GRB 050805B

J. Cummings (GSFC/NRC), S. Barthelmy (GSFC),  D. Burrows (PSU), 
M. Chester (PSU), N. Gehrels (GSFC),  M. Goad (U. Leicester), 
O. Godet (U. Leicester), J. Kennea (PSU), C. Markwardt (GSFC/UMD), 
A. Morgan (PSU), C. Pagani (PSU), K. Page (U. Leicester), D. Palmer (LANL), 
T. Sakamoto (GSFC/NRC)
on behalf of the Swift team:

At 20:41:26.7 UT, Swift-BAT triggered and located potential GRB 050805B
(trigger=149131).  The spacecraft slewed immediately.  The BAT
on-board calculated location is RA,Dec 306.005d, +37.213d {+20h 24m
01s, +37d 12' 46"} (J2000), with an uncertainty of 3 arcmin (radius,
90% containment, stat+sys).  The trigger duration is 32 milliseconds,
and the image significance was 6.3 sigma.  At that level, we consider
the BAT detection itself to be marginal.

XRT began observing the burst at 20:42:40.8 UT, 74 seconds after the BAT 
trigger.  The XRT was not able to centroid on a point source in the field, 
however the full field lightcurve shows a significant elevation above 
background, suggesting the presence of an X-ray source in the field. A 
catalogue search reveals no known X-ray sources in the field, suggesting 
this X-ray source is the X-ray afterglow.  There is evidence of fading in 
the lightcurve, which will require ground processing to confirm.

UVOT began observing the burst at 20:42:38.6 UT, 72 seconds after the BAT 
trigger.  In a preliminary ground-processed 100-sec image, no new sources 
are found when compared to the DSS catalog down to a 5-sigma limiting 
magnitude of V > 19.0.

V. Lipunov,  V.Kornilov, D.Kuvshinov,  N.Tyurina, A.Belinski,
E.Gorbovskoy,  A.Krylov, G.Borisov, V.Vladimirov, Krushinski V.

Sternberg Astronomical Institute, Moscow Union "Optic"

    MASTER (http://observ.pereplet.ru) responded to GRB 050805b (Swift 
trigger  149131). The first image  was 25 sec after Notice Time and  74 
sec  after SWIFT  detection     under the
  good weather condition. 
Optical limit is about 17.1 (30 sec exposition, unfiltred close to R).
Ther is no new object in error box (GRB on Milky Way).

The JPG-images   are available at
http://observ.pereplet.ru/images/GRB050805b/1.jpg  .


This work is supported by RFFI  04-02-16411 grant.
This message can be cited.
Mailto: lipunov@sai.msu.ru

Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report:

We imaged the field of GRB 050805b detected by SWIFT
(trigger 149131) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.

First image was acquired 5.2s after the GCN notice
(55.5s after GRB). The field had an elevation of
63 degrees above horizon and weather conditions were
excellents.

We detected no new source comparing our unfiltered images
with the DSS2-R and 2MASS-K ones and comparing our
succesive frames. From the first frame we give an
early limit:

T(sec since GRB)  Exp(s)  R-mag
   55.5 -  70.5         15  >17.0

Limiting magnitude was estimated with the nearby USNO-B1 stars.

This message can be cited.

Damerdji, Y. (CESR-OMP/OHP), Klotz, A. (CESR-OMP),
Boer M. (OHP), Atteia J.L. (LATT-OMP) report:

We imaged the field of GRB 050805b detected by SWIFT
(trigger 149131) with the 0.8m (F/15) telescope
located at the Observatoire de Haute Provence
Observatory (OHP), France.
Camera is an Andor 47-40 equiped by a R band filter.

First image was begined 16.4 min after the GRB.
Weather conditions were excellents.

We detected no new source comparing our
succesive frames. From the first frame we give an
limit:

TMid(min since GRB)  Exp(s)  R-mag
   18.87               300     >20.3

Limiting magnitude was estimated with the nearby USNO-B1 stars.

This message can be cited.

C. Markwardt (GSFC/UMD), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC)
J. Kennea (PSU), C. Pagani (PSU)
on behalf Swift team:

We report that trigger number 149131, previously designated GRB
050805B, is retracted.  This trigger is consistent with a cosmic ray
shower event in the detector, and a simultaneous random image
fluctuation.

Ground analysis of the XRT data does not show any X-ray source in the 
field. We therefore conclude from the XRT data that Trigger 149131 is not 
a GRB.

As a separate note, the BAT position notice was delayed by ~42 seconds
on board the spacecraft, due to a backlog of TDRSS telemetry caused by
a commanded procedure.

E. Pavlenko, Yu. Efimov, A. Shlyapnikov, A. Baklanov, V. Rumyantsev  (CrAO),
A.Pozanenko (IKI), M. Ibrahimov (MAO) on behalf of larger GRB follow up
collaboration report:

We observed the entire field of GRB 050805b detected by SWIFT (trigger
149131) with the Shain 2.6m  telescope. The set of  300 seconds images in R
filter were taken between August, 5 21:23:44 - 22:21:01 (UT). No fading
source was detected as compared between single images. The typical limiting
magnitude of the single image is 23.0m.

This message may be cited.