The host galaxy of GRB 990123

J. S. Bloom*, S. C. Odewahn, S. G. Djorgovski, S. R. Kulkarni, F. A. Harrison, C. Koresko, G. Neugebauer, L. Armus, D. A. Frail, R. R. Gal, R. Sari, G. Squires, G. Illingworth, D. Kelson, F. H. Chaffee, R. Goodrich, M. Feroci, E. Costa, L. Piro, F. FronteraS. Mao, C. Akerlof, T. A. McKay

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

53 Scopus citations

Abstract

We present deep images of the field of GRB 990123 obtained in a broadband UV/visible bandpass with the Hubble Space Telescope (HST) and deep near-infrared images obtained with the Keck I 10 m telescope. The HST image reveals that the optical transient (OT) is offset by 0″.67 (5.8 kpc in projection) from an extended, apparently interacting galaxy. This galaxy, which we conclude is the host galaxy of GRB 990123, is the most likely source of the absorption lines of metals at a redshift of z = 1.6 seen in the spectrum of the OT. With magnitudes of Gunn-r = 24.5 ± 0.2 and K = 22.1 ± 0.3 mag, this corresponds to an L ∼ 0.5L* galaxy, assuming that it is located at z = 1.6. The estimated unobscured star formation rate is ≈4 M yr-1, which is typical for normal galaxies at comparable redshifts. There is no evidence for strong gravitational lensing magnification of this burst, and some alternative explanation for its remarkable energetics (such as beaming) may therefore be required. The observed offset of the OT from the nominal host center, the absence of broad absorption lines in the afterglow spectrum, and the relatively blue continuum of the host do not support the notion that gamma-ray bursts (GRBs) originate from active galactic nuclei or massive black holes. Rather, the data are consistent with models of GRBs that involve the death and/or merger of massive stars. Indeed, the HST image suggests an intimate connection between GRB 990123 and a star-forming region.

Original languageAmerican English
Pages (from-to)L1-L4
JournalAstrophysical Journal
Volume518
Issue number1 PART 2
DOIs
StatePublished - 10 Jun 1999
Externally publishedYes

Bibliographical note

Funding Information:
We are grateful to S. Beckwith of STScI for the allocation of the director’s discretionary time for this project and to the entire BeppoSAX team and the staff of W. M. Keck Observatory for their efforts. We also thank L. Ferrarese for aiding us with HST observing and the anonymous referee for helpful and clarifying comments. This work was supported in part by a grant from STScI, grants from the NSF and NASA, and the Bressler Foundation.

Keywords

  • Cosmology: miscellaneous
  • Cosmology: observations
  • Gamma rays: bursts

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