Late-time observations of SN2006gy: Still Going Strong

• Published in: arXiv.org 2008-07
• Main Authors: Smith, Nathan, Foley, Ryan J, Bloom, Joshua S, Li, Weidong, Filippenko, Alexei V, Gavazzi, Raphael, Ghez, Andrea, Quinn Konopacky, Malkan, Matthew A, Marshall, Phillip J, Treu, Tommaso, Jong-Hak Woo
• Format: Article
• Language: English
• Subjects: Dust; Luminosity; Near infrared radiation; Radio emission; Radioactive decay; Stability; Wavelengths
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.0802.1743

Owing to its extremely high luminosity and long duration, SN2006gy radiated more energy in visual light than any other known SN. Two hypotheses to explain its high luminosity -- that it was powered by shock interaction with CSM as implied by its Type IIn spectrum, or that it was fueled by radioactive decay from a large mass of 56Ni synthesized in a pair-instability SN -- predicted different late-time properties. Here we present observations of SN2006gy obtained more than a year after discovery. We were unable to detect it at visual wavelengths, but clear near-IR K and H-band detections show that it is still at least as luminous as the peak of a normal SN II. We also present spectra giving an upper limit to the late-time Ha luminosity of about 1e39 erg/s. Based on the weak late-time Ha, X-ray, and radio emission, combined with the difficulty of explaining the shift to IR wavelengths, we can rule out ongoing CSM interaction as the primary late-time power source. Instead, we propose that the evolution of SN2006gy is consistent with one of two possible scenarios: (1) A pair-instability SN plus modest CSM interaction, where the radioactive decay luminosity shifts to the IR because of dust formation. (2) An IR echo, where radiation emitted during peak luminosity heats a pre-existing dust shell at radii near 1 light year, requiring the progenitor star to have ejected another 10 Msun shell about 1500 yr before the SN.