Gamma-Ray Bursts and Type I{bold c} Supernova SN 1998{bold bw}
- Lick Observatory, University of California Observatories, Santa Cruz, CA 95064 Lawrence Livermore National Laboratory, Livermore CA, 94550 (United States)
- Mount Stromlo and Siding Spring Observatories, Australian National University (Australia)
Recently a Type Ic supernova, SN 1998bw, was discovered coincident with a gamma-ray burst, GRB 980425. The supernova had unusual radio, optical, and spectroscopic properties. Among other things, it was especially bright for a Type Ic both optically and in the radio, and it rose quickly to maximum. We explore here models based upon helium stars in the range 9{endash}14 {ital M}{sub {circle_dot}} and carbon-oxygen stars 6{endash}11 {ital M}{sub {circle_dot}}, which experience unusually energetic explosions (kinetic energy 0.5{endash}2.8{times}10{sup 52} ergs). Bolometric light curves and multiband photometry are calculated and compared favorably with observations. No spectroscopic data are available at this time, but both LTE and non-LTE spectra are calculated for the model that agrees best with the light curve, a carbon-oxygen core of 6 {ital M}{sub {circle_dot}} exploded with a kinetic energy of 2.2{times}10{sup 52} ergs. We also examine potential mechanisms for producing the observed gamma-ray burst (GRB){emdash}shock breakout and relativistic shock deceleration in circumstellar material. {ital For spherically symmetric models}, both fail to produce a GRB of even the low luminosity inferred for GRB 980425. However, the high explosion energies required to understand the supernova are in contrast to what is expected for such massive stars and indicate that a new sort of explosion may have been identified, possibly the consequence of a collapsar. Indeed a more likely explanation for what was seen is a highly asymmetric explosion in which the GRB was produced by mildly relativistic matter ({Gamma}{approx}5) running into circumstellar matter along the line of sight to the Earth. The explosion itself was powered by black hole accretion and jets, but unlike {open_quotes}ordinary{close_quotes} gamma-ray bursts, the jets were not of sufficient energy and duration to effectively reach large values of {Gamma}. They may also not have been oriented in our direction. The ejected mass (but not the {sup 56}Ni mass) and explosion energy are then smaller. Other associations between luminous Type Ic supernovae and GRBs may exist and should be sought, but most Type Ib and Type Ic supernovae do not make GRBs. {copyright} {ital {copyright} 1999.} {ital The American Astronomical Society}
- OSTI ID:
- 365873
- Journal Information:
- Astrophysical Journal, Vol. 516, Issue 2; Other Information: PBD: May 1999
- Country of Publication:
- United States
- Language:
- English
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