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Date: Sun, 21 Sep 2003 10:51:34 -0700
From: Arne Henden <aah@nofs.navy.mil>
Subject: [vsnet-alert 7891] Re: Keck Image of OT near HX Peg
Michael,
I think it is premature to assume the Keck object that you
marked is your faded optical transient. On the Keck image, this
object looks extended, as it does on my poorer resolution V-band image;
this looks like a galaxy to me.
Once you reach the DSS2 limit, it gets very difficult for finding
optical transients. Above that limit, you just look for something "new",
or at least something fading, when dealing with gamma-ray bursts. Below that
limit, you have to take at least two epochs of images and compare.
It sure would have been nice to have at least one CCD image on the
first night; perhaps ASAS covered this field after the outburst (I know
Kato-san indicated an image 0.17d earlier).
You also asked:
>How do the GRB satellites schedule the runs? Would any of them have been
>covering this spot around Sep 20 08UT ?
There is only one "GRB" satellite (HETE-2), which runs continuously
but which only covers a portion of the full sky. It points antisolar
and so was covering your region at the time. It has not seen any
bursts since September 14. There are several other satellites that
carry gamma-ray detectors, but either not covering the full sky, or
with low sensitivity, so you cannot count on the non-detection as
meaning no gamma-ray burst took place for any random location.
However, the HETE non-detection in this case is pretty good evidence.
For where HETE was pointing (roughly, since it moves a few minutes/day), see:
http://space.mit.edu/HETE/mission_status.html#hetepointing
I think the jury is out regarding what you saw. Obviously,
a 14th magnitude asteroid is either well-known or a NEO which would
have shown movement. Any kind of flare star doesn't have that
kind of amplitude if your position is correct (if instead it was
coincident with the 155 comp, then we could be suspicious of
that star). A new CV could possibly have that kind of range,
but the field is pretty blank. Your best bet is if you can get
another set of images from Keck tonight.
Arne
Michael Linnolt wrote:
> I obtained a deep set of images from the Keck I telescope (10m) on Mauna
> Kea around 07UT Sep 21. I placed the R band along with Arne's earlier V
> band 1m image for comparison on my webpage:
>
> http://vsnet2.hawaii.edu/~linnolt/HXPegtransient.html
>
> It appears there is an object that has faded substantially in the
> intervening time, which is very near to the center of my original error
> box from the visual observation.
>
> Further followup of the Keck deep field would certainly help nail down
> which object here is the actual OT.
>
> Anyone have earlier images of sufficient depth to compare?
>
> Mike Linnolt
>
>
>
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