.31 (0.03) 13.84 (0.13) 14.03 (0.04) 13.79 (0.03) 13.81 (0.07) 14.00 (0.07) NOT (ALFOSC) 2017-12-29 58116.8 89.4 14.52 (0.15) 13.99 (0.15) 14.24 (0.09) 13.98 (0.09) 13.88 (0.1) 14.12 (0.04) NOT (ALFOSC) 2018-01-10 58128.7 101.3 14.90 (0.06) 14.38 (0.05) 14.54 (0.05) 14.21 (0.05) 14.19 (0.05) - Asiago Schmidt (Moravian) 2018-01-12 58130.8 103.4 14.98 (0.13) 14.31 (0.15) 14.68 (0.06) 14.27 (0.04) 14.19 (0.02) 14.29 (0.04) NOT (ALFOSC) 2018-01-19 58137.8 110.4 - 14.49 (0.18) 14.79 (0.07) 14.39 (0.12) 14.40 (0.03) - NOT (ALFOSC) 2018-05-19 58257.4 230.0 15.84 (0.02) 16.16 (0.03) 16.26 (0.03) 15.54 (0.03) 15.99 (0.04) 15.50 (0.05) LCO (fl03) 2018-05-22 58260.4 233.0 16.78 (0.03) 16.22 (0.04) 16.29 (0.04) 15.58 (0.04) 16.05 (0.05) 15.52 (0.06) LCO (fl03) 2018-05-28 58266.1 238.7 16.82 (0.1) - - 15.61 (0.09) 16.11 (0.05) 15.50 (0.05) LCO (fl16) 2018-06-02 58271.4 244.0 16.84 (0.04) 16.31 (0.04) 16.41 (0.02) 15.68 (0.03) 16.18 (0.04) 15.64 (0.05) LCO (fl15) 2018-06-11 58280.1 252.7 16.91 (0.03) 16.33 (0.02) 16.46 (0.01) 15.68 (0.03) 16.13 (0.04) 15.76 (0.08) LCO (fl06) 2018-06-17 58286.3 258.9 16.92 (0.05) 16.21 (0.02) 16.54 (0.05) 15.70 (0.04) 16.17 (0.06) 15.71 (0.05) LCO (fl03) 2018-06-22 58291.3 263.9 16.99 (0.03) 16.42 (0.05) 16.55 (0.02) 15.82 (0.04) 16.26 (0.05) - LCO (fl15) 2018-06-27 58296.4 269.0 17.00 (0.05) 16.51 (0.05) 16.63 (0.04) 15.82 (0.04) 16.33 (0.06) - LCO (fl15) 2018-07-07 58306.1 278.7 17.08 (0.04) 16.61 (0.04) 16.73 (0.03) 15.90 (0.03) - - LCO (fl06) 2018-07-07 58306.2 278.8 - - - - 16.44 (0.05) - LCO (fl06) 2018-07-11 58310.3 282.9 17.17 (0.03) 16.65 (0.03) 16.73 (0.02) 15.92 (0.02) 16.47 (0.04) - LCO (fl03) 2018-07-14 58313.8 286.4 17.17 (0.02) 16.70 (0.03) 16.79 (0.02) 16.00 (0.03) 16.55 (0.06) - LCO (fl11) 2018-07-20 58319.8 292.4 17.20 (0.03) 16.75 (0.03) 16.83 (0.02) 16.05 (0.02) 16.58 (0.04) - LCO (fl12) 2018-07-22 58321.8 294.4 17.29 (0.04) 16.79 (0.04) 16.87 (0.02) 16.09 (0.03) 16.62 (0.05) - LCO (fl12) 2018-07-23 58322.6 295.2 17.19 (0.06) 16.77 (0.05) 16.89 (0.03) 16.08 (0.03) 16.61 (0.06) - LCO (fl12) 2018-07-25 58324.8 297.4 17.31 (0.03) 16.81 (0.03) 16.92 (0.02) 16.13 (0.02) 16.67 (0.05) - LCO (fl12) 2018-07-29 58328.7 301.3 17.35 (0.04) 16.86 (0.05) 16.95 (0.03) 16.19 (0.03) 16.69 (0.05) - LCO (fl12) 2018-08-04 58334.8 307.4 17.43 (0.03) 16.95 (0.04) 17.03 (0.03) 16.24 (0.03) 16.83 (0.06) - LCO (fl11) 2018-08-11 58341.3 313.9 17.50 (0.05) 17.04 (0.08) 17.10 (0.05) 16.35 (0.07) 17.03 (0.08) - LCO (fl03) 2018-08-18 58348.1 320.7 17.49 (0.04) 17.13 (0.04) 17.12 (0.03) 16.45 (0.03) 17.10 (0.04) - LCO (fl06) A51, page 17 of 22 A&A 669, A51 (2023) Table A.1. continued. Date MJD Epoch B(err) V(err) g(err) r(err) i(err) z(err) Telescope (Instrument) (d) 2018-08-21 58351.5 324.1 17.64 (0.04) 17.21 (0.05) 17.18 (0.03) 16.46 (0.03) 17.18 (0.04) - LCO (fl12) 2018-09-01 58362.3 334.9 17.83 (0.06) 17.39 (0.06) 17.35 (0.05) 16.61 (0.04) 17.37 (0.06) - LCO (fl03) 2018-09-14 58375.7 348.3 17.89 (0.03) 17.54 (0.04) 17.47 (0.03) 16.83 (0.03) 17.56 (0.04) - LCO (fl12) 2018-09-28 58389.8 362.4 18.02 (0.04) 17.63 (0.05) 17.63 (0.03) 17.02 (0.04) 17.69 (0.05) - LCO (fl16) 2018-10-01 58392.1 364.7 18.20 (0.04) 17.76 (0.05) 17.83 (0.05) 17.21 (0.06) 17.55 (0.05) 17.09 (0.04) NOT (ALFOSC) 2018-10-14 58405.9 378.5 18.17 (0.05) 17.88 (0.08) 17.80 (0.05) 17.19 (0.04) 17.87 (0.07) - LCO (fl16) 2018-10-15 58406.0 378.6 - - - - 17.89 (0.06) - LCO (fl16) 2018-10-26 58417.2 389.8 18.30 (0.12) 18.05 (0.09) 18.03 (0.06) 17.40 (0.04) 17.99 (0.08) - LCO (fa03) 2018-10-29 58420.2 392.8 - 17.90 (0.08) 17.83 (0.04) 17.33 (0.1) 16.84 (0.77) - LCO (fa03) 2018-10-31 58422.2 394.8 18.54 (0.1) 18.15 (0.08) 18.02 (0.04) 17.46 (0.04) 18.16 (0.06) - LCO (fa03) 2018-11-04 58426.0 398.6 18.38 (0.07) 18.06 (0.06) 18.03 (0.04) 17.49 (0.05) 18.13 (0.08) - LCO (fa15) 2018-11-05 58427.4 400.0 18.24 (0.31) 18.24 (0.24) 17.94 (0.15) 16.63 (0.09) 18.11 (0.59) - LCO (fl11) 2018-11-16 58438.8 411.4 18.44 (0.17) - - - - - LCO (fa06) 2018-11-16 58438.9 411.5 - 18.25 (0.17) 18.30 (0.13) 17.74 (0.09) 18.15 (0.18) - LCO (fa06) 2018-11-20 58442.9 415.5 18.74 (0.06) 18.37 (0.07) 18.36 (0.07) 17.96 (0.04) 18.32 (0.03) 17.67 (0.05) NOT (ALFOSC) 2018-11-21 58443.9 416.5 18.49 (0.11) 17.99 (0.09) 17.97 (0.06) 17.64 (0.05) 18.15 (0.09) - LCO (fa06) 2018-11-24 58446.1 418.7 18.69 (0.08) 18.40 (0.06) 18.29 (0.05) - - - LCO (fa03) 2018-11-24 58446.2 418.8 - - - 17.77 (0.05) 18.45 (0.07) - LCO (fa03) 2018-11-27 58449.5 422.1 18.50 (0.2) 18.30 (0.05) 18.32 (0.03) 17.87 (0.03) 18.49 (0.06) - LCO (fl12) 2018-12-10 58462.1 434.7 18.86 (0.03) 18.55 (0.05) 18.47 (0.03) 17.99 (0.03) 18.58 (0.07) - LCO (fa03) 2018-12-21 58473.1 445.7 18.97 (0.1) 18.50 (0.08) 18.55 (0.07) 18.03 (0.05) 18.62 (0.1) - LCO (fa05) 2018-12-28 58480.9 453.5 18.97 (0.07) 18.64 (0.07) 18.67 (0.06) 18.30 (0.07) 18.54 (0.09) 18.19 (0.1) NOT (ALFOSC) 2019-06-05 58639.4 612.0 19.71 (0.1) 19.67 (0.12) 19.50 (0.11) 19.31 (0.12) 19.76 (0.37) - LCO (fa03) 2019-06-13 58647.2 619.8 19.83 (0.25) 19.76 (0.28) - - - - NOT (ALFOSC) 2019-06-20 58654.2 626.8 20.08 (0.16) 19.87 (0.07) 19.86 (0.04) 19.72 (0.05) 19.97 (0.12) 19.74 (0.1) NOT (ALFOSC) 2019-06-22 58656.8 629.4 20.06 (0.18) 19.77 (0.17) 19.37 (0.16) 19.59 (0.16) 19.25 (0.31) - LCO (fa11) 2019-07-12 58676.4 649.0 19.90 (0.08) 19.44 (0.1) 19.49 (0.08) 19.28 (0.15) 16.62 (0.76) - LCO (fa05) 2019-07-21 58685.2 657.8 20.25 (0.1) 19.97 (0.06) 20.04 (0.08) 19.84 (0.05) 20.11 (0.13) 20.03 (0.1) NOT (ALFOSC) 2019-07-24 58688.8 661.4 19.95 (0.11) 19.67 (0.12) 19.92 (0.07) 19.75 (0.08) 20.14 (0.2) - LCO (fa12) 2019-08-04 58699.8 672.4 20.24 (0.06) 20.15 (0.07) 20.06 (0.05) 19.89 (0.07) 20.17 (0.15) - LCO (fa11) 2019-08-05 58700.1 672.7 20.17 (0.29) 19.66 (0.18) 19.90 (0.06) 19.74 (0.09) 19.94 (0.12) 20.05 (0.12) NOT (ALFOSC) 2019-08-13 58708.0 680.6 19.98 (0.19) 19.55 (0.19) 19.88 (0.12) 19.26 (0.11) 19.71 (0.13) 19.53 (0.19) NOT (ALFOSC) 2019-08-17 58712.1 684.7 20.29 (0.27) 19.89 (0.28) 20.04 (0.19) 19.78 (0.23) 20.14 (0.34) 20.39 (0.8) NOT (ALFOSC) 2019-08-20 58715.2 687.8 19.96 (0.17) 19.96 (0.13) 19.87 (0.12) 19.68 (0.15) 20.06 (0.18) 20.23 (0.33) NOT (ALFOSC) 2019-08-20 58715.4 688.0 20.32 (0.33) 20.04 (0.27) 20.09 (0.23) 19.68 (0.18) 20.09 (0.34) - LCO (fa05) 2019-09-02 58728.3 700.9 20.29 (0.06) 20.07 (0.07) 20.01 (0.06) - - - LCO (fa15) 2019-09-02 58728.4 701.0 - - - 19.98 (0.07) 20.4 (0.15) - LCO (fa15) 2019-09-09 58735.0 707.6 19.91 (0.17) 19.26 (0.09) 19.78 (0.11) 18.89 (0.1) 19.16 (0.11) 19.09 (0.17) NOT (ALFOSC) 2019-09-16 58742.0 714.6 20.37 (0.16) 20.25 (0.14) 20.17 (0.13) 20.01 (0.15) 20.10 (0.28) 20.58 (0.3) NOT (ALFOSC) 2019-09-17 58743.2 715.8 20.70 (0.55) - - - - - LCO (fa05) 2019-09-17 58743.3 715.9 20.38 (0.44) 20.02 (0.33) 19.83 (0.23) 20.05 (0.48) 21.17 (1.6) - LCO (fa05) 2019-09-28 58754.3 726.9 20.39 (0.1) 20.14 (0.11) 20.06 (0.07) 19.88 (0.09) 20.58 (0.2) - LCO (fa03) 2019-10-09 58765.0 737.6 20.14 (0.35) 19.93 (0.67) 20.57 (1.44) 19.69 (0.75) 19.45 (0.6) - LCO (fa15) A51, page 18 of 22 S. Moran et al.: A long life of excess: The interacting transient SN 2017hcc Table A.1. continued. Date MJD Epoch B(err) V(err) g(err) r(err) i(err) z(err) Telescope (Instrument) (d) 2019-10-20 58776.2 748.8 19.89 (0.1) 19.36 (0.1) 19.65 (0.11) 19.63 (0.13) - - LCO (fa15) 2019-10-20 58776.3 748.9 - - - - 19.65 (0.16) - LCO (fa15) 2019-10-31 58787.0 759.6 19.97 (0.1) - - - - - LCO (fa03) 2019-10-31 58787.1 759.7 - 19.82 (0.13) 19.92 (0.09) 20.02 (0.09) 20.22 (0.16) - LCO (fa03) 2019-11-04 58791.0 763.6 20.20 (0.15) 19.98 (0.15) 20.33 (0.06) 20.09 (0.09) 19.92 (0.13) 20.02 (0.24) NOT (ALFOSC) 2019-11-11 58798.1 770.7 20.12 (0.31) - - - - - LCO (fa03) 2019-11-11 58798.2 770.8 - 19.55 (0.2) 19.72 (0.18) 19.42 (0.16) 20.29 (0.35) - LCO (fa03) 2019-11-17 58804.9 777.5 20.27 (0.16) 20.12 (0.15) 20.29 (0.06) 19.82 (0.1) 20.15 (0.11) 20.26 (0.21) NOT (ALFOSC) 2019-11-23 58810.0 782.6 20.29 (0.92) - - - - - LCO (fa07) 2019-11-23 58810.1 782.7 20.10 (0.22) 19.41 (0.13) 19.68 (0.1) 19.11 (0.15) 20.01 (0.51) - LCO (fa07) 2019-12-01 58818.9 791.5 20.71 (0.06) 20.42 (0.03) 20.44 (0.07) 20.26 (0.08) 20.00 (0.65) 20.72 (0.14) NOT (ALFOSC) 2019-12-03 58820.8 793.4 20.20 (0.17) 19.81 (0.17) - - - - LCO (fa14) 2019-12-03 58820.9 793.5 - - 19.87 (0.15) 19.37 (0.13) 19.69 (0.19) - LCO (fa14) 2020-01-15 58863.8 836.4 20.79 (0.11) 20.54 (0.06) 20.58 (0.06) 20.32 (0.15) 20.43 (0.28) 20.87 (0.15) NOT (ALFOSC) 2020-06-22 59022.2 994.8 20.98 (0.04) 20.77 (0.06) 20.65 (0.13) 20.52 (0.15) 21.04 (0.11) 21.40 (0.27) NOT (ALFOSC) 2020-07-25 59055.1 1027.7 20.95 (0.07) 20.62 (0.07) - - - - NOT (ALFOSC) 2020-07-25 59055.2 1027.8 21.09 (0.07) 20.82 (0.05) 20.64 (0.12) 20.59 (0.09) 21.06 (0.09) 21.07 (0.2) NOT (ALFOSC) 2020-08-21 59082.0 1054.6 21.02 (0.15) 20.77 (0.08) 20.70 (0.09) 20.62 (0.16) 21.04 (0.13) 21.22 (0.24) NOT (ALFOSC) 2020-09-14 59106.0 1078.6 21.14 (0.05) - - - - - NOT (ALFOSC) 2020-09-14 59106.1 1078.7 21.15 (0.06) 20.90 (0.05) 20.73 (0.16) 20.53 (0.19) 21.07 (0.1) 21.34 (0.2) NOT (ALFOSC) 2021-01-18 59232.8 1205.4 - - 20.87 (0.11) 20.82 (0.1) 21.18 (0.14) 21.34 (0.25) NOT (ALFOSC) 2021-01-18 59232.9 1205.5 - - - - 21.22 (0.14) - NOT (ALFOSC) 2021-07-06 59401.2 1373.8 21.19 (0.15) 20.90 (0.21) 20.88 (0.21) 20.90 (0.23) 21.40 (0.22) 21.47 (0.29) LRS (LRS) 2021-10-11 59498.1 1470.7 21.3 (0.05) 20.89 (0.13) 20.95 (0.13) 20.88 (0.12) 21.32 (0.11) - NOT (ALFOSC) 2021-11-12 59530.9 1503.5 - - 21.14 (0.13) - - - NOT (ALFOSC) 2021-11-13 59531.0 1503.6 21.41 (0.18) 20.85 (0.18) - 21.01 (0.11) 21.26 (0.16) - NOT (ALFOSC) 2022-07-07 59767.2 1739.8 - - - 21.16 (0.04) - - NOT (ALFOSC) 2022-07-16 59776.2 1748.8 21.34 (0.27) 20.85 (0.24) 21.04 (0.2) - - - NOT (ALFOSC) 2022-08-23 59814.2 1786.8 21.41 (0.08) 20.92 (0.13) 21.18 (0.11) - 21.40 (0.15) - NOT (ALFOSC) 2022-09-22 59844.0 1816.6 - - - 20.99 (0.11) - - NOT (ALFOSC) 2022-10-20 59872.9 1845.5 21.20 (0.12) 20.86 (0.11) 21.03 (0.12) 20.89 (0.18) 21.33 (0.15) - NOT (ALFOSC) Table A.2. Swift photometry (Vega magnitudes). Date MJD Epoch UVW2 (err) UV M2 (err) UVW1 (err) U(err) B(err) V(err) (d) 2017-10-28 58054.4 27.0 12.48 (0.04) 12.32 (0.04) 12.40 (0.04) 12.70 (0.04) 13.97 (0.04) 13.93 (0.05) 2017-10-30 58056.1 28.7 12.52 (0.04) - 12.40 (0.04) 12.68 (0.04) 13.90 (0.04) - 2017-11-04 58061.0 33.6 12.59 (0.04) 12.39 (0.04) 12.41 (0.04) 12.58 (0.04) 13.80 (0.04) 13.78 (0.04) 2017-11-05 58062.5 35.1 - 12.42 (0.04) - - - - 2017-11-05 58062.8 35.4 12.62 (0.04) 12.41 (0.04) 12.43 (0.04) 12.58 (0.04) 13.77 (0.04) 13.72 (0.04) 2017-11-10 58067.7 40.3 12.78 (0.04) 12.54 (0.04) 12.52 (0.04) 12.60 (0.04) 13.75 (0.04) 13.69 (0.04) 2017-11-16 58073.5 46.1 12.97 (0.04) 12.78 (0.04) 12.67 (0.04) 12.66 (0.04) 13.75 (0.04) 13.65 (0.04) 2017-11-19 58076.6 49.2 13.12 (0.04) 12.89 (0.04) 12.78 (0.04) 12.69 (0.04) 13.73 (0.04) 13.60 (0.04) 2017-11-22 58079.6 52.2 13.27 (0.04) 13.03 (0.04) 12.89 (0.04) 12.72 (0.04) 13.78 (0.04) 13.62 (0.04) 2017-11-30 58087.6 60.2 13.76 (0.04) 13.49 (0.04) 13.29 (0.04) 12.94 (0.04) 13.82 (0.04) 13.65 (0.04) 2017-12-04 58091.6 64.2 14.02 (0.05) 13.75 (0.05) 13.48 (0.04) 13.10 (0.04) 13.93 (0.04) 13.72 (0.04) 2017-12-09 58096.1 68.7 14.33 (0.05) 14.05 (0.05) 13.74 (0.04) 13.24 (0.04) 13.98 (0.04) 13.71 (0.04) 2017-12-12 58099.3 71.9 14.55 (0.05) 14.27 (0.05) 13.89 (0.05) 13.38 (0.04) 14.04 (0.04) 13.75 (0.04) A51, page 19 of 22 A&A 669, A51 (2023) Table A.3. Near-infrared photometry. Date MJD Epoch J(err) H(err) Ks (err) Telescope (Instrument) (d) 2017-11-10 58067.2 39.8 13.08 (0.14) 13.06 (0.17) 12.69 (0.09) NTT (SOFI) 2017-11-26 58083.0 55.6 12.85 (0.25) 13.09 (0.14) 12.71 (0.4) NTT (SOFI) 2017-12-14 58101.1 73.7 12.95 (0.15) 13.05 (0.27) 12.33 (0.13) NTT (SOFI) 2018-01-03 58121.9 94.5 13.25 (0.13) 13.19 (0.12) - NOT (NOTCAM) 2018-01-06 58124.0 96.6 13.14 (0.16) 12.79 (0.24) 12.34 (0.15) NTT (SOFI) 2018-08-19 58349.2 321.8 15.55 (0.14) 14.83 (0.19) 13.90 (0.14) NTT (SOFI) 2018-09-04 58365.1 337.7 15.62 (0.23) 14.80 (0.25) 13.09 (0.14) NOT (NOTCAM) 2018-11-03 58425.9 398.5 16.19 (0.19) 15.03 (0.21) 13.89 (0.11) NOT (NOTCAM) 2019-07-22 58686.2 658.8 18.44 (0.18) - - NOT (NOTCAM) 2019-08-18 58713.1 685.7 18.56 (0.18) 16.90 (0.21) 15.23 (0.21) NOT (NOTCAM) 2019-10-05 58761.0 733.6 19.09 (0.24) 17.16 (0.26) 15.29 (0.15) NOT (NOTCAM) 2020-06-25 59025.2 997.8 20.18 (0.33) 18.65 (0.23) 16.76 (0.12) NOT (NOTCAM) 2020-07-17 59047.1 1019.7 20.61 (0.35) 18.78 (0.38) - NOT (NOTCAM) 2020-07-17 59047.2 1019.8 - - 16.85 (0.1) NOT (NOTCAM) 2020-12-16 59199.9 1172.5 - - 17.44 (0.14) NOT (NOTCAM) Table A.4. NEOWISE photometry. Date MJD Epoch W1 (err) W2 (err) (d) 2017-12-01 58088.7 61.3 12.814 (0.009) 12.688 (0.020) 2018-06-18 58287.0 259.6 13.744 (0.019) 12.720 (0.034) 2018-11-27 58449.4 422.0 13.020 (0.010) 12.436 (0.019) 2019-06-17 58651.2 623.8 13.362 (0.014) 12.584 (0.014) 2019-11-26 58813.4 786.0 13.742 (0.022) 12.697 (0.026) 2020-06-18 59018.4 991.0 14.230 (0.030) 13.10 (0.04) 2020-11-27 59180.6 1153.2 14.555 (0.023) 13.315 (0.032) 2021-06-17 59382.7 1355.3 14.93 (0.05) 13.72 (0.16) 2021-11-26 59544.9 1517.5 14.932 (0.015) 13.79 (0.04) A51, page 20 of 22 S. Moran et al.: A long life of excess: The interacting transient SN 2017hcc Table A.5. Log of optical spectroscopic observations of SN 2017hcc. Date MJD Epoch Exposure time Slit width Wavelength range Telescope (instrument, grism) (d) (s) (Å) 2017-10-07 58033.4 6 900 2.0" 5000-9500 FTS (FLOYDS, red/blue) 2017-11-01 58058.9 31.5 300 1.0" 3200-9600 NOT (ALFOSC, #4) 2017-11-09 58066.2 38.8 600 1.0" 3380-7520 NTT (EFOSC, Gr#11) 2017-11-09 58066.2 38.8 600 1.0" 6015-10320 NTT (EFOSC, Gr#16) 2017-11-27 58071.8 44.4 1800 250 µm 3300-7000 Asiago 1.22m (B&C, 300tr) 2017-11-17 58075.0 47.6 420 1.3" 3200-9600 NOT (ALFOSC, #4) 2017-11-27 58083.9 56.5 1800 200 µm 3300-7000 Asiago 1.22m (B&C, 300tr) 2017-11-27 58084.1 56.7 600 1.0" 3380-7520 NTT (EFOSC, Gr#11) 2017-11-27 58084.1 56.7 600 1.0" 6015-10320 NTT (EFOSC, Gr#16) 2017-12-04 58090.8 63.4 1800 200 µm 3300-7000 Asiago 1.22m (B&C, 300tr) 2017-12-06 58094.0 66.6 420 1.3" 3200-9600 NOT (ALFOSC, #4) 2017-12-11 58096.8 69.4 1800 200 µm 3300-7000 Asiago 1.22m (B&C, 300tr) 2017-12-13 58100.1 72.7 600 1.0" 3380-7520 NTT (EFOSC, Gr#11) 2017-12-13 58100.1 72.7 600 1.0" 6015-10320 NTT (EFOSC, Gr#16) 2017-12-21 58107.7 80.3 1200 250 µm 3300-7000 Asiago 1.22m (B&C, 300tr) 2017-12-28 58115.9 88.5 600 0.9" 6330-6870 NOT (ALFOSC, #17) 2017-12-29 58116.8 89.4 420 1.0" 3200-9600 NOT (ALFOSC, #4) 2018-01-14 58132.0 104.6 600 1.0" 3380-7520 NTT (EFOSC, Gr#11) 2018-01-14 58132.1 104.7 600 1.0" 6015-10320 NTT (EFOSC, Gr#16) 2018-05-20 58258.4 231.0 900 1.0" 3380-7520 NTT (EFOSC, Gr#11) 2018-05-20 58258.4 231.0 900 1.0" 6015-10320 NTT (EFOSC, Gr#16) 2018-06-27 58296.2 268.8 900 1.0" 3200-9600 NOT (ALFOSC, #4) 2018-06-30 58299.3 271.9 1500 1.0" 3380-7520 NTT (EFOSC, Gr#11) 2018-06-30 58299.3 271.9 1500 1.0" 6015-10320 NTT (EFOSC, Gr#16) 2018-07-13 58312.2 284.8 900 1.3" 3200-9600 NOT (ALFOSC, #4) 2018-07-24 58323.1 295.7 900 1.0" 3200-9600 NOT (ALFOSC, #4) 2018-08-04 58334.2 306.8 1200 1.0" 3200-9600 NOT (ALFOSC, #4) 2018-08-08 58338.2 310.8 1200 1.3" 3200-9600 NOT (ALFOSC, #4) 2018-08-11 58341.1 313.7 1800 1.69" 3300-9300 Asiago 1.82m (AFOSC, VPH6+VPH7) 2018-08-27 58357.1 329.7 1200 1.0" 3200-9600 NOT (ALFOSC, #4) 2018-10-01 58392.1 364.7 2000 1.0" 3200-9600 NOT (ALFOSC, #4) 2018-10-18 58409.0 381.6 1900 1.0" 3200-9600 NOT (ALFOSC, #4) 2018-11-13 58436.0 408.6 2400 1.0" 3200-9600 NOT (ALFOSC, #4) 2018-12-04 58456.5 429.1 3600 2.0" 5400-10000 FTS (FLOYDS, red) 2018-12-06 58459.0 431.6 2400 1.3" 3200-9600 NOT (ALFOSC, #4) 2018-12-28 58480.9 453.5 2400 1.3" 3200-9600 NOT (ALFOSC, #4) 2019-05-13 58616.4 589.0 3600 1.0" 3380-7520 NTT (EFOSC, Gr#11) 2019-05-14 58617.4 590.0 3600 1.0" 6015-10320 NTT (EFOSC, Gr#16) 2019-06-13 58647.2 619.8 3600 1.0" 3200-9600 NOT (ALFOSC, #4) 2019-07-20 58684.1 656.7 3600 1.0" 3200-9600 NOT (ALFOSC, #4) 2019-07-28 58692.2 664.8 2373 - 4700-9400 VLT (MUSE, -) 2019-07-30 58694.2 666.8 3380 1.0" 3200-9600 NOT (ALFOSC, #4) 2019-08-05 58700.2 672.8 3000 1.0" 3200-9600 NOT (ALFOSC, #4) 2019-08-20 58715.2 687.8 3600 1.3" 3200-9600 NOT (ALFOSC, #4) 2019-11-17 58804.9 777.5 3600 1.3" 3200-9600 NOT (ALFOSC, #4) 2019-12-01 58819.0 791.6 3600 1.0" 3200-9600 NOT (ALFOSC, #4) 2020-07-02 59032.2 1004.8 1500x2 1.0" 3630-7500 GTC (OSIRIS, R1000B) 2020-10-12 59125.0 1107.6 1432, 1800 1.5" 3000-8430 TNG (DOLORES, LR-B) 2020-12-17 59200.8 1173.4 1800x2 1.5" 3000-8430 TNG (DOLORES, LR-B) 2021-07-06 59401.1 1373.7 1800x2 1.5" 3000-8430 TNG (DOLORES, LR-B) 2021-09-09 59466.0 1438.6 1800x2 1.0" 3000-8430 TNG (DOLORES, LR-B) 2022-08-01 59792.2 1764.8 1800x2 1.0" 5100-10000 GTC (OSIRIS, R1000R) A51, page 21 of 22 A&A 669, A51 (2023) Table A.6. Log of NIR spectroscopic observations of SN 2017hcc. Date MJD Epoch Exposure time Slit width Wavelength range Telescope (instrument, grism) (d) (s) (µm) 2017-11-10 58067.2 39.8 960 1.0" 0.95-1.64 NTT (SOFI, GB) 2017-11-10 58067.2 39.8 1500 1.0" 1.53-2.52 NTT (SOFI, GR) 2017-11-26 58083.1 55.7 2880 1.0" 0.95-1.64 NTT (SOFI, GB) 2017-11-26 58083.1 55.7 4500 1.0" 1.53-2.52 NTT (SOFI, GR) 2017-12-11 58098.2 70.8 4191 0.5" 0.8–2.4 IRTF (SpeX, ShortXD) 2017-12-14 58101.0 73.6 960 1.0" 0.95-1.64 NTT (SOFI, GB) 2017-12-14 58101.1 73.7 1500 1.0" 1.53-2.52 NTT (SOFI, GR) 2018-09-06 58367.3 339.9 719 0.5" 0.7–2.5 IRTF (SpeX, Prism) Table A.7. Comparison objects. Name Right ascension Declination Redshift Source(s) SN 2010jl 09:42:53.330 +09:29:41.78 0.0107 Stoll et al. 2011;Patat et al. 2011;Smith et al. 2011;Andrews et al. 2011;Zhang et al. 2012;Ofek et al. 2014;Fransson et al. 2014; Borish et al. 2015;Jencson et al. 2016;Li et al. 2022;Sarangi et al. 2018;Chugai 2018; Ofek et al. 2019;Bevan et al. 2020 SN 1998S 11:46:06.180 +47:28:55.49 0.0030 Leonard et al. 2000;Fassia et al. 2000,2001; Pozzo et al. 2004;Fransson et al. 2005 SN 2005ip 09:32:06.420 +08:26:44.41 0.0072 Smith et al. 2009;Stritzinger et al. 2012 SN 2015da 13:52:24.110 +39:41:28.60 0.0067 Tartaglia et al. 2020 HSC16aayt (SN 2016jiu) 10:02:05.570 +02:57:58.30 0.6814 Moriya et al. 2019 PTF12glz 15:54:53.040 +03:32:07.50 0.0799 Soumagnac et al. 2019 A51, page 22 of 22