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The Host Galaxy of GRB 990123  [PDF]
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. Chaffee,R. Goodrich,M. Feroci,E. Costa,L. Piro,F. Frontera,S. Mao,C. Akerlof,T. A. McKay
Physics , 1999, DOI: 10.1086/312059
Abstract: We present deep images of the field of gamma-ray burst (GRB) 990123 obtained in a broad-band UV/visible bandpass with the Hubble Space Telescope, and deep near-infrared images obtained with the Keck-I 10-m telescope. Both the HST and Keck images show that the optical transient (OT) is clearly offset by 0.6 arcsec from an extended object, presumably the host galaxy. This galaxy is the most likely source of the metallic-line absorption at z = 1.6004 seen in the spectrum of the OT. With magnitudes V_{C} ~ 24.6 +/- 0.2 and K = 21.65 +/- 0.30 mag this corresponds to an L ~ 0.7 L_* galaxy, assuming that it is located at z = 1.6. The estimated unobscured star formation rate is SFR ~ 6 M_sun/yr, which is not unusually high for normal galaxies at comparable redshifts. The strength of the observed metallic absorption lines is suggestive of a relatively high metallicity of the gas, and thus of a chemically evolved system which may be associated with a massive galaxy. It is also indicative of a high column density of the gas, typical of damped Ly-alpha systems at high redshifts. We conclude that this is the host galaxy of GRB 990123. No other obvious galaxies are detected within the same projected radius from the OT. There is thus no evidence for strong gravitational lensing magnification of this burst, and some alternative explanation for its remarkable energetics may be required. The observed offset of the OT from the center of its apparent host galaxy, 5.5 +/- 0.9 proper kpc (projected) in the galaxy's rest-frame, both refutes the possibility that GRBs are related to galactic nuclear activity and supports models of GRBs which involve the death and/or merger of massive stars. Further, the HST image suggests an intimate connection of GRB 990123 and a star-forming region.
BVRI CCD photometric standards in the field of GRB 990123  [PDF]
Nilakshi,R. K. S. Yadav,V. Mohan,A. K. Pandey,R. Sagar
Physics , 1999,
Abstract: The CCD magnitudes in Johnson $BV$ and Cousins $RI$ photometric passbands are determined for 18 stars in the field of GRB 990123. These measurements can be used in carrying out precise CCD photometry of the optical transient of GRB 990123 using differential photometric techniques during non--photometric sky conditions. A comparison with previous photometry indicates that the present photmetry is more precise.
Constraints on the Bulk Lorentz Factor of GRB 990123  [PDF]
Alicia M. Soderberg,Enrico Ramirez-Ruiz
Physics , 2002, DOI: 10.1063/1.1579332
Abstract: GRB 990123 was a long, complex gamma-ray burst accompanied by an extremely bright optical flash. We present the collective constraints on the bulk Lorentz factor for this burst based on estimates from burst kinematics, synchrotron spectral decay, prompt radio flash observations, and prompt emission pulse width. Combination of these constraints leads to an average bulk Lorentz factor for GRB 990123 of Gamma_0=1000 +/- 100 which implies a baryon loading of M_jet=8 (+17/-2) x 10^-8 Msolar. We find these constraints to be consistent with the speculation that the optical light is emission from the reverse shock component of the external shock. In addition, we find the implied value of M_jet to be in accordance with theoretical estimates: the baryonic loading is sufficiently small to allow acceleration of the outflow to Gamma > 100.
GRB990123, The Optical Flash and The Fireball Model  [PDF]
Re'em Sari,Tsvi Piran
Physics , 1999, DOI: 10.1086/312039
Abstract: We compare the ongoing observations of the remarkable burst GRB990123, the mother of all bursts, with the predictions of the afterglow theory. We show that the observations agree with the recent prediction that a reverse shock propagating into the ejecta would produce a very strong prompt optical flash. This reverse shock has also produced the 8.46GHz radio signal, observed after one day. The forward shock, which propagates into the ISM is the origin of the classical afterglow. It has produced the prompt X-ray signal as well as the late optical and IR emission. It would most likely produce a radio emission within the next few weeks. The observations suggest that the initial Lorentz factor of the ejecta was $\sim 200$. Within factors of order unity, this crude model explains all current observations of GRB990123.
GRB990123: The Case for Saturated Comptonization  [PDF]
E. P. Liang,A. Crider,M. Boettcher,I. A. Smith
Physics , 1999, DOI: 10.1086/312100
Abstract: The recent simultaneous detection of optical, X-ray and gamma-ray photons from GRB990123 during the burst provides the first broadband multi-wavelength characterization of the burst spectrum and evolution. Here we show that a direct correlation exists between the time-varying gamma-ray spectral shape and the prompt optical emission. This combined with the unique signatures of the time-resolved spectra of GRB990123 convincingly supports earlier predictions of the saturated Comptonization model. Contrary to other suggestions, we find that the entire continuum from optical to gamma-rays can be generated from a single source of leptons (electrons and pairs). The optical flux only appears to lag the gamma-ray flux due to the high initial Thomson depth of the plasma. Once the plasma has completely thinned out, the late time afterglow behavior of our model is the same as in standard models based on the Blandford-McKee (1976) solution.
BVRcIc photometry of GRB 980703 and GRB 990123 host galaxies  [PDF]
V. V. Sokolov,T. A. Fatkhullin,V. N. Komarova
Physics , 2000,
Abstract: We present a photometry of GRB 980703 and GRB 990123 host galaxies which was performed about 20 days and a half year after gamma-ray bursts occured, respectively. The contributions of the optical transiets (OT) were negligible in both cases. We derived broad band BVR_cI_c spectra of the host galaxies and compared them to continuum spectra of different Hubble-type galaxies and averaged spectra of starburst galaxies. For H_0=60 km s^{-1} Mpc^{-1} and three Friedmann cosmological models with matter density and cosmological constant parameters (Omega_m,Omega_Lambda) = (1,0),(0,0),(0,1) we estimated M_Brest and star-forming rates (SFRs) using the fluxes in photometric bands for the host galaxies. Within the range of cosmological parameters our estimates of the absolute magnitudes are: M_Brest = -20.60 .. -21.73 for the GRB 980703 host galaxy and M_Brest = -20.20 .. -21.82 for the GRB 990123 host galaxy. We obtained estimates of K-correction values and absolute magnitudes of the host galaxies using SEDs for star-forming galaxies.
Was GRB 990123 a unique optical flash?  [PDF]
Alicia M. Soderberg,Enrico Ramirez-Ruiz
Physics , 2001, DOI: 10.1046/j.1365-8711.2002.05286.x
Abstract: GRB 990123 was a long, complex gamma-ray burst accompanied by an extremely bright optical flash. We find different constraints on the bulk Lorentz of this burst to be consistent with the speculation that the optical light is emission from the reverse shock component of the external shock. Motivated by this currently favoured idea, we compute the prompt reverse shock emission to be expected for bursts in which multi-wavelength observations allow the physical parameters to be constrained. We find that for reasonable assumptions about the velocity of source expansion, a strong optical flash of approximately m_V=9 was expected from the reverse shocks, which were usually found to be mildly relativistic. The best observational prospects for detecting these prompt flashes are highlighted, along with the possible reasons for the absence of optical prompt detections in ongoing observations.
The Afterglow of GRB 990123 and a Dense Medium  [PDF]
Z. G. Dai,T. Lu
Physics , 1999, DOI: 10.1086/312127
Abstract: Recent observations show that the temporal decay of the R-band afterglow from GRB 990123 steepened about 2.5 days after the burst. We here propose a possible explanation for such a steepening: a shock expanding in a dense medium has undergone the transition from a relativistic phase to a nonrelativistic phase. We find that this model is consistent with the observations if the medium density is about $3\times 10^6 {\rm cm}^{-3}$. By fitting our model to the observed optical and X-ray afterglow quantitatively, we further infer the electron and magnetic energy fractions of the shocked medium and find these two parameters are about 0.1 and $2\times 10^{-8}$ respectively. The former parameter is near the equipartition value while the latter is about six orders of magnitude smaller than inferred from the GRB 970508 afterglow. We also discuss possibilities that the dense medium can be produced.
Discovery of a Radio Flare from GRB 990123  [PDF]
S. R. Kulkarni,D. A. Frail,R. Sari,G. H. Moriarty-Schieven,D. S. Shepherd,P. Udomprasert,A. C. S. Readhead,J. S. Bloom,M. Feroci,E. Costa
Physics , 1999, DOI: 10.1086/312227
Abstract: We report the discovery of a radio counterpart to GRB 990123. In contrast to previous well-studied radio afterglows which rise to peak flux on a timescale of a week and then decay over several weeks to months, the radio emission from this GRB was clearly detected one day after the burst, after which it rapidly faded away. The simplest interpretation of this ``radio flare'' is that it arises from the reverse shock. In the framework of the afterglow models discussed to date, a forward shock origin for the flare is ruled out by our data. However, at late times, some radio afterglow emission (commensurate with the observed late-time optical emission, the optical afterglow) is expected from the forward shock. The relative faintness of the observed late-time radio emission provides an independent indication for a jet-like geometry in this GRB. We use the same radio observations to constrain two key parameters of the forward shock, peak flux and peak frequency, to within a factor of two. These values are inconsistent with the notion advocated by several authors that the prompt optical emission detected by ROTSE smoothly joins the optical afterglow emission. Finally, with hindsight we now recognize another such radio flare and this suggests that one out of eight GRBs has a detectable radio flare. This abundance coupled with the reverse shock interpretation suggests that the radio flare phenomenon has the potential to shed new light into the physics of reverse shocks in GRBs.
LOTIS Upper Limits and the Prompt OT from GRB 990123  [PDF]
G. G. Williams,D. H. Hartmann,H. S. Park,R. A. Porrata,E. Ables,R. Bionta,D. L. Band,S. D. Barthelmy,T. cline,N. Gehrels,D. H. Ferguson,G. Fishman,R. M. Kippen,C. Kouveliotou,K. Hurley,R. Nemiroff,T. Sasseen
Physics , 1999, DOI: 10.1063/1.1361544
Abstract: GRB 990123 established the existence of prompt optical emission from gamma-ray bursts (GRBs). The Livermore Optical Transient Imaging System (LOTIS) has been conducting a fully automated search for this kind of simultaneous low energy emission from GRBs since October 1996. Although LOTIS has obtained simultaneous, or near simultaneous, coverage of the error boxes obtained with BATSE, IPN, XTE, and BeppoSAX for several GRBs, image analysis resulted in only upper limits. The unique gamma-ray properties of GRB 990123, such as very large fluence (top 0.4%) and hard spectrum, complicate comparisons with more typical bursts. We scale and compare gamma-ray properties, and in some cases afterglow properties, from the best LOTIS events to those of GRB 990123 in an attempt to determine whether the prompt optical emission of this event is representative of all GRBs. Furthermore, using LOTIS upper limits in conjunction with the relativistic blast wave model, we weakly constrain the GRB and afterglow parameters such as density of the circumburster medium and bulk Lorentz factor of the ejecta.
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