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Identification and Early Spectroscopic Observations
of the Optical Transient GRB090726

Russian version

    At 22:42:27 UT 26/07/09, the Burst Alert Telescope (BAT) on board of the SWIFT multi-wavelength space observatory triggered and located GRB 090726 gamma-ray burst event. A message about this burst was received by the observing researchers of the SAO RAS within minutes from its detection.

    About half an hour after the BAT trigger, the first images were obtained with the SAO RAS Zeiss-1000 telescope in four BVRI filters (see Fig.1). A fading object of the R st.magn.18.26 missing in the DSS images was detected within the initial SWIFT/XRT error circle of 3'. When the corrected coordinates from the SWIFT/XRT X-ray telescope became available, they coincided with our data.
    The spectrum of the optical transient was obtained with the SAO RAS 6-m BTA telescope 1.54 hours after the burst, using the SCORPIO instrument in the spectroscopic mode (Fig.2). The first telegram confirming the variable character of the detected optical source was published a few hours after the event trigger. The second telegram with results of the BTA spectrum analysis made in collaboration with the Spanish and Italian colleagues within the framework of an international GRB study program was published within one day from the event. A redshift of z=2.71 was determined, a number of absorption lines of highly ionized atoms and the Ly alpha line were identified. The spectrum of the object with the coordinates R.A.(J2000.0)=16:34:43.044, DEC(J2000.0)=+72:53:04.82 was obtained with the northernmost large telescope - BTA.
T.Fatkhullin, A.Moskvitin, A.Valeev, S.Fabrika, O.Sholukhova, V.Sokolov; in collaboration with A. de Ugarte Postigo (OAB-INAF, Italy); J.Gorosabel and A.Castro-Tirado (IAA-CSIC, Spain).

Contact - A.Moskvitin

Fig.2. The spectrum of the optical transient GRB090726 with identified lines, obtained with the BTA 1.54 hours after the burst.

Fig.1. Top: DSS image of the SWIFT/BAT error circle (R filter). Bottom: a direct image obtained with the SAO RAS Zeiss-1000 telescope 0.5 hours after the gamma-ray burst. The arrow points to the location of the optical transient GRB090726 (OT).