A Distinct Peak-flux Distribution of the Third Class of Gamma-ray Bursts: A Possible Signature of X-ray Flashes?

Gamma-ray bursts (GRBs) are the most luminous events in the universe. Going beyond the short-long classification scheme, we work in the context of three burst populations with the third group of intermediate duration and softest spectrum. We are looking for physical properties which discriminate the...

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Bibliographic Details
Published inThe Astrophysical journal Vol. 725; no. 2; pp. 1955 - 1964
Main Authors Veres, P, Bagoly, Z, Horváth, I, Mészáros, A, Balázs, L. G
Format Journal Article
LanguageEnglish
Published Bristol IOP Publishing 20.12.2010
IOP
Subjects
Astronomy
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
CALCULATION METHODS
COMPUTERIZED SIMULATION
COSMIC GAMMA BURSTS
COSMIC RADIATION
Earth, ocean, space
ELECTROMAGNETIC RADIATION
Exact sciences and technology
IONIZING RADIATIONS
MATHEMATICAL SOLUTIONS
MAXIMUM-LIKELIHOOD FIT
MONTE CARLO METHOD
NUMERICAL SOLUTION
PRIMARY COSMIC RADIATION
PROBABILISTIC ESTIMATION
PROBABILITY
RADIATIONS
RED SHIFT
SIMULATION
UNIVERSE
X RADIATION
Statistical method
Red shift
Monte Carlo methods
methods: statistical
Gamma radiation
Cosmic gamma sources
Classification
Probability
Gamma ray burst
Maximum likelihood
Physical properties
gamma rays: general
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Summary:Gamma-ray bursts (GRBs) are the most luminous events in the universe. Going beyond the short-long classification scheme, we work in the context of three burst populations with the third group of intermediate duration and softest spectrum. We are looking for physical properties which discriminate the intermediate duration bursts from the other two classes. We use maximum likelihood fits to establish group memberships in the duration-hardness plane. To confirm these results we also use k-means and hierarchical clustering. We use Monte Carlo simulations to test the significance of the existence of the intermediate group and we find it with 99.8% probability. The intermediate duration population has a significantly lower peak flux (with 99.94% significance). Also, long bursts with measured redshift have higher peak fluxes (with 98.6% significance) than long bursts without measured redshifts. As the third group is the softest, we argue that we have related them with X-ray flashes among the GRBs. We give a new, probabilistic definition for this class of events.
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ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/725/2/1955