GRB 090927
GCN Circular 9945
Subject
GRB 090927: Swift detection of a short burst
Date
2009-09-27T10:19:48Z (16 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
D. Grupe (PSU), J. R. Cummings (NASA/UMBC), C. Gronwall (PSU),
C. Guidorzi (U Ferrara), C. B. Markwardt (CRESST/GSFC/UMD),
P. T. O'Brien (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), P. Romano (INAF-IASFPA), M. H. Siegel (PSU),
T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the
Swift Team:
At 10:07:16 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090927 (trigger=370846). The BAT on-board calculated
location is RA, Dec 343.953, -70.978 which is
RA(J2000) = 22h 55m 49s
Dec(J2000) = -70d 58' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a single peak
structure with a duration of about 1.5 sec. The peak count rate
was ~4000 counts/sec (15-350 keV), at ~1 sec after the trigger.
Due to an observing constraint, Swift will not slew until
T0+33.8 minutes. There will be no XRT or UVOT data until
this time.
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 9946
Subject
GRB 090927: Swift/UVOT detection of an optical afterglow
Date
2009-09-27T10:58:19Z (16 years ago)
From
Caryl Gronwall at PSU/Swift-UVOT <caryl@astro.psu.edu>
C. Gronwall and D. Grupe (PSU) report on behalf of the Swift/UVOT team:
In response to GRB090927 (Swift/BAT trigger 370846) at 10:07:16 UT,
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 2141 seconds after the BAT trigger. There is a candidate
afterglow in
the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 22:55:53.41 = 343.97255
DEC(J2000) = -70:58:49.3 = -70.98037
with a 90%-confidence error radius of about 0.63 arc sec. This
position is 7.2
arc sec. from the center of the XRT error circle. The estimated
magnitude is
19.10 with a 1-sigma error of about 0.15. No correction has been made
for the
expected extinction corresponding to E(B-V) of 0.03.
GCN Circular 9950
Subject
GRB 090927: Enhanced Swift-XRT position
Date
2009-09-27T13:41:20Z (16 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1424 s of XRT Photon Counting mode data and 3 UVOT
images for GRB 090927, 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 = 343.97291, -70.98032 which is equivalent
to:
RA (J2000): 22h 55m 53.50s
Dec (J2000): -70d 58' 49.2"
with an uncertainty of 2.0 arcsec (radius, 90% confidence).
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).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 9952
Subject
GRB 090927: Swift XRT refined analysis
Date
2009-09-27T15:13:01Z (16 years ago)
From
Dirk Grupe at PSU/Swift-XRT <grupe@astro.psu.edu>
D. Grupe and L. Vetere (PSU) report on behalf of the Swift-XRT team:
Due to an observing constraint, the Swift XRT started observing the
field of GRB 090927 Grupe et al., GCN Circ. 9945) delayed at 10:43:03
UT, 2147s after the BAT trigger.
XRT found a faint, fading, uncatalogued X-ray source at
RA (J2000): 22h 55m 53.50s
Dec (J2000): -70d 58' 49.2"
with an uncertainty of 2.0 arcsec (radius, 90% confidence) as given
in Evens et al. (GCN Circular 9950). This location is 24.8" from
the BAT on-board calculated location (Grupe et al., GCN Circular
9945), inside the BAT error circle, and 0.5" from the UVOT position
given in Gronwall & Grupe (GCN Circular 9946).
Based on the Photon Counting mode (pc) mode data of the first orbit
with an exposure time of 1421s we extracted a spectrum which can be
fitted with a single absorbed power law model with Gamma =
1.64+/-0.49 and an absorption column density consistent with the
Galactic value of 2.92 x 10^20 cm^-2 (Kalberla et al. 2005).
The light curve can be modelled with a single power-law decay with
an index of alpha=1.76+2.05/-0.96. If the afterglow continues to
decay with this slope the predicted count rate 24 hours after
the trigger is 2.5e-4 counts s^-1 or 1.3e-14 ergs s^-1 cm^-2.
This circular is an official product of the Swift-XRT team.
GCN Circular 9954
Subject
Swift/UVOT observations of GRB 090927
Date
2009-09-27T18:58:12Z (16 years ago)
From
Paul Kuin at MSSL <npkuin@googlemail.com>
N.P.M. Kuin (MSSL-UCL) and D. Grupe (PSU) report on behalf
of the Swift/UVOT team:
The Swift/UVOT began a delayed observing the field of GRB 090927
2121s after the trigger due to an observing constraint (Grupe, GCN
Circ. 9945). We detect a fading optical afterglow in white, v,b,
and u filters at the position reported by UVOT (Gronwall et al.,
GCN Circ. 9946).
Preliminary magnitudes are reported below.
Filter T_start(s) T_stop(s) Exposure(s) Magnitude
===================================================
white(FC) 2141 2291 147.4 19.13 +/- 0.09
white 2372 2920 235.6 19.40 +/- 0.09
v 2121 2617 48.6 19.0 +/- 0.37
v 3131 3331 196.6 19.37 +/- 0.25
b 2348 2542 38.9 19.50 +/- 0.31
b 2696 2716 19.5 19.09 +/- 0.34
u 2323 2517 38.9 18.77 +/- 0.26
u 2671 2691 19.5 >18.89
uvw1 2299 3576 92.8 >19.63
uvm2 2446 3536 235.6 >19.89
uvw2 2397 2592 38.9 >18.84
====================================================
The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.03 mag (Schlegel et al.,
1998, ApJS, 500, 525). The photometry is on the UVOT photometric
system described in Poole et al. (2008, MNRAS, 383,627).
GCN Circular 9955
Subject
GRB 090927, Swift-BAT refined analysis of the possibly short burst
Date
2009-09-27T19:36:02Z (16 years ago)
From
Jay R. Cummings at NASA/GSFC/Swift <james.r.cummings@nasa.gov>
M. Stamatikos (OSU), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC),
E. E. Fenimore (LANL), N. Gehrels (GSFC), D. Grupe (PSU),
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), J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 090927 (trigger #370846)
(Grupe, et al., GCN Circ. 9945). The BAT ground-calculated position is
RA, Dec = 343.929, -70.973 deg which is
RA(J2000) = 22h 55m 42.9s
Dec(J2000) = -70d 58' 24.2"
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 55%.
The mask-weighted light curve shows a single irregular peak with an
overall roughly FRED shape. T90 (15-350 keV) is 2.2 +- 0.4 sec
(estimated error including systematics).
The time-averaged spectrum from T+0.0 to T+2.4 sec is best fit by a
simple power-law model. The power law index of the time-averaged
spectrum is 1.80 +- 0.20. The fluence in the 15-150 keV band is
2.0 +- 0.3 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from
T-0.01 sec in the 15-150 keV band is 2.0 +- 0.2 ph/cm2/sec. All the
quoted errors are at the 90% confidence level.
The classification of this burst as short or long is not clear. The
burst appears to have significant lag between energy bands, and
moreover is not particularly hard. We expect to perform a more
quantitative lag analysis and report the results in an additional
circular.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/370846/BA/
GCN Circular 9956
Subject
GRB 090927: Zadko Telescope observations
Date
2009-09-27T20:29:05Z (16 years ago)
From
Alain Klotz at CESR-CNRS <Alain.Klotz@free.fr>
A. Klotz, T.P. Vaalsta, Liang Yan, and J. Zadko
report on behalf of the Zadko Telescope Team.
A. Klotz (CESR, OHP), T.P. Vaalsta, Liang Yan, J. Zadko,
H. Miao, J. Moore, K. Frost, D. Coward, A. Imerito,
D. Blair, R. Burman, P. Luckas, S. Gordon, A. Fletcher,
A. Ahmet, (University of Western Australia)
M. Todd, M. Zadnik (Curtin University)
M. Boer, M. Laas (OHP), P. Thierry (Airbus)
The 1.0m F/4 Zadko telescope started imaging
the field of GRB 090927 (trigger=370846, Grupe
et al., GCN 9945) 110 minutes after the Swift
trigger. A fading source was found within the
XRT error circle (GCN 9946, Gronwall et al.).
The field was observed for 50 minutes using a
preliminary version of a robotic observation
mode.
Preliminary photometry of unfiltered images
taken with an iKon DW436BV camera show the
following initial magnitudes of the optical
afterglow:
tmid(min) Exp. Time R Magnitude
-------------------------------------
110 42s >16
126 540s 19.8 +/- 0.5
158 360s 20.0 +/- 0.5
The fading seems to have low decay
which is encouraging to perform
spectrocopy in the next hours.
GCN Circular 9958
Subject
GRB 090927: VLT redshift
Date
2009-09-28T07:44:23Z (16 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@astro.ku.dk>
Andrew J. Levan (Univ. Warwick), Johan P.U. Fynbo (DARK/NBI), Jens
Hjorth (DARK/NBI), Daniele Malesani (DARK/NBI), Paolo D'Avanzo
(INAF/OABr), Valerio D'Elia (INAF/OAR), report on behalf of a larger
collaboration:
We observed the afterglow of GRB 090927 (Grupe et al., GCN 9945;
Gronwall et al., GCN 9946), possibly short (Stamatikos et al., GCN
9955). Using FORS2 on the Very Large Telescope, we have obtained 3x30
min spectra (300V grism) of the optical afterglow (Gronwall & Grupe, GCN
9946; Klotz et al., GCN 9956). Observations started on Sep 27.11 UT,
about 16.5 hr after the burst. The afterglow had a magnitude R ~ 21.7 as
measured from the acquisition images.
The obtained spectrum shows Mg II and Fe II absorption lines
corresponding to z = 1.37. There is no evidence for higher redshift
systems or a Lyman-alpha and hence z = 1.37 is the likely redshift of
GRB 090927.
We acknowledge excellent support from the ESO observing staff, in
particular Yuri Beletsky and Stephane Brillant.
GCN Circular 9960
Subject
GRB 090927: Faulkes Telescope South Detection of the Optical Afterglow
Date
2009-09-28T16:42:32Z (16 years ago)
From
Zach Cano at ARI/John Moores Liverpool <zec@astro.livjm.ac.uk>
Z. Cano, A. Melandri, C. Mundell, D. Bersier, R.J. Smith, I. A. Steele, S.
Kobayashi, C.J. Mottram (Liverpool JMU), A. Gomboc (U. Ljubljana) report,
on behalf of the Liverpool GRB group:
The Faulkes Telescope South (Australia) observed the field of GRB
090927 (Swift trigger=370846, Grupe et al., GCN 9945) on 2009 September 27
and 28.
The afterglow candidate reported by Gronwell & Grupe (GCN 9946) is clearly
visible and fading at position:
RA(J2000): 22 55 53.42
Dec(J2000): -70 58 49.54
with the following magnitudes calibrated wrt USNO-B1 objects in the field:
I = 19.4 +/- 0.1 @ 3.66 hrs
I = 21.3 +/- 0.2 @ 27.23 hrs
R = 19.9 +/- 0.1 @ 4.21 hrs
Observations are on-going, but we derive preliminary decay rates using the
above FTS measurements and the R-band magnitude reported by Levan et al.
(GCN 9958) to be: alpha_I=0.9+/-0.2, alpha_R=1.2+/-0.2.
GCN Circular 9974
Subject
GRB 090927: Fermi GBM observation
Date
2009-09-30T13:01:46Z (16 years ago)
From
David Gruber at MPE <dgruber@mpe.mpg.de>
D. Gruber (MPE), E. Bissaldi (MPE) and S. McBreen (UCD/MPE)
report on behalf of the Fermi GBM Team:
"At 10:07:17.21 UT on 27 September 2009, the Fermi Gamma-Ray Burst
Monitor
triggered and located GRB 090927 (trigger 275738839 / 090927422),
which was also detected by the Swift-BAT (Grupe al. 2009, GCN 9945).
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 85 degrees.
The GBM light curve consists of one weak pulse with
a duration of about 2 seconds.
The time-averaged spectrum from T0-0.256 s to T0+0.896 s is
adequately fit by a simple power law function
with index -1.47 +/- 0.06 (C-stat 330 for 239 d.o.f.).
The event fluence (8-1000 keV) in this time interval is
(6.1 +/- 0.5)E-07 erg/cm^2. The 128-msec peak photon flux measured
starting from T0-0.128 s in the 8-1000 keV band
is 7.2 +/- 0.9 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
GCN Circular 10021
Subject
Radio observation of GRB090927 with ATCA
Date
2009-10-13T09:12:09Z (16 years ago)
From
Aquib Moin at CIRA/ATNF <aquib.moin@postgrad.curtin.edu.au>
Aquib Moin (Curtin Institute of Radio Astronomy / Australia Telescope
National Facility), Dale A. Frail (National Radio Astronomy
Observatory), Steven Tingay (Curtin Institute of Radio Astronomy),
Jean-Pierre Macquart (Curtin Institute of Radio Astronomy) report:
We observed the enhanced Swift-XRT position of the GRB090927 (GCN 9950)
at 5.5 GHz with the Australia Telescope Compact Array (ATCA) between
05:00:00 UT and 10:00:00 UT on October 01, 2009. The ATCA was in its
most compact configuration giving a synthesized beam of 126 x 76 arcsec.
We did not detect a radio source at the XRT position of the GRB090926a
(GCN 9950). The radio flux density at the GRB position found out to be
0.036 � 0.172 mJy/beam.
No further observations are planned.
The Australia Telescope Compact Array (/ Parkes telescope / Mopra
telescope / Long Baseline Array) is part of the Australia Telescope
which is funded by the Commonwealth of Australia for operation as a
National Facility managed by CSIRO.
See the GRB field image at:
http://cira.ivec.org/dokuwiki/doku.php/grb/grb090927_field_image