Details

Autor(en) / Beteiligte

• Smith, I. A
• Ryder, S. D
• Böttcher, M
• Tingay, S. J
• Stacy, A
• Pakull, M
• Liang, E. P

Titel

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

Ist Teil von

• The Astrophysical journal, 2007-11, Vol.669 (2), p.1130-1137

Ort / Verlag

Chicago, IL: IOP Publishing

Erscheinungsjahr

2007

Quelle

EZB Free E-Journals

Beschreibungen/Notizen

• (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 similar to 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 similar to 4 sigma 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.