X-ray flares in GRBs: general considerations and photospheric origin

Abstract

Observations of X-ray flares from Gamma Ray Bursts (GRBs) imply strong constraints on possible physical models. We provide a general discussion of these. In particular, we show that in order to account for the relatively flat and weak optical flux during the X-ray flares, the size of the emitting region should be $\lesssim 3\times 10^{14}$cm. The bolometric luminosity of flares also strongly constrain the energy budget, and are inconsistent with late time activity of a central engine powered by the spin-down of a magnetar. We provide a simple toy model according to which flares are produced by an outflow of modest Lorentz factor (a few tens instead of hundreds) that is launched more or less simultaneously with the highly relativistic jet which produced the prompt gamma-ray emission. The "slower" moving outflow produces the flare as it reaches its photosphere. The existence of such a component would naturally resolve the observational challenges imposed by flares, outlined in this work.

5 pages, 1 figure. Accepted for publication in MNRAS

References in corpus (8)

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Cited by in corpus (24)

• Prompt Gamma Ray Burst emission from gradual magnetic dissipation
• On the origin of the multi-GeV photons from the closest burst with intermediate luminosity: GRB 190829A
• Gamma-ray bursts afterglow physics and the VHE domain
• Flares in Gamma Ray Bursts: Disc Fragmentation and Evolution
• Gamma-ray burst afterglow blast waves
• The Mouse Pulsar Wind Nebula
• GRB 170817A as a Refreshed Shock Afterglow viewed off-axis
• The History of GRB Outflows: Ejection Lorentz Factor and Radiation Location of X-Ray Flares
• Fallback accretion on to a newborn magnetar: long GRBs with giant X-ray flares
• Steep Decay of GRB X-ray Flares: the Result of Anisotropic Synchrotron Radiation
• A MAD Model for Gamma-Ray Burst Variability
• Flares in gamma-ray burst X-ray afterglows as prompt emission from slightly misaligned structured jets
• The curious case of EP241021a: Unraveling the mystery of its exceptional rebrightening
• X-ray flares from dense shells formed in gamma-ray burst explosions
• Probing Magnetic Fields of GRB X-ray Flares with Polarization Observations
• Giant X-ray and optical Bump in GRBs: evidence for fall-back accretion model
• GRB X-Ray Flare Properties among Different GRB Subclasses
• Relativistic simulations of long-lived reverse shocks in stratified ejecta: the origin of flares in GRB afterglows
• The Signature of Refreshed Shocks in the of Afterglow of GRB030329
• Deciphering the properties of the central engine in GRB collapsars
• Viscous Evolution of Magnetized Clumps: a Source for X-ray Flares in Gamma-ray Bursts
• Multimessenger signatures of a deformed magnetar in gamma-ray bursts
• Plug Disintegration in GRB Jet Eruption
• Predicting Multiwavelength Emission Associated with X-Ray Flares and Extended Emission of Gamma-Ray Bursts