GRB 080121

E. Troja (INAF/IASFPA), and D. N. Burrows (PSU) report
on behalf of the Swift XRT team:

We have analysed 21 ks of XRT/PC data for the short GRB 080121 (trigger
301491; Cummings & Palmer, GCN 7209
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 ), starting 2.3 d after the burst.
No X-ray afterglow candidate is found within the BAT error circle
(GCN 7209
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 ). A faint source is detected within the BAT error circle at

RA(2000) = 09h 08m 46.36s,
Dec(J2000) = +41d 51' 21.1''

with an error radius 5 arcsec (90% containment). This source has a count
rate of ~2E-03 cts/s, and displays no fading behaviour.

We place a 3 sigma upper limit of 1E-03 cts/s on the X-ray afterglow count
rate, which corresponds to an unabsorbed flux of 3.7E-14 erg/cm^2/s (over
0.3-10 keV), assuming a Crab-like spectrum and a Galactic absorption of
1.23E+20 cm^-2 (Kalberla et al. 2005).

This circular is an official product of the Swift XRT Team.

A. Cucchiara (PSU), P. Schady (MSSL)
report on behalf of the Swift-UVOT team:

The Swift/UVOT observed the field of GRB080121 (trigger #301491)
starting 2.3 days after the BAT detection (J. R. Cummings et
al. 2008, GCN Circ. 7209
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 ). We do not find any new source in any
of the UVOT coadded observations inside the BAT error circle.

The 3-sigma upper limits (in the UVOT photometric system,
Breeveld et al., GCN Circ. 6614
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 ) are listed.

Filter     Tstart        Exp    Magnitude  
                         (s)
white       2.3 days     2015    >22.25
v           2.3 days     2268    >20.73
uvm2        3.4 days     1491    >21.13

The values quoted above are not corrected for the expected Galactic
extinction corresponding to a reddening of E_{B-V} = 0.02  mag in the
direction of the burst (Schlegel et al. 1998).

P. A. Evans reports,

The enhanced XRT position for GRB 081021 just reported (GCN Circ. 7124
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 )
was not the position of the GRB afterglow. This source is a serendipitous
source. We apologise for any confusion.

We are implementing further checks to ensure that circulars are only issued for
GRB afterglow candidates. Details of the XRT enhancement process are provided at
http://www.swift.ac.uk/team/xrt_positions/docs.php

P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 1003 s of overlapping XRT Photon Counting mode and UVOT
V-band data for GRB 080121, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 137.15169, +41.84639 which is equivalent
to:

RA (J2000): 09h 08m 36.41s
Dec (J2000): +41d 50' 47.0"

with an uncertainty of 3.5 arcsec (radius, 90% confidence).

This position may be improved as more data are received. The latest position
can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is
described by Goad et al. (2007, astro-ph/0708.0986
http://www.swift.ac.uk/xrt_positions/Goad.pdf).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

D. A. Perley, R. J. Foley, and J. S. Bloom (UC Berkeley) report:

Two SDSS spectroscopically-catalogued galaxies are present in NED* 
within the Swift-BAT error circle of GRB 080121 (Cummings et al., GCN 7209
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 ):

SDSS J090858.15+414926.5   09:08:58.1 +41:49:27 z=0.045322
SDSS J090904.12+415033.2   09:09:04.1 +41:50:33 z=0.046041

Several other, fainter extended sources are also present in the field, 
possibly indicating that this GRB may have occurred within a group or 
small cluster.  At a redshift of z=0.046, the isotropic energy release 
would be ~10^47 erg, several orders of magnitude less than typical 
short-hard bursts.

* The NASA/IPAC Extragalactic Database (NED) is operated by the Jet 
Propulsion Laboratory, California Institute of Technology, under 
contract with the National Aeronautics and Space Administration.

J. R. Cummings and D. M. Palmer for the Swift-BAT team

At 21:29:55 on Jan 21, 2008, BAT detected a weak short GRB 
(trigger #301491) at a ground-calculated location 
RA, Dec 137.235, +41.841, error radius 3 arcmin (90% confidence),
which is:
RA(J2000)  = 09h 08m 56s
Dec(J2000) = +41d 50' 29"
 
The significance of the source in the detection image was just 
below the alert threshold, so Swift did not slew immediately to 
the burst. In addition, the source location was in Moon constraint, 
so no late observation was made.

As seen in BAT, the burst was a single peak with T90 0.7 +- 0.2
seconds. Because of the weakness of the burst, a power-law fit to 
the spectrum from T-0.4 to T+0.4 sec is not well constrained. The 
power-law index is 2.6 +- 0.8. The fluence was 
(3 +- 2) x 10^-8 erg/cm2/sec. Quoted uncertainties are 90%
confidence including estimated systematic error.