GRB 090426
GCN Circular 9312
Subject
GRB 090426: optical observations
Date
2009-04-30T23:36:12Z (16 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
V. Rumyantsev, K. Antoniuk (CrAO), A. Pozanenko (IKI) report on behalf of
larger GRB follow-up collaboration:
We observed the afterglow (Cummings et al. GCN 9254, Xin et al., GCN 9255)
of the Swift GRB 090426 (Swift trigger 350479, Cummings et al. GCN 9254) in
R and B filters on Apr. 26 between (UT) 18:03:06 -- 19:47:38 with AZT-11
telescope of CrAO. We detect the afterglow in stacked image in R.
Astrometry of the afterglow is RA(J2000): 12 36 18.10 Dec(J2000): +32 59
08.77 with uncertainty of 0.5 arcsec is compatible with reported in GCN
9265 (Oates et al).
Preliminary photometry of combined images is based on USNO-B1.0
1230-0248707 star RA=12:36:18.03 Dec=+33:00:02.2 is following:
T0+ Filter, Exposure, mag., err.
(d) (s)
0.2342 R 15x180 21.3 +/-0.2
The combined image can de found at
http://grb.rssi.ru/GRB090426/GRB090426_AZT-11_R.gif
Taking together early observations (Yoshida et al, GCN 9266, Kinugasa et al,
GCN 9292, Mao et al, GCN 9285) with our photometry we estimate power law
decay index as ~0.9 which is compatible with decay index estimated by
Olivares et al (GCN 9268).
GCN Circular 9292
Subject
GRB 090426: GAO 150cm telescope Optical Observation
Date
2009-04-29T14:27:50Z (16 years ago)
From
Kenzo Kinugasa at Gunma Astro. Obs/Japan <kinugasa@astron.pref.gunma.jp>
K. Kinugasa, S. Honda, O. Hashimoto, H. Takahashi, H. Taguchi
(Gunma Astronomical Observatory) report:
The position of GRB 090426 (Cummings et al., GCN 9254) was
observed with the 150 cm telescope of Gunma Astronomical
Observatory. Starting at 13:20 and 13:48 UT (0.52 and 1.0 hours
after the trigger), Ic and Rc frames were acquired for sets of
3 x 3-min and 5 x 5-min exposures, respectively.
We detected the optical counterpart (e.g., Xin et al., GCN 9255;
Oates et al., GCN 9265) in all frames. We estimated the Rc and Ic
magnitudes relative to USNO-B1.0 R2 and I, respectively.
mid-UT exp mag.
-----------------------------------
13:24:45 3x3min Ic=18.5+-0.3
14:03:58 5x5min Rc=19.9+-0.1
-----------------------------------
GCN Circular 9285
Subject
GRB 090426: YNAO-GMG observations
Date
2009-04-29T09:10:30Z (16 years ago)
From
Jirong Mao at Yunnan Obs <jirongmao@ynao.ac.cn>
J. Mao (YNAO & INAF-OAB), G. Cha and J. Bai (YNAO) report on behalf of the GMG group:
We observed the optical counterpart of GRB 090426 (Cummings et al., GCN 9254) using
one 2.4-m telescope located at Gao-Mei-GU (GMG) about 2 hours after the trigger and
otained the following magnitudes:
Start UT Exposure Filter Mag Err
-------------------------------------
14:07:59 20 min I 19.18 0.06
14:52:19 20 min R 20.29 0.02
15:49:27 20 min V 20.97 0.04
and calibration was processed by a nearby SDSS star in the image.
The telescope is charged by Yunnan Observatory (YNAO), Chinese Academy of Sciences.
This message might be cited.
GCN Circular 9276
Subject
GRB 090426: R-band limit
Date
2009-04-28T02:53:10Z (16 years ago)
From
Myungshin Im at Seoul Nat U <mim@astro.snu.ac.kr>
M. Im, Y. Jeon, W. Park, I. Lee (CEOU/Seoul National Univ),
Y.-B. Jeon (KASI) and Y. Urata (NCU) on behalf of EAFON team.
We observed GRB090426 (Cummings et al. GCN 9254) in R using
the 1.0m telescope at Mt. Lemmon (Arizona, US) operated by
the Korea Astronomy Space Science Institute.
The R-band imaging started at 2009 April 27, 04:43:19 UT.
The mid-point of the R-band obseravation is April 27,
05:06:47 UT (16.3 hrs after the burst).
From a stacked image of 6 frames (3 min exp. each),
the afterglow is barely visible in the image where
the R-band magnitude limit is R = 21.7 at 5-sigma. Therefore,
we set an upper limit of the R-band magnitude to be R ~ 21.7,
which should be close to the afterglow brightness.
The photometry was calibrated against USNO-B1 stars in
the vicinity of GRB.
We thank the LOAO operator, I. Baek for her assistance for this
observation.
GCN Circular 9272
Subject
GRB 090426: Swift/BAT spectral lag results
Date
2009-04-27T20:43:47Z (16 years ago)
From
Hans Krimm at NASA-GSFC <hans.krimm@nasa.gov>
T. N. Ukwatta (GWU/GSFC), N. Gehrels (GSFC), H. A. Krimm
(CRESST/GSFC/USRA), T. Sakamoto (GSFC/UMBC),
S. D. Barthelmy (GSFC), M. Stamatikos (GSFC/ORAU)
(for the Swift-BAT team):
For GRB 090426 (Cummings et al GCN 9254), the spectral lag analysis
of the data from T-1 sec to T+2 sec yields a lag of -6 +/- 45 msec
for the 25-50 to 50-100 keV bands using light curve binnings of
16, 32 and 64 msec. With redshift of 2.609 (Levesque et al GCN 9264)
this lag value transforms to 1.7 +/- 12.5 ms in the GRB
rest frame. The lag is consistent with zero but has relatively large
uncertainty.
Furthermore, the observed T90 (1.2 +/- 0.3 sec; Swift/BAT 15-350 keV,
Sato et al., GCN 9263) and rest frame T90 (0.33 +/- 0.08 sec)
values suggest a short-hard burst. However, the spectral fit
to the BAT data (Sato et al., GCN 9263) indicates a relatively
soft spectrum (a power-law fit to the spectrum gives index
of 1.93 +/- 0.22).
In summary, the observed and rest frame T90 values for GRB 090426
point strongly toward a short-hard burst classification.
The spectral lag is consistent with zero, and the spectrum is
marginally softer than typical for a short-hard burst.
Our conclusion is that this burst could be either short or long,
but the BAT data leads toward a classification as short.
GCN Circular 9269
Subject
GRB 090426: VLT spectroscopy
Date
2009-04-27T13:43:49Z (16 years ago)
From
Johan U. Fynbo at U.Copenhagen <jfynbo@astro.ku.dk>
Christina C. Thoene (INAF/Brera), Daniele Malesani, Johan P. U. Fynbo,
Jens Hjorth (DARK/NBI), Pall Jakobsson (Univ. Iceland), Andrew J. Levan
(Univ. Warwick), Klaas Wiersema, Nial Tanvir (Univ. Leicester), Valerio
D'Elia (INAF/Roma and ASDC), Paul M. Vreeswijk (DARK/NBI), Paolo D'Avanzo
(Univ. Milano-Bicocca & INAF/Brera), Dong Xu (DARK/NBI) report on behalf
of a larger collaboration:
We observed the afterglow of GRB 090426 (Cummings et al., GCN 9254) with
the ESO VLT equipped with the FORS2 spectrograph. Observations were
carried out starting on 2009 Apr 27.048 UT (12.3 hr after the GRB). In the
acquisition image, the afterglow (Cummings et al., GCN 9254) had R ~ 21.65.
Spectra covering the wavelength range 3500-6500 AA were taken, for a total
exposure time of 1 hr. From detection of several absorption features,
including Lyalpha, SiIV 1394, SiIV 1403, CIV 1548/1551, as well as NV
1239/1243, we confirm the redshift z=2.609 derived by Levesque et al.
(GCN 9264).
We note the very low column density (rest EW = 2 AA) of the Lyalpha line,
corresponding to less than 10^19 cm^-2 in HI column density. This
contrasts with the strength of the high-ionization lines.
We acknowledge excellent support from the observing staff at Paranal, in
particular Paul Lynam, Elena Mason, and Jonathan Smoker.
GCN Circular 9268
Subject
GRB 090426: GROND Observations of the Optical/NIR Afterglow
Date
2009-04-27T03:28:00Z (16 years ago)
From
Aybuke Kupcu Yoldas at ESO <ayoldas@eso.org>
F. Olivares (MPE Garching), A. Kupcu Yoldas (ESO), J. Greiner, A. Yoldas
(both MPE Garching) report on behalf of the GROND team:
We observed the field of GRB 090424 (Swift trigger 350479; Cummings et
al., GCN #9254) 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).
Observations started at 01:08 UT on 27 April, ~12.5 hours after the GRB
trigger, and are continuing. They are performed at an average seeing of
1.2 and at an average airmass of 2.5.
We clearly detect the optical/near-infrared afterglow (Cummings et al.
GCN #9254; Xin et al. #GCN 9255; Oates et al. GCN #9265; Yoshida et al.
GCN #9266, #9267) in all GROND bands.
Preliminary photometry yields the following AB magnitudes in stacked
images, obtained using SDSS/2MASS stars as reference:
Filter Exp[s] AB Mag MagErr
----------------------------------------
g' 4x115 22.04 0.03
r' 4x115 21.24 0.24
i' 4x115 21.77 0.11
z' 4x115 21.43 0.09
J 48x10 20.40 0.10
H 48x10 20.09 0.12
K 48x10 19.83 0.17
Given magnitudes are not corrected for the expected Galactic foreground
extinction corresponding of E_(B-V)=0.02 mag (Schlegel et al. 1998).
Using these magnitudes combined with the results of previous
observations (Yoshida et al. GCN #9266) we estimate a simple power law
decay with an index of ~0.86.
GCN Circular 9267
Subject
GRB 090426: Near infrared observation with ISLE at OAO
Date
2009-04-26T23:50:04Z (16 years ago)
From
Michitoshi Yoshida at Okayama Astrophysical Obs <yoshida@oao.nao.ac.jp>
M. Yoshida, D. Kuroda, K. Yanagisawa, Y. Shimizu, S. Nagayama,
H. Toda (OAO, NAOJ) and N. Kawai (Tokyo Tech) report on behalf
of the MITSuME collaboration:
We detected the optical afterglow of GRB 090426 (Cummings et al.
GCN 9254; Xin et al. GCN 9255; Oates et al. GCN 9265; Yoshida et
al. GCN 9266) in near-infrared bands with the near-infrared
camera ISLE attached to the 188cm telescope of Okayama
Astrophysical Observatory.
Photometric results are listed below. We used 2MASS stars in the
FOV of ISLE for flux calibration.
Band #PDAY MID-UT T-EXP mag error
----------------------------------------------
J 0.03534 13:39:41 720.0 18.6 0.2
H 0.03960 13:45:49 720.0 18.0 0.2
Ks 0.04336 13:51:13 720.0 17.6 0.2
----------------------------------------------
GCN Circular 9266
Subject
GRB 090426: Okayama MITSuME optical observation
Date
2009-04-26T23:13:33Z (16 years ago)
From
Michitoshi Yoshida at Okayama Astrophysical Obs <yoshida@oao.nao.ac.jp>
M. Yoshida, D. Kuroda, K. Yanagisawa, Y. Shimizu, S. Nagayama,
H. Toda (OAO, NAOJ) and N. Kawai (Tokyo Tech) report on behalf
of the MITSuME collaboration:
We detected the optical afterglow of GRB 090426 (Cummings et al.
GCN 9254; Xin et al. GCN 9255; Oates et al. GCN 9265) with the
optical three color (g', Rc and Ic) CCD camera attached to the
MITSuME 50cm telescope of Okayama Astrophysical Observatory.
The observation started on 2009-04-26 12:49:50 UT (63 sec after
the alert). We found the afterglow at the UVOT position of the
GRB (Oates et al. GCN 9265) in all the three bands. It rapidly
faded from 1 min to 2 hours from the burst.
Photometric results listed below. We used GSC2.3 catalog for
flux calibration. We did not apply Galactic extinction to the
following results.
#PDAY MID-UT T-EXP g' g'_err Rc Rc_err Ic Ic_err
-----------------------------------------------------------------
0.00108 12:50:20 60.0 17.21 0.15 16.54 0.09 15.95 0.11
0.00436 12:55:04 540.0 17.81 0.08 17.30 0.08 16.90 0.10
0.01198 13:06:03 540.0 19.43 0.31 19.16 0.27 18.30 0.26
0.01116 13:04:52 1500.0 18.58 0.12 18.04 0.09 17.61 0.11
0.06343 14:20:08 3000.0 20.42 0.38 19.86 0.22 19.46 0.35
-----------------------------------------------------------------
GCN Circular 9265
Subject
GRB090426 Swift/UVOT observations
Date
2009-04-26T22:13:22Z (16 years ago)
From
Samantha Oates at MSSL <sro@mssl.ucl.ac.uk>
S. R. Oates (MSSL/UCL) and J. R. Cummings (NASA/UMBC) report on behalf of
the
Swift/UVOT team:
The Swift/UVOT started settled observations of the burst GRB090426
(Cummings et al. GCN Circ. 9254) with the finding chart (fc) exposure in
white, 89s after the BAT trigger. The afterglow is detected in the white,
b, u and filters and marginally in the v filter at the refined UVOT
position:
RA (J2000) 12:36:18.07
Dec (J2000) 32:59:09.6
with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence).
The lack of detection in the UV filters is consistent with a redshift
of 2.609, which was reported by Chornock et al. (GCN Circ. 9264).
The UVOT magnitudes and upper limits our reported below:
Filter Tstart(s) Tstop(s) Exp(s) Magnitude/3sig UL
###################################################
white (fc) 89 239 147 17.52 +/- 0.03
u (fc) 301 551 246 18.11 +/- 0.08
white 581 600 19 19.10 +/- 0.22
v 630 650 19 19.04 +/- 0.86 (1.3-sigma)
u 556 576 19 18.59 +/- 0.38
b 706 726 19 18.92 +/- 0.36
uvw1 680 2164 175 > 19.92
uvm2 655 2139 175 > 19.63
uvw2 606 2090 136 > 19.82
The values quoted above are in the UVOT photometric system (Poole et al.
2008, MNRAS, 383, 627) and are not corrected for the expected Galactic
extinction corresponding to a reddening of E(B-V)=0.02 mag in the
direction of the burst (Schlegel et al. 1998).
GCN Circular 9264
Subject
GRB 090426 Keck LRIS redshift
Date
2009-04-26T21:36:18Z (16 years ago)
From
Ryan Chornock at UC Berkeley <chornock@astro.berkeley.edu>
E. Levesque (IfA, U. Hawaii), R. Chornock (UC Berkeley), L. Kewley (IfA, U.
Hawaii), J. S. Bloom (UC Berkeley), J. X. Prochaska (UCO/Lick), D. A. Perley, S.
B. Cenko, and M. Modjaz (UC Berkeley) report:
We obtained optical spectra of the afterglow of GRB 090426 (Cummings et al., GCN
9254) using LRIS on the Keck-I telescope, covering the wavelength range of
3000-9940 Angstroms. Our first exposures started at 13:55 UT, 1.1 hrs after the
BAT trigger. Preliminary analysis of the spectra reveals a set of absorption
lines at 4387, 5030, 5061, and 5592 Angstroms, which we identify as Lyman-alpha,
Si IV 1394, Si IV 1403, and the C IV 1548/1551 doublet at a common redshift of
2.609. At this redshift, the observed T90 (Sato et al., GCN 9263) is 0.33 sec
in the rest frame of the burst. This burst may be on the short end of the long
GRB population, similar to recent examples such as GRB 090423 (Krimm et al. GCN
9198, Palmer et al. GCN 9204, Thoene et al. GCN 9216, Tanvir et al. GCN 9219,
Krimm et al. GCN 9241), but we encourage further high-energy analyses of this event.
GCN Circular 9263
Subject
GRB 090426: Swift-BAT refined analysis
Date
2009-04-26T20:40:16Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
G. Sato (ISAS), 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), D. M. Palmer (LANL),
A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. 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 090426 (trigger #350479)
(Cummings, et al., GCN Circ. 9254). The BAT ground-calculated position is
RA, Dec = 189.082, 32.978 deg, which is
RA(J2000) = 12h 36m 19.7s
Dec(J2000) = +32d 58' 40.6"
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 32%.
The mask-weighted light curve shows a few overlapping peaks starting
at ~T-0.1 sec, peaking at T+0.5 sec, and ending at ~T+1.5 sec.
T90 (15-350 keV) is 1.2 +- 0.3 sec (estimated error including systematics).
The time-averaged spectrum from T-0.0 to T+1.3 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.93 +- 0.22. The fluence in the 15-150 keV band is 1.8 +- 0.3 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.03 sec in the 15-150 keV band
is 2.4 +- 0.3 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/350479/BA/
GCN Circular 9262
Subject
GRB 090426: Swift-XRT refined analysis
Date
2009-04-26T20:27:04Z (16 years ago)
From
Cristiano Guidorzi at Ferrara U,Italy <guidorzi@fe.infn.it>
C. Guidorzi (Univ. Ferrara), R. Margutti (Univ. Bicocca & INAF-OAB),
J. Mao (INAF-OAB), and J. R. Cummings (NASA/UMBC) report on behalf of
the Swift-XRT team:
We have analysed the first two orbits of Swift-XRT data obtained for
GRB 090426 (Cummings et al. GCN Circ. 9254), covering 3.0 ks of
Photon Counting (PC) mode data, between 88 s and 13.8 ks after the trigger.
The UVOT-enhanced XRT position was given by Osborne et al. in GCN Circ.
9259.
The light-curve can be modelled by a simple power-law, with
a decaying index of 0.91 +/- 0.06 (chisq/dof=27.1/25).
The spectrum extracted from PC data in the time interval from 88 s
to 5.6 ks can be modelled with an absorbed power-law, with a photon
index of 1.96 +/- 0.10 and a column density consistent with the Galactic
value of 1.5e20 cm^-2 (Kalberla et al. 2005), with a 90% confidence upper
limit of 3.7e20 cm^-2. The observed (unabsorbed) 0.3 -10 keV flux over
this time interval is 1.1e-11 (1.2e-11) erg cm^-2 count^-1.
Uncertainties are given at 90% confidence.
If the light-curve continues to decay with alpha ~0.91, the count rate 24
hours after the burst is estimated to be 3.9e-3 count s^-1, which
corresponds to an observed flux of 1.7e-13 erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00350479 .
This circular is an official product of the Swift-XRT team.
GCN Circular 9259
Subject
GRB 090426: Enhanced Swift-XRT position
Date
2009-04-26T18:20:57Z (16 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester)
report on behalf of the Swift-XRT team.
Using 2159 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 090426, 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 = 189.07496, +32.98606 which is equivalent
to:
RA (J2000): 12h 36m 17.99s
Dec (J2000): +32d 59' 09.8"
with an uncertainty of 1.7 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 9258
Subject
GRB090426: Observation for Optical counterpart from MIRO
Date
2009-04-26T16:36:42Z (16 years ago)
From
Kiran S Baliyan at Physical Research Lab, Ahmedabad,India <baliyan@prl.res.in>
K.S. Baliyan, Sunil Chandra and J.K. Jain (MIRO-PRL, Ahmedabad, India)
report:
We observed the field around the position of the optical counterpart of
GRB 090426 (Cummings et al GCN 9254, Xin et GCN 9255) usinmg 1.2m
telescope and 1296x1152 pixels CCD. The observations were made in white
band (4x60s), R band (4x120s) starting at UT 14:41:05 on April 26, 2009.
After a careful comparison with the DSS field, we did not notice any new
source near (couple of arcsecs) the said position of the optical afterglow
of GRB 090426 as reported in GCNs 9254 & 9255, down to the limit of 19.3
in R.
This message may be cited.
GCN Circular 9257
Subject
GRB 090426, RIMOTS optical upper limits
Date
2009-04-26T15:53:43Z (16 years ago)
From
Kenta Kono at Miyazaki U <kenta0514@astro.miyazaki-u.ac.jp>
K.Kono, K.Noda, E.Sonoda, N.Ohmori, H.hayasi,
A.Daikyuji, Y.Nisioka, M.Yamauchi
(University of Miyazaki)
We have observed the field covering the error circle of
GRB090426 (Swift trigger 350479, GCN 9254, J. R. Cummings et al.)
with the unfiltered CCD camera on the 30-cm telescope
at University of Miyazaki.
The observation was started 12:50:29 UT (1.7 min. after the Swift trigger),
under cloudy condition.
First analyzable image was obtained at 12:57:06 UT (6.5 min. after the Swift trigger).
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 9254, J. R. Cummings et al.)
the upper limits are as follows:
--------------------------------------------------------------
Start(UT) End(UT) Num. of frames Limit (mag.)
--------------------------------------------------------------
12:57:06 12:57:36 1 15.3
12:57:06 13:17:26 10 16.8
---------------------------------------------------------------
GCN Circular 9256
Subject
GRB 090426: inspection of SDSS images
Date
2009-04-26T15:42:35Z (16 years ago)
From
Paolo D'Avanzo at INAF-OAB <paolo.davanzo@brera.inaf.it>
P. D'Avanzo (INAF-OAB/Univ. Bicocca), E. Palazzi (IASF-Bo), C. C. Thoene
(INAF-OAB), E. Maiorano (IASF-Bo), G. Chincarini (Univ. Bicocca). L.A.
Antonelli, S. Piranomonte (INAF-OAR) report, on behalf of the CIBO
collaboration:
Inspection of archival Sloan Digital Sky Survey images reveals no object
near the position of the optical afterglow (Cummings et al GCN 9254, Xin
et GCN 9255) of GRB 090426 down to the SDSS magnitude limits. The
nearest object is a faint (and apparently extended) source located at
the following position (J2000) :
RA = 12:36:19.49
DEC = +32:59:05.5
which is about 18" away from the optical afterglow position provided by
Cummings et al (GCN 9254). According to the SDSS this object have r =
19.71 � 0.04 and a photo-z of 0.3. At this redshift the angular
separation corresponds to about 80 kpc. Given the large offsets, this
object is unlikely to be related with GRB 090426.
GCN Circular 9255
Subject
GRB 090426: TNT confimation of optical counterpart
Date
2009-04-26T13:32:17Z (16 years ago)
From
W.K. Zheng at NAOC <zwk@bao.ac.cn>
L.P. Xin, W.K. Zheng, Y.L. Qiu, J.Y. Wei,
j. Wang, J.S. Deng, Y. Urata and J.Y. Hu
on behalf of EAFON report:
TNT quickly responsed to the GRB 090426 (Swift trigger 350479;
Cummings et al. GCN 9254) in automatical mode, the first
images was taken start 12:50:03 (UT), 76s after the burst.
We detect a fading source at the position consistent with the
UVOT coordinate (Cummings et al. GCN 9254) thus confirmed the
OT of burst GRB 090426. The brightness in white band
is ~16.4 at 76s after the burst calibrated with USNO A-2.0 R band.
Observation is still under going.
Spectral observation is encouraged.
This message may be cited.
[GCN OPS NOTE(26apr09): Per author's request, the word "short" was removed
removed from the second sentence.]
GCN Circular 9254
Subject
GRB 090426: Swift detection of a burst with an optical counterpart
Date
2009-04-26T13:02:36Z (16 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
J. R. Cummings (NASA/UMBC), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), C. Gronwall (PSU), C. Guidorzi (U Ferrara),
S. T. Holland (CRESST/USRA/GSFC), H. A. Krimm (CRESST/GSFC/USRA),
J. Mao (INAF-OAB), R. Margutti (Univ Bicocca&OAB),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
D. M. Palmer (LANL), B. A. Rowlinson (U Leicester),
M. H. Siegel (PSU) and T. N. Ukwatta (GSFC/GWU) report on behalf of
the Swift Team:
At 12:48:47 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090426 (trigger=350479). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 189.091, +32.966 which is
RA(J2000) = 12h 36m 22s
Dec(J2000) = +32d 57' 56"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed multiple narrow
peaks extending over 25 seconds. The peak count rate
was ~2500 counts/sec (15-350 keV), at ~0 sec after the trigger.
The XRT began observing the field at 12:50:11.8 UT, 84.6 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 189.07405, 32.98476 which is equivalent
to:
RA(J2000) = 12h 36m 17.77s
Dec(J2000) = +32d 59' 05.1"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 84 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
1.51e+20 cm^-2 (Kalberla et al. 2005).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 89 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
RA(J2000) = 12:36:18.07 = 189.07531
DEC(J2000) = +32:59:09.6 = 32.98600
with a 90%-confidence error radius of about 0.75 arc sec. This position is 86.2
arc sec. from the center of the BAT error circle. The estimated magnitude is
17.50 with a 1-sigma error of about 0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.02.
Burst Advocate for this burst is J. R. Cummings (jayc 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.)