Journal Article

Testing gamma-ray bursts as standard candles

Spyros Basilakos and Leandros Perivolaropoulos

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 391, issue 1, pages 411-419
Published in print November 2008 | ISSN: 0035-8711
Published online November 2008 | e-ISSN: 1365-2966 | DOI:
Testing gamma-ray bursts as standard candles

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Several interesting correlations among gamma-ray burst (GRB) observables with available redshifts have been recently identified. Proper evaluation and calibration of these correlations may facilitate the use of GRBs as standard candles constraining the expansion history of the universe up to redshifts of z > 6. Here we use the 69 GRB data set recently compiled by Schaefer and we test the calibration of five of the above correlations [(1) EpeakEγ, (2) EpeakL, (3) τlagL, (4) VL, (5) τRTL] with respect to two potential sources of systematics: evolution with redshift and cosmological model used in the calibration. In examining the model dependence we assume flat ΛCDM and vary Ωm. Our approach avoids the circularity problem of previous studies since we do not fix Ωm to find the correlation parameters. Instead we simultaneously minimize χ2 with respect to both the log–linear correlation parameters a, b and the cosmological parameter Ωm. We find no statistically significant evidence for redshift dependence of a and b in any of the correlation relations tested [the slopes of a(z) and b(z) are consistent with 0 at the 2σ level]. We also find that one of the five correlation relations tested (EpeakEγ) has a significantly lower intrinsic dispersion compared to the other correlations. For this correlation relation, the maximum likelihood method (χ2 minimization) leads to b1= 50.58 ± 0.04, a1= 1.56 ± 0.11, Ωm= 0.30+1.60−0.25, respectively. The other four correlation relations minimize χ2 for a flat matter dominated universe Ωm≃ 1. Finally, a cross-correlation analysis between the GRBs and type Ia supernova data for various values of Ωm has shown that the EpeakEγ relation traces well the SnIa regime (within 0.17 ≤z≤ 1.755). In particular, for Ωm≃ 0.15 and Ωm≃ 0.30 we get the highest correlation signal between the two populations. However, due to the large error bars in the cross-correlation analysis (small number statistics) even the tightest correlation relation (EpeakEγ) provides much weaker constraints on Ωm than current SnIa data.

Keywords: cosmology: observations; distance scale; gamma-rays: bursts

Journal Article.  6075 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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