Softness Ratio of SWIFT Gamma-ray Bursts and Relevant Correlations

2025/05/10 by Fan Xu, Xu, Fan, Yong-Feng Huang +17
Physics and Astronomy · #Astronomy and Astrophysical Research #FOS: Physical sciences #Gamma-ray bursts and supernovae #High Energy Astrophysical Phenomena (astro-ph.HE) #Pulsars and Gravitational Waves Research

paper · pdf · doi:10.48550/arxiv.2505.06508

openalex publication_date 2025/05/10 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

Abstract

The properties of X-ray flashes (XRFs) and X-ray rich gamma-ray bursts (XRRs) as compared with classical gamma-ray bursts (C-GRBs) have been widely discussed during the Swift era. It has been proposed that XRFs and XRRs are low-energy extensions of the GRB population so that they should follow similar correlations. To further examine this idea, we collect a sample of 303 GRBs detected by Swift over the past two decades, all of which have reliable redshifts and spectral parameters. The bursts are classified into XRFs, XRRs, and C-GRBs based on their softness ratio (SR), which is calculated by dividing the 25-50 keV fluence with the 50-100 keV fluence. A strong correlation is found among the isotropic energy E_iso, peak luminosity L_p, and rest frame burst duration T_{90, rest}, i.e., E_iso ∝ L_p^0.88±0.02 T_{90, rest}^0.58±0.02. Additionally, two tight three-parameter correlations involving SR and the rest-frame peak energy E_p are also derived, i.e. E_p ∝ E_iso^0.20±0.02 SR^-2.27±0.15 and E_p ∝ L_p^0.17±0.02 SR^-2.33±0.14. It is interesting to note that XRFs, XRRs, and C-GRBs all follow the above correlations. The implications of these correlations and their potential application in cosmology are discussed.

Citations

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Related

• Global Properties of X-Ray Flashes and X-Ray-Rich Gamma-Ray Bursts Observed by Swift
• A comprehensive statistical analysis of Swift X-ray light-curves: the prompt-afterglow connection in Gamma-Ray Bursts
• The prompt-afterglow connection in gamma-ray bursts: a comprehensive statistical analysis of Swift X-ray light curves
• Duration and hardness ratio of Swift GRBs
• What SWIFT has taught us about X-ray flashes and long-duration gamma-ray bursts