OPTICAL STUDIES IN THE FIELDS OF GAMMA-RAY BURST SOURCES .2. GRB-910219 AND THE DETECTION OF FLASHING OPTICAL COUNTERPART

We present here the results of the analysis of the error box of the ga mma ray bursts source GRB 910219 carried out on 9104 photographic plat es representing 2.06 years of exposure (the most extended archival sea rch for any particular GRBS position so far). One probable optical fla shing candidate has been found and analysed in detail to avoid any mis interpretation. This analysis has confirmed that the image detected on May 10, 1905, is a real object, reaching for less-than-or-equal-to 35 min the brightness of less-than-or-equal-to 5.8 mag. The image was no t caused by a plate defect (brightness more than 5 mag above plate lim it, presence of coma and halo like bright stars) or by a double exposu re (negative blinktest). Further, the object cannot be explained as a satellite glint or aircraft flash (the plate was taken in 1905), an as teroid or comet (very bright object with lack of trailing at high ecli ptic latitude, no image on adjacent plate), a novae (not found on adja cent plates), a dwarf novae (light amplitude greater-than-or-equal-to 15 mag, absent on adjacent plates) and/or a flare star (too large ampl itude). The image was found to show lack of trailing and inside of the error box of GRB 910219 as provided by the WATCH experiment onboard o f the GRANAT satellite. The parameters and the consequences of this op tical transient candidate are presented and discussed.