HEAD Division Meeting 1999, April 1999
Session 1. Gamma Ray Bursts
Oral, Monday, April 12, 1999, 8:30am-10:04am, Colonial Room

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[1.04] X-ray-Emitting Hypernova Remnants in M101: Relics of Gamma-Ray Bursts?

Q. Daniel Wang (Northwestern University)

Based on an ultra deep (230~ks) ROSAT HRI imaging of M101, we have detected 5 X-ray sources that coincide spatially with optical emission line features previously classified as supernova remnants in this nearby galaxy. 2 of these coincidences (SNR MF83 and NGC5471B) most likely represent the true physical association of X-ray emission with shock-heated interstellar gas. MF83, with a radius of ~ 134~pc, is one of the largest remnants known. NGC5471B, with a radius of 30~pc and a velocity of at least 350 {\rm~km~s-1} (FWZI), is extremely bright in both radio and optical. The X-ray luminosities of these two shell-like remnants are ~1 and 3 \times 1038 {\rm~ergs~s-1} (0.5-2~keV), about an order of magnitude brighter than the brightest supernova remnants known in our Galaxy and in Magellanic Clouds. The inferred blastwave energy is ~5 \times 1052~ergs for NGC5471B and ~5 \times 1053~ergs for MF83. Therefore, the remnants likely originate in hypernovae, which are \gtrsim 102 times more energetic than typical supernovae and are postulated as being responsible for \gamma-ray bursts observed at cosmological distances. The study of such hypernova remnants in nearby galaxies have the potential to provide important constraints on the progenitor type, rate, energetics, and beaming effect of \gamma-ray bursts.

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