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A&A 369, 537-543 (2001)
DOI: 10.1051/0004-6361:20010149
Correlations between various hardness ratios of gamma-ray bursts
Yi-Ping Qin1, 2, 3, 4, Guang-Zhong Xie1, 2, 4, En-Wei Liang1, 2, 5 and Xue-Tang Zheng61 Yunnan Observatory, Chinese Academy of Sciences, Kunming, Yunnan 650011, PR China
2 National Astronomical Observatories, Chinese Academy of Sciences
3 Chinese Academy of Science-Peking University joint Beijing Astrophysical Center
4 Yunnan Astrophysics Center
5 Physics Department, Guangxi University, Nanning, Guangxi 530004, PR China
6 Department of Physics, Nanjing University of Science and Technology, Nanjing, Jiangsu 210014, PR China
(Received 25 February 2000 / Accepted 4 December 2000 )
Abstract
We study correlations between various hardness ratios of gamma-ray bursts
(GRBs) and investigate if there are any differences between the short- and
long-duration classes of the objects in the distributions of the ratios. The
results show that most of the hardness ratios are mutually correlated, but
that the ratio defined at the lower energy bands is not correlated with
those defined at the higher energy bands; the most significant correlations
come from those ratios defined with both the lower and higher energy bands.
It is also shown that the short-duration bursts tend to have higher values
of hardness ratios. We reach these conclusions that the slope of the higher
part of the spectrum of most GRBs is independent of that of the lower part;
emissions at higher energy bands from the bursts of both short- and
long-duration classes are significantly different for different sources, but
radiations at lower energy bands are similar; the spectra of the
short-duration bursts is harder than that of the long-duration bursts. A
possible interpretation for these results involves Doppler boosting in the
relativistic beaming model. In addition, the study reveals that hardness
ratios of the long-duration class are more mutually correlated than those of
the short-duration class; the data of hardness ratios for the long-duration
class are much less scattered than those of the short-duration class. It is
found that this difference is at least partially due to measurement errors.
Key words: gamma rays: bursts -- methods: statistical
Offprint request: Yi-Ping Qin, ypqin@public.km.yn.cn
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