On the Correlation of Low-energy Spectral Indices and Redshifts of Gamma-ray Bursts

Abstract

It was found by Amati et al. in 2002 that for a small sample of 9 gamma-ray bursts, more distant events appear to be systematically harder in the soft gamma-ray band. Here, we have collected a larger sample of 65 gamma-ray bursts, whose time integrated spectra are well established and can be well fitted with the so called Band function. It is confirmed that a correlation between the redshifts ($z$) and the low-energy indices ($\alpha$) of the Band function does exist, though it is a bit more scattered than the result of Amati et al. This correlation can not be simply attributed to the effect of photon reddening. Furthermore, correlations between $\alpha$ and $E_{\mathrm{peak}}$ (the peak energy in the $\nu F_{\nu }$ spectrum in the rest frame), $\alpha$ and $E_{\mathrm{iso}}$ (the isotropic energy release), $\alpha$ and $L_{\mathrm{iso}}$ (the isotropic luminosity) are also found, which indicate that these parameters are somehow connected. The results may give useful constraints on the physics of gamma-ray bursts.

33 pages, 11 figures

References in corpus (15)

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• A Cosmology-Independent Calibration of Gamma-Ray Burst Luminosity Relations and the Hubble Diagram
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• A Significant Problem With Using the Amati Relation for Cosmological Purposes
• The impact of selection biases on the Ep-Liso correlation of Gamma Ray Bursts
• Correlation between Peak Energy and Peak Luminosity in Short Gamma-Ray Bursts
• Robust photometric redshift determinations of gamma-ray burst afterglows at z > 2
• Toward tight gamma-ray burst luminosity relations
• Functional biases in GRB's spectral parameter correlations

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• Statistical Study of Gamma-Ray Bursts with a Plateau Phase in the X-ray Afterglow
• Low-energy Spectra of Gamma-ray Bursts from Cooling Electrons
• MultiPulse {\it Fermi} Gamma-Ray Bursts. I. Evidence of the Transition from Fireball to Poynting-flux-dominated Outflow
• A comprehensive statistical study on gamma-ray bursts
• "Double-tracking" Characteristic of the Spectral Evolution of GRB 131231A: Synchrotron Origin?
• Distributions of Pseudo-Redshifts and Durations (Observed and Intrinsic) of Fermi GRBs
• Revisiting the Amati and Yonetoku Correlations with Swift GRBs
• Inverse Compton Scattering Spectra of Gamma-Ray Burst Prompt Emission
• Standard GRB Spectral Models "Misused"?
• A Spectral Analysis of Fermi-LLE GRBs
• Redshift Dependence of the Low-energy Spectral Index of Gamma-Ray Bursts Revisited