On The Origin Of High Energy Correlations in Gamma-ray Bursts

Abstract

I investigate the origin of the observed correlation between a GRB's nuFnu spectral peak Epk and its isotropic equivalent energy Eiso through the use of a population synthesis code to model the prompt gamma-ray emission from GRBs. By using prescriptions for the distribution of prompt spectral parameters as well as the population's luminosity function and co-moving rate density, I generate a simulated population of GRBs and examine how bursts of varying spectral properties and redshift would appear to a gamma-ray detector here on Earth. I find that a strong observed correlation can be produced between the source frame Epk and Eiso for the detected population despite the existence of only a weak and broad correlation in the original simulated population. The energy dependance of a gamma-ray detector's flux-limited detection threshold acts to produce a correlation between the source frame Epk and Eiso for low luminosity GRBs, producing the left boundary of the observed correlation. Conversely, very luminous GRBs are found at higher redshifts than their low luminosity counterparts due to the standard Malquest bias, causing bursts in the low Epk, high Eiso regime to go undetected because their Epk values would be redshifted to energies at which most gamma-ray detectors become less sensitive. I argue that it is this previously unexamined effect which produces the right boundary of the observed correlation. Therefore, the origin of the observed correlation is a complex combination of the instrument's detection threshold, the intrinsic cutoff in the GRB luminosity function, and the broad range of redshifts over which GRBs are detected. These simulations serve to demonstrate how selection effects caused by a combination of instrumental sensitivity and the cosmological nature of an astrophysical population can act to produce an artificially strong correlation between observed properties.

9 pages, 12 figures, submitted to ApJ

References in corpus (5)

• A Complete Catalog of Swift GRB Spectra and Durations: Demise of a Physical Origin for Pre-Swift High-Energy Correlations
• The Epeak-Eiso plane of long Gamma Ray Bursts and selection effects
• Global Properties of X-Ray Flashes and X-Ray-Rich Gamma-Ray Bursts Observed by Swift
• Peak energy of the prompt emission of long Gamma Ray Bursts vs their fluence and peak flux
• Generalized Tests for Selection Effects in GRB High-Energy Correlations

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• Short vs. Long Gamma-Ray Bursts: A Comprehensive Study of Energetics and Prompt Gamma-Ray Correlations
• Spectral analysis of Fermi-LAT gamma-ray bursts with known redshift and their potential use as cosmological standard candles
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• The Epeak-Eiso relation revisited with Fermi GRBs: Resolving a long-standing debate?
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• Accessing the population of high redshift Gamma Ray Bursts
• On Spectral Evolution and Temporal Binning in Gamma-Ray Bursts
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• The impact of selection biases on the Ep-Liso correlation of Gamma Ray Bursts
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• Evidence for New Relations between Gamma Ray Burst Prompt and X-ray Afterglow Emission from 9 Years of Swift
• There is a short gamma-ray burst prompt phase at the beginning of each long one
• Improving sampling and calibration of GRBs as distance indicators
• CGRO/BATSE Data Support the New Paradigm for GRB Prompt Emission and the New L${}_i^{nTh}$-E${}_{peak,i}^{nTh,rest}$ relation
• An analytic derivation of the empirical correlations of gamma-ray bursts
• Investigating the impact of optical selection effects on observed rest frame prompt GRB properties
• Revisiting the Spectral-Energy Correlations of GRBs with {\it Fermi} Data I: Model-wise Properties
• An overview of the current understanding of Gamma-ray Bursts in the Fermi era
• A comprehensive view of blackbody components in the X-ray spectra of GRBs
• Deciphering the properties of the central engine in GRB collapsars
• The Rest-Frame Golenetskii Correlation via a Hierarchical Bayesian Analysis
• A next generation Ultra-Fast Flash Observatory (UFFO-100) for IR/optical observations of the rise phase of gamma-ray bursts
• GRBs have preferred jet opening angles and bulk Lorentz factors