GRB 081024
GCN Circular 8398
Subject
GRB 081024: Swift detection of a burst
Date
2008-10-24T06:18:55Z (17 years ago)
From
Neil Gehrels at GSFC <gehrels@milkyway.gsfc.nasa.gov>
G. Stratta (ASDC), W. H. Baumgartner (GSFC/UMBC),
N. Gehrels (NASA/GSFC), E. A. Hoversten (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), M. Perri (ASDC) and
L. Vetere (PSU) report on behalf of the Swift Team:
At 05:53:08 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081024 (trigger=332516). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 27.898, +61.346 which is
RA(J2000) = 01h 51m 36s
Dec(J2000) = +61d 20' 47"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a short hard peak with
a duration of about 0.3 sec at T+0 with a short precursor peak at T-2.5 seconds.
The peak count rate was ~6,000 counts/sec (15-350 keV), at ~0 sec after
the trigger.
The XRT began observing the field at 05:54:21.1 UT, 72.3 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 27.8745,
61.3317 which is equivalent to:
RA(J2000) = 01h 51m 29.88s
Dec(J2000) = +61d 19' 54.1"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 65 arcseconds from the BAT onboard position, within the BAT
error circle. 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
7.71e+21 cm^-2 (Kalberla et al. 2005).
UVOT took a finding chart exposure of nominal 150 seconds with the White
(160-650 nm) filter starting 76 seconds after the BAT trigger. No afterglow
candidate has been found in the initial data products. Image catalog data are
not available at this time. The 8'x8' region for the list of sources generated
on-board covers 100% of the BAT error circle. The list of sources is typically
complete to about 18 mag. No correction has been made for the large, but
uncertain extinction expected.
This appears to be a short hard GRB with a precursor and a fading X-ray
afterglow. We note that the position in galactic coordinates is l=130deg,
b=-0.7 deg. It is not impossible that this is a galactic transient or
even an SGR.
Burst Advocate for this burst is G. Stratta (giulia.stratta AT asdc.asi.it).
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 8400
Subject
GRB 081024: Early Super-LOTIS Observations
Date
2008-10-24T08:10:37Z (17 years ago)
From
Grant Williams at Steward Observatory <ggwilli@gmail.com>
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 081024 (Swift Trigger 332516, Stratta et al. GCN 8398) at
05:53:49.9 UT, 41.9 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.
We do not detect any variable sources or afterglow candidates within
the XRT error box in our earliest exposure to the following 3-sigma
limiting magnitude determined from the nearby USNO-B1.0 star
1513-0063175 with R2=14.24:
t_start (UT) exp t (s) t_start-t_0 (s) Limit
------------------------------------------------------------
05:53:49.9 10 41.9 R > 17.6
The value quoted above is not corrected for the expected Galactic
extinction corresponding to a reddening of E(B-V)=1.64 mag in the
direction of the burst (Schlegel et al. 1998).
Additional observations and analysis are ongoing.
GCN Circular 8401
Subject
GRB 081024: KAIT Optical Limits
Date
2008-10-24T08:16:22Z (17 years ago)
From
Weidong Li at UC Berkeley KAIT/LOSS <weidong@astron.berkeley.edu>
W. Li, R. Chornock, and A. V. Filippenko, University of California
at Berkeley, on behalf of the KAIT GRB team, report:
The robotic 0.8-m KAIT located at Lick Observatory responded to
GRB 081024 (G. Stratta, GCN 8398) automatically and started
the first image at 05:54:42 UT (94 seconds after the burst).
A series of images were taken in the V, I, and clear filters.
No new sources were detected within the Swift/XRT error circle
in the KAIT images (single or stacked frames) when compared to
the DSS II. We set the following specific limiting magnitude
in a stacked unfiltered image (2s x 10; USNO B1 calibration):
start UT end UT t_exp(s) mlim
--------------------------------------------
05:54:42.0 05:55:16.0 20 18.8
GCN Circular 8402
Subject
GRB 081024: Faulkes Telescope North optical observations
Date
2008-10-24T10:56:02Z (17 years ago)
From
Andrea Melandri at Liverpool John Moores U <axm@astro.livjm.ac.uk>
A. Melandri, M. Burgdorf, R.J. Smith, I.A. Steele, D.F. Bersier,
C.G. Mundell, (Liverpool JMU), A. Gomboc (Ljubljana), C. Guidorzi
(INAF-OAB) on behalf of a larger collaboration report:
On 2008 October 24 at 05:54:45 UT (~50 seconds after the GRB trigger)
we observed the field of GRB 081024 (trigger = 332516, Stratta et al.,
GCN 8938) with the robotic 2m Faulkes Telescope North located in
Hawaii.
Observations were performed on BVRi filters. We do not detect any
fadind optical source within the XRT error circle (Stratta et al.,
GCN 8938) down to the following limits:
--------------------------------------------------
Dt_mid T_exp Filter Mag_lim
[min] [sec]
--------------------------------------------------
2.25 30 R > 21.4
112.8 600 R > 22.6
136.2 600 I > 21.2
--------------------------------------------------
Limiting magnitudes has been estimated using the R2 and I magnitudes
of the USNOB-1 catalogue. The reported values are not corrected for
the Galactic extinction.
GCN Circular 8403
Subject
GRB 081024: Enhanced Swift-XRT position
Date
2008-10-24T11:53:14Z (17 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
A.P. Beardmore, P.A. Evans, M.R. Goad and J.P. Osborne (U. Leicester)
report on behalf of the Swift-XRT team.
Using 1443 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 081024, 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 = 27.8738, +61.3314 which is equivalent
to:
RA (J2000): 01h 51m 29.72s
Dec (J2000): +61d 19' 53.0"
with an uncertainty of 1.9 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
http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an
extension of this method.
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 8404
Subject
GRB 081024, Swift-BAT refined analysis
Date
2008-10-24T14:51:55Z (17 years ago)
From
Jay R. Cummings at NASA/GSFC/Swift <jayc@milkyway.gsfc.nasa.gov>
S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD),
D. M. Palmer (LANL), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC),
G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), G. Stratta (ASDC),
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 081024 (trigger #332516)
(Stratta, et al., GCN Circ. 8398). The BAT ground-calculated position is
RA, Dec = 27.891, 61.352 deg which is
RA(J2000) = 01h 51m 33.8s
Dec(J2000) = +61d 21' 08.2"
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
This position is 1.3 arcmin from the enhanced XRT position (Beardmore et
al. GCN Circ. 8403). The partial coding was 97%.
The mask-weighted lightcurve shows a slightly softer precursor peak about
0.05 sec long at T-1.7 sec, a peak about 0.3 seconds long at T-0.2 sec and
the largest peak 0.1 seconds long at T0. T90 (15-350 keV) is 1.8 +- 0.6
sec
(estimated error including systematics).
The time-averaged spectrum from T-1.7 to T+0.3 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.23 +- 0.21. The fluence in the 15-150 keV band is
1.2 +- 0.2 x 10-07 erg/cm2. The 1-sec peak photon flux measured from
T-0.73 sec in the 15-150 keV band is 1.1 +- 0.1 ph/cm2/sec. 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/332516/BA/
GCN Circular 8405
Subject
GRB 081024: Swift-XRT refined analysis
Date
2008-10-24T20:31:08Z (17 years ago)
From
Matteo Perri at ISAC/ASDC <perri@asdc.asi.it>
G. Stratta (ASDC) reports on behalf of the Swift-XRT team:
We have analysed the first orbit of the XRT data obtained for
GRB 081024 (Stratta et al., GCN Circ. 8398). From T+78 s to T+105 s
after the burst, data were collected in Windowed Timing mode and
then XRT switched to Photon Counting mode. The Enhanced Swift-XRT
position was given by Beardmore et al. in GCN Circ. 8403.
The 0.3-10 keV flux from T+78 s to T+355 s shows a very steep decay with
a possible small re-brightening between ~T+145 s to ~T+205 s. Excluding
the re-brightening and assuming a power law decay, the best fit decay
index is alpha = 3.7 (+0.8,-0.5).
The spectrum of the WT data, with an integration time of 27s, can
be modelled with a power-law model with photon index of 1.6 (+0.6,- 0.3).
The total absorbing equivalent hydrogen column density is consistent
with the Galactic one NH = 7.71E+21 cm^-2 (Kalberla et al. 2005). The
observed (unabsorbed) 0.3-10 keV flux is 4.1(6.1)E-10 erg/cm^-2 s^-1
No source counts are detected after the first orbit, likely due to
the very steep flux decay.
This is an official product of the Swift-XRT team.
GCN Circular 8406
Subject
Swift UVOT observations of GRB 081024
Date
2008-10-25T11:53:56Z (17 years ago)
From
Patricia Schady at MSSL/Swift <ps@mssl.ucl.ac.uk>
M. De Pasquale (MSSL/UCL) and G. Stratta (ASDC) report on behalf of
the Swift UVOT team.
The Swift UltraViolet/Optical Telescope (UVOT) began its finding chart
exposure of GRB081024 (Swift BAT trigger
number 332516, Stratta et al., GCN Circ. 8398), 77s after the trigger.
We do not detect any new source at the XRT position reported in GCN
Circ. 8403 (Beardmore et al.) either
in the finding chart nor in in successive coadded observations.
The magnitude 3 sigma upper limits for detecting GRB081024 at the XRT
position are given below.
Filter Tstart(s) Tstop(s) Exp(s) Magnitude
wh 77 227 147 >20.8
wh 516 13395 1258 >22.0
v 565 758 39 >18.5
v 1041 7298 490 >19.9
b 491 856 58 >19.6
b 1140 12771 1358 >21.4
u 235 485 250 >20.1
u 639 11859 807 >21.0
uvw1 615 7615 436 >20.2
uvm2 590 7503 529 >20.5
uvw2 541 7093 529 >20.6
The values quoted above are on the UVOT Photometric System (Poole et
al, 2008, MNRAS 383,627). They are not
corrected for the unknown but expected large Galactic extinction in
the direction of this burst.
GCN Circular 8419
Subject
GRB 081024: No radio detection with the VLA
Date
2008-10-27T14:56:12Z (17 years ago)
From
Poonam Chandra at U Virginia/NRAO <pc8s@virginia.edu>
Poonam Chandra (RMC) and Dale 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
GRB 081024 (GCN 8398) at a frequency of 8.46 GHz at 2008 Oct. 25.27 UT.
The GRB radio afterglow is undetected and the peak radio flux at the
Swift XRT afterglow position (GCN 8403) is -36 � 52 uJy.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."