GRB 050713A, GRB 050713

D. Morris, D. N. Burrows, A. Falcone, P. Roming (PSU), K. Page, M. Goad 
(Leicester), M. Trippico (GSFC-SSAI), F. Marshall and N. Gehrels (GSFC) 
report on behalf of the Swift XRT team:

The Swift XRT has continued to monitor the light curve of GRB050713a with 
data taken as late as 10 days after the burst trigger.

We confirm the XMM observation of a decaying lightcurve with powerlaw slope 
consistent with alpha=1.45 during the epoch 20ks-50ks after the burst 
trigger (De Luca et al, GCN3695
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 ).  We note, however, that the entire XRT 
dataset, from 4ks to 1000ks after the burst trigger, shows a powerlaw shape 
very well fit by an alpha=1.15 decay index, with no evidence for a jet 
break.  We suggest that the steeper slope seen between 20ks-50ks may be due 
to flaring activity.

The XRT count rate during the last observation, on July 23rd, was 6e-4 
cts/s, equivalent to a flux of 4e-14 ergs/cm^2/s

Andrea De Luca (IASF Mi) on behalf of a larger collaboraton 
report:

We have analyzed the data from the XMM-Newton observation 
of GRB050713A, discovered by Swift on 2005, July 13 at 
04:29:02.39 UT (Falcone et al., GCN3581
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 ).

The XMM-Newton observation started on 2005, July 13 at 
10:18 UT and lasted for 30.7 ks. We report here on the 
analysis of data collected with the EPIC/pn detector, 
which started observing the field at 10:54 UT (~6h 20min 
after the GRB).

As reported by Loiseau et al. (GCN3594
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 ), the afterglow of 
GRB050713A is clearly detected in the pn image, at a 
position fully consistent with the refined Swift/XRT one 
(Morris et al., GCN3606
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 ). 
Extracting source events from a circle of 25 arcsec radius 
(containing ~80% of the total counts), the time-averaged, 
background-subtracted count rate in the 0.2-8 keV range 
is 0.547+/-0.005 cts/s.

The afterglow is clearly seen to fade along the XMM-Newton 
observation, spanning the time range 23.5-51.5 ks after 
the GRB. The background-subtracted light curve (0.5-5 keV) 
is well fitted (reduced chi2=0.9, 26 d.o.f.) by a power law 
decay with index delta=1.45+/-0.07 (90% c.l.). 
The afterglow decay has significantly steepened with 
respect to the epoch of the earlier Swift observation: 
Morris et al. (GCN 3606
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 ) observed an index delta=0.82+/-0.11
in the time range 5-10 ks after the burst using Swift/XRT data. 
This implies the presence of a break in the afterglow X-ray
light curve between 10 ks and 23.5 ks from the GRB.

We extracted the time-averaged spectrum and generated ad-hoc 
response and effective area files. We quote here errors at 
90% level for a single interesting parameter, unless otherwise 
specified.

A fit in the energy range 0.2-8 keV with an absorbed power 
law model yields a reduced chi2 of 1.25 for 172 d.o.f. 
The resulting NH=(3.25+/-0.15)x10^21 cm^-2 is higher than 
the expected Galactic value in the burst direction (NH=1.1x10^21 
cm^-2, Dickey & Lockman, 1990); the best fitting power law photon 
index is Gamma=2.16+/-0.05.
Such results are consistent with the XRT ones (Morris et al., 
GCN 3606
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 ), which implies no significant spectral evolution with
respect to the earlier phase of the afterglow.

A better fit to the pn spectrum (reduced chi2=0.97, 171 dof) 
may be obtained fixing the NH to the expected Galactic value 
(NH=1.1x10^21 cm^-2) and adding a neutral, redshifted absorber 
component to the spectral model. With a simple F-test we evaluate 
the chance occurrence probability of the improvement to be 
of 5x10^-11. The best fit value for the intrinsic NH is 4.0x10^21 
cm^-2, while the best fit value for the redshift z is 0.55.
At 90% c.l. for 2 parameters, we obtain the following ranges:
intrinsic NH=(0.4-3.2)x10^22 cm^-2; redshift z=(0.4-2.6).
Using such model, the resulting power law photon index is 
Gamma=2.04+/-0.05.
The observed flux is of 2.2x10^-12 erg cm^-2 s^-1 in 0.2-10 keV;
the corresponding unabsorbed flux is of 3.8x10^-12 erg cm^-2 s^-1.

As a last step, we divided the pn dataset into two time intervals 
of ~9500 s and ~14600 s (each containing about half of the counts 
from the afterglow) and we repeated the spectral analysis. 
We found no significant spectral changes in the two considered 
intervals.

P. B. Cameron reports on behalf of the Caltech-NRAO-Carnegie
collaboration:

"We observed the field of GRB050713a (GCN 3581
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 ) with the Very Large Array
at 8.5 GHz on July 17.51. No radio source is detected at the position of
the optical/NIR transient (GCN 3582
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 , 3583
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 ) with a 2-sigma upper limit of
96 uJy.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."

S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, and
T. Cline on behalf of the Konus-Wind team report:

The long GRB 050713A (Swift-BAT trigger #145675; 
Falcone et al., GCN 3581
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 , Palmer et al., GCN 3597
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 )
triggered Konus-Wind at T0=16141.745 s UT (04:29:01.745).
As observed by Konus-Wind it had a duration of ~16 s,
fluence (1.22 � 0.08)10-5 erg/cm2,
peak flux on 64-ms time scale (1.7 � 0.4)10-6  erg/cm2 s
(both in the 20 keV - 4 MeV energy range).
Konus-Wind did not detect additional smaller peaks,
reported by Swift-BAT.
Probably they were too weak to be detected by Konus-Wind.

The spectrum integrated over the most instense part of the GRB
(from T0 to T0+8.448 s) is well fitted (in 20 keV-4 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ E^(-alpha) exp(-E/E0) 
with alpha = 1.12 +/- 0.08,
and E0 = 355 � 70 keV.
The peak energy Ep = 312 � 50 keV.


-- 

Valentin Pal'shin

Ioffe Physico-Technical Institute
Laboratory for Experimental Astrophysics
26 Polytekhnicheskaya, St Petersburg 194021,
Russian Federation 

email: val@mail.ioffe.ru
Tel: (7)-812-2479177
Fax: (7)-812-2471963

D. Morris, D. N. Burrows, A. Falcone, P. Roming (PSU), K. Page, M. Goad (Leicester), M. Trippico (GSFC-SSAI), F. Marshall 
and N. Gehrels (GSFC) report on behalf of the Swift XRT team:

We have analysed the first three orbits of data for GRB050713a (GCN 3581
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 , 
Falcone et al., 2005).  Using xrtcentoid, the refined position is:

RA(J2000) = 21h 22m 09.9s
Dec(J2000) = +77d 04' 24.2"

RA(J2000) = 320.5411
Dec(J2000) = +77.0734

with an uncertainty of 6 arcsec. This is 6 arcsec from the original 
XRT position (GCN 3581
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 , Falcone et al., 2005).

The XRT began taking data at 04:30:14UT, just 72 seconds after the BAT trigger 
and while the prompt gamma-ray emission was still in progress. The early XRT
lightcurve shows flares coincident with the BAT reported peaks (GCN 3597
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 ,
Palmer et al., 2005) at T+65 (caught on the tail end of the peak) and at T+105.
A decay rate has not been determined for the first orbit due to the flaring
nature of the emission at that point, with count rates varying between 10-300 cts/s.

Data from the 2nd and 3rd orbits span the timeframe 5ks-10ks after the trigger and
show a smoothly decaying afterglow at much lower flux, fit well by a powerlaw with
alpha = 0.82+/- 0.11.

The spectrum from all 3 orbits are well fit by an absorbed power-law with NH significantly 
greater than the galactic value of 1.1e21

gamma=2.1+/-0.05
NH=4.5e21 � 0.5e21

The count rate at 5000s after the trigger is ~0.35 cts/s which converts to an 
unabsorbed flux of 2.24e-11 ergs cm^-2 s^-1.

J. Wren, W.T. Vestrand, P. Wozniak, R. White, S. Evans report
on behalf of the RAPTOR team.

The RAPTOR-S telescope at Los Alamos National Laboratory began
imaging the field of GRB 050713A (Swift trigger 145675) 22.4
seconds after the GRB trigger -- before the end of the interval
of prompt gamma-ray emission (Falcone et al. GCN circ 3581
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 ).
At the location of the fading optical and NIR counterpart identified
in later images by Malesani et al. (GCN circ 3582
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 ) and Hearty et al.
(GCN circ 3583
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 ), respectively, we detected a transient optical
counterpart.  In a stack of eight 10 second unfiltered images
starting at 04:29:24.8 UT (with midpoint at 99.3 s after the GRB
trigger), we measured the optical transient to have a R-band
magnitude of 18.4 (+/- 0.18).  Our preliminary transformation to
R-band magnitudes was based on field stars from the USNO-B1 catalog.

A. Blustin (MSSL), A. Falcone (PSU), D. Hinshaw
(GSFC-SPSYS), P. Meszaros (PSU) report on behalf of
the Swift UVOT team:

Using summed images from Swift/UVOT of the field of
GRB 050713A, taken from 75 seconds after the BAT
trigger, no new source is detected within the XRT
error circle (Falcone et al., GCN 3581
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 ) 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        129           252         17.98
B        36            351         18.08
U        39            309         17.81
UVW1     39            325         16.85
UVM2     39            311         17.13
UVW2     29            326         17.08

where T_mid is the mid-point of the summed observation.
The image background is significantly higher than
expected at this location due to the proximity of a 
6.56 V magnitude star (HD 204408).

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

D. Palmer (LANL), 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), J. Nousek (PSU), A. Parsons (GSFC),
T. Sakamoto (GSFC/NRC), G. Sato (ISAS), M. Suzuki (Saitama),
M. Tripicco (GSFC/SSAI), 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 050713A (Trigger #145675; Falcone et al., GCN
Circ 3581
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 ) yields a refined position of RA, Dec 320.587, +77.070 {21h
22m 21s, +77d 04' 12"} (J2000) with an uncertainty of 3 arcmin
(radius, 90% confidence, statistical+systematic).

The burst duration (T90) was determined to be 70 +/- 10 seconds (15-350
keV) starting at T-1.0 seconds.  There is an initial ~12 second long basically
square hump which shows some structure:  three separate peaks of roughly
equal intensity in the 15-50 keV energy band, but falling in intensity with time
above 100 keV.  There are additional, much smaller peaks at T-60, T+50
T+65, and T+105 seconds.

The spectrum over the interval from T-70 to T+121 seconds can be fit
with a power law with photon index 1.58 +/- 0.07 and yields a fluence of
9.1 +/- 0.6 X 10^-6 erg/cm^2 in the 15-350 keV band.  The peak flux
in a 1-sec wide window starting at T+1.2 seconds is 6.0 +/- 0.4 ph/cm^2/sec.

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

"We have imaged the GRB 050713A afterglow position (Malesani et al.;
Hearity et al.; Guziy et al.; and Monfardini et al.) at 10.3 hours
after the burst using Lulin 1-m telescope. The afterglow was not
detected in our R band co-add image (300s x 5 frames). Compare with
USNOB1.0 stars, we estimate the afterglow would be fainter than 22.4
mag during our observations.

This message may be cited."

N. Loiseau, P. Munuera, R. Gonzalez-Riestra,
M. Santos-Lleo, P. Calderon, and M. Sierra-Gonzalez report:

Quick-Look-Analysis of the XMM-Newton observation of the
GRB 050713A field based on the EPIC PN exposure started
at 10:54:50 UT, shows the presence of a source with 
coodinates coincident with SWIFT/XRT coordinates 
(Falcone et al., GCN Circ. 3581
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 ). 
The average EPIC PN source count rate for the first 3ks was 
estimated to be 1.0 [counts/sec]
GRB 050713A is also detected with the RGS spectrometer.

C. Rodgers, E. Hausel, and R. Canterna report on behalf of the Red Buttes Observatory GRB Team as part of the FUN GRB Collaboration. We responded to GRB 050713A (Swift trigger 145675; 4:29 UT) at 04:54 UT with a series of 5 minute R and I exposures centered on the location of the original Swift-BAT GRB position under excellent conditions.  We did not observe the afterglow candidate (Malesani GCN 3582
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 ) brighter than the following magnitude limits:

UT      Time Since   Filter     Limiting 
Start   GRB                      Magnitude 
04:56   0:27          R           19.4 
05:01   0:31          I           18.2 
06:02   1:33          R           19.4 
06:08   1:38          I           18.7 

10 sigma limiting magnitudes were derived from the USNO-B1.0 catalogue

A. Monfardini, A. Gomboc, C. Guidorzi, C.G. Mundell, R.J. Smith,
I. A. Steele, C.J. Mottram, D. Carter, M.F. Bode (Liverpool JMU) report:

"The 2-m Liverpool Telescope followed up robotically the GRB050713
detected by SWIFT (GCN 3581
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 ). Three prompt images (2-4 minutes) have 
been acquired. No later time observations have been acquired.
We clearly detect the first object suggested by Malesani (GCN 3582
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 ) at:

RA = 21:22:09.6,  DEC = +77:04:29 (1 arcsec error)

At a mean epoch of 3 minutes after the reported GRB time we preliminarly
estimate a magnitude of r'=19.2 with large errors due to comparison
with USNOB1.0 and magnitude conversion. Further analysis is ongoing. 
The afterglow is detected on individual images.

This message can be cited."

XMM-Newton will observe GRB 050713 at location 
(RA=21h 22m 09.6s, DEC=+77d 04' 30.3", J2000),
starting at 09:41:00 UT, on July 13, 2005,
for an exposure of 33000 seconds.

S. Guziy, A. J. Castro-Tirado, A. de Ugarte Postigo,
J. Gorosabel (IAA-CSIC Granada), J. de León Cruz
(IAC Tenerife),  O. Bogdanov (Nikolaev State Univ.)
and M. Jelínek (IAA-CSIC),

report:

"Following the detection of GRB 050713 by Swift
(Falcone et al. GCNC 3581), we obtained R-band
images at the 2.5m Nordic Optical Telescope
(+ ALFOSC) starting on June 13.295 UT (about
47 min after the burst onset). We confirm the
presence of an optical source fainter than the DSS-2
limiting magnitude within the reported Swift/XRT
error box, at RA(2000) = 21 22 09.53,  Dec(2000) =
+77 04 29.5 (+/- 0.4"), consistent with the position
reported by Malesani et al. (GCNC 3582). Further
observations are needed in order to confirm if this
is the optical afterglow to GRB 050713. "

This message can be cited.

F. Hearty (Colorado), G. Stringfellow (Colorado), D. Q. Lamb (Chicago), D.
G. York (Chicago), G. Wallerstein (Washington), V. Woolf (Washington), S.
Anderson (Washington), J. Dembicky (APO), J. Barentine (APO), R. McMillan
(APO), B. Ketzeback (APO), and D. Reichart (North Carolina) report on
behalf of the ARC GRB team of the FUN GRB collaboration:

We began observations of the localization of GRB 050713 (Falcone et al.,
GCN 3525
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 ) with NIC-FPS on the 3.5m ARC at APO beginning 53 min after the
burst.  We detect all three of the candidates identified by Malesani et al.
(GCN 3582
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 ) in J,H,Ks in 80-sec integrations, and identify their first
candidate as fading.

NIC-FPS is currently in its commissioning phase.

This message may be cited.

D. Malesani (SISSA), P. D'Avanzo (INAF-OAB), E. Palazzi (INAF/IASF, Bo), 
G.L. Israel (INAF, OARm), G. Chincarini (Univ. Milano-Bicocca), L. 
Stella (INAF, OARm), M. Pedani (INAF, TNG) report on behalf on a larger 
collaboration:

We observed the field of GRB 050713 (Falcone et al., GCN 3581
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 ) with the 
Italian TNG telescope, located at the Canary Islands.

The object was observed after twilight, with a seeing of ~1.4", starting 
at 5.274 UT (0.8 h after the GRB). A 2-minutes exposure was acquired in 
the I filter.

Inside the XRT error circle, we detect one source at the coordinates 
(J2000):

  alpha = 21:22:09.6,  delta = +77:04:29
   
with an uncertainty of ~1".

We note two further objects lying just outside the nominal XRT error circle:

  1: alpha = 21:22:11.8,  delta = +77:04:27
  2: alpha = 21:22:08.4,  delta = +77:04:39

All these object are fainter than the DSS limit, so we cannot confirm if 
any of them is related to the GRB. Further analysis is in progress.

A finding chart can be found here:
http://www.sissa.it/~malesani/GRB/050713/GRB050713_finder.jpg

This message can be cited.

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
(Leicester), N. Gehrels (GSFC)

At 04:29:02.39 UT, the Swift Burst Alert Telescope (BAT) triggered and
located on-board GRB050713 (trigger=145675).  The spacecraft slewed
immediately and was on target at approximately 70 seconds. The
flight-determined location is RA,Dec 320.536,+77.072 {+21h 22m 09s, +77d
04' 20"} (J2000) with an uncertainty of 3 arcmin (radius, stat+sys).
This is a bright burst with a peak count rate of 6000 cts/sec in the
15-350 keV band.  The brightest part of the burst duration is ~20
seconds, followed by smaller peaks at T+50, T+65 and T+105 seconds.

The spacecraft slewed immediately and the XRT began observing the burst
at 04:30:14.9 UT (72.6 s after the BAT trigger).  XRT found a very
bright, uncataloged, fading X-ray source at:

RA:   +21h 22m 09.6s (J2000),
DEC: +77d 04' 30.3" (J2000).

This position is 11 arcseconds from the BAT position.  The estimated
uncertainty is 6 arcseconds radius (90% containment).

The Swift Ultra Violet/Optical Telescope (UVOT) observations began at
04:30:17.7 UT, 75 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 125 sec after the BAT trigger.
Based on comparisons to the DSS and USNO, we detect no new source at the
XRT position. The 3-sigma upper limit in the V-filter is approximately
17.81 mag.

S.A. Yost, E.S. Rykoff, W. Rujopakarn (U Mich), K. Alatalo (Berkeley), B. 
Schaefer (Louisiana State) report on behalf of the ROTSE collaboration:

ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB
050713A (Swift trigger 145675), producing images beginning 10.7 s
after the GCN notice time. An automated response took the first image
at 04:29:24.8 UT, 22.4 s after the burst, under fair conditions. We
took 10 5-sec, 10 20-sec and 10 60-sec eposures. These unfiltered
images are calibrated relative to USNO A2.0 (R).

Comparison to the DSS (second epoch) reveals no new sources within the
3-sigma error circle or at the XRT position, for both single images
and coadding into sets of 10. Individual images have limiting
magnitudes ranging from 16.2-17.7; we set the following limit, noting
it is adversely affected by the glare from the nearby bright star SAO
10034 (V=6.6), 67" from the XRT position.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
04:29:24.8    4:30:46.8        82     17.7           22.4       Y