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[vsolj-alert 251] GRB 990123

GRB 990123


(fwd) GRB 990123 : call for monitoring the next lensed flash?!

From BOND@stsci.edu Tue Jan 26 06:31 JST 1999
Date: Mon, 25 Jan 1999 16:31:44 -0500 (EST)
From: "Howard E. Bond" <BOND@stsci.edu>
Subject: GRB 990123

Dear Dr. Kato:

I am writing about GRB 990123.  This gamma-ray burst was apparently
accompanied by an optical flash that reached 8th mag a few seconds after the
burst on 1999 Jan 23, for a duration of 5 or more seconds, as detected by the
Robotic Optical Transient Search Experiment (ROTSE;
http://vsnet.umich.edu/~rotse/) at Los Alamos, New Mexico, USA.   Several hours
later the optical transient was seen at 18th mag from Palomar Observatory. 
The J2000 position is 15:25:32.7, +44:44:30 according to the Palomar
observers.  An absorption-line redshift of 1.61 has been obtained from Keck

An exciting aspect of this object is the suggestion by S. G. Djorgovski et al.
that GRB 990123 was gravitationally lensed (which might account for the
extraordinary apparent luminosity).  This raises the possibility, emphasized
by E. Turner, that the gamma-ray and optical bursts may recur in the next few
days to months, due to lensing time delays along different paths to the Earth.

It would thus be very worthwhile for vsnet observers to monitor this position
constantly, even with small telescopes or binoculars, to search for such
repeated optical transients, which could in principle even reach to brighter
than 8th mag for a few seconds depending on the lensing amplification. 
Precise times, magnitude estimates, and other details should be determined for
any flashes that are seen. 

best regards,
Howard E. Bond
Space Telescope Science Institute

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