GRB 071003: Broadband Follow-up Observations of a Very Bright Gamma-Ray Burst in a Galactic Halo

Abstract

The optical afterglow of long-duration GRB 071003 is among the brightest yet to be detected from any GRB, with R ~ 12 mag in KAIT observations starting 42 s after the GRB trigger, including filtered detections during prompt emission. However, our high S/N ratio afterglow spectrum displays only extremely weak absorption lines at what we argue is the host redshift of z = 1.60435 - in contrast to the three other, much stronger Mg II absorption systems observed at lower redshifts. Together with Keck adaptive optics observations which fail to reveal a host galaxy coincident with the burst position, our observations suggest a halo progenitor and offer a cautionary tale about the use of Mg II for GRB redshift determination. We present early through late-time observations spanning the electromagnetic spectrum, constrain the connection between the prompt emission and early variations in the light curve (we observe no correlation), and discuss possible origins for an unusual, marked rebrightening that occurs a few hours after the burst: likely either a late-time refreshed shock or a wide-angle secondary jet. Analysis of the late-time afterglow is most consistent with a wind environment, suggesting a massive star progenitor. Together with GRB 070125, this may indicate that a small but significant portion of star formation in the early universe occurred far outside what we consider a normal galactic disk.

24 pages, 14 figures, 12 tables. Accepted for publication by ApJ. Contains minor revisions and additional authors

References in corpus (17)

• Long gamma-ray bursts and core-collapse supernovae have different environments
• The First Survey of X-ray Flares from Gamma Ray Bursts Observed by Swift: Temporal Properties and Morphology
• The Automated Palomar 60-Inch Telescope
• Reconciling the Metallicity Distributions of Gamma-ray Burst, Damped Lyman-alpha, and Lyman-break Galaxies at z=3
• Energy input and response from prompt and early optical afterglow emission in gamma-ray bursts
• On the Nature of Velocity Fields in High z Galaxies
• X-ray Hardness Evolution in GRB Afterglows and Flares: Late Time GRB Activity Without N_H Variations
• Smooth Light Curves from a Bumpy Ride: Relativistic Blast Wave Encounters a Density Jump
• Optical Photometry of GRB 021004: The First Month
• On the Perils of Curve-of-Growth Analysis: Systematic Abundance Underestimates for the Gas in Gamma-Ray Burst Host Galaxies
• Probing the Neutral Fraction of the IGM with GRBs during the Epoch of Reionization
• RAPTOR observations of delayed explosive activity in the high-redshift gamma-ray burst GRB 060206
• Improved $u^{\prime }{g}^{\prime }{r}^{\prime }{i}^{\prime }{z}^{\prime }$ to $UBV{R}_C{I}_C$ Transformation Equations for Main Sequence Stars
• X-ray Hardness Variations as an Internal/External Shock Diagnostic
• Pulse Width Evolution of Late Time X-rays Flares in GRBs: Evidence For Internal Shocks
• The Rapidly Flaring Afterglow of the Very Bright and Energetic GRB 070125
• GRB 070311: a direct link between the prompt emission and the afterglow

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• Phenomenology of Reverse-Shock Emission in the Optical Afterglows of Gamma Ray Bursts
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• Statistical studies of optically dark gamma-ray bursts in the Swift era
• Interpretation of Radio Afterglows in the framework of the Standard Fireball and Energy Injection models
• On the significance of the excess number of strong MgII absorbers observed towards Gamma-ray bursts
• Diagnosing Circumburst Environment with Multiband Gamma-Ray Burst Radio Afterglows
• Discovery and Analysis of Afterglows from Poorly Localised GRBs with the Gravitational-wave Optical Transient Observer (GOTO) All-sky Survey
• The second H.E.S.S. gamma-ray burst catalogue: 15 years of observations with the H.E.S.S. telescopes