GRB 081024B
GCN Circular 8513
Subject
GRB 081024B: Swift-XRT late-time observations
Date
2008-11-10T16:01:33Z (18 years ago)
From
Cristiano Guidorzi at INAF-OAB <cristiano.guidorzi@brera.inaf.it>
C. Guidorzi (INAF-OAB) on behalf of the Swift-XRT team reports:
Swift-XRT re-observed the field of the Fermi-LAT and Fermi-GBM
GRB 081024B (Omodei et al. GCN Circ. 8407; Connaughton et al GCN Circ. 8408)
from 13.1 to 15.1 days after the burst with a net exposure of 9.8 ks.
We compared this with our previous observations (Guidorzi et al. GCN Circ.
8410, 8416, 8454). We still detect source 2, identified in our first
observation (Guidorzi et al. GCN Circ. 8410), with a count rate of
(1.1 +- 0.4)e-3 count/s, which is compatible with a constant rate
source throughout the entire XRT observations.
We also derived an upper limit to the possible power-law decay
index of alpha<0.4 from ~1e5 to ~1.3e6 s (90% confidence).
We conclude that source 2, initially proposed as possibly associated
with GRB 081024B (Guidorzi et al. GCN Circ. 8416, 8454), is not the
corresponding X-ray afterglow.
This circular is an official product of the Swift-XRT team.
GCN Circular 8456
Subject
GRB 081024B: BTA deep optical observations
Date
2008-11-01T10:35:39Z (18 years ago)
From
Vladimir Sokolov at SAO RAS <sokolov@sao.ru>
T. Fatkhullin, A. Moskvitin (SAO-RAS Niznij Arkhyz), A.J. Castro-Tirado
(IAA-CSIC Granada), on behalf of a larger collaboration, report:
"We observed the field of the short duration GRB081024B (Omodei, GCNC
8407; Connaughton and Briggs, GCNC 8408) in the Rc-band with the 6-m
telescope of the SAO RAS in Caucasus. In total two runs were performed
starting on 28 Oct 2008 (20:16 UT) and 29 Oct. 2008 (15:22 UT).
Integration times were 24 and 14 min respectively. Using SExtractor
software (Bertin & Arnouts 1996, A&AS 117, 393) and source "O1"
(Cenko & Kasliwal GCNC 8417; Kann et al. GCNC 8423) as a reference star,
we estimated the following magnitudes of the sources within the XRT error box:
28 Oct. 29 Oct.
O1: Rc = 20.55 +/- 0.04 Rc = 20.55 +/- 0.04 (from GCN 8423)
O2: Rc = 22.62 +/- 0.06 Rc = 22.65 +/- 0.06 (within 3.6 arcsec aperture)
O3: Rc = 23.19 +/- 0.15 Rc = 23.18 +/- 0.10 (within 3.6 arcsec aperture)
O4: Rc = 22.46 +/- 0.06 Rc = 22.53 +/- 0.06 (within 3.6 arcsec aperture)
The second epoch image (29 Oct.) shows that extended object "O2"
as noted from Palomar 200 inch Hale telescope observations (Cenko &
Kasliwal GCNC 8417) is most likely superposition of two objects.
These objects seem also to be extended in our image.
we conclude that all four sources showed no variability during the
time interval covered by our observations (including source "O2", whose
magnitude is comparable to the one reported by Cenko & Kasliwal).
As it is already mentioned by Guidorzi et al. (GCNC 8454) by means of
Swift/XRT observations, we can not confirm that the source "O2"
is fading in brightness, i.e. its relation to GRB081024B. This second
epoch image can be retrieved via anonymous FTP:
ftp://ftp.sao.ru/pub/grb/GRB081024B/GRB081024B_BTA_2nd_epoch.jpg ."
This message can be cited.
GCN Circular 8454
Subject
GRB 081024B: new Swift-XRT observations
Date
2008-10-31T19:06:29Z (18 years ago)
From
Cristiano Guidorzi at INAF-OAB <cristiano.guidorzi@brera.inaf.it>
C. Guidorzi, J. Mao, R. Margutti (INAF-OAB) on behalf
of the Swift-XRT team report:
Swift-XRT re-observed the field of the Fermi-LAT and Fermi-GBM
GRB 081024B (Omodei et al. GCN Circ. 8407; Connaughton et al GCN Circ. 8408)
from 2.75 to 6.1 days after the burst with a net exposure of 13 ks.
We combined this with our previous observation (Guidorzi et al. GCN Circ.
8416) for a resulting net exposure of 27 ks.
Source 2 identified in our earliest report (Guidorzi et al. GCN Circ. 8410)
as the only possibly fading source within the LAT error circle (GCN 8416)
and possibly associated with the variable optical object O2
(Cenko & Kasliwal GCN Circ. 8417; Kann et al. GCN Circ. 8423),
was finally detected with an average rate of (7.4 +- 2.2)e-4 counts/s
from 1.5 to 6.1 days. From the comparison with the first observation
(GCN 8410), in which the count rate was estimated to be (1.58 +- 0.54)e-3
counts/s, we estimate the probability of a constant rate source of 12%.
We also derived an upper limit to the possible power-law decay
index of alpha<0.8 from ~1 to ~5e5 s (90% confidence).
Therefore, at the moment we cannot confirm source 2 as the X-ray
afterglow candidate.
Further Swift-XRT observations are planned in order to clarify this issue.
This circular is an official product of the Swift-XRT team.
GCN Circular 8451
Subject
GRB 081024B: VLA radio observation
Date
2008-10-29T21:01:56Z (18 years ago)
From
Poonam Chandra at U Virginia/NRAO <pc8s@virginia.edu>
P. Chandra (RMC), S. B. Cenko (Berkeley), D. A. Frail (NRAO) and
F. Harrison (Caltech) report on behalf of a larger GRB Collaboration:
"We used the Very Large Array to observe the Fermi-LAT detected
short hard burst GRB 081024B (GCN 8407) at a frequency of 8.46
GHz on 2008 Oct. 28.99 UT. The VLA field of view was centered at
RA: 21:31:37.63 Dec: +21:16:33.0 (J2000.0) for the observation.
We don't see any radio source in the VLA field of view. The map
rms is 38 uJy.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 8444
Subject
GRB 081024B: Suzaku WAM observation of the prompt emission
Date
2008-10-29T09:50:05Z (18 years ago)
From
Yoshitaka Hanabata at Hiroshima U <hanabata@hep01.hepl.hiroshima-u.ac.jp>
Y. Hanabata, T. Uehara, T. Takahashi, Y. Fukazawa, C. Kira (Hiroshima U.),
T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo), S. Sugita,
K. Yamaoka (Aoyama Gakuin U.), M. Ohno, M. Kokubun, M. Suzuki,
T. Takahashi (ISAS/JAXA), Y.E. Nakagawa, T. Tamagawa (RIKEN),
M. Tashiro, Y. Terada, Y. Urata, A. Endo, K. Onda,
N. Kodaka, K. Morigami, T. Sugasahara, W. Iwakiri (Saitama U.),
E. Sonoda, M. Yamauchi, H. Tanaka, R. Hara, N. Ohmori (Univ. of Miyazaki),
S. Hong (Nihon U.), on behalf of the Suzaku WAM team, report:
The short/hard GRB081024B (Fermi-LAT detected ; Omodei GCN8407,
Fermi-GBM triggered ; Connaughton and Briggs, GCN 8408) triggered the
Suzaku Wide-band All-sky Monitor (WAM) which covers an energy range
of 50 keV - 5 MeV at 21:22:40.526 UT (=T0).
The observed light curve shows double-peaked structure with a duration
(T90) of about 0.4 second.
The fluence in 100 - 1000 keV was 2.7(+0.7, -1.0) X 10^-7 erg/cm^2.
The peak flux within 0.5 second was 1.1(+0.3, -0.5) photons/cm^2/s in
the same energy range.
Preliminary result shows that even at least 2 MeV photons have been
detected, and the time-averaged spectrum from T0 to T0+0.5s is well
fitted by a single power-law with a photon index of 1.24(+0.25, -0.19)
(chi^2/d.o.f = 12.3/14). All the quoted errors are at statistical 90%
confidence level, in which the systematic uncertainties are not included.
The light curves for this burst are availabel at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html
GCN Circular 8423
Subject
Fermi LAT/GBM short-hard GRB 081024B: Possible TLS Afterglow (Corrected)
Date
2008-10-28T01:44:03Z (18 years ago)
From
Alexander Kann at TLS Tautenburg <kann@tls-tautenburg.de>
D. A. Kann, S. Schulze and C. Hoegner (TLS Tautenburg) report:
We observed the LAT error circle of the Fermi-LAT (Omodei, GCN 8407) and
Fermi-GBM (Connaughton and Briggs, GCN 8408) detected short/hard GRB
081024B with the TLS Tautenburg 1.34m Schmidt telescope in full frame mode
(field of view 42' x 42'), covering the complete error circle to about 2
sigma confidence level. We obtained 24 x 300 sec images in the Rc band
under good observing conditions, at mid-time 0.88644 days after the GRB.
We report the following analysis of the three XRT sources (Guidorzi et
al., GCN 8410), of which source 1 and 3 seem to remain constant (Guidorzi
& Margutti, GCN 8416), whereas source 2 may be fading and thus represent
the X-ray afterglow of GRB 081024B:
Source 1: We find a relatively bright stellar object which is clearly
visible in the DSS.
Source 3: We find a moderately faint stellar object which is under the DSS
limit.
Source 2: We detect all four objects reported by Cenko & Kasliwal (GCN
8417). Source O3 is close to the detection limit, implying that it is ~ Rc
> 23.5, similar to that of the P200 image.
We use several nearby, isolated USNOB1.0 stars to determine the image zero
point. We find that the zero point error is 0.04 magnitudes from four
stars, better than the pessimistic estimation (0.3 magnitudes) of Cenko &
Kasliwal (which also includes bandpass differences). Photometry was done
using a 7 pixel aperature (matched to the typical seeing) on sources O1
and O4 (which are reasonably isolated). For sources O2 (close to a bright
star) and O3 (close to O2), we used a 3 pixel aperature and used two
bright, isolated stars to compute the aperature correction (a factor of
2).
We derive the following magnitudes for the four sources (in brackets, we
give the magnitudes of Cenko & Kasliwal):
O1 (bright, stellar): Rc = 20.55 +/- 0.04 (20.6)
O2 (extended in P200): Rc = 22.25 +/- 0.10 (22.6)
O3 (faint): Rc = 23.48 +/- 0.34 (23.4)
O4 (faint, stellar): Rc = 22.53 +/- 0.16 (22.6)
All sources except O2 agree well with the P200 magnitudes obtained 0.36
days later, to within +/- 0.08 magnitudes despite the multiple differences
(comparison stars, bandpass, etc.). Only source O2 is brighter, by ~ 0.35
magnitudes. While the source is close to a bright (~ magnitude of O1)
star, which may contaminate the photometry even in the reduced aperature,
O2 is clearly brighter in our image than O4, whereas they have identical
magnitudes (as reported by Cenko & Kasliwal) in the P200 images. Since
Cenko & Kasliwal report this source to be extended, this may indicate that
we are seeing the optical afterglow as well as the underlying host galaxy
of GRB 081024B. Still, caution is advised.
This GRB is of special interest. It is the first Fermi-detected short/hard
GRB reported so far, and possibly the first one with a detection at >> 1
GeV (the very bright GRB 930131, the "Superbowl Burst", was only detected
to ~ 1 GeV by CGRO EGRET, Sommer et al. 1994, ApJL, 422, L63), and,
similar to GRB 930131 and also the AGILE-Grid-detected long GRB 080514B
(Guiliani et al. 2008, A&A, in press), emission is seen for several
seconds longer than at lower energies. Therefore, additional deep
follow-up and spectroscopy of extended source O2 is highly encouraged.
Further observations at TLS are planned (to perform image subtraction) in
case we ever see the stars again.
We are indebted to Antonio de Ugarte Postigo for pointing out the
suspicious lack of authors in the first version.
This message may be cited.
GCN Circular 8422
Subject
Fermi LAT/GBM short-hard GRB 081024B: Possible TLS Afterglow
Date
2008-10-28T01:22:45Z (18 years ago)
From
Alexander Kann at TLS Tautenburg <kann@tls-tautenburg.de>
We observed the LAT error circle of the Fermi-LAT (Omodei, GCN 8407) and
Fermi-GBM (Connaughton and Briggs, GCN 8408) detected short/hard GRB
081024B with the TLS Tautenburg 1.34m Schmidt telescope in full frame mode
(field of view 42' x 42'), covering the complete error circle to about 2
sigma confidence level. We obtained 24 x 300 sec images in the Rc band
under good observing conditions, at mid-time 0.88644 days after the GRB.
We report the following analysis of the three XRT sources (Guidorzi et
al., GCN 8410), of which source 1 and 3 seem to remain constant (Guidorzi
& Margutti, GCN 8416), whereas source 2 may be fading and thus represent
the X-ray afterglow of GRB 081024B:
Source 1: We find a relatively bright stellar object which is clearly
visible in the DSS.
Source 3: We find a moderately faint stellar object which is under the DSS
limit.
Source 2: We detect all four objects reported by Cenko & Kasliwal (GCN
8417). Source O3 is close to the detection limit, implying that it is ~ Rc
> 23.5, similar to that of the P200 image.
We use several nearby, isolated USNOB1.0 stars to determine the image zero
point. We find that the zero point error is 0.04 magnitudes from four
stars, better than the pessimistic estimation (0.3 magnitudes) of Cenko &
Kasliwal (which also includes bandpass differences). Photometry was done
using a 7 pixel aperature (matched to the typical seeing) on sources O1
and O4 (which are reasonably isolated). For sources O2 (close to a bright
star) and O3 (close to O2), we used a 3 pixel aperature and used two
bright, isolated stars to compute the aperature correction (a factor of
2).
We derive the following magnitudes for the four sources (in brackets, we
give the magnitudes of Cenko & Kasliwal):
O1 (bright, stellar): Rc = 20.55 +/- 0.04 (20.6)
O2 (extended in P200): Rc = 22.25 +/- 0.10 (22.6)
O3 (faint): Rc = 23.48 +/- 0.34 (23.4)
O4 (faint, stellar): Rc = 22.53 +/- 0.16 (22.6)
All sources except O2 agree well with the P200 magnitudes obtained 0.36
days later, to within +/- 0.08 magnitudes despite the multiple differences
(comparison stars, bandpass, etc.). Only source O2 is brighter, by ~ 0.35
magnitudes. While the source is close to a bright (~ magnitude of O1)
star, which may contaminate the photometry even in the reduced aperature,
O2 is clearly brighter in our image than O4, whereas they have identical
magnitudes (as reported by Cenko & Kasliwal) in the P200 images. Since
Cenko & Kasliwal report this source to be extended, this may indicate that
we are seeing the optical afterglow as well as the underlying host galaxy
of GRB 081024B. Still, caution is advised.
This GRB is of special interest. It is the first Fermi-detected short/hard
GRB reported so far, and possibly the first one with a detection at >> 1
GeV (the very bright GRB 930131, the "Superbowl Burst", was only detected
to ~ 1 GeV by CGRO EGRET, Sommer et al. 1994, ApJL, 422, L63), and,
similar to GRB 930131 and also the AGILE-Grid-detected long GRB 080514B
(Guiliani et al. 2008, A&A, in press), emission is seen for several
seconds longer than at lower energies. Therefore, additional deep
follow-up and spectroscopy of extended source O2 is highly encouraged.
Further observations at TLS are planned (to perform image subtraction) in
case we ever see the stars again.
This message may be cited.
GCN Circular 8417
Subject
GRB081024B: P200 Observations
Date
2008-10-27T05:23:08Z (18 years ago)
From
S. Bradley Cenko at Caltech <cenko@srl.caltech.edu>
S. B. Cenko (UC Berkeley) and M. M. Kasliwal (Caltech) report on behalf of
a larger collaboration:
We have imaged the error circle of the short duration GRB081024B (Omodei,
GCN 8407; Connaughton and Briggs, GCN 8408) with the Large Format Camera
mounted on the Palomar 200 inch Hale telescope. Images were taken in
the Sloan r' and i' filters at a mean epoch of approximately Oct 26.1 (~
30 hours after the burst).
We detect several sources inside or near the potential X-ray afterglow
(XRT Source 2; Guidorzi, Margutti, and Mao, GCN 8410; Guidorzi and
Margutti, GCN 8416). Calibrating with respect to several nearby objects
in the USNO-B1 catalog, we note the following positions and magnitudes for
the four nearest sources:
O1 - RA: 21:31:36.95 Dec: +21:16:35.4 (J2000.0)
R = 20.6 mag
O2 - RA: 21:31:37.63 Dec: +21:16:33.0 (J2000.0)
R = 22.6 mag
O3 - RA: 21:31:37.42 Dec: +21:16:36.4 (J2000.0)
R = 23.4 mag
O4 - RA: 21:31:37.32 Dec: +21:16:25.1 (J2000.0)
R = 22.6 mag
We estimate the astrometric precision for each source is 0.5" in each
coordinate. The photometric precision for the above reported magnitudes
is likely large (~ 0.3 mag) due to both zeropoint uncertainty and
bandpass differences. The limiting magnitude of our co-added image is
approximately R > 23.5 mag.
We note that source O1 appears to be present in the DSS plates of this
field. Additionally, source 02 is clearly extended. None of the objects
show evidence for variability over the (limited) duration of our
observations.
An image of the field is posted at:
http://www.srl.caltech.edu/~cenko/public/grb081024b.jpg
Further observations to search for variability are encouraged.
GCN Circular 8416
Subject
GRB 081024B: Swift-XRT further observations
Date
2008-10-26T23:17:31Z (18 years ago)
From
Cristiano Guidorzi at INAF-OAB <cristiano.guidorzi@brera.inaf.it>
C. Guidorzi and R. Margutti (INAF-OAB) report on behalf of the
Swift-XRT team:
Swift re-observed the field of the Fermi-LAT GRB 081024B (Omodei et
al., GCN Circ. 8407) 127 ks after the burst. From 13.5 ks of Photon
Counting mode data, we found that sources 1 and 3 mentioned in our
previous report (Guidorzi et al. GCN Circ. 8410) are still detected
with a count rate compatible with being constant between the two
observations. Although source 2 is no longer detected, we estimate
that the fading is not statistically significant yet.
Further data will allow us to determine the possible fading.
This circular is an official product of the Swift-XRT team.
GCN Circular 8413
Subject
Swift UVOT observations of GRB081024B
Date
2008-10-26T17:44:33Z (18 years ago)
From
Patricia Schady at MSSL/Swift <msslba@yahoo.co.uk>
P. Schady (MSSL/UCL) and C. Guidorzi (INAF-OAB) report on behalf of the Swift UVOT team.
The Swift UltraViolet/Optical Telescope (UVOT) began observations of Fermi-LAT GRB 081024B (Omodei et al., GCN Circ. 8407) 70.3 ks after the trigger.
Source 1 and Source 2 in GCN Circ. 8410 (Guidorzi et al.) are outside the UVOT field of view, and no new source is detected at the position of Source 3 (GCN Circ 8410; Guidorzi et al.) down to the following 3 sigma upper limits:
Filter Tstart(dys) Exp(s) 3-sigma UL
v 1.215 885 > 20.33
b 0.824 864 > 21.26
u 0.814 2641 > 21.42
uvw1 0.894 1531 > 21.07
uvm2 0.883 2548 > 21.36
uvw2 1.163 1201 > 21.07
The values quoted above are on the UVOT Photometric System (Poole et al, 2008, MNRAS 383,627). They are not corrected for the expected Galactic extinction corresponding to a reddening of E(B-V)=0.07 mag in the direction of the burst (Schlegel et al. 1998).
GCN Circular 8410
Subject
GRB 081024B: Swift-XRT observations
Date
2008-10-26T10:43:34Z (18 years ago)
From
Cristiano Guidorzi at INAF-OAB <cristiano.guidorzi@brera.inaf.it>
C. Guidorzi, R. Margutti, J. Mao (INAF-OAB) report on behalf of
the Swift-XRT team:
Swift began observing the field of the Fermi-LAT GRB 081024B (Omodei et
al., GCN Circ. 8407) 70.3 ks after the trigger. In 9.9 ks of Photon
Counting mode data, we detect three uncatalogued sources within the
Fermi-LAT error circle at the following positions:
Source 1:
RA(J2000): 21 31 47.85
Dec(J2000): +21 08 33.7
with an uncertainty of 6.6 arcsec.
Source 2:
RA(J2000): 21 31 37.22
Dec(J2000): +21 16 32.1
with an uncertainty of 5.4 arcsec.
Source 3:
RA(J2000): 21 31 29.26
Dec(J2000): +21 16 43.3
with an uncertainty of 5.5 arcsec.
Uncertainty radii are given at 90% containment.
All of the sources have count rates of ~1.3e-3 counts/s during this
observation.
It is not possible to determine whether these sources are fading
given the current statistics.
This circular is an official product of the Swift-XRT team.
GCN Circular 8408
Subject
GRB 081024B: Fermi Gamma-ray Burst Monitor detection
Date
2008-10-25T19:00:20Z (18 years ago)
From
Valerie Connaughton at MSFC <valerie@nasa.gov>
Valerie Connaughton and Michael Briggs (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 21:22:40.86 UT on 24 October 2008, the Fermi Gammay-Ray Burst
Monitor (GBM) triggered on GRB 081024B (trigger 246576161 /
081024.891). The calculated location is consistent with the
Fermi LAT-detected GRB reported by N. Omodei in GCN Circular 8407.
This GRB was about 800 ms long with 2 main peaks. The first peak
lasted 200 ms and its spectrum is best fit using a power-law index
with an exponential cutoff. The power-law index is -0.70 � 0.13, and
the cutoff energy, parameterized as EPeak, is 1583 � 520 keV. The
seond peak lasted 600 ms and is best fit by a power-law spectrum
with an index of -1.28 � 0.04.
The fluence between 50 and 300 keV of this short burst is
3.4 � 0.1 x 10-7 erg/cm2, with a peak flux measured over
a 64 ms timescale of of 4.2 � 0.2 photons/cm2/sec. Between
15 and 150 keV the 64 ms peak flux is 7.4 � 0.4 photons/cm2/sec.
The analysis results presented above are preliminary and further
analysis is being performed; the final results will be published
in the GBM GRB Catalog."
GCN Circular 8407
Subject
Fermi-LAT observation of GRB 081024B
Date
2008-10-25T14:07:58Z (18 years ago)
From
Nicola Omodei at INFN(Pisa)/GLAST <nicola.omodei@pi.infn.it>
Nicola Omodei (INFN Pisa),
on behalf of the Fermi-LAT Collaboration
The Fermi LAT telescope detected an increased count rate at 2008/10/24
(21:22:41),
associated with a GRB detected also by the Fermi GBM (Trigger
number:246576161).
The location of the GRB reported by Fermi LAT data ground analysis is:
Ra=322.9, Dec=21.204
which corresponds to
Ra (J2000) = 21:31:36.00
Dec (J200) = 21:12:14.4
within a statistical uncertainty of 0.16 degrees (68% containment radius).
The emission from this point source was seen up to 3 GeV, in the first 5
seconds after the trigger.
The Fermi LAT point of contact for this burst is Nicola Omodei
(nicola.omodei@pi.infn.it).
The Fermi LAT is a pair conversion telescope designed to cover the
energy band from 20 MeV to greater than 300 GeV.
It is the product of an international collaboration between NASA and DOE
in the U.S. and many scientific institutions across France, Italy, Japan
and Sweden.
This message can be cited.