GRB 050422

K. McGowan (MSSL), A. Blustin (MSSL), S. Rosen (MSSL),
L. Barbier (GSFC), S. Hunsberger (PSU), M. Still (GSFC),
P. Smith (MSSL), N. Gehrels (GSFC), K. Mason (MSSL),
J. Nousek (PSU), on behalf of the Swift UVOT team

Starting with the data taken ~113s after the BAT trigger
(Barbier et al, GCN 3314
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 ) we have co-added the data of
GRB 050422 in each of the Ultra-Violet/Optical Telescope
(UVOT) V, B and U bands.  The co-added image for the V-band
is made up of 1 x 100 s and 5 x 10 s exposures, the co-added
B-band and U-band images are made up of 5 x 10 s exposures.
The XRT error circle (Pagani et al., GCN 3315
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 ) falls
partially on a known source from the DSS.  No new source
is detected in any of the bands; we estimate the five
sigma magnitude upper limits from the co-added images to be:

Filter  Upper Limit  Duration(s)  T_start(s)  T_mid(s)
   V        17.9        148.7        112.9      374.1
   B        18.2         48.8        258.6      432.5
   U        17.8         48.8        244.5      418.0

Where T_start is time after trigger, and T_mid is the midpoint
of the summed exposure.

The magnitudes are based on preliminary zero-points, measured
in orbit, and will require refinement with further calibration.

We note that the reddening in this direction is E_{B-V} = 1.4.

M. Suzuki (Saitama), L. Barbier (GSFC), S. Barthelmy (GSFC), 
J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), 
D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), 
G. Sato (ISAS), J. Tueller (GSFC), J. Cannizzo (GSFC/UMBC),
M. Ajello (MPE), M. Chester (PSU)  on behalf of the Swift/BAT team:

At 07:52:39 UT Swift-BAT detected GRB 050422 (trigger= 115214)
(GCN Circ 3314
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 , Barbier et al.).  The refined BAT ground position
is (RA,Dec) = 324.454, 55.798, [deg; J2000] +- 3 arcmin, (95%
containment).  The partial coding was 98%.  

The light curve shows multiple peaks, with the main peak 
starting about T+42 seconds after the trigger and with another
hard peak at T+102 seconds.  T90 (15-350 keV) is (59.2 +- 0.3) 
seconds (estimated error including systematics).  

The photon index of the time-averaged spectrum is 1.4 +- 0.2.  
The fluence in the 15-350 keV band is (1.2 +- 0.2) x 10^-6 erg/cm2.  
The 1-s peak photon flux measured from T0+53.1 seconds in the 15-350 
band is (0.7 +- 0.1 ) ph/cm2/s.  All the quoted errors are at the 90% 
confidence level.

C. Pagani (INAF-OAB), D. N. Burrows (PSU), A. P. Beardmore (U. Leicester), 
and N. Gehrels (GSFC) report on behalf of the Swift XRT team:

The Swift BAT instrument detected a GRB at 07:52:40 UT on 22nd April 2005 
(GCN Circ 3314
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 ). The spacecraft executed a prompt slew and the XRT began 
taking data on the target at 07:54:29.4 UT.  Due to the presence of a 
cosmic ray in the initial image the on-board software could not properly 
centroid on the GRB, and the position generated on-board and sent out 
automatically through BACODINE was incorrect (the Notice indicated that 
this position was probably a cosmic ray).  From ground processed data we 
find a uncataloged, rapidly X-ray source within the BAT error circle, 
located at:

RA(J2000) = 21:37:54.5,
Dec(J2000) = +55:46:46.6.

We estimate an uncertainty of about 5 arcseconds radius (90% 
containment).  This position is 84 arcseconds from the BAT position 
reported in GCN 3314
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 .

L. Barbier (GSFC), D. Palmer (LANL), D. Burrows (PSU), A. Blustin (MSSL),
H. Krimm (GSFC/USRA), N. Gehrels (GSFC), K. McGowan (MSSL),
M. Chester (PSU) 

At 07:52:40 UT, the Swift Burst Alert Telescope (BAT) triggered and
located on-board GRB050422  (trigger #115214).   The BAT on-board
calculated location is RA, dec 324.454, +55.799 (J2000) with an
uncertainty of 4 arcmin (radius, 3-sigma, including estimated
systematic uncertainty). The BAT light curve showed a multipeak 
structure with a duration of  about 60 seconds. The peak
count rate measured by BAT was about 1000 counts/sec in the 15 - 
350 keV band, occurring 50 seconds after the trigger.

The Swift spacecraft slewed at about T+60 seconds onto the BAT position.
No BAT position message was received from TDRSS due to the fact that
the burst occurred during a Malindi pass.

The spacecraft executed a prompt slew and the XRT began taking data
on the target at 07:54:29.4 UT.  The XRT image looks like a cosmic 
ray hit, not a real source.  Therefore the XRT position may be incorrect.  
However, the XRT spectra and lightcurve look like there is a real source 
in the field of view.  Verification of the XRT position will require 
analysis of ground-processed data following the next ground station pass.

The Swift Ultra Violet/Optical (UVOT) observations began at
07:54:32.2 UT, 112 seconds after the BAT trigger.  The 
first data taken after the spacecraft settled was a 100 sec exposure
using the V filter with the midpoint of the observation at 162 sec after 
the BAT trigger. This image was sent directly to
the ground via TDRSS with the FOV pixel binning set at 8x8 pixels to
reduce telemetry. A comparison against the Digitized Sky Survey
reveals no new source inside the BAT error circles at RA, dec
324.454, 55.799 (J2000) with a radius of 4 arcmin.