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تسجيل مستخدم جديدArchival searches for transient optical emission in the error box of the 1991 January 22 gamma-ray burst
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We present here the results of a study carried out at the Harvard College Observatory Plate Collection. We examined 3995 plates covering the error box of the gamma-ray burst GRB 910122, over a time span of 90 yr (from 1889 to 1979). The total exposure time is ~0.55 yr. No convincing evidence of optical transient emission was found within the GRB 910122 IPN error box. However, a possible OT was found outside the GRB 910122 error box. Optical ground based observations have revealed a V~22.3 object consistent with the position of the new object. The colours of the object are typical of a K7/M0 star or a reddened galaxy, which could have caused the OT, but the fact that the object is far away from the GRB error box makes both events unrelated.
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The optical transient of the faint Gamma Ray Burst 990308 was detected by the QUEST camera on the Venezuelan 1-m Schmidt telescope starting 3.28 hours after the burst. Our photometry gives $V = 18.32 pm 0.07$, $R = 18.14 pm 0.06$, $B = 18.65 pm 0.23$
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Optical Transients from gamma-ray burst sources, in addition to offering a distance determination, convey important information on the physics of the emission mechanism, and perhaps also about the underlying energy source. As the gamma-ray phenomenon
is extremely diverse, with time scales spanning several orders of magnitude, some diversity in optical counterpart signatures appears plausible. We have studied the Optical Transient, which accompanied the gamma-ray burst of May 8, 1997 (GRB 970508). Observations conducted at the 2.5-m Nordic Optical Telescope (NOT) and the 2.2-m telescope at the German-Spanish Calar Alto observatory (CAHA) cover the time interval starting 3 hours 5 minutes to 96 days after the high energy event. This brackets all other published observations, including radio. When analyzed in conjunction with optical data from other observatories, evidence emerges for a composite light curve. The first interval, from 3 to 8 hours after the event was characterized by a constant, or slowly declining brightness. At a later moment the brightness started increasing rapidly, and reached a maximum approximately 40 hours after the GRB. From that moment the GRB brightness decayed approximately as a power-law of index -1.21. The last observation, after 96 days, m_R = 24.28+-0.10, is brighter than the extrapolated power-law, and hints that a constant component, m_R = 25.50+-0.40 is present. The OT is unresolved (FWHM 0.83) at the faintest magnitude level. The brightness of the optical transient, its duration and the general shape of the light curve sets this source apart from the single other optical transient known, that of the February 28, 1997 event.
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