GRB 081226
GCN Circular 8729
Subject
GRB 081226: Swift detection of a possible short-hard burst
Date
2008-12-26T01:21:22Z (16 years ago)
From
David Burrows at PSU/Swift <dxb15@psu.edu>
O. Godet (U Leicester), W. H. Baumgartner (GSFC/UMBC),
D. N. Burrows (PSU), E. A. Hoversten (PSU), J. A. Kennea (PSU) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:
At 01:03:37 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081226 (trigger=338177). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 120.527, -69.006 which is
RA(J2000) = 08h 02m 06s
Dec(J2000) = -69d 00' 20"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a short hard burst
structure with a duration of about 0.5 sec. The peak count rate
was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 01:05:11.9 UT, 94.6 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 120.50054, -69.02994 which is
equivalent to:
RA(J2000) = 08h 02m 0.13s
Dec(J2000) = -69d 01' 47.8"
with an uncertainty of 4.5 arcseconds (radius, 90% containment). This
location is 92 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
1.19e+21 cm^-2 (Kalberla et al. 2005).
The UVOT data has not yet been received so it is not possible to
comment on the UV/optical nature of the burst at this time. There is
a 7th magnitude source nearby which will complicate UVOT observations.
Burst Advocate for this burst is O. Godet (og19 AT star.le.ac.uk).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)
GCN Circular 8730
Subject
GRB 081226: ROTSE-III Optical Limits
Date
2008-12-26T01:32:34Z (16 years ago)
From
Brad Schaefer at LSU <schaefer@grb.phys.lsu.edu>
B. E. Schaefer (Louisiana State), E.S. Rykoff (UCSB), F. Yuan (U Mich),
report on behalf of the ROTSE collaboration:
ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia,
responded to GRB 081226 (Swift trigger 338177; Godet, GCN 8729), producing
images beginning 8.8 s after the GCN notice time. An automated response
took the first image at 01:04:02.8 UT, 25.4 s after the burst, under
excellent conditions. We took 10 5-sec, 20 20-sec exposures. These
unfiltered images are calibrated relative to USNO A2.0 (R). Imaging is on
going.
Comparison to the DSS (second epoch) reveals no new sources within the
3-sigma Swift/BAT error circle or the XRT error circle, for both single
images and coadding into sets of 10; the field is not crowded. Individual
images have limiting magnitudes ranging from 16.8-17.4; we set the
following specific limits.
start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd?
--------------------------------------------------------------------
01:04:02.8 01:04:07.8 5 17.0 25.4 N
01:04:02.9 01:05:19.0 76 17.8 25.5 Y
GCN Circular 8731
Subject
GRB 081226: GROND afterglow candidate
Date
2008-12-26T03:08:29Z (16 years ago)
From
Paulo M. J. Afonso at MPE <pafonso@mpe.mpg.de>
GRB 081226: GROND afterglow candidate
P. Afonso, T. Kruehler (both MPE Garching), S. Klose (TLS Tautenburg), and
J. Greiner (MPE Garching) report on behalf of the GROND team:
GROND (Greiner et al. 2008, PASP 120, 405), mounted at the 2.2m ESO/MPI
telescope at La Silla Observatory (Chile),started observations of the field
of GRB 081226 (Godet et al. 2008, GCN #8729) in g'r'i'z'JHK at 01:14 UTC, 11
min after the burst. We detect a faint optical source in the XRT error
circle (Godet et al. 2008, GCN #8729) at:
RA(J2000): 08:01:59.92
DEC(J2000): -69:01:47.4
with uncertainties of 0.5".
At a midtime of 01:57 UTC, we measure a rough preliminary r' band magnitude
of 24.3 calibrated with the GROND zeropoint.
No statement about variability can be made at this point. Observations are
ongoing.
GCN Circular 8732
Subject
GRB 081226: Gemini-South imaging
Date
2008-12-26T03:26:41Z (16 years ago)
From
Edo Berger at Harvard <eberger@cfa.harvard.edu>
E. Berger (Harvard), A. Cucchiara, and D. B. Fox (Penn State) report:
"We imaged the error circle of GRB 081226 (GCN 8729) with GMOS on the
Gemini-S telescope starting on 2008 Dec 26.04 UT. In a single 300 sec
r-band image we detect the object located by GROND within the XRT
error circle (GCN 8731). In addition, we find a second, fainter source
within the error circle at (J2000):
RA = 08:02:00.44
DEC = -69:01:48.9
with an uncertainty of about 0.5" in each coordinate. Additional
observations are on-going to determine if either of these two sources is
fading."
GCN Circular 8733
Subject
GRB 081226: Gemini-South spectrum of possible afterglow
Date
2008-12-26T04:51:20Z (16 years ago)
From
Edo Berger at Harvard <eberger@cfa.harvard.edu>
E. Berger (Harvard), A. Cucchiara, and D. B. Fox (Penn State) report:
"We obtained spectroscopic observations of the possible afterglow of GRB
081226 (GCNs 8731, 8732) with GMOS on the Gemini-South telescope using the
R400 grating with a central wavelength of 6000A for a total of 2400 sec.
We detect smooth continuum emission but no obvious absorption or emission
features in the wavelength range 4000-8000A. Further analysis is
on-going."
GCN Circular 8736
Subject
GRB 081226: Second epoch of Gemini-South imaging
Date
2008-12-26T16:27:15Z (16 years ago)
From
Edo Berger at Harvard <eberger@cfa.harvard.edu>
E. Berger, A. M. Soderberg (Harvard), A. Cucchiara, and D. B. Fox (Penn
State) report:
"We re-observed the error circle of GRB 081226 (GCN 8729) with GMOS on the
Gemini-South telescope on 2008 Dec 26.349 UT (7.31 hours post burst). A
comparison to our first epoch of imaging, taken on 2008 Dec 26.112 UT
(1.62 hours post burst; GCN 8732), reveals that neither of the two objects
within the XRT error circle (GCN 8732) have varied in brightness. This
is confirmed using digital image subtraction with the ISIS package."
GCN Circular 8738
Subject
GRB 081226: Swift-XRT refined analysis
Date
2008-12-26T22:40:57Z (16 years ago)
From
Olivier Godet at U.of Leicester <og19@star.le.ac.uk>
O. Godet (U Leicester) on behalf the Swift-XRT team:
The Swift-XRT started observing the field of GRB 081226 (trigger number
338177, Godet et al., GCN Circ. 8729) at 2008-12-26 01:05:11.9 UT, 94.5
seconds after the trigger. Using 11.6 ks of photon counting (PC) mode data,
the best XRT position is located at RA, Dec 120.50152, -69.02924 which is
equivalent to:
RA(J2000) = 08h 02m 00.36s
Dec(J2000) = -46d 01' 45.2"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 2.8 arcseconds from the XRT position given in Godet et al. (GCN
Circ. 8729). It is also consistent with the position of the possible
optical counterpart reported by Afonso et al. (GCN Circ. 8731).
The X-ray light curve presently spans 11.6 ks of PC mode data from T+109 s
to T+42 ks. Due to poor statistics, it is difficult to properly model the
light-curve, which shows a decay (with a slope around 1.8) possibly followed
by a flattening at later time.
The PC X-ray spectrum from the same interval can be well fit by an absorbed
power-law with a photon index of 2.60 +1.61/-0.98 and a column density of
(6.4 +8.8/-4.6) x 10^21 cm^-2 (the Galactic value is 1.19 x 10^21 cm^-2 in
the direction of the burst - Kalberla et al. 2005). The observed 0.4-10.0
keV flux is (1.8 +0.8/-1.3) x 10^-13 erg cm^-2 s^-1 which corresponds to
an unabsorbed flux of (4.7 +1.4/-2.5) x 10^-13 erg cm^-2 s^-1.
No more Swift observations are planned for this burst.
This is an official product of the Swift-XRT team.