The Bright Gamma-Ray Burst 991208 - Tight Constraints on Afterglow Models from Observations of the Early-Time Radio Evolution

Abstract

The millimeter wavelength emission from GRB 991208 is the second brightest ever detected, yielding a unique data set. We present here well-sampled spectra and light curves over more than two decades in frequency for a two-week period. This data set has allowed us for the first time to trace the evolution of the characteristic synchrotron self-absorption frequency nu_a and peak frequency nu_m, and the peak flux density F_m: we obtain nu_a \propto t^{-0.15 +- 0.12}, nu_m \propto t^{-1.7 +- 0.4}, and $_m \propto t^{-0.47 +- 0.11}. From the radio data we find that models of homogeneous or wind-generated ambient media with a spherically symmetric outflow can be ruled out. A model in which the relativistic outflow is collimated (a jet) can account for the observed evolution of the synchrotron parameters, the rapid decay at optical wavelengths, and the observed radio to optical spectral flux distributions that we present here, provided that the jet transition has not been fully completed in the first two weeks after the event. These observations provide additional evidence that rapidly decaying optical/X-ray afterglows are due to jets and that such transitions either develop very slowly or perhaps never reach the predicted asymptotic decay F(t) \propto t^{-p}.

15 pages, 4 figures, submitted to ApJ Letters

References in corpus (4)

• Wind Interaction Models for Gamma-Ray Burst Afterglows: The Case for Two Types of Progenitors
• Afterglow Emission from Naked Gamma-Ray Bursts
• The Enigmatic Radio Afterglow of GRB 991216
• Interplanetary Network Localization of GRB991208 and the Discovery of its Afterglow

Cited by in corpus (28)

• The Shape of Spectral Breaks in GRB Afterglows
• The 21 cm Forest: Radio Absorption Spectra as Probes of Minihalos Before Reionization
• XRF 100316D / SN 2010bh and the Nature of Gamma Ray Burst Supernovae
• The extraordinarily bright optical afterglow of GRB 991208 and its host galaxy
• GRB Afterglows from Anisotropic Jets
• Millimeter Observations of GRB 030329: Continued Evidence for a Two-Component Jet
• Jets, Structured Outflows, and Energy Injection in GRB Afterglows: Numerical Modelling
• Pre-ALMA observations of GRBs in the mm/submm range
• Infrared and Optical Observations of GRB 030115 and its Extremely Red Host Galaxy: Implications for Dark Bursts
• GRB 000418: A Hidden Jet Revealed?
• Gamma-Ray Burst Afterglow emission with a decaying magnetic field
• Wind Interaction Models for the Afterglows of GRB 991208 and GRB 000301C
• On the radio afterglow of gamma ray bursts
• Synchrotron Self-inverse Compton Radiation From Reverse-shock on GRB120326A
• The Slow Decay of Some Radio Afterglows, a Puzzle for the Simplest GRB Fireball Model
• Nobeyama Millimeter Array Observations of GRB 030329: a Decay of Afterglow with Bumps and Molecular Gas in the Host Galaxy
• The late-time radio behavior of GRB afterglows: testing the standard model
• Continued Radio Monitoring of the Gamma Ray Burst 991208
• SCUBA sub-millimeter observations of gamma-ray bursters: II. GRB 991208, 991216, 000301C, 000630, 000911, 000926
• Extragalactic Millimeter Transients in the Era of Next Generation CMB Surveys
• Dark Matter Constraints from a Cosmic Index of Refraction
• Radio Observations of the Afterglow of GRB 030329
• On the optical counterparts of radio transients and variables
• Light Curves of Jetted Gamma-Ray Burst Afterglows in Circumstellar Clouds
• Fireballs and cannonballs confront the afterglow of GRB 991208
• Diagnosing Circumburst Environment with Multiband Gamma-Ray Burst Radio Afterglows
• Radio Observations of GRB Afterglows
• Discovery and Analysis of Afterglows from Poorly Localised GRBs with the Gravitational-wave Optical Transient Observer (GOTO) All-sky Survey