NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-08-20 T07:27:58 PDT
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For refcode 2018ApJ...862..107B:
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2018ApJ...862..107B ASASSN-15nx: A Luminous Type II Supernova with a "Perfect" Linear Decline Bose, Subhash; Dong, Subo; Kochanek, C. S.; Pastorello, Andrea; Katz, Boaz; Bersier, David; Andrews, Jennifer E.; Prieto, J. L.; Stanek, K. Z.; Shappee, B. J.; Smith, Nathan; Kollmeier, Juna; Benetti, Stefano; Cappellaro, E.; Chen, Ping; Elias-Rosa, N.; Milne, Peter; Morales-Garoffolo, Antonia; Tartaglia, Leonardo; Tomasella, L.; Bilinski, Christopher; Brimacombe, Joseph; Frank, Stephan; Holoien, T. W.-S.; Kilpatrick, Charles D.; Kiyota, Seiichiro; Madore, Barry F.; Rich, Jeffrey A. Abstract. We report a luminous Type II supernova, ASASSN-15nx, with a peak luminosity of {M}_V_=-20 mag that is between those of typical core-collapse supernovae and super-luminous supernovae. The post-peak optical light curves show a long, linear decline with a steep slope of 2.5 mag (100 day)^-1^ (i.e., an exponential decline in flux) through the end of observations at phase ~ 260 {day}. In contrast, the light curves of hydrogen-rich supernovae (SNe II-P/L) always show breaks in their light curves at phase ~100 day, before settling onto ^56^Co radioactive decay tails with a decline rate of about 1 mag (100 day)^-1^. The spectra of ASASSN-15nx do not exhibit the narrow emission-line features characteristic of Type IIn SNe, which can have a wide variety of light-curve shapes usually attributed to strong interactions with a dense circumstellar medium (CSM). ASASSN-15nx has a number of spectroscopic peculiarities, including a relatively weak and triangular-shaped Halpha emission profile with no absorption component. The physical origin of these peculiarities is unclear, but the long and linear post-peak light curve without a break suggests a single dominant powering mechanism. Decay of a large amount of {}^56^{Ni} (M_Ni_ = 1.6 +/- 0.2 {M}_sun_) can power the light curve of ASASSN-15nx, and the steep light-curve slope requires substantial gamma-ray escape from the ejecta, which is possible given a low-mass hydrogen envelope for the progenitor. Another possibility is strong CSM interactions powering the light curve, but the CSM needs to be sculpted to produce the unique light-curve shape and avoid producing SN IIn-like narrow emission lines. Key words: supernovae: general, supernovae: individual: ASASSN-15nx
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