GRB 060923A, GRB 060923
GCN Circular 5673
Subject
GRB 060923A: Probable host galaxy in the R-band
Date
2006-10-01T17:32:56Z (20 years ago)
From
Andrew Levan at U.of Leicester <anl@star.le.ac.uk>
A.J. Levan (Hertfordshire), N.R. Tanvir (Leicester), J. Gorosabel (IAA-CSIC)
report for a larger collaboration:
We observed the location of GRB 060923A (Tanvir et al. GCN Circ 5587; Fox
et al. GCN Circ 5597) in the R-band using the VLT and FORS2. At the
location of the afterglow we find a faint, extended source (angular size
~2") with R~25.5. We suggest this is likely to be the host galaxy of GRB
060923A.
If this galaxy is the host of GRB 060923A then its detection in the R-band
implies an upper limit for the redshift of z~5. Therefore we believe that
extinction is the most likely cause for the extremely red J-K colour for
the afterglow at early times.
We that the staff of the VLT for their excellent support.
GCN Circular 5671
Subject
GRB 060923A: VLA K-band Observations
Date
2006-10-01T00:58:58Z (20 years ago)
From
Poonam Chandra at U Virginia/NRAO <pc8s@virginia.edu>
P. Chandra (UVA/NRAO) and D. A. Frail (NRAO) report on behalf of
the Caltech-NRAO-Carnegie GRB Collaboration:
"We used the Very Large Array to observe the field of view toward
GRB060923A (GCN 5583) at a frequency of 22.5 GHz on 2006 September
30 starting at 19.65 UT. The peak radio brightness at the position of the
afterglow of Fox et al. (GCN 5597) is -200 uJy � 260 uJy.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 5624
Subject
GRB 060923A: Schedule of Spitzer Space Telescope Observations
Date
2006-09-27T01:31:24Z (20 years ago)
From
Derek Fox at PSU <dfox@astro.psu.edu>
D.B. Fox (Penn State) reports on behalf of a larger collaboration:
"We have activated a sequence of Spitzer Space Telescope IRAC imaging
observations of the afterglow of GRB 060923A (Stamatikos et al., GCN
5583). Projected start times for these observations are:
Epoch 1: 10:45 UT on 27 Sep 2006
Epoch 2: 04:00 UT on 29 Sep 2006 (est.)
Epoch 3: 15:15 UT on 3 Oct 2006 (est.)
Observations for each epoch will last approximately 80 minutes.
Observers interested in coordination with Epochs 2 and 3 should
contact the author by email in advance to confirm the final schedule."
GCN Circular 5620
Subject
GRB 060923A: Radio Observations
Date
2006-09-26T22:23:15Z (20 years ago)
From
Dale A. Frail at NRAO <dfrail@nrao.edu>
Dale A. Frail (NRAO) and P. Chandra (NRAO/UVA) report on behalf of a
larger collaboration:
"We used the Very Large Array to observe the field of view toward
GRB060923A (GCN 5583) at a frequency of 8.46 GHz on 2006 October 26.06 UT.
The peak radio brightness at the position of the afterglow of Tanvir
et al. (GCN 5587) and Fox et al. (GCN 5597) is -30 uJy +/- 55 uJy.
Further observations are planned.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 5605
Subject
GRB 060923A: Gemini Second Epoch and Afterglow Confirmation
Date
2006-09-24T22:34:47Z (20 years ago)
From
Derek Fox at PSU <dfox@astro.psu.edu>
D.B. Fox (Penn State) reports on behalf of a larger collaboration:
"We have imaged the Swift XRT localization region for GRB060923A
(Stamatikos et al., GCN 5583) with Gemini-North + NIRI on a second
occasion. The candidate afterglow of Tanvir et al. (GCN 5587) and Fox
et al. (GCN 5597) is no longer detected, and we estimate its
brightness as:
K-band: Ks>21.5 mag at 05:05 UT, 24 Sep (mean epoch)
using the same photometric calibration as for the previous night (GCN
5597). Fading of the candidate by >~1 mag between our two epochs is
separately confirmed in an image subtraction analysis.
This confirms the afterglow nature of the source, and thus the highly
reddened, high-redshift and/or highly-extinguished nature of the
afterglow of GRB 060923A."
GCN Circular 5599
Subject
GRB 060923A: Swift XRT refined analysis
Date
2006-09-23T19:14:02Z (20 years ago)
From
Maria Laura Conciatore at ASDC <conciatore@asdc.asi.it>
M.L. Conciatore, M. Capalbi, M. Perri, D.N. Burrows (PSU) and M.
Stamatikos (NASA/ORAU) report on behalf of the Swift XRT team:
We have analysed the first five orbits of Swift XRT data from GRB
060923A (Stamatikos et al., GCN 5583). A ~2.5ks PC mode image provides
a refined X-ray position of:
RA(J2000) = 16h 58m 28.2s
Dec(J2000) = +12d 21' 40.0"
with an uncertainty of 6.0 arcseconds radius (90% containment).This is
3.4 arcseconds from the XRT position given by Stamatikos et al.(GCN
5583) and 74.8 arcsec from the refined (ground-calculated) BAT
position (Tueller et al., GCN 5589). This position is 1.14 arcseconds
from the detected source reported by Tanvir et al. (GCN 5587), and
1.32 arcseconds from the one reported by Fox et al. (GCN 5597) as a
candidate counterpart afterglow.
X-ray light curve shows an initial power-law decay with a decay index
of 2.7+/-0.3. Then, after a slow rebrightening starting at ~650s, from
T+4200 the source decays with a slope of 1.23 +/-0.1.
An absorbed power-law fit to the X-ray spectrum from T+100s to T+960s
gave a photon index of 2.1+/-0.2 and a column density of (1.2+/0.1)e21
cm**-2. We note the galactic hydrogen column density in the direction
of the burst is 5.1e20 cm**-2. The 0.2-10.0 keV observed flux for this
spectrum is 4.1e-11 ergs cm**-2 s**-1, which corresponds to an unabsorbed
flux of 4.9e-11 ergs cm**-2 s**-1.
Assuming that the X-ray emission continues to decline at the same
rate, we predict a 0.2-10 keV XRT count rate of 0.006 count/s at
T+24hr, which corresponds to an observed 0.2-10 keV flux of 2.4e-13
erg/cm**2/s.
This circular is an official product of the Swift XRT Team.
[GCN OPS NOTE(24sep06): Per author's request, the author list was added.]
GCN Circular 5597
Subject
GRB 060923A: Keck and Gemini Observations
Date
2006-09-23T18:17:24Z (20 years ago)
From
Derek Fox at PSU <dfox@astro.psu.edu>
D.B. Fox (Penn State), A. Rau (Caltech), & E.O. Ofek (Caltech) report
on behalf of a larger collaboration:
"We have imaged the Swift XRT localization region for GRB060923A
(Trigger 230662; Stamatikos et al., GCN 5583) with Keck-I + LRIS
(I-band) and Gemini-North + NIRI (J- and K-band). We identify the
candidate afterglow of Tanvir et al. (GCN 5587) in our K-band images
as the only point source consistent with the XRT localization, with a
brightness estimated as follows:
K-band: Ks~20.6 mag at 07:04 UT
We estimate its brightness (without correcting for Galactic
extinction) by reference to the 2MASS star at R.A. 16:58:31.463,
Dec. +12:22:12.88 (J2000), which has J=15.175 mag, H=14.585 mag, and
Ks=14.457 mag in that catalog.
The position of the source by reference to NOMAD catalog sources in
the vicinity is:
R.A. 16:58:28.15, Dec. +12:21:38.9 (J2000)
with an estimated uncertainty of less than 0.5" in each coordinate.
The source is undetected in our earlier J-band and I-band images. Our
upper limits on the brightness of the source in these bands are:
I-band: I>23.5 mag at 06:11 UT
J-band: J>23.7 mag at 06:42 UT
The I-band photometry is referenced to the SDSS imaging of this field
(Cool et al., GCN 5585) while the J-band zero-point is derived from
the 2MASS star referenced above. Magnitudes have not been corrected
for Galactic extinction.
If this source is the afterglow of GRB060923A, the red colors are
suggestive of a highly extinguished or high-redshift burst. In
particular, correcting for the Schlegel, Finkbeiner & Davis (1998)
estimate of E(B-V)=0.058 mag Galactic extinction, and assuming a
temporal decay of t^(-1) and an intrinsic afterglow spectrum of F_nu ~
nu^(-1), these limits indicate suppression of the afterglow flux
(relative to K-band) by a factor of >18 at 0.9 micron (I-band) and by
a factor of >14 at 1.23 micron (J-band).
GCN Circular 5589
Subject
GRB 060923, Swift-BAT refined analysis
Date
2006-09-23T10:28:17Z (20 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. Tueller (GSFC) L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU),
G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU)
on behalf of the Swift-BAT team:
Using the data set from T-240 to T+879 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 060923 (trigger #230662)
(Stamatikos, et al., GCN Circ. 5583). The BAT ground-calculated position
is RA,Dec = 254.623, 12.341 deg {16h 58m 29.6s, 12d 20' 28.1"} (J2000)
+- 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 33%.
The burst started with a 6-sec wide peak at T-42 sec. The main peak starts
at T-5 sec, peaks at T+1 sec, and ends at T+20 sec. There is a possible
third peak at T+19 sec. T90 (15-350 keV) is 51.7 +- 1 sec
(estimated error including systematics).
The time-averaged spectrum from T-42.3 to T+11.5 is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.69 +- 0.23. The fluence in the 15-150 keV band is 8.7 +- 1.3 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.03 sec in the 15-150 keV band
is 1.3 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence level.
GCN Circular 5588
Subject
GRB 060923: Early Super-LOTIS Observations
Date
2006-09-23T08:42:34Z (20 years ago)
From
Grant Williams at Steward Observatory <ggwilli@mmto.org>
G. G. Williams (MMTO) and P. A. Milne (Steward Observatory), on behalf of
the Super-LOTIS Collaboration, report:
The robotic 0.6-m Super-LOTIS telescope began observing the error box of
GRB 060923 (Swift Trigger 230662, Stamatikos et al. GCN 5583) at
05:12:56.1 UT, 41.1 seconds after the trigger. Our initial observations
include 5 x 10s exposures, 5 x 20s exposures, and 30 x 60s exposures, all
in the R-band. The observations began at a high airmass of 2.92.
We do not detect any variable sources or afterglow candidates within the
XRT error box in our earliest exposure or in the sum of our first five
exposures to the following 3-sigma limiting magnitudes determined from
nearby USNO-B1.0 stars:
t_start (UT) exp t (s) t_start-t_0 (s) Limit
--------------------------------------------------------
05:12:56.1 10.0 41.1 R > 16.6 +/- 0.15
05:12:56.1 5 x 10.0 41.1 R > 18.3 +/- 0.15
The errors are dominated by scatter in the USNO-B1.0 stars.
GCN Circular 5587
Subject
GRB 060923: UKIRT nIR observations - candidate afterglow
Date
2006-09-23T07:57:00Z (20 years ago)
From
Nial Tanvir at IofA U.Cambridge <nrt@ast.cam.ac.uk>
N. Tanvir (U. Leicester), A. Levan (U. Hertfordshire), M. Jarvis
(U. Oxford), T. Wold (JACH)
We observed the field of GRB 060923 with UFTI on UKIRT, beginning
at 06:07 (UT), approximately 55 minutes post-burst. We detect a
faint source in the K-band image at approximately:
16 58 28.18 +12 21 38.9
This position (based on provisional astrometry) is only 4.6 arcsec
from the reported XRT position (Stamatikos et al. GCN 5583).
The source appears to have faded in another (shallower) K-band
observation made 30 mins later, and therefore is likely to be
the afterglow of this burst.
Further analysis is ongoing.
GCN Circular 5586
Subject
GRB060923: Faulkes Telescope North optical observations
Date
2006-09-23T06:56:20Z (20 years ago)
From
Andreja Gomboc at LT,ARI,Liverpool JMU <ag@astro.livjm.ac.uk>
A. Melandri (Liverpool JMU) and A. Gomboc (University of Ljubljana) report
on behalf of the RoboNet-1.0 collaboration:
The 2m Faulkes North Telescope (Hawaii) automatically reacted to the Swift
burst GRB060923 (trigger 230662, Stamatikos et al. GCN 5583). Observations
started 2.8 min after the trigger time. In first images we do not detect
any new source brighter than R~19.
Further analysis are ongoing.
GCN Circular 5585
Subject
GRB060923 - SDSS Pre-Burst Observations
Date
2006-09-23T06:18:37Z (20 years ago)
From
Richard J. Cool at U.of AZ/Steward Obs <rcool@as.arizona.edu>
Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona), David
W. Hogg (NYU), Michael R. Blanton (NYU), David J. Schlegel (LBNL),
J. Brinkmann (APO), Donald Q. Lamb (Chicago), Donald P. Schneider
(PSU), and Daniel E. Vanden Berk (PSU) report:
The Sloan Digital Sky Survey (SDSS) imaged the field of burst
GRB060923 prior to the burst. As these data should be useful
as a pre-burst comparison and for calibrating photometry, we are
supplying the images and photometry measurements for this GRB field
to the community.
Data from the SDSS, including 5 FITS images, 3 JPGS, and
3 files of photometry and astrometry, are being placed at
http://mizar.as.arizona.edu/~grb/public/GRB060923
We supply FITS images in each of the 5 SDSS bands of a 8'x8' region
centered on the GRB position (ra=254.618 (16:58:28.3), dec=12.3620
(12:21:43.2); GCN 5583), as well as 3 gri color-composite JPGs (with
different stretches). The units in the FITS images are nanomaggies
per pixel. A pixel is 0.396 arcsec on a side. A nanomaggie is
a flux-density unit equal to 10^-9 of a magnitude 0 source or,
to the extent that SDSS is an AB system, 3.631e-6 Jy. The FITS
images have WCS astrometric information.
In the file GRB060923_sdss.calstar.dat, we report photometry
and astrometry of 1668 bright stars (r<20.5) within 15' of the
burst location. The magnitudes presented in this file are asinh
magnitudes as are standard in the SDSS (Lupton 1999, AJ, 118,
1406). Beware that some of these stars are not well-detected in
the u-band; use the errors and object flags to monitor data quality.
In the files GRB060923_sdss.objects_flux.dat and
GRB060923_sdss.objects_magnitudes.dat, we report photometry
of 2573 objects detected within 6' of the GRB position.
We have removed saturated objects and objects with model
magnitudes fainter than 23.0 in the r-band. The fluxes listed
in GRB060923_sdss.objects_flux.dat are in nanomaggies while the
magnitudes listed in GRB060923_sdss.objects_magnitudes.dat are
asinh magnitudes.
All quantities reported are standard SDSS photometry, meaning that
they are very close to AB zeropoints and magnitudes are quoted
in asinh magnitudes. Photometric zeropoints are known to about
2% rms. None of the photometry is corrected for dust extinction.
The Schlegel, Finkbeiner, and Davis (1998) predictions for this
region are A_U=0.287 mag, A_g=0.211 mag, A_r = 0.153 mag, A_i=0.116
mag, and A_z=0.082 mag.
There are currently no objects within 6 arcminutes of the GRB
position in the SDSS spectroscopic database.
SDSS astrometry is generally better than 0.1 arcsecond per
coordinate. Users requiring high precision astrometry should take
note that the SDSS astrometric system can differ from other systems
such as those used in other notices; we have not checked the offsets
in this region.
More detailed information pertaining to our SDSS GRB releases
can be found in our initial data release paper (Cool et al. 2006,
astro-ph/0601218). See the SDSS DR4 documentation for more details:
http://www.sdss.org/dr5.
These data have been reduced using a slightly different pipeline
than that used for SDSS public data releases. We cannot guarantee
that the values here will exactly match those in the data release
in which these data are included. In particular, we expect the
photometric calibrations to differ by of order 0.01 mag.
This note may be cited, but please also cite the SDSS data release
paper, Adelman-McCarthy et al. (2006, ApJS, 162, 38), when using
the data or referring to the technical documentation.
grb@mizar:/home/grb/public_html/private/sdss/GRB060923
GCN Circular 5584
Subject
GRB 060923: KAIT observations
Date
2006-09-23T06:07:28Z (20 years ago)
From
Weidong Li at UC Berkeley KAIT/LOSS <weidong@astron.berkeley.edu>
W. Li, N. Butler, J. S. Bloom, and A. V. Filippenko, University of
California, Berkeley, on behalf of the KAIT GRB team, report:
The robotic 0.76-m Katzman Automatic Imaging Telescope (KAIT)
at Lick Observatory observed GRB 060923, detected with Swift
(Trigger 230662; Stamatikos et al. GCN 5583). The automatic sequence
started at 05:12:33, 18 s after the burst. The first two images,
however, failed due to some technical issues. In subsequent images,
Our image processing pipeline did not find any new objects, and
reported the following photometry limits (calibrated with USNO B1.0):
======================================================================
Start UT t(GRB) Filter Exp(s) 3sigma-limit
05:13:57 102s I 15.0 <16.9
05:14:21 126s clear 20.0 <17.9
05:14:52 157s V 45.0 <16.9
05:15:48 213s I 45.0 <17.5
05:16:43 268s clear 45.0 <18.5
05:17:39 324s V 60.0 <17.2
========================================================================
More analyses are in progress.
GCN Circular 5583
Subject
GRB 060923: Swift detection of a burst
Date
2006-09-23T05:41:32Z (20 years ago)
From
David Burrows at PSU/Swift <dxb15@psu.edu>
M. Stamatikos (NASA/ORAU), D. N. Burrows (PSU), M. Capalbi (ASDC),
M.L. Conciatore (ASDC), N. Gehrels (NASA/GSFC),
C. Guidorzi (Univ Bicocca&INAF-OAB), S. T. Holland (GSFC/USRA),
D. M. Palmer (LANL), M. Perri (ASDC), T. Sakamoto (NASA/ORAU) and
D. E. Vanden Berk (PSU) report on behalf of the Swift Team:
At 05:12:15 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060923 (trigger=230662). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA,Dec 254.623, +12.379 {16h 58m 30s, +12d 22' 45"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed at least two peaks,
lasting 12 seconds. The peak count rate
was ~1200 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began taking data at 05:13:36 UT, 81 seconds after the BAT
trigger. The XRT found a previously uncatalogued X-ray source in
the field of view at the following coordinates:
RA(J2000) = 16 58 28.27
Dec(J2000)= +12 21 43.3
with an uncertainty of 6.9 arcseconds radius (90% containment).
This position lies 67 arcseconds from the center of the BAT error circle.
The approximate initial flux is 1.7e-11 erg/cm2/sec (0.2-10 keV).
UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 85 seconds after the BAT trigger. No
afterglow candidate has been found in the initial data products. The
overlap of the sub-image and the XRT error circle is 100%. The
overlap of the 8'x8' region for the list of sources generated
on-board and the XRT error circle is 100%. The limiting magnitude of
the finding chart image is approximately 18.5. No correction has
been made for the expected extinction corresponding to E(B-V) of
0.06.