Re: gamma-ray burst 021021

[Arne Henden <aah@nofs.navy.mil>]

Michael,
   It would be *highly* unlikely to find anything in a wide-field
image hours after a gamma-ray burst.  If you look at the decay
rate from even the brightest bursts, they are 18th magnitude
about 4hrs after the burst.  This particular burst was an
Xray Flash; that is, essentialy no gamma rays, and weak at that.
   As another example, there are several wide-field rapid response
telescopes that have been following GRBs for years (ROTSE and
LOTIS are examples).  While reaching a GRB localization within
seconds after the burst, only one afterglow has been detected amongst
dozens of searches to 15th magnitude.
   I'm being pessimistic here because I've been chasing these things
for years.  For small (10cm) telescopes, you basically have to be
there within the first hour.  So when the full Mark IV complement
is up and running, ASAS is working well, LINEAR/LONEOS/LSST/etc. are
operational, then we might have something close to full sky coverage
on an hourly basis and will have a reasonable chance to catch one of
these bursts "serendipitously" (or even to look for the elusive
"orphan afterglows").
   On the other hand, there are plenty of transient events occuring
all of the time.  For example, the peculiar novae V838 Mon (that I
have been following for the past 10 months) was discovered around
January 7.  Jim Bedient went back and looked at the previous few months
of StarDial imagery and both came up with an upper limit to the brightness
last year, plus obtained a half-dozen datapoints on the outburst rise.
Likewise, Tim McKay and colleagues (2001ApJ...557L..97W) went back
and searched the ROTSE database after J1118+480 was discovered, and
obtained an archival lightcurve.  So there are plenty of reasons for
keeping archival all-sky data, just that GRBs are probably far down
ths list.
Arne

Stupendous Man wrote:
>   I've just received a notice about a gamma-ray burst
> which might possibly be of interest to TASSians.  You can 
> find the notice at 
> 
>       http://gcn.gsfc.nasa.gov/gcn/gcn3/1649.gcn3
> 
> but the bottom line is:
> 
> 
>>At 18:43:00.00 UTC (67380.00 s UT) on 21 Oct 2002, the HETE FREGATE
>>and WXM instruments detected a faint, untriggered XRF.
>>
>>Ground analysis of the WXM data for the burst produced a location,
>>which was reported in a GCN Notice at 10:58:44 UT on 22 Oct 2002,
>>about 16 hours after the burst.  The WXM localization SNR was 6.
>>The WXM location can be expressed as a 90% confidence circle that
>>is 20 arcminutes in radius and is centered at
>>
>>RA = 00h 17m 23s, Dec = -01d 37' 00" (J2000).
> 
> 
>   Now, the time of the burst corresponds to EDT Monday Oct 21 (yesterday)
> at about 2:43 in the afternoon.  If anyone happened to be looking at the
> equator last night (Monday night), he might have taken images
> of the field containing this burst.  In fact, I was using the Mark IV
> for a short time last night, until a bunch of stupid clouds got in
> the way.  Unfortunately, I wasn't looking at the equator :-(
> 
>   But perhaps some other people happened to be looking at the 
> equator last night.  If so, please reply to this list.  I (and lots
> of other people, too) would be happy to help you look at your
> images to see if any new object appears in them ...
> 
>                                  Michael Richmond
> 
> 
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