ASASSN-15nx: A Luminous Type II Supernova with a “Perfect” Linear Decline
Kochanek, C. S.
Andrews, Jennifer E.
Prieto, J. L.
Stanek, K. Z.
Shappee, B. J.
Milne, P. A.
Holoien, T. W.-S.
Kilpatrick, Charles D.
Madore, Barry F.
Rich, Jeffrey A.
AffiliationUniv Arizona, Steward Observ
MetadataShow full item record
PublisherIOP PUBLISHING LTD
CitationSubhash Bose et al 2018 ApJ 862 107
Rights© 2018. The American Astronomical Society. All rights reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at email@example.com.
AbstractWe 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 approximate to 260 day. In contrast, the light curves of hydrogen-rich supernovae (SNe II-P/L) always show breaks in their light curves at phase similar to 100 day, before settling onto Co-56 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 H alpha 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 Ni-56 (M-Ni = 1.6 +/- 0.2 M-circle dot) 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.
VersionFinal published version
SponsorsNSFC ; China Postdoctoral Science Foundation [2016M600848]; PRIN-INAF 2014 project "Transient Universe: Unveiling New Types of Stellar Explosions with PESSTO"; U.S. National Science Foundation (NSF) [AST-1515927, AST-1515876]; Ministry of Economy, Development, and Tourism's Millennium Science Initiative [IC120009]; CONICYT through FONDECYT grants [3150238, 1151445]; NSF [AST-1515927, AST-1312221, AST-1515559, AST-0908816, AST-9987045, AST-1108693]; University of Cadiz [PR2017-64]; Robert Martin Ayers Sciences Fund; "The Strategic Priority Research Program: the Emergence of Cosmological Structures" of the Chinese Academy of Sciences [11 XDB09000000]; Special Fund for Astronomy from the Ministry of Finance; Gordon and Betty Moore Foundation [GBMF5490]; Mt. Cuba Astronomical Foundation; Center for Cosmology and AstroParticle Physics at the Ohio State University; Chinese Academy of Sciences South America Center for Astronomy (CASSACA); Villum Foundation; Smithsonian Astrophysical Observatory; UK Science and Technology Facilities Council (STFC); NSF Telescope System Instrumentation Program (TSIP); Ohio Board of Regents; Ohio State University Office of Research