Time-Resolved Spectroscopy of the 3 Brightest and Hardest Short Gamma-Ray Bursts Observed with the FGST Gamma-Ray Burst Monitor

Abstract

From July 2008 to October 2009, the Gamma-ray Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope (FGST) has detected 320 Gamma-Ray Bursts (GRBs). About 20% of these events are classified as short based on their T90 duration below 2 s. We present here for the first time time-resolved spectroscopy at timescales as short as 2 ms for the three brightest short GRBs observed with GBM. The time-integrated spectra of the events deviate from the Band function, indicating the existence of an additional spectral component, which can be fit by a power-law with index ~-1.5. The time-integrated Epeak values exceed 2 MeV for two of the bursts, and are well above the values observed in the brightest long GRBs. Their Epeak values and their low-energy power-law indices (α) confirm that short GRBs are harder than long ones. We find that short GRBs are very similar to long ones, but with light curves contracted in time and with harder spectra stretched towards higher energies. In our time-resolved spectroscopy analysis, we find that the Epeak values range from a few tens of keV up to more than 6 MeV. In general, the hardness evolutions during the bursts follows their flux/intensity variations, similar to long bursts. However, we do not always see the Epeak leading the light-curve rises, and we confirm the zero/short average light-curve spectral lag below 1 MeV, already established for short GRBs. We also find that the time-resolved low-energy power-law indices of the Band function mostly violate the limits imposed by the synchrotron models for both slow and fast electron cooling and may require additional emission processes to explain the data. Finally, we interpreted these observations in the context of the current existing models and emission mechanisms for the prompt emission of GRBs.

arXiv comment14 pages, 10 figures, 9 tables, Accepted for publication in the Astrophysical Journal September, 23 2010 (Submitted May, 16 2010) Corrections: 1 reference updated, figure 10 caption

References in corpus (46)

• Collapsars - Gamma-Ray Bursts and Explosions in "Failed Supernovae"
• The Physics of Gamma-Ray Bursts
• The Fermi Gamma-Ray Burst Monitor
• Unsteady Outflow Models for Cosmological Gamma-Ray Bursts
• The Progenitor Stars of Gamma-Ray Bursts
• Short-Hard Gamma-Ray Bursts
• The BATSE Gamma-Ray Burst Spectral Catalog. I. High Time Resolution Spectroscopy of Bright Bursts using High Energy Resolution Data
• Testing Einstein's special relativity with Fermi's short hard gamma-ray burst GRB090510
• Particle acceleration in relativistic collisionless shocks: Fermi process at last?
• The Fourth BATSE Gamma-Ray Burst Catalog (Revised)
• Gamma-ray bursts from internal shocks in a relativistic wind: temporal and spectral properties
• Short Gamma-Ray Bursts with Extended Emission
• Fermi Observations of GRB 090902B: A Distinct Spectral Component in the Prompt and Delayed Emission
• Relativistic Jets in Collapsars
• Discerning the physical origins of cosmological Gamma-ray bursts based on multiple observational criteria: the cases of z=6.7 GRB 080913, z=8.3 GRB 090423, and some short/hard GRBs
• Fermi Observations of GRB 090510: A Short Hard Gamma-Ray Burst with an Additional, Hard Power-Law Component from 10 keV to GeV Energies
• Collisional mechanism for GRB emission
• Variability in GRBs - A Clue
• On the structure of relativistic collisionless shocks in electron-ion plasmas
• Large scale magnetic fields and their dissipation in GRB fireballs
• Identification and properties of the photospheric emission in GRB090902B
• BATSE Observations of Gamma-Ray Burst Spectra. II. Peak Energy Evolution in Bright, Long Bursts -
• Klein-Nishina Effects on Optically Thin Synchrotron and Synchrotron Self-Compton Spectrum
• Helium Star/Black Hole Mergers: a New Gamma-Ray Burst Model
• Temporal Evolution Of Thermal Emission From Relativistically Expanding Plasma
• Short versus Long Gamma-Ray Bursts: spectra, energetics, and luminosities
• Constraints on the emission mechanisms of gamma-ray bursts
• The expected thermal precursors of gamma-ray bursts in the internal shock model
• Prompt high-energy emission from gamma-ray bursts in the internal shock model
• Ion dynamics and acceleration in relativistic shocks
• Merging White Dwarf/Black Hole Binaries and Gamma-Ray Bursts
• Gamma-Ray Burst Spectral Evolution Through Crosscorrelations of Discriminator Light Curves
• Optical and near-infrared follow-up observations of four Fermi/LAT GRBs : Redshifts, afterglows, energetics and host galaxies
• The onset of the GeV afterglow of GRB 090510
• A new definition of the intermediate group of gamma-ray bursts
• Physical parameters and emission mechanism in Gamma-Ray Bursts
• The spectra of short Gamma-Ray Bursts
• Hadronic Models for the Extra Spectral Component in the short GRB 090510
• Correlations Between Lag, Luminosity, and Duration in Gamma-ray Burst Pulses
• On the Spectral Lags of the Short Gamma-Ray Bursts
• Observational Limits on Inverse Compton Processes in GRBs
• On the nature of X-Ray Flashes
• Interpretations of gamma-ray burst spectroscopy. I. Analytical and numerical study of spectral lags
• Modeling Spectral Variability of Prompt GRB Emission within the Jitter Radiation Paradigm
• Spectral Properties of Short Gamma-Ray Bursts
• Neutron Star Binaries as Central Engines of GRBs

Cited by in corpus (63)

• Short-Duration Gamma-Ray Bursts
• The First Fermi LAT Gamma-Ray Burst Catalog
• The Afterglows of Swift-era Gamma-Ray Bursts II.: Type I GRB versus Type II GRB Optical Afterglows
• Detection of a Thermal Spectral Component in the Prompt Emission of GRB 100724B
• The 2nd Fermi GBM Gamma-Ray Burst Catalog: The First Four Years
• The Fermi GBM Gamma-Ray Burst Spectral Catalog: The First Two Years
• Spectral properties of 438 GRBs detected by Fermi/GBM
• Evidence for a Photospheric Component in the Prompt Emission of the Short GRB120323A and its Effects on the GRB Hardness-Luminosity Relation
• A Comprehensive Analysis of Fermi Gamma-ray Burst Data: II. $E_{\mathrm{p}}$-Evolution Patterns and Implications for the Observed Spectrum-Luminosity Relations
• Discovery and confirmation of the shortest gamma ray burst from a collapsar
• The Fermi GBM Gamma-Ray Burst Catalog: The First Two Years
• Gamma Ray Bursts
• Time-resolved Analysis of Fermi GRBs with Fast and Slow-Cooled Synchrotron Photon Models
• Revisiting the Long/Soft-Short/Hard Classification of Gamma-Ray Bursts in the Fermi Era
• Comparing the spectral lag of short and long gamma-ray bursts and its relation with the luminosity
• Towards a Better Understanding of the GRB Phenomenon: a New Model for GRB Prompt Emission and its effects on the New Non-Thermal L${}_{\mathrm{i}}^{\mathrm{NT}}$-E${}_{\mathrm{peak},\mathrm{i}}^{\mathrm{rest},\mathrm{NT}}$ relation
• Gamma Ray Bursts in the Swift-Fermi Era
• An Analysis of Chandra Deep Follow-up GRBs: Implications for Off-Axis Jets
• Neutron Star Mergers and How to Study Them
• Spectral analysis of Fermi-LAT gamma-ray bursts with known redshift and their potential use as cosmological standard candles
• Cosmic Neutron Star Merger Rate and Gravitational Waves constrained by the R Process Nucleosynthesis
• Gamma Ray Burst Prompt correlations
• GRB 131014A: a Laboratory to Study the Thermal-Like and Non-Thermal Emissions in Gamma-Ray Bursts, and the new L${}_{\mathrm{i}}^{\mathrm{nTh}}$-E${}_{\mathrm{peak},\mathrm{i}}^{\mathrm{nTh},\mathrm{rest}}$ relation
• Temporal Deconvolution study of Long and Short Gamma-Ray Burst Light curves
• Fermi/GBM and BATSE Gamma-Ray Bursts: comparison of the spectral properties
• Spectral evolution in gamma-ray bursts: predictions of the internal shock model and comparison to observations
• Bayesian Time-Resolved Spectroscopy of GRB Pulses
• Short and Long GRBs: same emission mechanism?
• A comprehensive statistical study on gamma-ray bursts
• On Spectral Evolution and Temporal Binning in Gamma-Ray Bursts
• A faint optical flash in dust-obscured GRB 080603A - implications for GRB prompt emission mechanisms
• Gamma-Ray Bursts as Sources of Strong Magnetic Fields
• Clustering of gamma-ray burst types in the Fermi-GBM catalogue: indications of photosphere and synchrotron emissions during the prompt phase
• Fermi GBM Observations of GRB 150101B: A Second Nearby Event with a Short Hard Spike and a Soft Tail
• GRB 090227B: the missing link between the genuine short and long GRBs
• First-year Results of Broadband Spectroscopy of the Brightest Fermi-GBM Gamma-Ray Bursts
• There is a short gamma-ray burst prompt phase at the beginning of each long one
• Gamma-ray Bursts Induced by Turbulent Reconnection
• Synchrotron Cooling in Energetic Gamma-Ray Bursts Observed by the Fermi Gamma-Ray Burst Monitor
• Gamma Ray Bursts
• A Unified Model for GRB Prompt Emission from Optical to $\gamma$-Rays: Exploring GRBs as Standard Candles
• The 999th Swift gamma-ray burst: Some like it thermal
• Closure relations of Gamma Ray Bursts in high energy emission
• Emission from accelerating jets in gamma-ray bursts: Radiation dominated flows with increasing mass outflow rates
• Limits on quantum gravity effects from Swift short gamma-ray bursts
• CGRO/BATSE Data Support the New Paradigm for GRB Prompt Emission and the New L${}_i^{nTh}$-E${}_{peak,i}^{nTh,rest}$ relation
• High-Energy Non-Thermal and Thermal Emission from GRB141207A detected by Fermi
• Short GRBs and dark matter seeding in neutron stars
• The role of hadronic cascades in GRB models of efficient neutrino production
• Instrumental Tip-of-the-iceberg Effects on the Prompt Emission of Swift/BAT Gamma-ray Bursts
• A short gamma-ray burst from a proto-magnetar remnant
• GRB Spectrum from Gradual Dissipation in a Magnetized Outflow
• Spectral components in the bright, long GRB 061007: properties of the photosphere and the nature of the outflow
• Photospheric Emission in the Joint GBM and Konus Prompt Spectra of GRB 120323A
• Hard X-ray/Soft gamma-ray experiments and missions: overview and prospects
• GRB 090510: a disguised short GRB with the highest Lorentz factor and circumburst medium
• Investigation of Primordial Black Hole Bursts using Interplanetary Network Gamma-ray Bursts
• The Fermi view of gamma-ray bursts
• Multiple Components in the Broadband $\gamma$-ray Emission of the Short GRB 160709A
• Self-Similarities and Power-laws in the Time-resolved Spectra of GRB 190114C, GRB 130427A, GRB 160509A, and GRB 160625B
• A Comprehensive Study of Bright Fermi-GBM Short Gamma-Ray Bursts: I. Multi-Pulse Lightcurves and Multi-Component Spectra
• High energy time lags of Gamma Ray Bursts
• A Comprehensive Study of Bright Fermi-GBM Short Gamma-Ray Bursts: II. Very Short Burst and Its Implications