Environment and Energy Injection Effects in GRB Afterglows

Abstract

In a recent paper (Dai & Lu 1999), we have proposed a simple model in which the steepening in the light curve of the R-band afterglow of the gamma-ray burst (GRB) 990123 is caused by the adiabatic shock which has evolved from an ultrarelativistic phase to a nonrelativistic phase in a dense medium. We find that such a model is quite consistent with observations if the medium density is about $3\times 10^6{\mathrm{cm}}^{-3}$. Here we discuss this model in more details. In particular, we investigate the effects of synchrotron self absorption and energy injection. A shock in a dense medium becomes nonrelativistic rapidly after a short relativistic phase. The afterglow from the shock at the nonrelativistic stage decays more rapidly than at the relativistic stage. Since some models for GRB energy sources predict that a strongly magnetic millisecond pulsar may be born during the formation of GRB, we discuss the effect of such a pulsar on the evolution of the nonrelativistic shock through magnetic dipole radiation. We find that after the energy which the shock obtains from the pulsar is much more than the initial energy of the shock, the afterglow decay will flatten significantly. When the pulsar energy input effect disappears, the decay will steepen again. These features are in excellent agreement with the afterglows of GRB 980519, GRB 990510 and GRB 980326. Furthermore, our model fits very well all the observational data of GRB 980519 including the last two detections.

21 pages, LaTeX, accepted for publication in ApJ, one paragraph added

References in corpus (15)

• Jets in GRBs
• The Dynamics and Light Curves of Beamed Gamma Ray Burst Afterglows
• The unusual afterglow of GRB 980326: evidence for the gamma-ray burst/supernova connection
• Formation Rates of Black Hole Accretion Disk Gamma-Ray Bursts
• Gamma-Ray Burst Environments and Progenitors
• Dust sublimation by GRBs and its implications
• Optical and Radio Observations of the Afterglow from GRB990510: Evidence for a Jet
• A Generic Dynamical Model of Gamma-ray Burst Remnants
• BVRI Observations of the Optical Afterglow of GRB 990510
• On Beaming Effects in Afterglow Light Curves
• The Afterglow of GRB 990123 and a Dense Medium
• The Rapidly Fading Optical Afterglow of GRB 980519
• The Radio Afterglow From GRB 980519: A Test of the Jet and Circumstellar Models
• Non-thermal Radiation of Cosmological gamma-ray Bursters
• The X-ray afterglow of GRB980519

Cited by in corpus (28)

• Gamma-Ray Bursts
• Theories of Gamma-Ray Bursts
• Analytic Light-Curves of Gamma-Ray Burst Afterglows: Homogeneous versus Wind External Media
• Overall Evolution of Jetted Gamma-ray Burst Ejecta
• Afterglow Emission from Highly Collimated Jets with Flat Electron Spectra: Application to the GRB 010222 Case?
• Relativistic Wind Bubbles and Afterglow Signatures
• Optical Flash of GRB 990123: constraints on the physical parameter of the reverse shock
• The Inverse Compton Emission Spectra in the Very Early Afterglows of Gamma-Ray Bursts
• Gamma-ray bursts: optical afterglows in the deep Newtonian phase
• Neutrino Afterglows and Progenitors of Gamma-Ray Bursts
• GRB Afterglows from Anisotropic Jets
• Hydrodynamics of Relativistic Blast Waves in a Density-Jump Medium and Their Emission Signature
• Gamma-Ray Bursts: Afterglows and Central Engines
• Analytical light curves in the realistic model for GRB afterglows
• Energy Injection in GRB Afterglow Models
• A Late-Time Flattening of Afterglow Light Curves
• Gamma-ray burst afterglows from jetted shocks in wind environments
• Could the Unusual Optical Afterglow of GRB 000301c Arise from a Non-relativistic Shock with Energy Injection?
• Early Re-brightenings in GRB Afterglows as Signatures of Low-to-High Density Boundary
• Overall Temporal Synchrotron Emissions from Relativistic Jets: Adiabatic and Radiative Breaks
• Light Curves of Jetted Gamma-Ray Burst Afterglows in Circumstellar Clouds
• Afterglow Light Curve Modulated by a Highly Magnetized Millisecond Pulsar
• Gamma-Ray Burst Afterglows with Energy Injection: Homogeneous Versus Wind External Media
• GRB Afterglow of the Sub-relativistic Materials with Energy Injection
• Statistical Shapes of the Highest Pulses in Gamma--Ray Bursts
• Optical light curve of GRB 121011A: a textbook for the onset of GRB afterglow in a mixture of ISM and wind-type medium
• X-ray afterglows of gamma-ray bursts in the synchrotron self-Compton dominated regime
• The GROND GRB sample: II. Fireball parameters for four GRB afterglows