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Kangas, T, Fruchter, AS, Cenko, SB, Corsi, A, de Ugarte Postigo, A, Pe'er, A, Vogel, SN, Cucchiara, A, Gompertz, B, Graham, J, Levan, A, Misra, K, Perley, DA, Racusin, J and Tanvir, N (2020) The Late-time Afterglow Evolution of Long Gamma-Ray Bursts GRB 160625B and GRB 160509A. Astrophysical Journal, 894 (1). ISSN 0004-637X
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The Late-time Afterglow Evolution of Long Gamma-Ray Bursts GRB 160625B and GRB 160509A.pdf - Accepted Version Download (1MB) | Preview |
Abstract
We present post-jet-break Hubble Space Telescope, Very Large Array, and Chandra observations of the afterglow of the long γ-ray bursts GRB 160625B (between 69 and 209 days) and GRB 160509A (between 35 and 80 days). We calculate the post-jet-break decline rates of the light curves and find the afterglow of GRB 160625B is inconsistent with a simple t −3/4 steepening over the break, expected from the geometric effect of the jet edge entering our line of sight. However, the favored optical post-break decline (${f}_{\nu }\propto {t}^{-1.96\pm 0.07}$) is also inconsistent with the f ν ∝ t −p decline (where p ≈ 2.3 from the pre-break light curve), which is expected from exponential lateral expansion of the jet; perhaps suggesting lateral expansion that only affects a fraction of the jet. The post-break decline of GRB 160509A is consistent with both the t −3/4 steepening and with f ν ∝ t −p . We also use boxfit to fit afterglow models to both light curves and find both to be energetically consistent with a millisecond magnetar central engine, but the magnetar parameters need to be extreme (i.e., E ~ 3 × 1052 erg). Finally, the late-time radio light curves of both afterglows are not reproduced well by boxfit and are inconsistent with predictions from the standard jet model; instead, both are well represented by a single power-law decline (roughly f ν ∝ t −1) with no breaks. This requires a highly chromatic jet break (${t}_{j,\mathrm{radio}}\gt 10\times {t}_{j,\mathrm{optical}}$) and possibly a two-component jet for both bursts.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | 0201 Astronomical and Space Sciences, 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics, 0306 Physical Chemistry (incl. Structural) |
| Subjects: | Q Science > QB Astronomy Q Science > QC Physics |
| Divisions: | Astrophysics Research Institute |
| Publisher: | American Astronomical Society; IOP Publishing |
| Related URLs: | |
| Date Deposited: | 06 Aug 2020 08:34 |
| Last Modified: | 04 Sep 2021 06:51 |
| DOI or ID number: | 10.3847/1538-4357/ab8799 |
| URI: | https://researchonline.ljmu.ac.uk/id/eprint/13451 |
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