Modeling GRB 050904: Autopsy of a Massive Stellar Explosion at z=6.29

Abstract

GRB 050904 at redshift z=6.29, discovered and observed by Swift and with spectroscopic redshift from the Subaru telescope, is the first gamma-ray burst to be identified from beyond the epoch of reionization. Since the progenitors of long gamma-ray bursts have been identified as massive stars, this event offers a unique opportunity to investigate star formation environments at this epoch. Apart from its record redshift, the burst is remarkable in two respects: first, it exhibits fast-evolving X-ray and optical flares that peak simultaneously at t~470 s in the observer frame, and may thus originate in the same emission region; and second, its afterglow exhibits an accelerated decay in the near-infrared (NIR) from t~10^4 s to t~3 10^4 s after the burst, coincident with repeated and energetic X-ray flaring activity. We make a complete analysis of available X-ray, NIR, and radio observations, utilizing afterglow models that incorporate a range of physical effects not previously considered for this or any other GRB afterglow, and quantifying our model uncertainties in detail via Markov Chain Monte Carlo analysis. In the process, we explore the possibility that the early optical and X-ray flare is due to synchrotron and inverse Compton emission from the reverse shock regions of the outflow. We suggest that the period of accelerated decay in the NIR may be due to suppression of synchrotron radiation by inverse Compton interaction of X-ray flare photons with electrons in the forward shock; a subsequent interval of slow decay would then be due to a progressive decline in this suppression. The range of acceptable models demonstrates that the kinetic energy and circumburst density of GRB 050904 are well above the typical values found for low-redshift GRBs.

45 pages, 7 figures, and ApJ accepted. Revised version, minor modifications and 1 extra figure

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• Gamma-Ray Bursts
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• GRB efficiency and Possible Physical Processes Shaping the Early Afterglow
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• Dissecting the Circumstellar Environment of Gamma-Ray Burst Progenitors
• Implications of the Early X-Ray Afterglow Light Curves of Swift GRBs
• The Onset of Gamma-Ray Burst Afterglow
• GeV-TeV and X-ray flares from gamma-ray bursts
• An Energetic Afterglow From A Distant Stellar Explosion
• Optical and X-Ray Observations of GRB 060526: A Complex Afterglow Consistent with An Achromatic Jet Break
• The prompt optical/near-infrared flare of GRB 050904: the most luminous transient ever detected
• Swift Discovery of Gamma-Ray Bursts without Jet Break Feature in their X-Ray Afterglows
• The Gamma-ray burst 050904 : evidence for a termination shock ?
• HST and Spitzer Observations of the Host Galaxy of GRB 050904: A Metal-Enriched, Dusty Starburst at z=6.295
• Swift observations of GRB050904: the most distant cosmic explosion ever observed
• The role of afterglow break-times as GRB jet angle indicators

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• Population III GRB Afterglows: Constraints on Stellar Masses and External Medium Densities
• Probing Pre-galactic Metal Enrichment with High-Redshift Gamma-Ray Bursts
• GRB 120521C at z~6 and the Properties of High-redshift GRBs
• Evidence for Supernova-Synthesised Dust from the Rising Afterglow of GRB 071025 at z~5
• Gamma-ray burst optical light-curve zoo: comparison with X-ray observations
• No evidence for dust extinction in GRB 050904 at z ~ 6.3
• Discovery of Radio Afterglow from the Most Distant Cosmic Explosion
• Compton Scattering of Self-Absorbed Synchrotron Emission
• Revisiting the Contributions of Supernova and Hypernova Remnants to the Diffuse High-Energy Backgrounds: Constraints on Very-High-Redshift Injections
• Is GRB 050904 at z=6.3 absorbed by dust?
• Probing the Birth of Post-merger Millisecond Magnetars by X-ray and Gamma-ray Emission
• High Energy Neutrino Emission from the Earliest Gamma-Ray Bursts
• Reverse Shock Emission in Gamma-ray Bursts Revisited
• Testing Blandford-Znajek mechanism in black hole hyperaccretion flows for long-duration gamma-ray bursts
• Fires in the deep: The luminosity distribution of early-time gamma-ray-burst afterglows in light of the Gamow Explorer sensitivity requirements
• Gamma Ray Bursts -- A radio perspective
• Monte Carlo Simulations of the Photospheric Process
• The late jet in gamma-ray bursts and its interactions with a supernova ejecta and a cocoon
• Gamma-ray burst radio afterglows from Population III stars: Simulation methods and detection prospects with SKA precursors
• Direct conversion of the flux of kinetic energy into radiation in gamma-ray burst