Looking into the fireball: Rotse-III and swift observations of early gamma-ray burst afterglows

Authors

E. S. Rykoff, University of California, Santa Barbara
F. Aharonian, Max Planck Institute for Nuclear Physics
C. W. Akerlof, University of Michigan, Ann Arbor
M. C.B. Ashley, UNSW Sydney
S. D. Barthelmy, NASA Goddard Space Flight Center
H. A. Flewelling, University of Michigan, Ann Arbor
N. Gehrels, NASA Goddard Space Flight Center
E. Göǧüş, Sabancı Üniversitesi
T. Güver, The University of Arizona
Ü Kiziloǧlu, Middle East Technical University (METU)
H. A. Krimm, NASA Goddard Space Flight Center
T. A. McKay, University of Michigan, Ann Arbor
M. Özel, Çağ Üniversitesi
A. Phillips, UNSW Sydney
R. M. Quimby, California Institute of Technology
G. Rowell, The University of Adelaide
W. Rujopakarn, The University of Arizona
B. E. Schaefer, Louisiana State University
D. A. Smith, Guilford College
W. T. Vestrand, Los Alamos National Laboratory
J. C. Wheeler, The University of Texas at Austin
J. Wren, Los Alamos National Laboratory
F. Yuan, University of Michigan, Ann Arbor
S. A. Yost, College of Saint Benedict Saint John's University

Document Type

Article

Publication Date

1-1-2009

Abstract

We report on a complete set of early optical afterglows of gamma-ray bursts (GRBs) obtained with the Robotic Optical Transient Search Experiment (ROTSE-III) telescope network from 2005 March through 2007 June. This set is comprised of 12 afterglows with early optical and Swift/X-Ray Telescope observations, with a median ROTSE-III response time of 45 s after the start of γ-ray emission (8 s after the GCN notice time). These afterglows span 4 orders of magnitude in optical luminosity, and the contemporaneous X-ray detections allow multi-wavelength spectral analysis. Excluding X-ray flares, the broadband synchrotron spectra show that the optical and X-ray emission originate in a common region, consistent with predictions of the external forward shock in the fireball model. However, the fireball model is inadequate to predict the temporal decay indices of the early afterglows, even after accounting for possible long-duration continuous energy injection. We find that the optical afterglow is a clean tracer of the forward shock, and we use the peak time of the forward shock to estimate the initial bulk Lorentz factor of the GRB outflow, and find 100 ≲ Γ0 ≲ 1000, consistent with expectations. © 2009 The American Astronomical Society. All rights reserved.

Publication Source (Journal or Book title)

Astrophysical Journal

First Page

489

Last Page

505

Recommended Citation

Rykoff, E., Aharonian, F., Akerlof, C., Ashley, M., Barthelmy, S., Flewelling, H., Gehrels, N., Göǧüş, E., Güver, T., Kiziloǧlu, Ü., Krimm, H., McKay, T., Özel, M., Phillips, A., Quimby, R., Rowell, G., Rujopakarn, W., Schaefer, B., Smith, D., Vestrand, W., Wheeler, J., Wren, J., Yuan, F., & Yost, S. (2009). Looking into the fireball: Rotse-III and swift observations of early gamma-ray burst afterglows. Astrophysical Journal, 702 (1), 489-505. https://doi.org/10.1088/0004-637X/702/1/489