GRB 090812
GCN Circular 9768
Subject
GRB 090812: Swift detection of a burst with an optical counterpart
Date
2009-08-12T06:20:46Z (16 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
M. Stamatikos (NASA/ORAU), J. R. Cummings (NASA/UMBC),
P. A. Evans (U Leicester), 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) and R. L. C. Starling (U Leicester) report on
behalf of the Swift Team:
At 06:02:08 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090812 (trigger=359711). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 353.194, -10.595 which is
RA(J2000) = 23h 32m 47s
Dec(J2000) = -10d 35' 39"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a triple-peaked
structure with a duration of about 70 sec. The peak count rate
was ~6500 counts/sec (15-350 keV), at ~25 sec after the trigger.
The XRT began observing the field at 06:03:25.7 UT, 76.8 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 353.20133, -10.60457 which
is equivalent to:
RA(J2000) = 23h 32m 48.32s
Dec(J2000) = -10d 36' 16.5"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 43 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
2.26e+20 cm^-2 (Kalberla et al. 2005).
The initial flux in the 2.5 s image was 4.95e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 250 seconds with the U filter starting
298 seconds after the BAT trigger. There is a candidate afterglow in the
rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 23:32:48.53 = 353.20222
DEC(J2000) = -10:36:17.3 = -10.60481
with a 90%-confidence error radius of about 0.78 arc sec. This position is 5.1
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.62 with a 1-sigma error of about 0.16. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.02.
Burst Advocate for this burst is M. Stamatikos (michael AT milkyway.gsfc.nasa.gov).
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 9769
Subject
GRB 090812: P60 Confirmation of Optical Afterglow
Date
2009-08-12T06:53:20Z (16 years ago)
From
S. Bradley Cenko at Caltech <cenko@srl.caltech.edu>
S. B. Cenko (UC Berkeley) reports on behalf of a larger collaboration:
We have imaged the field of GRB090812 (Stamatikos et al., GCN 9768) with
the automated Palomar 60 inch telescope. Observations were obtained in
the Sloan r', i', and z' filters beginning at 6:34 UT (~ 2.5 minutes after
the burst).
Near the XRT afterglow we detect a point source at coordinates (J2000.0):
RA: 23:32:48.55
Dec: -10:36:17.0
with an estimated uncertainty of ~ 0.3" in each coordinate. This is
consistent with the position reported by the UVOT.
We measure the following magnitudes for the source, calculated with
respect to the SDSS DR7:
Time (UT mid-point) Exposure (s) Filter Magnitude
-----------------------------------------------------------------------
06:05:02 60 r' 16.18
06:06:27 60 i' 16.39
06:09:28 60 r' 17.30
06:10:43 60 i' 17.34
The fading nature confirms this is the afterglow of GRB090812.
Further observations are planned.
GCN Circular 9770
Subject
GRB 090812: Liverpool Telescope afterglow confirmation
Date
2009-08-12T07:19:41Z (16 years ago)
From
Cristiano Guidorzi at Ferrara U,Italy <guidorzi@fe.infn.it>
R.J. Smith (Liverpool JMU), A. Gomboc (U. Ljubljana), C. Guidorzi (U.
Ferrara),
C.G. Mundell, I.A. Steele, A. Melandri, S. Kobayashi, C.J. Mottram, D.F.
Bersier,
Z. Cano (Liverpool JMU) report on behalf of a large collaboration:
On 2009 August 12 at 06:03:54 UT the 2-m Liverpool Telescope automatically
began observing the Swift GRB 090812 (Stamatikos et al., GCN Circ. 9768)
using the r' and i' filters.
We clearly detected the fading optical afterglow reported by Swift-UVOT
and P60 (Cenko et al. GCN Circ. 9769) with the following values:
Mid Time Delay from BAT Total Exp Filter Mag
(UT) trigger (s) (s)
----------------------------------------------------------
06:03:59 111 10 r' 15.51 +- 0.04
06:06:26 258 10 r' 16.60 +- 0.10
----------------------------------------------------------
Magnitudes have been calibrated from nearby SDSS stars.
GCN Circular 9771
Subject
GRB 090812 VLT redshift
Date
2009-08-12T09:02:26Z (16 years ago)
From
Antonio Deugarte at IAA-CSIC <deugarte@iaa.es>
A. de Ugarte Postigo (INAF-OAB), J. Gorosabel (IAA-CSIC),
J.P.U. Fynbo (DARK/NBI), K. Wiersema and N. Tanvir (Leicester)
report on behalf of a larger collaboration
We have observed the afterglow of GRB 090812 (Stamatikos et al.
GCNC 9768) using FORS2 at the VLT (Paranal observatory) starting
at 06:54 UT (52min after the burst). In the spectrum we detect strong
absorption lines, including Ly-alpha, SiII, SiII*, CII, SiIV, CIV,
SiII, AlII,
AlIII, FeII, ZnII, MnII and TiII at a common redshift of 2.452 which we
identify as the redshift of the GRB. We also detect absorption lines
from an
unidentified intervening system. Further analysis is ongoing.
We acknowledge the excellent support from Paranal staff, in particular
Jonathan Smoker, Cedric Ledoux and Karla Aubel.
GCN Circular 9772
Subject
GRB 090812: Enhanced Swift-XRT position
Date
2009-08-12T10:25:05Z (16 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team.
Using 456 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 090812, 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 = 353.20225, -10.60489 which is equivalent
to:
RA (J2000): 23h 32m 48.54s
Dec (J2000): -10d 36' 17.6"
with an uncertainty of 1.8 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, arXiv:0812.3662).
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 9773
Subject
GRB 090812: GROND Observations of the Optical/NIR Afterglow
Date
2009-08-12T11:54:31Z (16 years ago)
From
Thomas Kruehler at MPE/MPI <kruehler@mpe.mpg.de>
Adria Updike (Clemson University), Arne Rau, Thomas Kruehler, Felipe
Olivares, and Jochen Greiner (all MPE Garching) report on behalf of the
GROND team:
We observed the field of GRB 090812 (Swift trigger 359711; Stamatikos et
al., GCN #9768) simultaneously in g'r'i'z'JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2 m ESO/MPI telescope at La Silla
Observatory (Chile).
Due to cloud coverage, observations started only at 08:13 UT on August 12,
2 hours and 11 minutes after the GRB trigger. They were performed at an
average seeing of 1.1" and at an average airmass of 1.2 with light cirrus,
and continued until twilight.
We clearly detect the afterglow in stacked images (Stamatikos et al. GCN
#9768, Cenko GCN #9769). Based on the first 4 min of total exposures, we
estimate preliminary magnitudes and upper limits (all in AB system) of
g' = 22.15 +- 0.15 mag,
r' = 21.50 +- 0.08 mag,
i' = 21.30 +- 0.13 mag,
z' = 21.02 +- 0.12 mag,
J = 20.57 +- 0.15 mag,
H > 19.8 mag,
K > 18.9 mag
The given magnitudes are calibrated against SDSS as well as 2MASS field
stars and are not corrected for the expected Galactic foreground extinction
corresponding to a reddening of E_(B-V)=0.02 mag in the direction of the
burst (Schlegel et al. 1998).
The foreground extinction corrected spectral energy distribution is well
fit with a pure power law and a spectral index of beta = 1.1+/-0.2 and no
strong evidence of excess extinction.
The flux difference between the g' band magnitude and the extrapolation of
the power law as defined by r'i'z'J is consistent with Lyman-alpha
absorption at a redshift of 2.45 as reported by de Ugarte Postigo et al.
(GCN #9771).
GCN Circular 9774
Subject
GRB090812: Swift/UVOT observations
Date
2009-08-12T13:52:31Z (16 years ago)
From
Patricia Schady at MSSL/Swift <ps@mssl.ucl.ac.uk>
P. Schady (MSSL-UCL) and M. Stamatikos (NASA/ORAU) report on behalf of the
Swift UVOT team:
The Swift/UVOT began settled observations of the field of GRB 090812 86s
after the BAT trigger (Stamatikos et al., GCN Circ. 9768). An
uncatalogued, fading source is detected in the UVOT white, v, b and u band
filters at the position reported in Stamatikos et al. (GCN Circ. 9768),
consistent with the refined XRT error circle (Goad et al., GCN Circ.
9772). The detection of the afterglow in the white, v, b and u filters is
consistent with the spectroscopic redshift of z=2.452 reported by Ugarte
Postigo et al. (GCN Circ. 9771). Early time UVOT obserations indicate a
decay rate of alpha~1.5.
The magnitudes and 3-sigma upper limits for the UVOT observations of GRB
090812 in each filter are as follows:
Filter T_start(s) T_stop(s) Exp(s) Mag/3-sig UL
white 86 235 146 17.35+/-0.03
v 628 647 19 18.17+/-0.41
b 554 573 19 18.62+/-0.28
u 299 548 246 18.65+/-0.11
uvw1 677 1124 58 > 19.20
uvm2 652 1099 58 > 18.72
uvw2 603 1050 58 > 19.13
The values quoted above are not corrected for the Galactic extinction due
to the reddening of E(B-V) = 0.02 in the direction of the burst (Schlegel
et al. 1998). The photometry is on the UVOT photometric system described
in Poole et al. (2008, MNRAS, 383, 627).
GCN Circular 9775
Subject
GRB 090812 Swift-BAT Refined Analysis
Date
2009-08-12T15:09:27Z (16 years ago)
From
Michael Stamatikos at OSU/GSFC <michael.stamatikos-1@nasa.gov>
W. H. Baumgartner (GSFC/UMBC), S. D. Barthelmy (GSFC),
J. R. Cummings (GSFC/UMBC), 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), M. Stamatikos (OSU/NASA/GSFC),
J. Tueller (GSFC), T. N. Ukwatta (GWU) on behalf of the Swift-BAT team:
Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090812 (trigger #359711)
(Stamatikos, et al., GCN Circ. 9768). The BAT ground-calculated position is
RA, Dec = 353.200, -10.609 deg which is
RA(J2000) = 23h 32m 47.9s
Dec(J2000) = -10d 36' 34.1"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 78%.
The burst starts at ~T-4 sec and ends at ~T+120 sec, with 3 peaks at ~T+5 sec,
~T+27 sec and ~T+55 sec, respectively. T90 (15-350 keV) is 66.7 +- 14.7 sec
(estimated error including systematics).
The time-averaged spectrum from T-5.4 to T+113.9 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.24 +- 0.05. The fluence in the 15-150 keV band is 5.8 +- 0.2 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+26.82 sec in the 15-150 keV band
is 3.6 +- 0.2 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/359711/BA/.
[GCN OPS NOTE(13aug09): Per author's request, the "080912" was changed
to "090812" in the Subject line.]
GCN Circular 9776
Subject
GRB 090812, RIMOTS optical upper limits
Date
2009-08-12T15:14:43Z (16 years ago)
From
Kazuhiro Noda at Miyazaki U <kaz1206@astro.miyazaki-u.ac.jp>
K.Noda, A.Daikyuji, K.Kono, E.Sonoda,
N.Ohmori, H.hayasi, M.Yamauchi
(University of Miyazaki)
We have observed the field covering the error circle of
GRB 090812 (Swift trigger 359711, GCN 9768, M. Stamatikos et al.)
with the unfiltered CCD camera on the 30-cm telescope
at University of Miyazaki.
The observation was started 12:30:59 UT, about 6.5 hr
after the Swift trigger time.
We have compared our data of 30 sec exposures
with the USNO-A2.0 catalog,
There is no new source at the reported position.
((GCN 9768(M. Stamatikos et al.), GCN 9769(S. B. Cenko et al.)
GCN 9770(R.J. Smith et al.), GCN 9772(M.R. Goad et al.)
GCN 9773(Adria Updike et al.), GCN 9774(P. Schady et al.))
the upper limits are as follows:
--------------------------------------------------------------
Start(UT) End(UT) Num. of frames Limit (mag.)
--------------------------------------------------------------
12:30:59 12:31:29 1 12.1
12:30:59 13:45:22 62 17.3
---------------------------------------------------------------
GCN Circular 9777
Subject
GRB 090812: Swift XRT refined analysis
Date
2009-08-12T15:19:27Z (16 years ago)
From
Rhaana Starling at U of Leicester <rlcs1@star.le.ac.uk>
R. Starling (U. Leicester) and M. Stamatikos (NASA/ORAU) report on behalf
of the Swift-XRT team:
We have analysed the first two orbits of Swift XRT data for GRB 090812
(trigger=359711, Stamatikos et al. GCN Circ. 9768) spanning T0+78 s to
T0+12.4 ks. The UVOT-enhanced XRT position was given by Goad et al. in GCN
Circ. 9748.
The light curve shows initial flaring, with two large flares overlaid on a
power law of decay slope alpha1=1.5+/-0.5. The power law then breaks at
approximately 960 s to a shallower slope of alpha=1.05+/-0.10.
A power law is an acceptable fit to a spectrum formed from the first orbit
windowed timing (WT) mode data centred at T0+230 s, with a photon index,
Gamma, of 1.97+/-0.03. The resulting column density at the source
(z=2.452, de Ugarte Postigo et al. GCN Circ. 9771) is (1.00+/-0.09)e22
cm^-2 in addition to the Galactic column of 2.26e20 cm^-2 (Kalberla et al.
2005).
The 0.3-10 keV observed (unabsorbed) count to flux conversion is 1 ct =
3.4e-11 (4.2e-11) erg/cm2/s.
A fit to the spectrum formed from the first and second orbit photon
counting (PC) mode data centred at T0+2760 s is consistent with the WT
spectral results.
Interestingly, the X-ray spectral slope we derive is consistent with slope
reported for the optical data from GROND, centred at T0+7860 s (Updike et
al. GCN Circ. 9773.), which may imply a single spectral slope between
the X-ray and optical bands several thousand seconds after the trigger.
While we only have two orbits of data, if we assume the light curve
continues to decay with a power law of index alpha=1.05, the
predicted count rate at T+24 hours will be 0.023 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.7e-13
(9.5e-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00359711.
This circular is an official product of the Swift-XRT team.
GCN Circular 9778
Subject
GRB 090812: RAPTOR detections during the burst
Date
2009-08-12T17:15:03Z (16 years ago)
From
James Wren at LANL <jwren@nis.lanl.gov>
J. Wren, W.T. Vestrand, P.R. Wozniak, H. Davis, B. Norman
of Los Alamos National Laboratory report:
The RAPTOR telescope system responded to Swift trigger
359711 (Stamatikos et al., GCN 9768) under good observing conditions.
Our narrow-field instruments began observing the location at
06:02:32.9 UTC, 24.0 s after the Swift trigger (7.0 s after
receipt of GCN message). We obtained simultaneous observations
during the gamma-ray emitting interval in Cousins V, R, and I
bands as well as unfiltered data. We detect the optical
counterpart in all color bands. Initial analysis of our unfiltered
data calibrated to the USNO-B1 R-band revals the counterpart
brightening until ~T=70s after the trigger and then beginning a
steady decline. The following table gives selected observations,
not corrected for extinction, from this event. Further analysis
of the multi-color data is underway.
t-mid(s) exp(s) mag mag-err
--------------------------------------------
26.48 5.0 15.98 0.18
46.08 5.0 15.39 0.11
73.55 5.0 14.84 0.07
91.71 5.0 15.13 0.09
101.21 5.0 15.25 0.10
141.62 10.0 15.63 0.10
GCN Circular 9779
Subject
GRB 090812: Faulkes Telescope South Continued Optical Monitoring
Date
2009-08-12T18:02:44Z (16 years ago)
From
Zach Cano at ARI/John Moores Liverpool <zec@astro.livjm.ac.uk>
Z. Cano (Liverpool JMU), C. Guidorzi (U. Ferrara), C. Mundell, R.J. Smith,
D. Bersier, A. Melandri, I.A. Steele, S. Kobayashi, C.J. Mottram,
(Liverpool JMU), A. Gomboc (U. Ljubljana) report, on behalf of a large
collaboration:
Following our report of observations on the Liverpool Telescope (Smith et
al. GCN 9520) we continued monitoring the field of GRB090812 (Swift
trigger 359711, Stamatikos et al. GCN 9768) on the Faulkes Telescope South
(Australia) from 5.88 hours to 8.40 hours post burst in r' and i' bands.
We find from 6 x 300s stacked images:
t_exp filter t-T0 R-mag
----------------------------------------------------------
30min i' 5.88 hours 22.43 +/- 0.25
30min i' 8.40 hours 22.85 +/- 0.25
30min r' 6.60 hours 22.31 +/- 0.09
----------------------------------------------------------
The calibration is still preliminary and determined against stars in
the sdss field.
Finally, we find the decay rate in i' from 111s to 2.35ks post burst is
consistent with alpha ~ 1.25 +/- 0.1
GCN Circular 9780
Subject
GRB 090812: WIRO NIR upper limit
Date
2009-08-12T20:06:03Z (16 years ago)
From
Jay Norris at U. of Denver <jaypnorris@gmail.com>
Alexander Kutyrev (CRESST/UMCP/GSFC), Jay Norris (U. Denver),
report on behalf of the Goddard/U. Wyoming NIR camera collaboration.
We observed the afterglow position of GRB 090812 as reported by Cenko
(GCN Circ. 9769) with the 2.3-meter WIRO telescope and the Goddard
NIR camera, commencing 10:28 UT, 4.4 hrs after the Swift trigger
(Stamatikos et al., GCN Circ. 9768).
Using stacked J-band images with a total exposure time of 1360 s,
via comparison with two adjacent 2-MASS stars, we derive the following
3 sigma upper limit for the afterglow:
������ Tmid (UT)��� Mag
������� 10:46���� J-band > 21.2
GCN Circular 9814
Subject
VLA radio non-detection of GRB 090812
Date
2009-08-16T02:03:58Z (16 years ago)
From
Poonam Chandra at U Virginia/NRAO <pc8s@virginia.edu>
Poonam Chandra (RMC) and Dale A. Frail (NRAO) report on behalf of a
larger collaboration:
"We used the Very Large Array to observe the field of view toward
GRB 090812 (GCN 9768) at a frequency of 8.46 GHz at two epochs, on
2009 Aug. 13.37 UT and Aug. 15.41 UT. The GRB radio afterglow is
undetected in both the observations. The peak fluxes at the P60
optical afterglow position (GCN 9769) in the two observations are
104+/-43 uJy and 63+/-62 uJy, respectively.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 9816
Subject
GRB 090812: Suzaku WAM observation of the prompt emission
Date
2009-08-17T09:36:54Z (16 years ago)
From
Kazuhiro Noda at Miyazaki U <kaz1206@astro.miyazaki-u.ac.jp>
K. Noda, E. Sonoda, N. Ohmori, K. Kono, H. Hayashi,
A. Daikyuji, Y. Nishioka, M. Yamauchi (Univ. of Miyazaki),
Y. Hanabata, T. Uehara, T. Takahashi, Y. Fukazawa (Hiroshima U.),
M. Ohno, M. Suzuki, M. Kokubun, T. Takahashi (ISAS/JAXA),
W. Iwakiri, M. Tashiro, Y. Terada, A. Endo, K. Onda,
T. Sugasahara (Saitama U.), Y. Urata (NCU),
T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo),
K. Yamaoka, S. Sugita (Aoyama Gakuin U.), Y. E. Nakagawa,
T. Tamagawa (RIKEN), S. Hong (Nihon U.), N. Vasquez (Tokyo Tech.),
on behalf of the Suzaku WAM team, report:
The long GRB 090812 (Swift/BAT trigger #359711;
Stamatikos et al., GCN 9768; Baumgartner et al., GCN 9775)
triggered the Suzaku Wide-band All-sky Monitor (WAM) which covers an
energy range of 50 keV - 5 MeV at 2009-08-12 06:02:33.68 UT (=T0).
The observed light curve shows a double-peaked structure, starting at
T0-30 s and ending at T0+40 s, with a total duration (T90) of about 36 s.
The fluence in 100 - 1000 keV was 1.50(-0.46, +0.40) x10-6 erg/cm2.
The 1-s peak flux measured from T0+2 s was 2.77(-0.35, +0.23) photons/cm2/s
in the same energy range.
Preliminary result shows that the time-averaged spectrum from
T0-30 s to T0+40s is well fitted by a power-law with exponential cutoff model:
dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
alpha: 1.31(-1.09, +0.81), and
Epeak: 340(-138, +254) keV (chi2/d.o.f. = 36.6/37).
All the quoted errors are at statistical 90% confidence level,
in which the systematic uncertainties are not included.
The light curves for this burst will be available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html
GCN Circular 9821
Subject
GRB 090812: Konus-Wind and Swift/BAT joint spectral analysis
Date
2009-08-17T15:28:46Z (16 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@mail.ioffe.ru>
V. Pal'shin, S. Golenetskii, R.Aptekar, E. Mazets, D. Frederiks, and
T. Cline on behalf of the Konus-Wind team,
T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC),
W. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),
D. Palmer (LANL), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), and T. Ukwatta (GWU)
report:
The most intense pulse of the long GRB 090812 (Swift/BAT trigger
#359711: Stamatikos et al., GCN Circ. 9768, Baumgartner et al. GCN Circ.
9775) triggered Konus-Wind at T0(KW)=21758.942 s UT (06:02:38.942).
Since the Konus-Wind trigger record misses the early weaker part of this
GRB, we have only Konus-Wind 3-channel spectral data for the whole burst
which cover the energy range from 23 keV to 1.4 MeV.
We performed the Konus-Wind and Swift/BAT joint spectral analysis of
this GRB to derive the broad-band spectral and energetic parameters of
this burst.
The time interval of the spectral data is chosen from
T0(BAT)-6.7 to T0(BAT)+58.1 sec where T0(BAT) is the trigger time
of BAT at 06:02:08.897 UTC. The energy ranges which we used in the
joint spectral analysis are 23-1400 keV and 15-150 keV for the
Konus-Wind and the Swift/BAT respectively. The spectral data of two
instruments are fitted with the spectral model multiplied by the
constant factor to take into account the systematic effective area
uncertainties in the response matrices of each instrument.
The spectrum is well fitted with a power-law with exponential cutoff
model: dN/dE ~ E^{alpha}*exp(-(2+alpha)*E/Epeak). The constant factors
of each instrument agree within 15%. No systematic residual from the
best fit model is seen in the spectral data of each instrument. The
best fit spectral parameters are: alpha = -1.03(-0.06, +0.07) and Epeak
= 586(-152, +243) keV (chi2/dof = 59.3/57). The best fit spectral
parameters for the GRB (Band) model fixing beta = -2.5 are:
alpha = -1.03 +/- 0.07, and Epeak = 572(-159, +251) keV (chi2/dof =
59.6/57). The energy fluence in the 15-1400 keV band calculated by a
power-law with exponential cutoff model for this 64.8 sec interval is
(2.61 +/- 0.34)x10^-5 erg/cm2 (assuming the constant factor of the
Konus-Wind is fixed to 1).
Assuming z = 2.452 (de Ugarte Postigo et al. GCN Circ. 9771) and a
standard cosmology model with H_0 = 71 km/s/Mpc, Omega_M = 0.27,
Omega_Lambda = 0.73, the isotropic energy release is E_iso = 4.4 (-0.6,
+0.7)x10^53 erg in 1 keV to 10 MeV at the GRB rest frame extrapolating
the best Band function fit fixing beta = -2.5, and the rest frame peak
energy is Epeak_rest = 2.0(-0.5, +0.9) MeV.
All the quoted errors are at the 90% confidence level.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB090812_T21758/
GCN Circular 9999
Subject
GRB 090812: Skynet/PROMPT and GORT Observations
Date
2009-10-08T04:54:57Z (16 years ago)
From
Josh Haislip at U.North Carolina <haislip@physics.unc.edu>
J. Haislip, D. Reichart, K. Ivarsen, L. Cominsky, K. McLin, T. Graves, G.
Spear, 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 090812 (Stamatikos et
al., GCN 9768) with four of the 16" PROMPT telescopes at CTIO beginning 3.9
minutes after the trigger in UBVRI through variable cloud cover.
Skynet continued observing with the 14" GORT telescope at Hume Observatory
in California beginning 48.4 minutes after the the trigger in RI.
We detect the afterglow (Stamatikos et al., GCN 9768). Stacking only
images that increase the limiting magnitude yields:
mean 1-sig. 1-sig.
time sys. stat.
since cal. cal. cal.
trig. tel. exp. fil. magnitude stars* unc. unc.
(# x s) (mag) (mag)
15.0 m PROMPT-4 2 x 80 R > 17.7 (3 sig.) 50 SDSS 7 0.008 0.010
15.0 m PROMPT-5 2 x 80 I > 17.0 (3 sig.) 20 SDSS 7 0.026 0.010
15.0 m PROMPT-2 2 x 80 V > 17.4 (3 sig.) 15 SDSS 7 0.030 0.020
32.1 m PROMPT-3 2 x 80 B > 18.5 (3 sig.) 25 SDSS 7 0.028 0.031
32.6 m PROMPT-2 4 x 80 V > 18.3 (3 sig.) 15 SDSS 7 0.039 0.010
+ 1 x 40
32.7 m PROMPT-4 5 x 80 R > 18.4 (3 sig.) 50 SDSS 7 0.008 0.005
32.7 m PROMPT-5 5 x 80 I > 17.8 (3 sig.) 20 SDSS 7 0.026 0.005
62.0 m GORT 6 x 80 R > 18.8 (3 sig.) 34 SDSS 7 0.039 0.003
76.8 m GORT 9 x 80 I > 18.7 (3 sig.) 43 SDSS 7 0.097 0.003
117.3 m PROMPT-2 8 x 80 V > 18.7 (3 sig.) 17 SDSS 7 0.019 0.006
119.1 m PROMPT-4 11 x 80 R > 19.1 (3 sig.) 62 SDSS 7 0.229 0.003
119.2 m PROMPT-5 11 x 80 I > 18.4 (3 sig.) 25 SDSS 7 0.117 0.003
120.0 m PROMPT-3 10 x 80 B > 19.4 (3 sig.) 26 SDSS 7 0.085 0.011
3.2 h PROMPT-3 24 x 80 B > 21.3 (3 sig.) 26 SDSS 7 0.085 0.003
3.2 h GORT 16 x 80 I > 19.2 (3 sig.) 43 SDSS 7 0.097 0.002
3.4 h GORT 20 x 80 R > 20.0 (3 sig.) 34 SDSS 7 0.039 0.001
3.5 h PROMPT-2 67 x 80 V 21.05 +0.35 -0.27 17 SDSS 7 0.019 0.001
3.5 h PROMPT-5 66 x 80 I 20.60 +0.26 -0.21 25 SDSS 7 0.117 0.001
3.5 h PROMPT-4 65 x 80 R 21.35 +0.28 -0.22 62 SDSS 7 0.229 0.001
3.6 h PROMPT-3 37 x 80 U > 19.5 (3 sig.) 30 SDSS 7 0.015 0.012
* Transformed using Jester et al., 2005, ApJ, 130, 873.