[AZ-Observing] GRB summary

Brian Skiff <Brian.Skiff@xxxxxxxxxx> · Wed, 2 Apr 2003 13:42:43 -0700 (MST)

     For those interested, here is a good summary of activity on the recent
bright GRB from Arne Henden (USNO-Flagstaff), which was sent to the AAVSO
GRB alert list.  The citations he makes with GCN numbers are to reports that
are archived here:

http://lheawww.gsfc.nasa.gov/docs/gamcosray/legr/bacodine/gcn3_archive.html

\Brian

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From: Arne Henden <aah@xxxxxxxxxxxxx>
To: agrb <aavso-grb-list@xxxxxxxxxxxxxxxxxxxxxxxxx>
Subject: [AAVSO-GRB] grb030329, summary to date
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Date: Wed, 02 Apr 2003 10:52:54 -0700


I know email has been flying fast and furious, so I thought
it might be useful to summarize what has happened on this
burst so far.
   The burst was detected by HETE (GCN 1997) and was considered
a long, extremely bright GRB.  The best localization was from
the SXC instrument, giving a 90% confidence circle that
was 2arcmin in radius and centered at
     10:44:50 +21:30:54 J2000
The burst occurred at 11:37:14.67 UT, and was reported at
12:50:24 UT, a delay of 73minutes due to the necessity of
a ground analysis for this particular burst.  This alert was
too late for any U.S. observation.
   Peterson and Price (GCN 1985), observing from Siding Spring,
found an optical transient at 12th magnitude in R and reported it
at 13:27UT.  At 13:43UT,  the RIKEN group confirmed this OT.
The coordinates of this transient were given in GCN 1987 as
   RA: 10:44:50.0   Dec: 21:31:17.8   (J2000)
A contemporaneous CONCAM observation (Ofek et al., GCN 2031)
gives a prompt emission limit of magnitude ~ 3.5; this is
quite bright and perhaps can be extended downward with careful
reduction.  It would seem the on-board HETE optical camera should
give a fainter limit as well.
   Numerous other groups then started reporting photometry as the
field became observable at their site.  Finally, a decent redshift
was reported by Greiner et al. (GCN 2020) as z=0.168; the closest
GRB except for GRB980425 (SN1998bw), which is most likely why
the afterglow is so bright.  Observations were made
in the X-ray region by RXTE (Marshall et al., GCN 1996, 2052),
who indicated that this was one of the brightest afterglows ever
detected by RXTE.  J-band data was given by Lamb, et al. (GCN 2040);
this data shows the burst to be relatively bright in the near-IR,
especially since it is quite blue in the visible wavelengths.
Radio observations were given by Berger, et al. (GCN 2014)
and Pooley (GCN2043) and also indicated that this was the
brightest radio afterglow ever observed.
   One of the more interesting aspects of this burst were the
visual observations from Henriksson and Tuukkanen (GCN 2010),
two Finnish observers, who saw the OT while it was still around
V=14.2.
   First-day reports indicated a bump in the general decline, similar
to GRB021004.  Likewise, there were reports of light curve breaks,
etc., showing that the light curve was not smooth, but had bumps
and wiggles.  It will take a few days before a clean light curve
is available since few people used common comparison stars.
   There have been reports from many AAVSO members; good going!
These have resulted in two GCNs so far: 2058 and 2071.
The current light curve shows general fading, reaching V=17.5 last
night, but with many bumps and wiggles.  It may rebrighten, but
in any case seems to be flattening out.  If you can get decent
statistics at R=17 with ~1hr exposures, I would continue to observe
this OT, concentrating on Rc.  I calibrated the field (GCN2023)
and recommend everyone use that calibration since only zeropoint
shifts will be necessary.  You should *not* use USNO-A for
photometric calibration.

Arne

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