Peremennye Zvezdy (Variable Stars) 45, No. 7, 2025 Received 24 February; accepted 6 March.	Article in PDF
	DOI: 10.24412/2221-0474-2025-45-77-81

MASTER OT J095321.02+202721.2: Luminous Type II-L Supernova

D. Yu. Tsvetkov, V. M. Lipunov, P. V. Balanutsa, A. S. Kuznetsov

M.V.Lomonosov Moscow State University, Sternberg Astronomical Institute, Universitetskii pr.13, 119234 Moscow, Russia

Modern wide-field sky surveys discover many transients, and a significant part of them remain unclassified. Most of the unclassified transients are fainter than , but sometimes, even much brighter objects remain unexplored. One of them is MASTER OT J095321.02+202721.2 (an abbreviated designation Mast953 is used hereafter). It was discovered by the MASTER-Kislovodsk auto-detection system at (J2000), on 2014-10-08.05230 UT, its unfiltered magnitude was . The object was located West and North of the center of the galaxy 2MASX J09532220+2026551 at (Balanutsa et al. 2014). The transient was also detected by Catalina Sky Survey (CSS) and designated CSS 141025:095321+202721¹.

Our photometric observations were performed by MASTER telescopes at Kislovodsk and Tunka sites (Lipunov et al. 2010) and at the 60-cm telescope of the Crimean Astronomical Station of Sternberg Astronomical Institute (SAI CAS), Lomonosov Moscow University. The standard image reductions and photometry were made using IRAF². Photometric measurements of the SN were made relative to local standard stars using PSF fitting with the IRAF DAOPHOT package.

The image of SN Mast953 and comparison stars is shown in Fig. 1. The stars were calibrated using Gaia synthetic photometry³. The SN is located in an area with low surface brightness, and subtraction of galaxy background is not necessary.

The results of photometry are reported in Table 1, and the light curves are shown in Fig. 2. In the Table, the uncertainties are presented in parentheses, the telescope codes are: M40, 40-cm MASTER telescopes; C60, the 60-cm telescope of the SAI CAS. Unfiltered MASTER images were calibrated with -band magnitudes of the comparison stars. We also plot the data retrieved from the CSS site, they agree quite well with our -band magnitudes. There are no observations on the rising branch of the light curve, and the maximum cannot be determined reliably.

The brightness in the  band decreased nearly linearly during days after discovery, with a rate mag/day. The decline rate slowed down at about JD2457025, and after this date, it was about 0.009 mag/day, which is close to the rate expected from the radioactive decay of Co to Fe. The photometric evolution is typical of SNe II-L.

This is confirmed by comparison of the light curve of SN Mast953 in absolute -band magnitudes to those for four type II-L SNe: 1979C, 1980K, 1998S and 2016gsd (Balinskaia et al. 1980; Buta 1982; Fassia et al. 2000; Reynolds et al. 2020), which is shown in Fig. 3. The distance to SN Mast953 was estimated from the galaxy's redshift, using  km s Mpc; the distance modulus is . We corrected the magnitudes for small Galactic extinction ⁴. The location of SN Mast953 in the host galaxy allows us to assume that host extinction is negligible. The distances and extinctions for the SNe from comparison sample were taken from the papers cited above.

The absolute magnitude of SN Mast953 at discovery is about , and it may be even brighter because the maximum could not be determined reliably. This value is high even for type II-L SNe, for which the mean absolute magnitude was estimated by Richardson et al. (2014): . Type II SNe have quite blue colors near maximum, for example, for SN 1998S the color was (Fassia et al. 2000), so the mean is close to mean , and SN Mast953 is at least about brighter than an average SN II-L.

The light curves presented in Fig. 3 are similar in shape and luminosity, SN 1998S appears to be the best match for SN Mast953. We conclude that this comparison permits a definite classification of SN Mast953 as type II-L SN with a very high luminosity at maximum.

Acknowledgements

The study was conducted under the state assignment of Lomonosov Moscow State University.

References:

Balanutsa, P., Denisenko, D., Lipunov, V., et al. 2014, Astronomer's Telegram, No. 6554

Balinskaia, I. S., Bychkov, K. V., & Neizvestnyi, S.I. 1980, Astron. & Astrophys., 85, No. 3, L19

Buta, R.J. 1982, Publ. Astron. Soc. Pacific, 94, 578

Fassia, A., Meikle, W. P. S., Vacca, W. D., et al. 2000, Monthly Notices Roy. Astron. Soc., 318, No. 4, 1093

Lipunov, V., Kornilov, V., Gorbovskoy, E., et al. 2010, Advances in Astronomy, article id. 349171

Reynolds, T. M., Fraser, M., Mattila, S., et al. 2020, Monthly Notices Roy. Astron. Soc., 493, No. 2, 1761

Richardson, D., Jenkins, R. L., Wright, J., Maddox, L. 2014, Astron. J., 147, article id. 118

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