GRB 050713B

S. Vaughan (Leicester), A. Falcone (PSU), D. Palmer (LANL),
A. Blustin (MSSL), S. Barthelmy (GSFC), J. Cummings
(GSFC/NRC), H. Krimm (GSFC/USRA), D. Burrows, D. Morris, C.
Gronwall (PSU), C. Markwardt (GSFC/UMD), K. Page, M. Goad
(Leicester), S Rosen (MSSL), N. Gehrels (GSFC)

At 12:07:17.62 UT, the Swift Burst Alert Telescope (BAT)
triggered and located on-board GRB050713B (trigger=145754).
The spacecraft slewed immediately.  The flight-determined
location is RA,Dec 307.843,+60.920 {20h 31m 22s,+60d 55'
12"} (J2000) with an uncertainty of 3 arcmin (radius, 90%
c.l. stat+sys).  The burst lightcurve has 1 (maybe 2) peaks
within ~30 sec duration.  It is riding on top of two long
bumps which are believed to be background, but without the
full Malindi data, we can not determine if the bumps are
background or burst-related. The peak rate (without bumps)
is ~1000 cnts/sec in the 15-350 keV band.

The spacecraft slewed immediately and the XRT began
observing the burst at 12:09:33 UT (136 s after the BAT
trigger). XRT found a bright, uncataloged, fading X-ray
source at:

RA:  +20h 31m 15.5s (J2000),
DEC: +60d 56' 38.4" (J2000).

This position is 100 arcseconds from the BAT position.  The
estimated uncertainty is 6 arcseconds radius (90%
containment).

The Swift Ultra Violet/Optical Telescope (UVOT) observations
began at 12:09:33 UT, 136 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 186 sec after the BAT trigger. Based on
comparisons to the DSS, we detect no new source at the XRT
position.

C. Guidorzi, R.J. Smith, C.G. Mundell, A. Monfardini, A. Gomboc, I. A.
Steele, C.J. Mottram, D. Carter, M.F. Bode (Liverpool JMU), P. O'Brien, N.
Bannister, E. Rol (Leicester), on behalf of the RoboNet-1.0 collaboration
report:
  
"The 2-m Faulkes North Telescope followed up robotically the GRB050713B
detected by SWIFT (Vaughan et al., GCN 3590
Loading...
 
 ) 3.3 min after the GRB trigger
time. The automatic "detection mode" procedure didn't detect any obvious
candidate to about R=18.2 from 3 10-s images (mean epoch of 3.8 min
after the GRB), with FOV of 4.6'x4.6' centred on the BAT in-flight
location. The above limit is also confirmed by visual inspection of the
images.
 
The limiting magnitude is automatically calculated with respect to the
USNOB1.0 'R2' values of the field objects.
 
Further observations are ongoing.

This message can be cited"

Z.Y. lin(NCU), K.Y. Huang, W.H. Ip (NCU), Y. Urata(RIKEN),
Y. Qiu (BAO), Y.Q. Lou (THCA) on behalf of EAFON report:

" We have performed R-band imaging for the entire error region of GRB
050713b (Vaughan et al. GCN 3590
Loading...
 
 ) from 24 min after the burst with
Lulin 1-m telescope. No source was detected at position of the fading
X-ray source during our observation with following limiting magnitude
derived from the USNO-B1.0 catalogue.

UT      Exposure    Filter     Limiting 
Start   Time                      Magnitude 
12:31   300 s       R          21.2
12:37   300 s       R          21.6
12:43   300 s       R          21.3
12:49   300 s       R          21.6
12:54   300 s       R          21.6

This message may be cited."

A. Parsons (GSFC), S. Barthelmy, L. Barbier (GSFC),
J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Hullinger (GSFC/UMD), H. Krimm (GSFC/USRA),
C. Markwardt (NASA GSFC/UMD), F. Marshall (GSFC), D. Palmer (LANL),
T. Sakamoto (GSFC/NRC), G. Sato (ISAS), A. Smale (NASA HQ),
M. Suzuki (Saitama), J. Tueller (GSFC)
on behalf of the Swift-BAT team:

Using the full data set from the recent telemetry downlink, further
analysis of Swift-BAT GRB 050713B (Trigger #145754; Vaughn et al.,
GCN Circ 3590
Loading...
 
 ) yields a refined position of RA, Dec 307.820,
+60.938 {20h 31m 17s, +60d 56' 17"} (J2000) with an uncertainty
of 3 arcmin (radius, 90% confidence, statistical+systematic).  The
light curve shows a FRED-like profile of total duration ~75 seconds.

The spectrum over the interval from T-2 to T+178 seconds can be fit
with a power law with photon index 1.56 +/- 0.13 and yields a fluence
of 8.2 +/- 1.0 X 10^-6 erg/cm^2 in the 15-350 keV band.  The peak
flux in a 1-sec wide window starting at T+4.4 seconds is
2.2 +/- 0.6 ph/cm^2/sec.

K. Page, S. Vaughan, M. Goad (Leicester), D. N. Burrows (PSU), M. Ajello 
(MPE), R. Fink and N. Gehrels (GSFC) report on behalf of the Swift XRT team:

We have analysed the first two orbits of data for GRB050713b (GCN 3590
Loading...
 
 , 
Vaughan et al., 2005).  Using xrtcentoid, the refined position is:

RA(J2000) = 20h 31m 15.5s
Dec(J2000) = +60d 56' 40.4"

with an uncertainty of 6 arcsec. This is only 2 arcsec from the original 
XRT position (GCN 3590
Loading...
 
 , Vaughan et al., 2005).

The light-curve shows a steeply fading afterglow during the first orbit, 
with a decay slope of
alpha = 2.88 +/- 0.12 between 143 and 600 seconds after the trigger.  After 
~5000 seconds (i.e. on the second orbit), the light-curve flattens 
significantly; more data are required to constrain the slope following the 
break in the light curve.

The WT spectrum can be fitted by an absorbed power-law with a spectral
index, Gamma = 1.70 +0.11/-0.09 and excess NH of (1.97 +0.50/-0.43)e21
cm^-2.

The unabsorbed 0.3-10 keV flux (averaged over 143 and 330 seconds after
the burst) is (9.02 +0.16/0.80)e-10 erg cm^-2 s^-1.

S. Rosen (MSSL), S. Vaughan (Leicester), R. Fink
(GSFC-SPSYS), M. Chester (PSU) report on behalf of
the Swift UVOT team:

Using summed images from Swift/UVOT of the field of
GRB 050713B, taken from 136 seconds after the BAT
trigger, no new source is detected within the XRT
error circle (Vaughan et al., GCN 3590
Loading...
 
 ) in any of
the six filters down to the following 3-sigma
magnitude upper limits:

Filter   Exposure (s)  T_mid (s)   3-sig limit
V        252           598         19.26
B         88           624         19.58
U         88           610         19.31
UVW1      88           596         19.46
UVM2      88           582         19.83
UVW2      88           639         19.87

where T_mid is the mid-point of the summed observation.

We caution that the instrument is not yet fully
calibrated and that the magnitude limits presented here
may need to be refined.

I. Bikmaev, A. Galeev, N. Sakhibullin (KSU/AST),
I. Khamitov, Z. Aslan (TUG), U. Kiziloglu (METU), A. Alpar (SabUni),
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI), report:

    We have observed the field  of GRB050713b (Vaughan et al. GCN 3590
Loading...
 
 )
on July 14, 2005, in Rc-band with ANDOR CCD attached to the  1.5-m
Russian-Turkish telescope (RTT150, Antalya, Turkey).
    The set of 30 sec exposures has been made with total exposure
time of 15 min and midpoint at UT = 22h 26min (~ 22 hours after
the burst). No new optical source was detected at the position of the 
X-ray source in the co-added frame with limiting magnitude of Rc = 22.4 mag.

This message may be cited.

D. Sharapov,  M. Ibrahimov (MAO), V.Rumyantsev (CrAO), A.Pozanenko (IKI) on
behalf of larger GRB follow up collaboration report:


We observed the error box of GRB050713b (Trigger #145754; Vaughn et al., GCN
3590
Loading...
 
 ,   Parsons et al., GCN 3600
Loading...
 
 ) with 1.5m telescope (Maidanak Astronomical
Observatory) on July 13, 14, and 15. Limiting magnitude of stacked image of
observation obtained on July 13 (start time July 13 UT 18:06, i.e. ~6.0 h
after burst) is R=23.2.   We detected optical sources S1 which is offset
~1.9
arcsec of the refined XRT error circle (Page et al., GCN3602
Loading...
 
 ) and have the
following coordinates (uncertainty in each coordinate is about 1 arcsec):

S1 RA(J2000)= 20 31 15.96   Dec(J2000) = +60 56 36.4

Photometry of the source based on USNO A2.0 catalog is following:

Mean time         Exposure   S1
  (UT)               sec.    mag.

July 13, 18:56    15x300     24.13 +/-0.74
July 14, 19:44     8x300     22.90 +/-0.44
July 15, 19:31     9x300     22.93 +/-0.30


Since the S1 source does not demonstrate fading behavior, it is unlikely
that S1
is an OT of GRB050713b.

Stacked image of July 13 observations can be found in
http://grb.rssi.ru/GRB050713b.

This message may be cited.