2007/08/31 by En-Wei Liang, E. Liang, Judith L. Racusin +6 · 209 citations
Physics and Astronomy · #Achromatic lens #Afterglow #Astro and Planetary Science #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Gamma-ray burst #Gamma-ray bursts and supernovae #Jet (fluid) #Light curve #Physics #Swift #astro-ph
paper · pdf · doi:10.1086/524701
published in The Astrophysical Journal 675(1), 528-552 (IOP Publishing) · 48 pages, including 5 tables and 8 figures. Accepted for publication in ApJ. This is the third paper of a series. Paper I and II see astro-ph/0612246 (ApJ, 2007, 666,1002) and arXiv:0705.1373 (ApJ, 2007, 669, n2,in press)
arxiv created 2007/10/17 · openalex publication_date 2008/03/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The Swift/XRT data of 179 GRBs (from 050124 to 070129) and the optical afterglow data of 57 pre- and post-Swift GRBs are analyzed, in order to systematically investigate the jet-like breaks in the X-ray and optical afterglow lightcurves. We find that not a single burst can be included in the ``Platinum'' sample, in which the data satisfy all the criteria of a jet break. By releasing one or more requirements to define a jet break, some candidates of various degrees could be identified. In the X-ray band, 42 out of the 103 well-sampled X-ray lightcurves have a decay slope of the post-break segment >1.5 (``Bronze'' sample), and 27 of them also satisfy the closure relations of the forward models (``Silver'' sample). The numbers of the ``Bronze'' and ``Silver'' candidates in the optical lightcurves are 27 and 23, respectively. Thirteen bursts have well-sampled optical and X-ray lightcurves, but only seven cases are consistent with an achromatic break, but even in these cases only one band satisfies the closure relations (``Gold'' sample). The observed break time in the XRT lightcurves is systematically earlier than that in the optical bands. All these raise great concerns in interpreting the jet-like breaks as jet breaks and further inferring GRB energetics from these breaks. By assuming that these breaks are jet breaks, we perform a similar analysis as previous work to calculate the jet opening angle (thetaj) and energetics (Ek) with the ``Silver'' and ``Gold'' jet break candidates. The derived EK distribution reveals a much larger scatter than the pre-Swift sample. A tentative anti-correlation between thetaj and EK,iso is found for both the pre-Swift and Swift GRBs, indicating that the EK could still be quasi-universal, if the breaks in discussion are indeed jet breaks(abridge).