GRB 991216 joins the jet set: Discovery and monitoring of its optical afterglow

被引:85
作者
Halpern, JP
Uglesich, R
Mirabal, N
Kassin, S
Thorstensen, J
Keel, WC
Diercks, A
Bloom, JS
Harrison, F
Mattox, J
Eracleous, M
机构
[1] Columbia Univ, Dept Astron, New York, NY 10027 USA
[2] Ohio State Univ, Dept Astron, Columbus, OH 43210 USA
[3] Dartmouth Coll, Dept Phys & Astron, Hanover, NH 03755 USA
[4] Univ Alabama, Dept Phys & Astron, Tuscaloosa, AL 35487 USA
[5] CALTECH, Palomar Observ, Pasadena, CA 91125 USA
[6] Boston Univ, Dept Astron, Boston, MA 02215 USA
[7] Penn State Univ, Dept Astron & Astrophys, Davey Lab 525, University Pk, PA 16802 USA
关键词
gamma rays : bursts;
D O I
10.1086/317134
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
The optical light curve of the energetic gamma -ray burst GRB 991216 is consistent with jetlike behavior in which a power-law decay steepens from t(-1.22+/-0.04) at early times to t(-1.53+/-0.05) in a gradual transition at around 2 days. The derivation of the late-time decay slope takes into account the constant contribution of a host or intervening galaxy, which was measured 110 days after the event at R = 24.56 +/- 0.14, although the light curve deviates from a single power law whether or not a constant term is included. The early-time spectral energy distribution of the afterglow can be described as F-nu proportional to nu (-0.74+/-0.05) or flatter between optical and X-ray, which, together with the slow initial decay, is characteristic of standard adiabatic evolution in a uniformly dense medium. Assuming that a reported absorption-line redshift of 1.02 is correct, the apparent isotropic energy of 6.7 x 10(53) ergs is reduced by a factor of approximate to 200 in the jet model, and the initial half-opening angle is approximate to 6 degrees. GRB 991216 is the third good example of a jetlike afterglow (following GRB 990123 and GRB 990510), supporting a trend in which the apparently most energetic gamma -ray events have the narrowest collimation and a uniform interstellar medium environment. This, plus the absence of evidence for supernovae associated with jetlike afterglows, suggests that these events may originate from a progenitor in which angular momentum plays an important role but a massive stellar envelope or wind does not, e.g., in the coalescence of a compact binary.
引用
收藏
页码:697 / 703
页数:7
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