Shallow decay phase of X-ray afterglows

R. Sato, K. Ioka, K. Toma, T. Nakamura, J. Kataoka, N. Kawai, T. Takahashi

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

1 Citation (Scopus)


We investigated the characteristics of the shallow decay phase in the early X-ray afterglows of GRBs observed by Swift X-Ray Telescope (XRT) during the period of January 2005 to December 2006. We found that the intrinsic break time at the shallow-to-normal decay transition in the X-ray light curve T brk0 is moderately well correlated with the isotropic X-ray luminosity in the end of the shallow decay phase (LX,end) as Tbrk0=(9.39±0.64)×103s(L X,end/1047ergsṡs-1) -0.71±0.03. Using Tbrk0-L X,end relation we have determined the pseudo redshifts of 33 GRBs. We compared the pseudo redshifts of 11 GRBs with measured redshifts and found the rms error to be 0.17 in logz. From this pseudo redshift, we estimate that ∼15% of the Swift GRBs have z>5. The advantages of this distance indicator is that (1) it requires only X-ray afterglow data while other methods such as Amati and Yonetoku correlations require the peak energy (Ep) of the prompt emission, (2) the redshift is uniquely determined without redshift degeneracies unlike the Amati correlation, and (3) the redshift is estimated in advance of deep follow-ups so that possible high redshift GRBs might be selected for detailed observations.

Original languageEnglish
Title of host publicationGamma-Ray Bursts 2007 - Proceedings of the Santa Fe Conference
Number of pages4
Publication statusPublished - 2008
EventSanta Fe Conference on Gamma-Ray Bursts 2007, GRB 2007 - Santa Fe, NM, United States
Duration: 2007 Nov 52007 Nov 9

Publication series

NameAIP Conference Proceedings
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616


ConferenceSanta Fe Conference on Gamma-Ray Bursts 2007, GRB 2007
Country/TerritoryUnited States
CitySanta Fe, NM


  • X-ray afterglows


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