Cenko, S. B. and Fox, D. B. and Cucchiara, A. and Penprase, B. E. and Price, P. A. and Berger, E. (2008) GRB 070125: The First Long-Duration Gamma-ray Burst in a Halo Environment. In: Gamma-ray bursts 2007 : proceedings of the Santa Fe conference, Santa Fe, New Mexico, 5-9 November 2007. AIP Conference Proceedings, 1000 (1000). American Institute of Physics , Melville, NY, pp. 342-345. ISBN 978-0-7354-0533-2 http://resolver.caltech.edu/CaltechAUTHORS:20100707-134352471
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We present the discovery and high signal-to-noise spectroscopic observations of the optical afterglow of the long-duration gamma-ray burst GRB 070125. Unlike all previously observed long-duration afterglows in the redshift range 0.5 ≾ z ≾ 2.0, we find no strong (rest-frame equivalent width W_r ≳ 1.0 Å) absorption features in the wavelength range 4000–10000 Å. The sole significant feature is a weak doublet that we identify as Mg II λλ 2796 (W_r = 0.18±0.02 Å), 2803 (Wr = 0.08±0.01 Å) at z = 1.5477±0.0001. The low observed Mg II and inferred H I column densities are typically observed in galactic halos, far away from the bulk of massive star formation. Deep ground-based imaging reveals no host directly underneath the afterglow to a limit of R>25.4 mag. Either of the two nearest blue galaxies could host GRB 070125; the large offset (d ≳ 27 kpc) would naturally explain the low column densities. To remain consistent with the large local (i.e. parsec scale) circum-burst density inferred from broadband afterglow observations, we speculate GRB 070125 may have occurred far away from the disk of its host in a compact star-forming cluster. Such distant stellar clusters, typically formed by dynamical galaxy interactions, have been observed in the nearby universe, and should be more prevalent at z>1 where galaxy mergers occur more frequently.
|Item Type:||Book Section|
|Additional Information:||© 2008 American Institute of Physics. Issue Date: 22 May 2008.|
|Subject Keywords:||gamma-rays : bursts|
|Classification Code:||PACS: 98.70.Rz; 95.55.Qf; 98.62.Py; 98.35.Jk|
|Official Citation:||GRB 070125: The First Long-Duration Gamma-ray Burst in a Halo Environment S. B. Cenko, D. B. Fox, A. Cucchiara, B. E. Penprase, P. A. Price, and E. Berger, AIP Conf. Proc. 1000, 342 (2008), DOI:10.1063/1.2943479|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||09 Jul 2010 17:58|
|Last Modified:||26 Dec 2012 12:12|
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