The Density and Ionization Profile of Optically Dark and High Redshift GRBs Probed by X-ray Absorption

Abstract

The X-ray column density (NHX) of gamma-ray bursts (GRBs) can probe the local environment of their progenitors over a wide redshift range. Previous work has suggested an increasing trend as a function of redshift. The relevance of the current analysis relies on investigating the selection bias method, such as the effect of the X-ray spectrum in high-redshift GRBs, which complicates the measurement of small NHX, have yet to be fully evaluated or discussed elsewhere. In this work, we evaluated these effects through simulations to define appropriate observational limits in the NHX versus redshift plane. We then applied a one-sided nonparametric method developed by Efron and Petrosian. Within the framework of this method, we investigated the redshift dependence of NHX and the local distribution function. Our results show that the evolution of NHX with redshift firmly exists with a significance of more than four sigma and follows a power law of $(1+z{)}^{1.39(+0.22,-0.27)}$. Based on these analyses and previous studies, the GRB progenitor mass varies but is more massive in the high redshift environment and has a higher gas column density. This suggests that part of the luminosity evolution of GRBs, which has been widely reported, may be due to the evolution of the progenitor's mass. Using the same method, we demonstrate that optically dark GRBs show a consistent evolution as $(1+z{)}^{1.15(+0.67,-0.83)}$. By applying the Kolmogorov-Smirnov (KS) test, it is shown that optically dark GRBs have statistically identical flux and photon index distributions compared to normal GRBs, but the NHX is systematically larger. This result suggests that the darkness of some GRB populations is not due to an intrinsic mechanism, but that a higher density surrounds them.

References in corpus (18)

• The Evolution of Stellar Mass and the Implied Star Formation History
• Swift Identification of Dark Gamma-Ray Bursts
• The Host Galaxies of Swift Dark Gamma-Ray Bursts: Observational Constraints on Highly Obscured and Very High-Redshift GRBs
• The optically unbiased GRB host (TOUGH) survey. I. Survey design and catalogs
• The X-ray fundamental plane of the Platinum Sample, the Kilonovae and the SNe Ib/c associated with GRBs
• Cosmological Evolution of Long Gamma-ray Bursts and Star Formation Rate
• An unexpectedly low-redshift excess of Swift gamma-ray burst rate
• Unveiling the Secrets of Metallicity and Massive Star Formation Using DLAs along Gamma-ray Bursts
• Selection effects in Gamma Ray Bursts correlations: consequences on the ratio between GRB and star formation rates
• The dark nature of GRB 051022 and its host galaxy
• The extreme, red afterglow of GRB 060923A: Distance or dust?
• Dust reddening and extinction curves towards gamma-ray bursts at z > 4
• The impact of metallicity-dependent mass loss versus dynamical heating on the early evolution of star clusters
• Gamma-ray Bursts as Distance Indicators by a Statistical Learning Approach
• Chandra and Hubble Space Telescope observations of dark gamma-ray bursts and their host galaxies
• Using realistic host galaxy metallicities to improve the GRB X-ray equivalent total hydrogen column density and constrain the intergalactic medium density
• Detailed multi-wavelength modelling of the dark GRB 140713A and its host galaxy
• Diverse Properties of Interstellar Medium Embedding Gamma-Ray Bursts at the Epoch of Reionization

Cited by in corpus (1)

• GRB Redshift Estimation using Machine Learning and the Associated Web-App