GRB 050726
GCN Circular 3682
Subject
GRB050726: Swift-BAT detection of a weak burst
Date
2005-07-26T13:08:21Z (20 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
S. Barthelmy (GSFC), D. Palmer (LANL), T. Sakamoto (GSFC), S.T. Holland (GSFC),
D. Burrows (PSU), M. Chester (PSU), S. Hunsberger (PSU), A. Moretti (OAB),
S. Covino (OAB), P. Romano (OAB), A. Antonelli (INAF-OAR), T. Poole (MSSL),
N. Gehrels (GSFC)
on behalf of the Swift team:
At 05:00:17 UT, Swift-BAT triggered and located GRB050726 (trigger=147788).
The spacecraft slewed immediately. But since there was a gap in the TDRSS
coverage at the moment of the burst, the TDRSS messages were lost, and
therefore there were no real-time GCN notifications. The following comes
from the analysis of the full data set after the regularly scheduled
data downlink pass. The BAT ground-calculated location is RA,Dec
200.052,-32.072 {13h 20m 12s,-32d 04' 19"} (J2000), with an uncertainty
of 3 arcmin (radius, 90% containment, stat+sys). The BAT light curve
shows a broad weak peak with a hint of structure with a total duration
of ~30 sec (starting before the trigger at ~T-15 extending to ~T+15 sec).
The power law photon index of the time-averaged spectrum is 1.04 +- 0.16.
The fluence in the 15-350 keV band are (4.3 +- 0.7) x 10^-6 erg/cm2.
The 1-s peak photon flux measured from T0+1.0 second in the 15-350 keV
band is (2.0 +- 0.4) ph/cm2/s. All the quoted errors are at the 90%
confidence level.
An uncatalogued, fading X-ray source was detected by XRT at the following
position: RA,Dec 13h 20m 12.30s -32d 03m 50.8s} (J2000) with an uncertainty
of 6 arcsec (90% containment). This is 28.4 arcsec from the BAT position
reported above.
The Swift Ultra-Violet/Optical Telescope (UVOT) observations began
at 05:02:07 UT, 110 seconds after the BAT trigger. The first data
taken in the V band after the spacecraft settled was a 100 sec exposure
with the midpoint of the observation at 223 sec after the BAT trigger.
A comparison against the DSS catalogue reveals a possible new source
inside the BAT and XRT error circles 13h 20m 11.9s,-32d 03' 51.9" (J2000),
although this could also be a known source with a high proper motion.
The V band magnitude was 17.6 +- 0.2.
[GCN OPS NOTE(31jul05): Per author's request, the Dec in the 3rd pragraph
was changed from "-3d" to "-32d".]
GCN Circular 3683
Subject
GRB 050726: early Swift XRT analysis results
Date
2005-07-26T16:08:12Z (20 years ago)
From
Alberto Moretti at Obs Brera Merate <moretti@merate.mi.astro.it>
A. Moretti (INAF-OAB), S. Campana (INAF-OAB), P. Romano (INAF-OAB), L.A.
Antonelli (INAF-OAR), M. Chester (PSU), P. Boyd (GSFC-UMBC) on behalf of
the Swift-XRT Team report.
We have analyzed the Swift XRT data from the first 3 orbit observation
of GRB 050726 (Bathelmy et al., GCN 3682). As already reported an
uncatalogued, fading X-ray source was detected by XRT at the following
position: RA,Dec 13h 20m 12.30s -32d 03m 50.8s} (J2000) with an
uncertainty of 6 arcsec (90% containment).
The observations in Windowed Timing (WT) and Photon Counting (PC) mode
start 132 and 334 seconds from the BAT trigger (T0) respectively.
A preliminary spectral fit (simple absorbed power-law) to the WT data
yields a photon index of 1.98-/+0.1 in the [0.5-10] keV band. The
derived NH is (1.3)E21 cm^-2, which is higher than the Galactic value
(0.4E+21 cm-2; Dickey & Lockman 1990). A preliminary spectral fitto the
PC data yields values well consistent with the WT data.
The light curve shows 2 highly significant flares in the first 200
seconds and then a monotonic fading which can be fitted with a power law
of slope 1.06+-0.10
The unabsorbed 0.5-10.0 keV flux at 24 hours after the burst is then
estimated to be 5E-13 ergs/s/cm2.
GCN Circular 3687
Subject
GRB 050726: PROMPT Rc Observations
Date
2005-07-27T01:45:23Z (20 years ago)
From
Josh Haislip at U.North Carolina <haislip@physics.unc.edu>
J. Haislip, J. Kirschbrown, C. MacLeod, A. Crain, M. Nysewander, D.
Reichart report on behalf of the UNC team of the FUN GRB Collaboration:
Under the control of Skynet, PROMPT automatically began observing the
localization of GRB 050726 (Barthelmy et al., GCN 3682) 18.5 hours after
the burst in Rc. A quick look reveals no new sources within or around the
XRT localization down to the limit of the DSS2-Red. Observations are
ongoing.
PROMPT is still being built and commissioned.
GCN Circular 3693
Subject
GRB 050726, SMARTS optical/IR observations
Date
2005-07-28T05:18:50Z (20 years ago)
From
Bethany Cobb at Yale U <cobb@astro.yale.edu>
B. E. Cobb and C. D. Bailyn (Yale), part of the larger SMARTS
consortium, report:
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 050726
(GCN 3682, Barthelmy et al.) with a mid-exposure time of
2005-07-27 00:39 UT, which is ~19.6 hours post-burst.
Total summed exposure times amounted to 36 minutes in I and 30 minutes in
J, resulting in approximate limiting magnitudes of I>22 and J>20.
In comparison with SDSS and 2MASS frames, no new optical
or IR sources are detected in the vicinity of the
reported X-ray afterglow.
[GCN OPS NOTE(28jul05): Per author's request, the Subject-line
was changed from "050124" to "050726".]
GCN Circular 3698
Subject
GRB050726: Swift UVOT observations
Date
2005-07-29T15:26:48Z (20 years ago)
From
Tracey Poole at MSSL <tsp@mssl.ucl.ac.uk>
T. Poole (MSSL), A. Moretti (OAB), S. T. Holland (GSFC), M. Chester
(PSU), L. Angelini (GSFC-JHU), N. Gehrels (GSFC) on behalf of the Swift
UVOT team
The Swift Ultra-Violet/Optical Telescope (UVOT) began observations of
GRB050726 (Barthlemy et al. GCN 3682) on 26th July 2005 at 05:02:07 UT.
We confirm the detection of a source inside the BAT and XRT error circle
(Barthlemy et al. GCN 3682, A. Moretti et al. GCN 3683) in the V band
only. The source is detected in the initial V band observation, then
drops below the 3 sigma detection threshold. It is not detected in
the U, B or the UV filters.
The aperture used for all observations was 6 arcsec. The limiting
magnitudes are given to a 3 sigma limit.
V filter
start exposure mid magnitude
time time time
after after
burst burst
(s) (s) (s)
123 100 173 17.35+/-0.09 - source detection
298 10 303 17.47 - limiting magnitude
382 10 387 17.43 - limiting magnitude
466 10 471 17.36 - limiting magnitude
551 10 556 17.29 - limiting magnitude
635 10 640 17.49 - limiting magnitude
720 10 725 17.40 - limiting magnitude
9825 900 10275 19.76 - limiting magnitude
21647 900 22097 19.83 - limiting magnitude
Other filters - limiting magnitudes
Filter start exposure mid limiting
time time time magnitude
after after
burst burst
(s) (s) (s)
b 269 59 485 19.38
b 4992 1800 6189 21.31
b 29659 12 29665 18.72
u 255 59 216 19.23
u 4124 2700 16888 21.06
uvw1 241 59 457 19.29
uvw1 4020 100 4070 19.49
uvw1 11639 2003 17763 21.44
uvm2 352 68 196 19.41
uvm2 10731 1800 19738 21.48
uvw2 284 89 500 19.88
uvw2 5939 1300 13820 21.62
The magnitudes are based on preliminary zero points, measured in orbit,
and will require refinement with further calibration.
This message may be cited.
GCN Circular 3719
Subject
GRB 050726: PROMPT Rc Observations
Date
2005-08-01T04:50:37Z (20 years ago)
From
Josh Haislip at U.North Carolina <haislip@physics.unc.edu>
J. Haislip, D. Reichart report on behalf of the UNC team of the FUN GRB
Collaboration:
Under the control of Skynet, PROMPT observed the localization of GRB 050726
(Barthelmy et al., GCN 3582) beginning 18.5 hours after the burst in Rc
(Haislip et al., GCN 3687).
We do not detect any new sources within or around the XRT localization.
3-sigma limiting magnitudes are based on 3 USNO-B1.0 stars:
Mean Time Integration Filter Limiting Telescope
Since GRB Time Magnitude
19h 46m 205 x 40s Rc 22.2 PROMPT-5
PROMPT is still being built and commissioned.