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Hubble Space Telescope and Palomar Imaging of GRB 990123: Implications for the Nature of Gamma-Ray Bursts and Their Hosts

Fruchter, Andrew S. and Thorsett, S. E. and Metzger, Mark R. and Sahu, Kailash C. and Petro, Larry and Livio, Mario and Ferguson, Henry and Pian, Elena and Hogg, David W. and Galama, Titus and Gull, Theodore R. and Kouveliotou, Chryssa and Macchetto, Duccio and van Paradijs, Jan and Pedersen, Holger and Smette, Alain (1999) Hubble Space Telescope and Palomar Imaging of GRB 990123: Implications for the Nature of Gamma-Ray Bursts and Their Hosts. Astrophysical Journal, 519 (1). L13-L16. ISSN 0004-637X. doi:10.1086/312094.

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We report on Hubble Space Telescope and Palomar optical images of the field of GRB 990123, obtained in 1999 February 8 and 9. We find that the optical transient (OT) associated with GRB 990123 is located on an irregular galaxy, with a magnitude of V = 24.20 ± 0.15. The strong metal absorption lines seen in the spectrum of the OT, along with the low probability of a chance superposition, lead us to conclude that this galaxy is the host of the gamma-ray burst (GRB). The OT is projected within the ~1'' visible stellar field of the host, nearer the edge than the center. We cannot, on this basis, rule out the galactic nucleus as the site of the GRB, since the unusual morphology of the host may be the result of an ongoing galactic merger, but our demonstration that this host galaxy has extremely blue optical-to-infrared colors more strongly supports an association between GRBs and star formation. We find that the OT magnitude in 1999 February 9.05, V = 25.45 ± 0.15, is about 1.5 mag fainter than expected from the extrapolation of the decay rate found in earlier observations. A detailed analysis of the OT light curve suggests that its fading has gone through three distinct phases: an early, rapid decline (f_ν ∝ t^(-1.6) for t < 0.1 days); a slower, intermediate decline power-law decay (f_ν ∝ t^(-1.1) for 0.1 < t < 2 days); and then a more rapid decay (at least as steep as f_ν ∝ t^(-1.8) for t > 2 days). The break to a steeper slope at late times may provide evidence that the optical emission from this GRB was highly beamed.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Sahu, Kailash C.0000-0001-6008-1955
Ferguson, Henry0000-0001-7113-2738
Hogg, David W.0000-0003-2866-9403
Kouveliotou, Chryssa0000-0003-1443-593X
Alternate Title:HST and Palomar Imaging of GRB 990123: Implications for the Nature of Gamma-Ray Bursts and their Hosts
Additional Information:© 1999 The American Astronomical Society. Received 1999 February 17; accepted 1999 April 28; published 1999 June 2. We wish to thank Steven Beckwith, the Director of STScI, for using director’s discretionary time to observe GRB 990123 and for making the data public. We also thank Jen Christensen for assistance in creating appropriate STIS dark files. Note that the reduced HST images discussed in this Letter can be retrieved in FITS format at˜fruchter/GRB/990123.
Subject Keywords:cosmology: observations—gamma rays: bursts—stars: formation
Issue or Number:1
Record Number:CaltechAUTHORS:20190611-081023153
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Official Citation:Andrew S. Fruchter et al 1999 ApJ 519 L13
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:96265
Deposited By: Tony Diaz
Deposited On:11 Jun 2019 16:51
Last Modified:16 Nov 2021 17:19

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