- GCN Circular #12307
K. Hurley, on behalf of the MESSENGER GRB team,
I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin,
on behalf of the HEND-Odyssey GRB team,
W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr, on
behalf of the GRS-Odyssey GRB team,
K. Yamaoka, M. Ohno, Y. Hanabata, Y. Fukazawa, T. Takahashi, M. Tashiro,
Y. Terada, T. Murakami, and K. Makishima on behalf of the Suzaku WAM team,
S. Barthelmy, J. Cummings, N. Gehrels, H. Krimm, and D. Palmer, on behalf of
the Swift-BAT team,
J. Goldsten, on behalf of the MESSENGER NS GRB team,
G. Di Cocco, F. Fuschino, M. Galli, C. Labanti, M. Marisaldi,
on behalf of the AGILE MCAL team, and
V. Connaughton, M. S. Briggs, and C. Meegan, on behalf of the Fermi
GBM team, report
GRB110825A (=Fermi GBM trigger 335932012) was observed by AGILE MCAL
(outside the coded field of view of SuperAGILE), Fermi GBM, MESSENGER
GRNS, Odyssey HEND, Suzaku WAM, and Swift BAT (outside the coded field
of view). We have triangulated it to a preliminary, 3 sigma error
box whose area is 252 square arcminutes and whose coordinates are:
RA DEC
CENTER: 44.896 o= 2 h 59 m 35.1 s 15.407 o= 15 o 24' 25"
CORNERS: 45.160 o= 3 h 00 m 38.3 s 14.528 o= 14 o 31' 39"
44.959 o= 2 h 59 m 50.1 s 15.336 o= 15 o 20' 11"
44.834 o= 2 h 59 m 20.1 s 15.478 o= 15 o 28' 42"
44.595 o= 2 h 58 m 22.7 s 16.428 o= 16 o 25' 40"
This preliminary error box has been posted at ssl.berkeley.edu/ipn3/110825A;
it can be improved.
A Swift ToO has been carried out, and the results of that observation,
as well as the details of the burst, will be reported in forthcoming
GCN Circulars.
- GCN Circular #12308
B.-B. Zhang (PSU) and D. Grupe (PSU) reports on behalf of the Swift-XRT
team:
Swift began a target of opportunity observation of the IPN-detected
burst: GRB110825A (Hurley et al. et al. GCN Circ. 12307) on August 26,
2011 at 01:05 UT, approximately 22.7 hours after the burst was detected
by IPN. Swift data for these observations utilize Target ID 20183.
We have analysed 2.9 ks of XRT data for this burst, from 81.3 ks to
94.0 ks after the IPN trigger. The data are entirely in Photon Counting
(PC) mode. An X-ray source is detected within the XRT field-of-view.
The refined XRT position is RA, Dec = 44.79846, +15.42733 which is
equivalent to:
RA (J2000): 02 59 11.63
Dec(J2000): +15 25 38.4
with an uncertainty of 3.9 arcsec (radius, 90% confidence). This
position is 346 arcsec from the IPN position and about 180 arcsec from
the edge of IPN error box (see
http://www.personal.psu.edu/buz12/IPN_ERRORBOX_VS_XRT_GRB110825A.png).
We cannot determine at the present time whether the source is fading.
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.8 (+0.8, -0.4). The
best-fitting absorption column is consistent with the Galactic value of
9.9 x 10^20 cm^-2 (Kalberla et al. 2005). The count rate for the X-ray
source is about 0.01 count/sec, which is relatively bright when
comparing to other GRB's X-ray afterglow at t-T0=10^5 seconds. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.9 x 10^-11 (4.7 x 10^-11) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 0 (+1.7, -0) x 10^21 cm^-2
Galactic foreground: 9.9 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.8 (+0.8, -0.4)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020183.
No source was found from UVOT data within the XRT error circle.
Preliminary 3-sigma up-limits are :
Filter EXPOSURE Mag
---------------------------------------------------
v & 579 & >19.19
u & 1365 & >20.79
white & 895.63 & >21.40
---------------------------------------------------
We notice that there is no known source at the X-ray source position in
Simbad or the NED. We also notice that the RASS data for this position
were not deep enough to detect a source of this flux (0.01 count/sec).
We have scheduled further Swift TOO for this target.
This circular is an official product of the Swift-XRT team.
Burst Advocate for this burst is B.-B. Zhang (bbzhang AT psu.edu).
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 #12309
D. Xu reports on behalf of a larger collaboration:
We inspected the archival datasets of the XRT field (Zhang & Grupe,
GCN 12308) of GRB 110825A (Hurley et al., GCN 12307). We found an
extended (in the SE-NW direction) object centered at
RA (J2000): 02:59:11.966
Dec(J2000): +15:25:41.34
which is 5.7 arcsec to the center of the XRT error circle with a
radius of 3.9 arcsec (90% confidence; GCN 12308). Therefore, if the
XRT source is really the counterpart of IPN-triangulated GRB110825A or
even of a new burst (as the XRT position is outside the IPN error
box), the extended object could be the host galaxy of this event.
Inspection of the archives reveals the extended object: (1) being
U1050_00797295 (USNO at ESO) with r=18.4 mag and b=19.2 mag; (2) being
02591193+1525410 (2MASS at CADC) with J=16.493+/-0.140 mag,
H=15.810+/-0.134 mag, and K=15.210+/-0.149 mag; and (3) being
1054-0031516 (USNO B1 at CDS) with R1=18.91 mag and B1=19.84 mag.
In addition, preliminary UVOT photometry (standard 5arcsec aperture
photometry) centered on the above location reveals
v(AB)>19.28
u(AB)>21.90
wh(AB)=21.55 +/- 0.21
More accurate UVOT photometry is required as the OT is extended and
relatively faint for the UVOT telescope.
Considering the above possible host galaxy is brighter than usual GRB
hosts, this source might be a low-redshift one.
- GCN Circular #12311
D. Xu (WIS), S. Schulze, P. Jakobsson (U. Iceland), and F. Faedi (QUB) report:
We observed the field (Zhang & Grupe, GCN 12308) of GRB 110825A
(Hurley et al., GCN 12307) with the Nordic Optical Telescope (NOT)
equipped with ALFOSC. We obtained 4x300s R-band imaging, starting at
05:07:08 UT on 27th August 2011. Only the first frame is useful due to
cloudy weather and relatively bright background towards the morning
twilight.
An optical object was weakly detected within the XRT error circle (GCN
12308), localised at
RA (J2000): 02:59:11.674
Dec(J2000): +15:25:39.84
Error circle radius: ~0.2 arcsec
which is about 3.9 arcsec to the extended object reported in our
previous GCN 12309. The source has R~23.6 mag calibrated to nearby
stars in the USNO B1 catalog.
No further observation with the NOT is planned.
- GCN Circular #12313
W. Zheng & C. Akerlof (U Mich), report on behalf of the ROTSE collaboration:
ROTSE-IIId, located at the Turkish National Observatory at
Bakirlitepe, Turkey, responded to GRB 110801A (Hurley et al.
GCN 12307; GBM trigger 335932012) near dawn condition.
The first image started at Aug. 25 02:30:44 UT, ~ 242 seconds
after the GBM trigger. Observation was performed in 4x4 tiling
mode around the center of the GBM trigger with exposure time
of 20 seconds for each image. Useful image last up to ~1000
seconds after trigger due to bright dawn background after that.
The optical afterglow location (Xu et al. GCN 110825) within XRT
error (Zhang & Grupe GCN 12308) is covered in 8 ROTSE images.
We do not detecte the optical afterglow. We summarize the upper
limit result below (clear band data, calibrated to USNO A-1.0):
------------------------------------
t-t0(s) exp(s) 3-sigma upper limit
301.3 20.0 15.6
418.8 20.0 15.3
448.2 20.0 15.3
477.5 20.0 15.3
771.1 20.0 14.6
888.2 20.0 14.5
917.4 20.0 14.5
946.7 20.0 14.4
- GCN Circular #12314
X. H. Zhao (YNAO), D. Xu (WIS), J. M. Bai (YNAO), report on behalf of a larger collaboration:
We observed the XRT field (Zhang & Grupe, GCN 12308) of GRB 110825A
(Hurley et al., GCN 12307) with the 2.4m Gao-Mei-Gu (GMG) telescope
equipped with YFOSC in Yunan, China. Observations started at 19:02:36
UT on 27th August 2011 and 3x1200s R-band images were obtained.
The possible optical afterglow candidate, derived from a weak
detection from a single frame (Xu et al., GCN 12311) is not detected
in our stacked R-band image, which gives rise to a 3sigma upper limit
of R~23.9 mag for the XRT error circle, calibrated with the same USNO
reference star in GCN 12311.
No further observation with the GMG telescope is planned.
- GCN Circular #12315
K. Yamaoka (Aoyama Gakuin U.), N. Ohmori, M. Akiyama,
M. Yamauchi (Univ. of Miyazaki), M. Ohno, Y. Hanabata,
T. Uehara, T. Takahashi, M. Mizuno, Y. Fukazawa (Hiroshima U.),
S. Sugita (Nagoya U.), T. Yasuda, Y. Terada, W. Iwakiri,
K. Takahara, M. Asahina, S. Kobayashi, M. Tashiro (Saitama U.),
M. Kokubun, T. Takahashi (ISAS/JAXA), Y. E. Nakagawa (Waseda U.),
Y. Urata, P. Tsai, C-J. Chuang (NCU), K. Nakazawa,
K. Makishima (Univ. of Tokyo), on behalf of the Suzaku WAM team, report:
The bright, long GRB110825A (localized by IPN; Hurley et al. GCN 12307)
triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers an
energy range of 50 keV - 5 MeV at 02:27:03.410 UT (=T0).
The observed light curve shows multiple peaks starting at T0-3 s, ending
at T0+8 s, with a duration (T90) of about 6.9 seconds. The fluence in
the 100 - 1000 keV range was 1.88 +/- 0.14 x 10^-5 erg/cm^2.
The 1-s peak flux measured from T0+3 s was 17.0 +/- 0.8 photons/cm^2/s
in the same energy range.
Preliminary result shows that the time-averaged spectrum from T0-3 s to
T0+8 s is well fitted by a power-law with exponential cutoff model:
dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
alpha : 1.28 (-0.40, +0.34), and
Epeak : 248 (-47, +41) keV (chi^2/d.o.f. = 19.4/21).
All the quoted errors are at statistical 90% confidence level,
in which systematic uncertainties are not included.
The light curves for this burst are available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html
- GCN Circular #12318
S. McGlynn (MPE/Excellence Cluster) reports on behalf of the Fermi GBM Team:
"At 02:26:50.94 UT on 25 August 2011, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 110825A (trigger 335932012 / 110825102),
which was also localised by the IPN
(Hurley et al. 2011, GCN 12307).
The angle from the Fermi LAT boresight at trigger time was 65 degrees.
Approximately 100 s from trigger time, the Fermi spacecraft executed
an automatic maneuver in response to a command from GBM, in
order to place the burst closer to the LAT boresight.
The GBM light curve shows a soft precursor (~2s) followed by 2 bright
peaks from T0+10s to T0+25s, with a possible soft tail at T0+75 to
T0+85s. The duration (t90) is 62.5 +/- 0.2 s (50-300 keV).
The time-averaged spectrum from T0-0.64 s to T0+82.3 s is
best fit by a Band function with Epeak = 233.6 (+21.9/-19.9) keV,
alpha = -1.23 (+/-0.03), and beta = -2.04 (+0.06/-0.08)
(C-Stat 719.72 for 490 d.o.f.).
The event fluence (10-1000 keV) in this time interval is
(5.45 +/- 0.70)E-5 erg/cm^2. The 1 s peak photon flux measured
starting from T0+15.5 s in the 10-1000 keV band
is 53.7 +/- 0.4 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
- GCN Circular #12334
B.-B. Zhang (PSU), D. Grupe (PSU), D. N. Burrows (PSU), J. Gelbord (PSU)
and S. D. Barthelmy (GSFC) report on behalf of the Swift-XRT team:
We report further observations of the possible X-ray counterpart
(Zhang & Grupe, GCN 12308) of the IPN-detected burst GRB 110825A
(Hurley etal., GCN 12307). The Swift/XRT found a relatively bright
X-ray source located at
RA (J2000): 02 59 11.63
Dec(J2000): +15 25 38.4.
We performed follow-up XRT observations of this field at T0+1 day,
T0+5 days,T0+12 days and T0+16 days (where T0 = 2011 Aug 25 at
02:26:48.0 UT ), in order to determine whether or not the X-ray source
had faded. The observed count rates in the 0.3-10 keV band are as follows :
T-T0 Count Rate
(8.7+/-0.6)x10^3 s 0.0129+/-0.0025 count/s
(4.8+/-0.2)x10^5 s 0.0045+/-0.0011 count/s
(1.1+/-0.01)x10^6 s 0.0065+/-0.0025 count/s
(1.4+/-0.07)x10^6 s 0.0083+/-0.0018 count/s
We find that this source is now at a count rate consistent with
that of our first observation on T0+1 day at the 1.5 sigma level.
The chance probability for the source being steady is about 0.015,
indicating that it is variable, but it is not decaying as expected for
a GRB. We conclude that this source is not the afterglow of GRB 110825A.
Thus, no afterglow was detected by XRT for this burst.
We note that the variability of this X-ray counterpart in the last two weeks
suggests that it may be a background AGN.
The updated results of the XRT-team automatic analysis are available
at <http://www.swift.ac.uk/xrt_products/00020183>.
- GCN Circular #12403
V. Sudilovsky, J. Greiner, A. Rau (All MPE Garching), and S. Klose (TLS
Tautenburg) report on behalf of the GROND team:
We observed the field of the IPN GRB 110825A (Hurley et al., GCN 12307)
on 2011 August 29 at 08:55 UT (52hr post trigger) simultaneously in
g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at
the 2.2m MPI/ESO telescope at La Silla Observatory (Chile).
With an exposure time of 3000s we do not find any source within the XRT
error circle (Zhang et al., GCN 12308). In particular, the object
reported by Xu et al. (GCN 12311) is not detected with a 3-sigma
limiting magnitude of r' ~ 24.5 calibrated against USNO B1. This is
consistent with the non-detection reported by Zhao et al (GCN 12314) and
suggests that the source must have faded by at least 0.9mag within the
first 48hr after the trigger. The optical decline is in agreement with a
similar decay by a factor of 3 seen in the XRT lightcurve between day 1
and day 5 (Zhang et al., GCN 12334). While this could suggest the source
detected by Xu et al. to be the afterglow of GRB110825A, the very late
re-brightening observed in X-rays (Zhang et al., GCN 12334) makes this
interpretation unlikely.
Further deep optical imaging and X-ray monitoring are encouraged to
resolve the nature of this source.
We thank Kim Page and Phil Evans for providing helpful details
concerning the XRT observations of GRB 110825A.
Previous IAU Circulars 
