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

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 02 23 4 v 2 1 7 Fe b 19 99 OB ASSOCIATIONS

ar X iv : a st ro - p h / 99 02 19 0 v 1 1 2 Fe b 19 99 LOTIS Search for Early Time Optical Afterglows : GRB 971227

We report on the very early time search for an optical afterglow from GRB 971227 with the Livermore Optical Transient Imaging System (LOTIS). LOTIS began imaging the ‘Original’ BATSE error box of GRB 971227 approximately 14 s after the onset of gamma-ray emission. Continuous monitoring of the position throughout the evening yielded a total of 499 images (10 s integration). Analysis of these ima...

ar X iv : a st ro - p h / 99 03 43 8 v 1 2 9 M ar 1 99 9 GRB 990123 : The Case for Saturated Comptonization

We find that the optical magnitudes of GRB990123 observed by ROTSE correlates with the magnitudes extrapolated from the simultaneous BATSE spectra, strongly suggesting that the optical, X-ray and gamma-ray photons originate from a single source. We then show that the broadband optical-gamma-ray spectra can be naturally fit by the saturated Compton model. We also derive the parameters of the Com...

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 ...