GRB 090926B
GCN Circular 9935
Subject
GRB 090926B: Swift detection of a burst
Date
2009-09-26T22:20:28Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
D. Grupe (PSU), S. D. Barthelmy (GSFC), J. R. Cummings (NASA/UMBC),
J. A. Kennea (PSU), P. T. O'Brien (U Leicester),
P. Romano (INAF-IASFPA), M. Stamatikos (OSU/NASA/GSFC),
M. A. Stark (PSU) and L. Vetere (PSU) report on behalf of the Swift
Team:
At 21:55:48 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090926B (trigger=370791). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 46.318, -39.011 which is
RA(J2000) = 03h 05m 16s
Dec(J2000) = -39d 00' 40"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows a single peak
with a duration of about 20 sec. The peak count rate
was ~1600 counts/sec (15-350 keV), at ~1 sec after the trigger.
The XRT began observing the field at 21:57:16.8 UT, 88.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 46.30693,
-39.00545 which is equivalent to:
RA(J2000) = 03h 05m 13.66s
Dec(J2000) = -39d 00' 19.6"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). 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
1.91e+20 cm^-2 (Kalberla et al. 2005).
The initial flux in the 2.5 s image was 3.15e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 98 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag.
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.02.
Burst Advocate for this burst is D. Grupe (grupe AT astro.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 9939
Subject
GRB 090926B: Swift-BAT refined analysis
Date
2009-09-27T03:51:16Z (16 years ago)
From
Jay R. Cummings at NASA/GSFC/Swift <james.r.cummings@nasa.gov>
W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC),
J. R. Cummings (GSFC/UMBC), D. Grupe (PSU), E. E. Fenimore (LANL),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD),
D. M. Palmer (LANL), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC),
G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC),
T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-61 to T+243 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 090926 (trigger #370791)
(Grupe, et al., GCN Circ. 9935). The BAT ground-calculated position is
RA, Dec = 46.310, -38.997 deg which is
RA(J2000) = 03h 05m 14.3s
Dec(J2000) = -38d 59' 50.9"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 26%.
The mask-weighted light curve shows a sharp rise at T-20 sec, then a
complex peak reaching a maximum at T-1 sec, followed by an approximately
exponential decay. T90 (15-350 keV) is 109.7 +- 11.3 sec (estimated
error including systematics).
The time-averaged spectrum from T-21.6 to T+133.2 sec is best fit by a
power law with an exponential cutoff. This fit gives a photon index
0.52 +- 0.24, and Epeak of 78.3 +- 7.0 keV (chi squared 57.75 for 56
d.o.f.). For this model the total fluence in the 15-150 keV band is
7.3 +- 0.2 x 10^-06 erg/cm2 and the 1-sec peak flux measured from
T-1.31 sec in the 15-150 keV band is 3.2 +- 0.3 ph/cm2/sec. A fit to a
simple power law gives a photon index of 1.54 +- 0.00 (chi squared
125.34 for 57 d.o.f.). All the quoted errors are at the 90% confidence
level.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/370791/BA/
GCN Circular 9940
Subject
GRB 090926B: Swift XRT refined analysis
Date
2009-09-27T04:16:40Z (16 years ago)
From
Dirk Grupe at PSU/Swift-XRT <grupe@astro.psu.edu>
D. Grupe (PSU), P.A. Evans and M.R. Goad (U. Leicester) report
on behalf of the Swift-XRT team:
We have analysed the first two orbits of XRT data of GRB090926B
(Grupe et al. GCN Circ. 9935). The data comprise 307 s in Windowed
Timing (WT) mode and 1985 s in Photon Counting (PC) mode.
Using 1692 s of XRT Photon Counting mode data and 1 UVOT
images, we find an astrometrically corrected X-ray position (using
the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue): RA, Dec =
46.30840, -39.00600 which is equivalent to:
RA (J2000): 03 05 14.01
Dec (J2000): -39 00 21.5
with an uncertainty of 1.7" (radius, 90% confidence). This
position is 32.7" from the BAT ground-calculated position given in
Baumgartner et al (GCN circular 9939).
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions.
Position enhancement is described by Goad et al. (2007, A&A, 476,
1401) and Evans et al. (2009, MNRAS, 397, 1177).
A spectrum formed from the WT mode data can be fitted with an
absorbed power-law with a photon spectral index of 1.84+/-0.07
with an absorption column of (1.70+/-0.22)e21 cm^-2 which is in
excess of the Galactic value of 1.91 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum results is a slightly flatter X-ray
spectrum with Gamma = 1.58+0.22-0.20. The absorption column density,
however, is consistent with the WT result. Based on the excess
absorption, according to Grupe et al. (2007, AJ, 133, 2216), the
redshift of this burst is most likely less than 4.0.
The light curve can be modelled with a broken power-law decay with an
index of alpha=2.00+/-0.05, followed by a break at T+712+190/-160 s
to an alpha of 1.23 (-0.17, +0.07). If the afterglow continues to
dacay with a slope of 1.23, the predicted count rate 24 hours after
the trigger is 3.4e-3 counts s^-1 or 1.6e-13 ergs s^-1 cm^-2.
This circular is an official product of the Swift-XRT team.
GCN Circular 9941
Subject
GRB 090926B: NOT optical observation
Date
2009-09-27T05:05:31Z (16 years ago)
From
Dong Xu at DARK,NBI <dong@astro.ku.dk>
D. Xu, D. Malesani (DARK/NBI), S. Barros (Queen Univ., Belfast), P.
Jakobsson (Univ. Iceland), report on behalf of a larger collaboration.
We observed the field of GRB 090926B (Grupe et al., GCN 9935) with the
NOT equipped with ALFOSC. Observations were carried out in the R and I
bands, at high airmass (~2.5), starting on 2009 Sep 27.122 UT (4.99 hr
after the GRB) and 27.146 UT (5.58 hr after the GRB), respectively.
No source is visible inside the enhanced X-ray error circle (Grupe et
al., GCN 9940; http://www.swift.ac.uk/xrt_positions), down to a limiting
magnitude R ~ 23 based on USNO-B1 stars in the field.
GCN Circular 9943
Subject
GRB 090926B: MAXI GSC detection
Date
2009-09-27T07:27:48Z (16 years ago)
From
Nobuyuki Kawai at Tokyo Tech <nkawai@hp.phys.titech.ac.jp>
M. Morii (Tokyo Tech), M. Nakajima (Nihon U.), M. Matsuoka,
K. Kawasaki, S. Ueno, H. Tomida, M. Suzuki, M. Ishikawa (JAXA),
T. Mihara, M. Kohama, Y.E. Nakagawa, M. Sugizaki, T. Yamamoto (RIKEN),
N. Kawai, K. Sugimori (Tokyo Tech), A. Yoshida, K. Yamaoka,
S. Nakahira (AGU), H. Tsunemi, M. Kimura (Osaka U.), H. Negoro,
S. Miyoshi, H. Ozawa, R. Ishiwata, (Nihon U.), Y. Ueda, N. Isobe,
S. Eguchi, K. Hiroi (Kyoto U.) report on behalf of the MAXI team:
The Gas Slit Camera (GSC) of MAXI, the all-sky X-ray monitor on the ISS,
detected a bright X-ray source at the position consistent with GRB 090926B
(Grupe et al, GCN Circ. 9935) in the energy range of 2-30 keV.
The nominal location of the source as measured by GSC is
(R.A., Dec.) = (46.3 deg, -39.1 deg) = (03:05:12, -39:06:00)(J2000)
with an estimated systematic uncertainty of about 1 degree.
The start time of the source detection (above 3 sigma level) was
21:55:31 UT on 26 September 2009, and seen until 21:55:55 UT.
The start time was 17 sec earlier than the Swift-BAT trigger time,
approximately consistent with the rise epoch (T-20) reported in the BAT
refined analysis (Baumgartner et al., GCN Circ. 9939).
The X-ray flux at the peak was about 0.3 Crab (uncorrected).
There are significant time structures within the transit light curve,
which would be simply triangular for a steady source.
The all-sky image and the light curve is shown at the MAXI web site
http://maxi.riken.jp/ at the "News" section.
MAXI is currently in the commissioning phase that runs for three months.
The systematic uncertainty in localization will be significantly improved
with the progress of the alignment calibration.
GCN Circular 9944
Subject
GRB 090926B: optical object in error circle
Date
2009-09-27T07:45:32Z (16 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@astro.ku.dk>
Daniele Malesani, Johan P. U. Fynbo (DARK/NBI) and V. D'Elia (ASDC and
INAF/OAR) report on behalf of a larger collaboration:
We observed the field of GRB 090926B (Grupe et al., GCN 9935; Morii et
al., GCN 9943) with the VLT UT1 equipped with FORS2. Seeing was
0.8-0.9". Preliminary inspection of the image reveals a faint, slightly
extended source at a position consistent with the revised XRT error
circle (Grupe et al., GCN 9940; http://www.swift.ac.uk/xrt_positions).
Its coordinates are (0.5" error):
RA(J2000) = 03:05:13.94
Dec(J2000) = -39:00:22.2
and its magnitude (based on archival zeropoints) is R ~ 23 on 2009 Sep
27.246 UT (7.97 hr after the GRB). Inspection of the NOT images (Xu et
al., GCN 9941) reveals a faint nebulosity, with a luminosity level
consistent with the VLT measurement.
Presently, it is not clear whether this source is related to the GRB or
not. It may be the host galaxy, or the blend of two faint, adjacent
objects. Further observations are planned to evaluate its variability.
We gladly acknowledge excellent support from the ESO observing staff
during a busy night, in particular Yuri Beletsky, and Stephane Brillant.
GCN Circular 9947
Subject
GRB 090926B: VLT spectroscopy
Date
2009-09-27T11:21:59Z (16 years ago)
From
Pall Jakobsson at U of Iceland <pja@raunvis.hi.is>
Johan P. U. Fynbo, Daniele Malesani (DARK/NBI), Pall Jakobsson
(U. Iceland) and Valerio D'Elia (ASDC and INAF/OAR) report on
behalf of a larger collaboration:
We observed the afterglow of GRB 090926B (Grupe et al, GCN 9935;
Morii et al., GCN 9943). Using FORS2 on the Very Large Telescope,
we have obtained 3*30 min spectra (300V grating) of the optical
afterglow candidate (Malesani et al., GCN 9944). Observations
commenced roughly 8 hours after the burst.
The combined spectrum shows an emission line, presumably
corresponding to [O II] 3727 at z = 1.24. At his redshift we
find several other absorption features, including Mg II, Fe II
and Al III. Hence, we interpret the spectrum as a combination
of the GRB afterglow and the host galaxy.
We acknowledge excellent support from the ESO observing staff,
in particular Yuri Beletsky and Stephane Brillant.
GCN Circular 9949
Subject
GRB090926B: Swift/UVOT Upper Limits
Date
2009-09-27T12:42:23Z (16 years ago)
From
Samantha Oates at MSSL <sro@mssl.ucl.ac.uk>
S. R. Oates (MSSL-UCL) and D. Grupe (PSU) report on behalf of the
Swift/UVOT team:
The Swift/UVOT began settled observations of the field of
GRB 090926B 98s after the BAT trigger (Grupe et al., GCN 9935).
We do not detect any source at the position reported by
VLT (Malesani et al., GCN 9944) and the enhanced Swift XRT
position (Grupe et al. GCN 9940).
The 3-sigma upper limits for the finding charts (FC) and summed images
are:
Filter T_start T_stop Exp(s) Mag (3-sigma upper limit)
-------------------------------------------------------------
white(FC) 98 248 147 > 21.02
white 591 2053 303 > 21.21
v 641 2103 175 > 19.19
b 567 5976 226 > 20.32
u(FC) 310 560 246 > 20.30
u 715 5900 333 > 20.22
uvw1 691 5695 333 > 20.25
uvm2 5290 5490 197 > 19.77
uvw2 616 1389 58 > 19.09
-------------------------------------------------------------
The quoted upper limits have not been corrected for the expected
Galactic extinction along the line of sight of E_(B-V) = 0.02 mag.
All photometry is on the UVOT photometric system described in Poole et
al. (2008, MNRAS, 383, 627).
GCN Circular 9957
Subject
GRB 090926B: Fermi GBM detection
Date
2009-09-28T01:34:51Z (16 years ago)
From
Michael S. Briggs at UAH and MSFC <michael.briggs@nasa.gov>
Michael S. Briggs (UA Huntsville), reports on behalf of the Fermi GBM Team:
"At 21:55:28.53 UT on 26 Sept 2009, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 090926B (trigger 275694930 / 090926.914),
which also triggered the Swift BAT 19 seconds later (D. Grupe et al.,
GCN 9935). The GBM location is consistent with the Swift BAT location.
The angle from the Fermi LAT boresight is approximately 100 degrees.
The GBM light curve shows multiple peaks with a duration (T90)
of 81 +/- 13 s (10 to 1000 keV). The time-averaged spectrum from T0 to
T0+48.6 s is best fit by cutoff power law with Epeak = 91 +/- 2 keV and
index
= -0.13 +/- 0.06. The fluence (10 to 1000 keV) in this time interval is
(8.7 +/- 0.3)E-06 erg/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
GCN Circular 9996
Subject
GRB 090926B: Skynet/PROMPT Observations
Date
2009-10-06T04:07:49Z (16 years ago)
From
Josh Haislip at U.North Carolina <haislip@physics.unc.edu>
J. Haislip, D. Reichart, K. Ivarsen, A. LaCluyze, A. Foster, J. Moore, A.
Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander
report:
Skynet observed the Swift/BAT localization of GRB 090926B (Grupe et al.,
GCN 9935) with four of the 16" PROMPT telescopes at CTIO beginning 2.7
hours after the trigger in UVRI.
We do not detect the afterglow (Grupe et al., GCN 9935; Malesani, Fynbo &
D'Elia, GCN 9944). Stacking only images that increase the limiting
magnitude yields:
mean 1-sig. 1-sig.
time 3-sig. sys. stat.
since lim. cal. cal. cal.
trig. tel. exp. fil. mag. stars unc. unc.
(h) (# x s) (mag) (mag)
2.7 PROMPT-4 4 x 80 R 19.9 40 USNO B1 0.424 0.002
2.7 PROMPT-2 4 x 80 V 18.2 11 NOMAD 0.099 0.003
2.7 PROMPT-5 3 x 80 I 18.2 32 USNO B1 0.414 0.003