GRB 050822
GCN Circular 3849
Subject
GRB 050822: Swift detection of a long burst
Date
2005-08-22T04:29:32Z (20 years ago)
From
Scott Barthelmy at NASA/GSFC <Scott@lheamail.gsfc.nasa.gov>
A. Blustin (UCL-MSSL), S. Barthelmy (GSFC), D. Burrows (PSU), M. Chester (PSU),
J. Cummings (GSFC/NRC), N. Gehrels (GSFC), J. Kennea (PSU), F. Marshall (GSFC),
D. Palmer (LANL), T. Sakamoto (GSFC)
on behalf of the Swift team:
At 03:49:29 UT, Swift-BAT triggered and located GRB050822 (trigger=151486).
The BAT on-board calculated location is RA,Dec 51.080d,-46.023d
{03h 24m 19s,-46d 01' 22"} (J2000), with an uncertainty of 2 arcmin
(radius, 90% containment, stat+sys). The BAT light curve shows two peaks
(at T+5 sec and T+50 sec) with a total duration of 70 sec. The peak count rate
was ~1500 counts/sec (15-350 keV), at ~5 sec after the trigger.
The spacecraft slewed promptly and the XRT began observing the GRB
at 03:51:05 UT (96 sec after the BAT trigger). A bright source was found
by the on-board centroiding algorithm at RA=03h 24m 26.7s, Dec=-46d 01' 58"
(J2000), with an estimated uncertainty of 8 arcsec (90% containment radius).
This is 86 arcsec from the BAT position. The count rate decreases during
the first 100 sec, although the fact that Swift was exiting from the SAA
could contribute to this.
The UVOT began observing the field of GRB050822 at 03:51:47, 138 sec
after the BAT trigger. No new source with respect to the DSS image is
detected at the XRT position in a 100 s V-band exposure down to a 3-sigma
upper limit of 18.4 mag.
GCN Circular 3850
Subject
GRB 050822: ROTSE-III Prompt Optical Limits
Date
2005-08-22T04:43:28Z (20 years ago)
From
Eli Rykoff at U of Michigan/ROTSE <erykoff@umich.edu>
E.S. Rykoff (U Mich) reports on behalf of the ROTSE collaboration:
ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia,
responded to GRB 050822 (Swift trigger 151486), producing images
beginning 5.8 s after the GCN notice time. An automated response took
the first image at 03:50:00.8 UT, 31.7 s after the start of the burst,
and during the gamma-ray emission (GCN 3849). These observations were
affected by proximity to the full moon as well as early twilight. We
took 10 5-sec, and 70 20-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 BAT error circle or at the XRT position, for both single images
and coadding into sets of 10. Individual images have limiting magnitudes
ranging from 15.0-16.2; we set the following specific limits.
start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd?
--------------------------------------------------------------------
03:50:00.8 3:50:05.8 5 15.1 31.7 N
03:50:00.8 3:51:24.8 84 16.6 31.7 Y
03:51:25.5 3:56:12.0 286 17.5 412.6 Y
GCN Circular 3856
Subject
GRB 050822: Swift-BAT refined analysis
Date
2005-08-22T17:47:01Z (20 years ago)
From
Takanori Sakamoto at NASA/GSFC <takanori@milkyway.gsfc.nasa.gov>
D. Hullinger (UMD), L. Angelini (GSFC-JHU), L. Barbier (GSFC),
S. Barthelmy (GSFC), M. Chester (PSU), J. Cummings (GSFC/NRC),
E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC),
on behalf of the Swift-BAT team:
Using the full data set from the recent telemetry downlink, we report
further analysis of Swift-BAT GRB 050822 (trigger #151486)
(Blustin, et al., GCN 3849). The refined BAT ground position
is (RA,Dec) = 51.098, -46.031 {03:24:19.2, -46:01:22.8} [deg; J2000]
+-2 arcmin, (90% containment). This is 27 arc-seconds from the
XRT position reported in GCN 3849. The partial coding was 44%.
The light curve has two main peaks. The first peak starts from
T0-4 sec, peaking at T0, and then ending at T0+20 sec with a gradual
decay. The second peak contains multiple sub-peaks. It starts
from T0+20 sec and ends at T0+75 sec. There is a smaller, somewhat
softer peak from T+100 to T+104 seconds while Swift was pointing at
the source and the XRT was taking data. T90 (15-350 keV) is (102 +- 2)
seconds (estimated error including systematics).
The power law index of the time-averaged spectrum is 2.5 +- 0.1.
Thus, the time-averaged spectrum turns out to be soft.
The fluence in the 15-350 keV band is (3.4 +- 0.3) x 10^-6 erg/cm2.
The 1-s peak photon flux measured from T0+47.6 second in the 15-350 keV
band is (2.9 +- 0.3) ph/cm2/s. All the quoted errors are at the 90%
confidence level.
GCN Circular 3859
Subject
GRB050822: Swift/UVOT upper limits
Date
2005-08-22T20:10:52Z (20 years ago)
From
Alexander Blustin at MSSL-UCL <ajb@mssl.ucl.ac.uk>
M. J. Page, H. Ziaeepour, A. J. Blustin (UCL-MSSL), M. Chester (PSU),
R. Fink (GSFC), N. Gehrels (GSFC) on behalf of the Swift UVOT team
The Swift/UVOT began observing the field of GRB050822 at 03:51:47,
138 s after the BAT trigger (Blustin et al., GCN 3849). No new source
(with respect to the DSS image) is observed at the XRT position in
summed images from any of the six filters down to the following
3-sigma magnitude upper limits:
Filter T_range (s) Exp (s) 3-sig UL (mag)
V 138-1090 278 19.5
B 284-1453 135 19.7
U 270-1402 188 19.4
UVW1 257-1298 188 20.0
UVM2 242-1194 188 20.6
UVW2 300-986 88 20.0
Where T_range is the time range post-trigger over which images were
co-added.
The magnitudes have not been corrected for extinction. These
magnitudes are based on preliminary zero-points, measured in orbit,
and will require refinement with further calibration.
GCN Circular 3873
Subject
GRB 050822: refined XRT analysis
Date
2005-08-25T09:48:17Z (20 years ago)
From
Kim Page at U.of Leicester,Swift SDC <kpa@star.le.ac.uk>
O. Godet, K.L. Page, J.P. Osborne (U. Leicester), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), K. Hurley (Berkeley), M. Chester (PSU) report on
behalf of the Swift XRT team:
We have analysed the Swift XRT data taken up to 200 ksec (2.3 days) from
the burst GRB 050822. The refined coordinates are:
RA(J2000) = 03h 24m 26.70s
Dec(J2000) = -46d 02' 01.7"
with an uncertainty of 6 arcseconds radius (90% containment).
This position is consistent with that reported by Blustin et al. (GCN
3849).
Initial data show a rapid decay until ~1000 sec, followed by a shallow
decay (power law decline index ~0.4) until ~20 ksec. After this the flux
declines more steeply, with an index ~1.2.
The X-ray spectrum before and after the ~20 ksec break is well fit
by a power-law with Gamma = 2.17+/-0.28 (90% confidence) and an
absorbing column of ~1.4e21 cm^-2 in excess of Galactic in the observer
frame.
At 200 ksec after the burst the XRT count rate was 0.007 c/s,
corresponding to an unabsorbed 0.3-10 keV flux of 3x10^-13 erg/cm2/s.