Photosphere emission in the X-Ray Flares of Swift Gamma-Ray Bursts and Implications for the Fireball Properties

Abstract

X-ray flares of gamma-ray bursts (GRBs) are usually observed in the soft X-ray range and the spectral coverage is limited. In this paper, we present an analysis of 32 GRB X-ray flares that are simultaneously observed by both BAT and XRT on board the Swift mission, so a joint spectral analysis with a wider spectral coverage is possible. Our results show that the joint spectra of 19 flares are fitted with the absorbed single power-law or the Band function models. More interestingly, the joint spectra of the other 13 X-ray flares are fitted with the absorbed single power-law model plus a black body (BB) component. Phenomenally, the observed spectra of these 13 flares are analogous to several GRBs with a thermal component, but only with a much lower temperature of $kT=1\sim 3$ keV. Assuming that the thermal emission is the photosphere emission of the GRB fireball, we derive the fireball properties of the 13 flares that have redshift measurements, such as the bulk Lorentz factor ${\Gamma }_{\mathrm{ph}}$ of the outflow. The derived ${\Gamma }_{\mathrm{ph}}$ range from $50$ to $150$ and a relation of ${\Gamma }_{\mathrm{ph}}$ to the thermal emission luminosity is found. It is consistent with the ${\Gamma }_0-L_{\mathrm{iso}}$ relation that are derived for the prompt gamma-ray emission. We discuss the physical implications of these results within the content of jet composition and radiation mechanism of GRBs and X-ray flares.

31 pages, 8 figures, and 4 tables. Accepted for publication in ApJ

References in corpus (17)

• The Internal-Collision-Induced Magnetic Reconnection and Turbulence (ICMART) Model of Gamma-Ray Bursts
• X-Ray Flares from Postmerger Millisecond Pulsars
• Detection of a Thermal Spectral Component in the Prompt Emission of GRB 100724B
• A Comprehensive Analysis of Fermi Gamma-Ray Burst Data. I. Spectral Components and Their Possible Physical Origins of LAT/GBM GRBs
• The First Survey of X-ray Flares from Gamma Ray Bursts Observed by Swift: Temporal Properties and Morphology
• GRB110721A: An extreme peak energy and signatures of the photosphere
• The First Survey of X-ray Flares from Gamma Ray Bursts Observed by Swift: Spectral Properties and Energetics
• Quasi-blackbody component and radiative efficiency of the prompt emission of gamma-ray bursts
• A new method of determining the initial size and Lorentz factor of gamma-ray burst fireballs using a thermal emission component
• Hyper-accreting black hole as GRB central engine. I: Baryon loading in GRB jets
• A Comprehensive Analysis of Fermi Gamma-ray Burst Data: II. $E_{\mathrm{p}}$-Evolution Patterns and Implications for the Observed Spectrum-Luminosity Relations
• Internal Energy Dissipation of Gamma-Ray Bursts Observed with Swift: Precursors, Prompt Gamma-rays, Extended emission and Late X-ray Flares
• The photospheric radiation model for the prompt emission of Gamma-ray Bursts: Interpreting four observed correlations
• On the Implications of Late Internal Dissipation for Shallow-Decay Afterglow Emission and Associated High-Energy Gamma-Ray Signals
• Spectral evolution in gamma-ray bursts: predictions of the internal shock model and comparison to observations
• An Observed Correlation Between Thermal and Non-Thermal Emission in Gamma-Ray Bursts
• GRB 990413: Insight into the thermal phase evolution

Cited by in corpus (17)

• Photosphere emission from a hybrid relativistic outflow with arbitrary dimensionless entropy and magnetization in GRBs
• Detection of Low-energy Breaks in Gamma-Ray Burst Prompt Emission Spectra
• Very Bright Prompt and Reverse Shock Emission of GRB 140512A
• The History of GRB Outflows: Ejection Lorentz Factor and Radiation Location of X-Ray Flares
• Constraining the Braking Index and Energy Partition of Magnetar spindown with {\em Swift}/XRT data
• Flares in gamma-ray burst X-ray afterglows as prompt emission from slightly misaligned structured jets
• Magnetar as Central Engine of Gamma-Ray Bursts: Central Engine-Jet Connection, Wind-Jet Energy Partition, and Origin of Some Ultra-Long Bursts
• The ultra-long GRB 220627A at z=3.08
• Constraining the bulk Lorentz factor from the photosphere emission
• A Novel Model for the MeV Emission Line in GRB 221009A
• Thermal components in the early X-ray afterglows of GRBs: likely cocoon emission and constraints on the progenitors
• A comprehensive view of blackbody components in the X-ray spectra of GRBs
• The Spectral Sharpness Angle of Gamma-ray Bursts
• Constraining External Reverse Shock Physics of GRBs from ROTSE-III Limits
• $L_{\mathrm{syn}}-E_{\mathrm{syn},\mathrm{p}}-\delta$ relation in Active Galactic Nucleus Jets and Implication for the physical origin of the $L_{\mathrm{p}}-E_{\mathrm{p},\mathrm{z}}-{\Gamma }_0$ relation of Gamma-Ray Bursts
• The Double-Burst Nature and Early Afterglow Evolution of Long GRB 110801A
• Predicting Multiwavelength Emission Associated with X-Ray Flares and Extended Emission of Gamma-Ray Bursts