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




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Abstract: We discuss our radio Australia Telescope Compact Array and Australian LongBaseline Array and X-ray XMM-Newton monitoring observations of the unusualultraluminous supernova SN 1978K in NGC 1313 at ~25 years after the explosion.SN 1978K is a rare example of a Type IIn supernova that has remained brightenough to have long-term X-ray and radio observations. The observations probethe dense medium that was ejected by the progenitor star prior to itsexplosion; the star might have been a Luminous Blue Variable. The radio imagingshows that the source remains compact, but it may be marginally resolved. Theradio monitoring shows deviations from a smooth decay suggesting thatinhomogeneities are present in the radio emitting region. It appears that amajor change occurred in the mass-loss rate of the progenitor star shortlybefore the supernova event. The X-ray emission between 2000 and 2006 isconsistent with the radiation coming from two shocks. All the X-ray data can befit using the same model with no systematic evolution or short-termvariability but this has a surprising requirement: the X-ray emitting regionshave a very large abundance of helium. This would be consistent with the X-rayemitting shocks being located in a helium-rich layer that was ejected by theprogenitor star, or helium-rich material was ejected in the supernovaexplosion. The unusual properties of the supernova motivated a search for anassociated gamma-ray burst GRB. We show that SN 1978K was inside the ~4 sigmaerror box of GRB 771029. If this association is correct, the GRB wasexceptionally underluminous. However, the quality of the gamma-ray burstlocations at that time was poor, and this is likely just a chance alignment.



Autor: I. A. Smith, S. D. Ryder, M. Boettcher, S. J. Tingay, A. Stacy, M. Pakull, E. P. Liang

Fuente: https://arxiv.org/







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