ar X iv : a st ro - p h / 99 02 27 2 v 2 1 M ar 1 99 9 The afterglow , the redshift , and the extreme energetics of the γ - ray burst 990123

ar X iv : a st ro - p h / 99 04 02 5 v 1 2 A pr 1 99 9 The Afterglow of GRB 990123 and a Dense Medium

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 ...

ar X iv : a st ro - p h / 99 02 29 8 v 2 1 3 A pr 1 99 9 New limits on Ω Λ and Ω M from old galaxies at high redshift

ar X iv : a st ro - p h / 99 02 19 6 v 2 1 7 Fe b 19 99 Optical follow up of the GRB 990123 source from UPSO , Nainital

The CCD magnitudes in Johnson BV and Cousins R photometric passbands are determined for the optical transient of GRB 990123. These observations have been taken approximately 12 hours after trigger of the gamma-ray burst. BVR photometric light curves are obtained by combining the published data with the present measurements. They indicate that the flux decay constants in BV and R passbands are a...

ar X iv : a st ro - p h / 99 02 19 6 v 1 1 3 Fe b 19 99 Optical follow up of the GRB 990123 source from UPSO , Nainital

The CCD magnitudes in Johnson BV and Cousins R photometric passbands are determined for the optical transient of GRB 990123. These observations have been taken approximately 12 hours after trigger of the gamma-ray burst. BVR photometric light curves are obtained by combining the published data with the present measurements. They indicate that the flux decay constants in BV and R passbands are a...

ar X iv : a st ro - p h / 99 12 40 2 v 1 1 8 D ec 1 99 9 LOTIS Upper Limits and the Prompt OT from GRB 990123

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, ...