Multiwavelength Monitoring of the Unusual Ultraluminous Supernova SN 1978K in NGC 1313 and the Search for an Associated Gamma-Ray Burst

Details Multiwavelength Monitoring of the Unusual Ultraluminous Supernova SN 1978K in NGC 1313 and the Search for an Associated Gamma-Ray Burst Multiwavelength Monitoring of the Unusual Ultraluminous Supernova SN 1978K in NGC 1313 and the Search for an Associated Gamma-Ray Burst

Nov 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007apj...669.1130s&link_type=abstract

The Astrophysical Journal, Volume 669, Issue 2, pp. 1130-1137.

Astronomy and Astrophysics

Astronomy

5

Galaxies: Individual: Ngc Number: Ngc 1313, Gamma Rays: Bursts, Ism: Supernova Remnants, Stars: Supernovae: Individual: Alphanumeric: Sn 1978K

Scientific paper

We discuss our radio (Australia Telescope Compact Array and Australian Long Baseline Array) and X-ray (XMM-Newton) monitoring observations of the unusual ultraluminous supernova SN 1978K in NGC 1313 at ~25 yr after the explosion. SN 1978K is a rare example of a Type IIn supernova that has remained bright enough to have long-term X-ray and radio observations. The observations probe the dense medium that was ejected by the progenitor star prior to its explosion; the star might have been a luminous blue variable. The radio imaging shows that the source remains compact, but it may be marginally resolved. The radio monitoring shows deviations from a smooth decay, suggesting that inhomogeneities are present in the radio-emitting region. It appears that a major change occurred in the mass-loss rate of the progenitor star shortly before the supernova event. The X-ray emission between 2000 and 2006 is consistent with the radiation coming from two shocks. All the X-ray data can be fit using the same model (with no systematic evolution or short-term variability), but this has a surprising requirement: the X-ray-emitting regions have a very large abundance of helium. This would be consistent with the X-ray-emitting shocks being located in a helium-rich layer that was ejected by the progenitor star, or helium-rich material was ejected in the supernova explosion. The unusual properties of the supernova motivated a search for an associated gamma-ray burst (GRB). We show that SN 1978K was inside the ~4 σ error box of GRB 771029. If this association is correct, the GRB was exceptionally underluminous. However, the quality of the gamma-ray burst locations at that time was poor, and this is likely just a chance alignment.

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