RADIO EMISSION FROM SUPERNOVAE AND GAMMA-RAY BURSTERS

• Published in: Annual review of astronomy and astrophysics Vol. 40; no. 1; pp. 387 - 438
• Main Authors: Weiler, Kurt W, Panagia, Nino, Montes, Marcos J, Sramek, Richard A
• Format: Journal Article
• Language: English
• Published: Palo Alto, CA 94303-0139 Annual Reviews 01-01-2002; 4139 El Camino Way, P.O. Box 10139; USA
• Subjects: afterglows; GRB000301C; GRB970508; GRB980329; GRB980425; GRB980519; GRB991208; GRB991216; SN1998bw
• ISSN: 0066-4146; 1545-4282
• DOI: 10.1146/annurev.astro.40.060401.093744

Study of radio supernovae over the past 20 years includes two dozen detected
objects and more than 100 upper limits. From this work it is possible to
identify classes of radio properties, demonstrate conformance to and deviations
from existing models, estimate the density and structure of the circumstellar
material and, by inference, the evolution of the presupernova stellar wind, and
reveal the last stages of stellar evolution before explosion. It is also
possible to detect ionized hydrogen along the line of sight, to demonstrate
binary properties of the stellar system, and to show clumpiness of the
circumstellar material. More speculatively, it may be possible to provide
distance estimates to radio supernovae.
Over the past four years the afterglow of gamma-ray bursters has
occasionally been detected in the radio, as well in other wavelengths bands. In
particular, the interesting and unusual gamma-ray burst GRB980425, thought to
be related to SN1998bw, is a possible link between supernovae and gamma-ray
bursters. Analyzing the extensive radio emission data avaliable for SN1998bw,
one can describe its time evolution within the well-established framework
available for the analysis of radio emission from supernovae. This allows
relatively detailed description of a number of physical properties of the
object. The radio emission can best be explained as the interaction of a mildly
relativistic (Γ ∼ 1.6) shock with a dense preexplosion stellar
wind-established circumstellar medium that is highly structured both
azimuthally, in clumps or filaments, and radially, with observed density
enhancements. Because of its unusual characteristics for a Type Ib/c supernova,
the relation of SN1998bw to GRB980425 is strengthened and suggests that at
least some classes of GRBs originate in massive star explosions. Thus,
employing the formalism for describing the radio emission from supernovae and
following the link through SN1998bw/GRB980425, it is possible to model the
gross properties of the radio and optical/infrared emission from the half-dozen
GRBs with extensive radio observations. From this we conclude that at least
some members of the "slow-soft" class of GRBs can be attributed to
the explosion of a massive star in a dense, highly structured circumstellar
medium that was presumably established by the preexplosion stellar system.