Probing the Neutral Fraction of the IGM with GRBs during the Epoch of Reionization

Abstract

We show that near-infrared observations of the red side of the Ly-alpha line from a single gamma ray burst (GRB) afterglow cannot be used to constrain the global neutral fraction of the intergalactic medium (IGM), x_H, at the GRB's redshift to better than ~0.3. Some GRB sight-lines will encounter more neutral hydrogen than others at fixed x_H owing to the patchiness of reionisation. GRBs during the epoch of reionization will often bear no discernible signature of a neutral IGM in their afterglow spectra. We discuss the constraints on x_H from the z = 6.3 burst, GRB050904, and quantify the probability of detecting a neutral IGM using future spectroscopic observations of high-redshift, near-infrared GRB afterglows. Assuming an observation with signal-to-noise similar to the Subaru FOCAS spectrum of GRB050904 and that the column density distribution of damped Ly-alpha absorbers is the same as measured at lower redshifts, a GRB from an epoch when x_H = 0.5 can be used to detect a partly neutral IGM at 98% confidence level 10% of the time (and, for an observation with three times the sensitivity, 30% of the time).

10 pages, 8 figures, submitted to MNRAS

References in corpus (9)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• The James Webb Space Telescope
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• Minihalo photoevaporation during cosmic reionization: evaporation times and photon consumption rates
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• Lyman-alpha Damping Wing Constraints on Inhomogeneous Reionization
• The prompt optical/near-infrared flare of GRB 050904: the most luminous transient ever detected

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• GRB 071003: Broadband Follow-up Observations of a Very Bright Gamma-Ray Burst in a Galactic Halo
• Introducing SPHINX-MHD: The Impact of Primordial Magnetic Fields on the First Galaxies, Reionization, and the Global 21cm Signal
• Perspectives on Gamma-Ray Burst Physics and Cosmology with Next Generation Facilities
• Future Constraints on the Reionization History and the Ionizing Sources from Gamma-ray Burst Afterglows
• Constraining Reionization in Progress at z=5.7 with Lyman-$\alpha$ Emitters: Voids, Peaks, and Cosmic Variance
• Using Artificial Neural Networks to Constrain the Halo Baryon Fraction during Reionization
• Gaussian Process Reconstruction of Reionization History
• The Impact of Cosmic Variance on Inferences of Global Neutral Fraction Derived from Ly$\alpha$ Luminosity Functions During Reionization
• Probing the Early History of Cosmic Reionization by Future Cosmic Microwave Background Experiments
• Dark Twilight Joined with the Light of Dawn to Unveil the Reionization History
• Clues to the nature of dark matter from first galaxies
• Model-independent Reconstruction of UV Luminosity Function and Reionization Epoch
• Expected Gamma-Ray Burst Detection Rates and Redshift Distributions for the BlackCAT CubeSat Mission
• Reionization in Protocluster Environments at $z>7$ with JWST/NIRSpec
• GRBs as Probes of the IGM
• Fast Luminous Blue Transients in the Reionization Era and Beyond
• Exploration of the high-redshift universe enabled by THESEUS