GRB 090926A
GCN Circular 10113
Subject
GRB 090926a, SMARTS optical/IR afterglow observations
Date
2009-10-30T07:27:25Z (16 years ago)
From
Bethany Cobb at UC Berkeley <bcobb@astro.berkeley.edu>
B. E. Cobb (UC Berkeley) reports:
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 090926a
(GCN 9933, Bissaldi et al.) over several epochs. For each epoch,
total summed exposure times amounted to 36 minutes in I and
30 minutes in J.
The afterglow of GRB 090926a (e.g. GCN 9937, Haislip et al.;
GCN 9938, Gronwall et al.) is detected in our images with
the following magnitudes (calibrated using Landolt standard stars
in the optical and 2MASS stars in the IR):
time
post-burst I mag J mag
20.60 hrs 18.17+/-0.06 17.28+/-0.07
71.74 hrs 19.53+/-0.07 18.35+/-0.09
119.18 hrs 20.33+/-0.10 19.16+/-0.13
Between ~21 and 119 hours post-burst, the afterglow fades
with a rate of alpha ~ -1.1+/-0.1 (where afterglow flux is
proportional to t^alpha).
GCN Circular 10049
Subject
GRB 090926A: Late-time Gemini South Observations and Possible Jet Break
Date
2009-10-20T22:10:04Z (16 years ago)
From
S. Bradley Cenko at Caltech <cenko@srl.caltech.edu>
S. B. Cenko, D. A. Perley, B. E. Cobb, J. S. Bloom, and N. R. Butler (UC
Berkeley) report on behalf of a larger collaboration:
We have imaged the field of the Fermi GRB090926A (Bissaldi et al., GCN
9933; Uehara et al., GCN 9934) with the Gemini Multi-Object Spectrograph
mounted on the 8-m Gemini South telescope. Observations were taken in
the Sloan g', r', and i' filters beginning at 2:28 UT on 19 October 2009
(~ 22.9 d after the GBM trigger).
We detect a faint source in all filters at the location of the optical
afterglow (Haislip et al., GCN 9937, Gronwall et al., GCN 9938). Using
several unsaturated USNO-B objects in the field of view, along with the
filter transformations of Jordi, Grebel, and Ammon (2006 A&A 460, 339), we
measure a magnitude of r' ~ 23.7 for this source. Along with its
relatively blue color (g' - i' ~ 0), the object appears marginally
extended, suggesting it is likely dominated by emission from the host
galaxy of GRB090926A. We caution, however, that the host candidate is
partially blended with a nearby object (~ 1.5" in the SW direction, just
outside the optical and X-ray afterglow error circle) of comparable
magnitude, which likely affects the photometry.
Comparing with the last reported R-band detection (R ~ 21.5 at t ~ 11.1 d;
Haislip et al., GCN 10003), the optical decay must have significantly
steepened from previous measurements (power-law index alpha >~ 2.5). A
similar steepening is hinted at in the latest XRT observations of this
source (see http://astro.berkeley.edu/~nat/swift/00020113/bat_xrt.jpg),
suggesting a possible jet break. Using the measured redshift of z = 2.1
(Malesani et al., GCN 9942), the isotropic gamma-ray energy derived from
the Konus-Wind instrument (E_iso ~ 2e54 erg; Golenetskii et al., GCN
9959), and assuming expansion into a constant density medium (n ~ 1
cm^-3) with a gamma-ray efficiency ~ 20%, we infer an opening angle ~ 0.1
rad. The collimation-corrected prompt energy release would therefore be
large, E ~ 1e52 erg.
GCN Circular 10020
Subject
Radio observation of GRB090926a with ATCA
Date
2009-10-13T09:10:17Z (16 years ago)
From
Aquib Moin at CIRA/ATNF <aquib.moin@postgrad.curtin.edu.au>
Aquib Moin (Curtin Institute of Radio Astronomy / Australia Telescope
National Facility), Dale A. Frail (National Radio Astronomy
Observatory), Steven Tingay (Curtin Institute of Radio Astronomy),
Jean-Pierre Macquart (Curtin Institute of Radio Astronomy) report:
We observed the UVOT-enhanced XRT position (GCN 9936) of the Fermi
LAT/GBM burst GRB090926a (GCN 9933, 9972) at 5.5 GHz with the Australia
Telescope Compact Array (ATCA) between 05:00:00 UT and 10:00:00 UT on
October 01, 2009. The ATCA was in its most compact configuration giving
a synthesized beam of 138 x 78 arcsec.
We did not detect a radio source at the XRT position of the GRB090926a
(GCN 9936). The radio flux density at the GRB position found out to be
-0.271 � 0.727 mJy/beam.
No further observations are planned.
The Australia Telescope Compact Array (/ Parkes telescope / Mopra
telescope / Long Baseline Array) is part of the Australia Telescope
which is funded by the Commonwealth of Australia for operation as a
National Facility managed by CSIRO.
See the GRB field image at:
http://cira.ivec.org/dokuwiki/doku.php/grb/grb090926a_field_image
GCN Circular 10009
Subject
RT-2 observation of the bright GRB 090926A
Date
2009-10-11T06:48:11Z (16 years ago)
From
Sandip K. Chakrabarti at S.N. Bose Nat. Centre for Basic Sci. <chakraba@bose.res.in>
S. K. Chakrabarti, A. Nandi, D. Debnath, T. C. Kotoch (ICSP, Kolkata, India),
A. R. Rao, J. P. Malkar, M. K. Hingar, V. K. Agrawal (TIFR, Mumbai, India),
T. R. Chidambaram, P. Vinod, S. Sreekumar (VSSC, Thiruvananthapuram, India),
Y. D. Kotov, A. S. Buslov, V. N. Yurov, V. G. Tyshkevich, A. I. Arkhangelskij,
R. A.Zyatkov (MephI, Moscow, Russia) report:
The very bright GRB 090926A (FERMI-GBM trigger 275631628 / 090926181;
Bissaldi, GCN 9933) is detected by RT-2 Experiment onboard CORONAS-PHOTON
satellite at T0 = 04h 20m 27s (UT). The satellite was in LIGHT mode (pointing
towards the SUN) for a short duration at a high latitude in its orbit. During
this time, the GOOD time (away from the polar and SAA regions) observation was
for 348 sec starting at 04h 16m 55sec (UT) and ending at 04h 22m 43sec (UT).
The burst light curve consists of multiple peaks of total duration of ~ 17
sec, followed by a weak tail ending at ~ T0+30 sec. The strongest peak count
rate is ~ 1200 cts/sec.
This burst is also independently detected by KONUS-RF, another instrument
onboard CORONAS-PHOTON satellite (Golenetskii et al., 2009, GCN 9959).
Both RT-2/S and RT-2/G detectors have registered the burst profile of this
bright GRB in the energy band of 15 � ~1000 keV with strongest emission in the
energy band of 60 � 215 keV.
The light curve is available at the web-site:
http://csp.res.in/rt2_files/grb090926-lc.html
GCN Circular 10003
Subject
GRB 090926A: Skynet/PROMPT Observations of Day 6 - 11 Fading
Date
2009-10-09T17:24:40Z (16 years ago)
From
Josh Haislip at U.North Carolina <haislip@physics.unc.edu>
J. Haislip, D. Reichart, K. Ivarsen, A. LaCluyze, A. Foster, J. Moore, A.
Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander
report:
Skynet has continued to observe the afterglow (Haislip et al., GCN 9937) of
GRB 090926A (Bissaldi, GCN 9933) with two of the 16" PROMPT telescopes at
CTIO in RI.
After peaking in brightness approximately 1 day after the trigger (Haislip
et al., GCN 9953) and fading with a power-law index of around -1.4 until
approximately 4 days after the trigger (Haislip, et al., GCN 9982), the
afterglow faded with a shallower power-law index of around -0.8 until
approximately 6 days after the trigger (Haislip et al., GCN 9984).
Between 6 and 11 days after the trigger, the afterglow has been fading with
a steeper power-law index of around -1.7.
At 11.1 days after the trigger, its magnitude is R = 21.45 +0.22 -0.18
(statistical) +/- 0.57 (systematic; calibrated to 172 USNO B1 stars).
Skynet's most recent BVRI light curve, calibrated to USNO B1 and NOMAD
stars, can be found here:
http://skynet.unc.edu/grb/grb090926a.jpg
Continued observations with larger telescopes are encouraged.
GCN Circular 9984
Subject
GRB 090926A: Skynet/PROMPT Observations of Day 4 - 6 Fading Rate
Date
2009-10-03T20:49:13Z (16 years ago)
From
Josh Haislip at U.North Carolina <haislip@physics.unc.edu>
J. Haislip, D. Reichart, K. Ivarsen, A. LaCluyze, A. Foster, J. Moore, A.
Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander
report:
Skynet has continued to observe the afterglow (Haislip et al., GCN 9937) of
GRB 090926A (Bissaldi, GCN 9933) with four of the 16" PROMPT telescopes at
CTIO in BVRI.
After peaking in brightness approximately 1 day after the trigger (Haislip
et al., GCN 9953), the afterglow had been fading with a power-law index of
approximately -1.4 until approximately 4 days after the trigger (Haislip,
et al., GCN 9982).
Between 4 and 6 days after the trigger, the afterglow has been fading with
a shallower power-law index of approximately -0.8.
At 6.1 days after the trigger, its magnitude is R = 20.40 +0.11 -0.10
(statistical) +/- 0.57 (systematic; calibrated to 172 USNO B1 stars).
Skynet's most recent BVRI light curve, calibrated to USNO B1 and NOMAD
stars, can be found here:
http://skynet.unc.edu/grb/grb090926a.jpg
GCN Circular 9982
Subject
GRB 090926A: Skynet/PROMPT Observations of Post-Peak Fading
Date
2009-10-01T04:36:16Z (16 years ago)
From
Josh Haislip at U.North Carolina <haislip@physics.unc.edu>
J. Haislip, D. Reichart, K. Ivarsen, A. LaCluyze, A. Foster, J. Moore, A.
Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander
report:
Skynet has continued to observe the afterglow (Haislip et al., GCN 9937) of
GRB 090926A (Bissaldi, GCN 9933) with four of the 16" PROMPT telescopes at
CTIO in BVRI.
Since peaking in brightness approximately 1 day after the trigger (Haislip
et al., GCN 9953), the afterglow has been fading with a power-law index of
approximately -1.4.
At 4.1 days after the trigger, it's magnitude is R = 20.09 +0.10 -0.09
(statistical) 0.57 (systematic; calibrated to 172 USNO B1 stars).
Skynet's most recent BVRI light curve, calibrated to USNO B1 and NOMAD
stars, can be found here:
http://skynet.unc.edu/grb/grb090926a.jpg
GCN Circular 9972
Subject
GRB 090926A: Fermi LAT and GBM refined analysis
Date
2009-09-29T21:20:20Z (16 years ago)
From
Elisabetta Bissaldi at MPE <ebs@mpe.mpg.de>
Elisabetta Bissaldi (MPE), Michael S. Briggs (UA Huntsville),
Frederic Piron (IN2P3/LPTA), Hiromitsu Takahashi and
Takeshi Uehara (Hiroshima University)
report on behalf of the Fermi LAT and GBM teams:
Further analysis of GRB 090926A (Bissaldi GCN 9933, Uehara et al. GCN 99934,
Vetere et al. GCN 9336) reveals it is detected in the Fermi Large Area
Telescope (LAT) at least until 300 s after the Fermi Gamma-Ray Burst Monitor
(GBM) trigger time, T0=04:20:26.99 UT, with some indication for very
extended emission up to a few kilo-seconds.
Spectral analysis of the main emission episode, from T0 to T0+20.7 s, is
well-fit by a Band function with Epeak = 268 +/- 4 keV,
alpha = -0.693 +/ 0.009 and beta = -2.342 +/- 0.011
(C-STAT 1277 for 699 d.o.f.). Additionally, an effective area correction
of 0.8 and 0.85 is applied to both BGO detectors with respect to the NaI
detectors and LAT.
The brightest interval, i.e. from T0+8.5 s to T0+10.5 s, includes a bright,
narrow spike that is present from ~10 keV to >100 MeV. It shows a deviation
from the Band function. The parameters for this multi-component fit
(C-STAT = 781 for 697 d.o.f.) are Band_Epeak = 233 +/- 8,
Band_alpha = -0.43 +/- 0.06, Band_beta = -3.00 +/- 0.13,
and a power-law index of -1.845 +/- 0.019 for the additional component.
In this case, the effective area correction applied to both BGOs is 0.76.
The fluence between 10 keV and 10 GeV is (2.47 +/- 0.03)E-04 erg/cm^2
within the 21 seconds (the GBM T90) following the GBM trigger.
The points of contact for this burst are:
Takeshi Uehara (uehara@hep01.hepl.hiroshima-u.ac.jp) and
Elisabetta Bissaldi (ebs@mpe.mpg.de).
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.
GCN Circular 9961
Subject
GRB090926A: Swift-XRT refined analysis
Date
2009-09-28T21:59:52Z (16 years ago)
From
Loredana Vetere at PSU <vetere@astro.psu.edu>
L. Vetere (PSU) reports on behalf of the Swift-XRT team:
We have analyzed the first 21.8 ks of Swift-XRT data of FERMI
GRB090926A (Bissaldi et al., GCN Circ. 9933). The UVOT-enhanced XRT
position for this burst was given in GCN Circ.9936 (Vetere et al.).
The data are entirely in Photon Counting (PC) mode from T+46.7 ks
to T+203 ks. The light curve shows a decaying behaviour with some
flaring activity. It is best fitted by a power-law with decay index
1.29+/-0.2. Assuming the X-ray emission from the burst continues
to decline at the present rate, the predicted count rate at T+3d
is 0.009 cts/s.
The average spectrum is best fit by an absorbed power-law model
with a photon spectral index of 2.6 (+0.3,-0.2) and an absorption
column density of 1.0 (+0.5,-0.3)e21 cm-2 in excess of the Galactic
value of 2.7e20 cm-2 (Kalberla et al. 2005). The counts-to-observed
0.3-10 keV flux conversion factor deduced from this spectrum is
3.5e-11 erg cm-2 count-1. The average observed (unabsorbed) fluxes
are 1.3 (1.9)E-12 ergs cm-2 s-1. Errors are given at the 90%
confidence level.
This circular is an official product of the Swift-XRT team.
GCN Circular 9959
Subject
Konus-Wind and Konus-RF observations of GRB 090926A
Date
2009-09-28T16:42:28Z (16 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@mail.ioffe.ru>
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks,
P. Oleynik, M. Ulanov, and D. Svinkin on behalf of
the Konus-Wind and Konus-RF teams, and
T. Cline on behalf of the Konus-Wind team, report:
The long bright GRB 090926A (Fermi-GBM trigger 275631628 / 090926181:
Bissaldi, GCN 9933) localized by Fermi-LAT (Uehara et al., GCN 9934)
triggered Konus-Wind at T0=15628.683 s UT (04:20:28.683).
It was also detected by Konus-RF instrument onboard CORONAS-PHOTON s/c
in the waiting mode while being at high latitudes.
The burst light curve shows a multipeaked structure with a total
duration of ~16 s, followed by a weak tail seen up to ~T0+50 s.
As observed by Konus-Wind the burst
had a fluence of 1.80(-0.07, +0.08)x10^-4 erg/cm2,
and a 16-ms peak flux measured from T0+8.944 s
of 2.91(-0.54, +0.56)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum of the burst
(from T0 to T0+26.880 s) can be fitted (in the 20 keV - 10 MeV
range) by GRB (Band) model for which:
the low-energy photon index alpha = -0.76 +/- 0.03,
the high energy photon index beta = -2.59(-0.13, +0.10),
the peak energy Ep = 321 +/- 12 keV (chi2 = 106.0/84 dof).
The emission is clearly seen up to ~10 MeV.
All the quoted errors are at the 90% confidence level.
Assuming z = 2.1062 (Malesani et al., GCN 9942)
and a standard cosmology model with H_0 = 70 km/s/Mpc, Omega_M = 0.27,
Omega_\Lambda = 0.73, the isotropic energy release E_iso ~2.0x10^54 erg,
the peak luminosity (L_iso)_max ~ 1.0x10^54 erg/s, and Ep_rest ~1000 keV.
The Konus-Wind light curve of this GRB is available
at http://www.ioffe.ru/LEA/GRBs/GRB090926_T15628/
GCN Circular 9953
Subject
GRB 090926A: Skynet/PROMPT Continued Observations
Date
2009-09-27T18:49:04Z (16 years ago)
From
Josh Haislip at U.North Carolina <haislip@physics.unc.edu>
J. Haislip, D. Reichart, K. Ivarsen, A. LaCluyze, A. Foster, J. Moore, A.
Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander
report:
Skynet continued to observe the afterglow (Haislip et al., GCN 9937) of GRB
090926A (Bissaldi, GCN 9933) with four of the 16" PROMPT telescopes at CTIO
throughout the night in BVRI.
We find that the light curve brightens from the beginning of our
observations (about 19 hours after the trigger) to about 1 day after the
trigger in all bands, which is consistent with the findings of Oates &
Vetere (GCN 9948) in UVOT's u band.
Around 1 day, the light curve peaks at R = 17.8 mag (calibrated to 82 USNO
B1 stars) and begins to fade. A second, smaller rebrightening begins
around 26 hours and peaks at R = 18.0 mag around 27 hours.
GCN Circular 9951
Subject
GRB 090926A: Suzaku WAM observation of the prompt emission
Date
2009-09-27T14:52:07Z (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 very bright, Fermi-LAT detected GRB 090926A (Fermi-GBM trigger
#275631628/ 090926181; Bissaldi, GCN 9933; Uehara et al., GCN 9934)
triggered the Suzaku Wide-band All-sky Monitor (WAM)
which covers an energy range of 50 keV - 5 MeV at 04:20:27.168 UT (=T0).
The observed light curve shows a multi-peaked structure, lasting from
T0-0.5 s to T0+16.5 s, followed by a weak tail seen up to ~T0+34.5s.
The total duration (T90) was about 13 s and the fluence in
100 - 1000 keV was 9.71(-0.40, +0.22)x 10-5 erg/cm2.
The 1-s peak flux measured from T0+3.5 s was 30.6(-2.3, +1.6) photons/cm2/s
in the same energy range.
Preliminary result shows that the time-averaged spectrum from
T0-0.5 s to T0+34.5 s is well fitted by a GRB Band model as follows.
the low-energy photon index alpha: -1.09 (-0.27, +0.37),
the high-energy photon index beta: -2.63 (-0.17, +0.11),
and the peak energy Epeak: 434 (-30, +32) keV (chi2/d.o.f = 29.7/23).
All the quoted errors are at statistical 90% confidence level,
in which the systematic uncertainties are not included.
The light curves for this burst is now available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html
GCN Circular 9948
Subject
GRB090926A: Swift/UVOT observations
Date
2009-09-27T12:41:56Z (16 years ago)
From
Samantha Oates at MSSL <sro@mssl.ucl.ac.uk>
S. R. Oates (MSSL-UCL) and L. Vetere (PSU) report on behalf
of the Swift/UVOT team:
The Swift/UVOT began observerving the field of Fermi GRB 090926A
47ks after the Fermi GBM and LAT trigger (Bissaldi., GCN Circ. 9933;
Uehara ., GCN Circ. 9934). We detect a fading optical afterglow in
white,
v and u filters at the position reported by UVOT (Gronwall et al.,
GCN Circ. 9938) and Skynet/PROMPT (Haislip et al., GCN Circ 9937).
The lightcurve appears to rebrighten from 70ks to the end of
current observations.
Preliminary magnitudes are reported below.
Filter T_start(s) T_stop(s) Exposure Mag Err
-------------------------------------------------------
white 46977 47341 358 18.71 +/- 0.04
white 69902 70369 459 19.32 +/- 0.05
v 47348 47712 358 18.45 +/- 0.16
u 46608 46972 358 18.21 +/- 0.07
u 69429 69896 459 18.85 +/- 0.09
u 86050 86613 554 18.52 +/- 0.07
-------------------------------------------------------
The above magnitudes are not corrected for the Galactic extinction
corresponding to a reddening of E_{B-V} = 0.02 mag (Schlegel et al.,
1998, ApJS, 500, 525). The photometry is on the UVOT flight system
described in Poole et al. (2008, MNRAS, 383,627).
GCN Circular 9942
Subject
GRB 090926A: VLT/X-shooter redshift
Date
2009-09-27T06:48:04Z (16 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@astro.ku.dk>
D. Malesani (DARK/NBI), P. Goldoni (APC/Univ. Paris 7 and SAp/CEA), J.
P. U. Fynbo (DARK/NBI), V. D'Elia (ASDC and INAF/OAR), S. Covino
(INAF/OABr), H. Flores (Paris Obs.), A.J. Levan (Univ. Warwick), S. D.
Vergani (APC/Univ. Paris 7), K. Wiersema (Univ. Leicester), report on
behalf of the X-shooter GRB collaboration:
We observed the afterglow of GRB 090926A (Bissaldi, GCN 9933; Uehara et
al., GCN 9934; Vetere et al., GCN 9936; Haislip et al., GCN 9937) with
the X-shooter spectrograph mounted on the ESO-VLT UT2. Observations were
taken as part of the instrument Science Verification phase. X-shooter is
a broad-band single-object spectrograph covering the wavelength range
from the UV to the infrared (3300-22000 AA).
At the beginning of the observation (22.0 hr after the GRB), the
afterglow had R = 17.9 as measured from the acquisition image. Four
spectra lasting 1800 s each were secured.
The spectrum has high signal to noise and shows a wealth of absorption
features, together with a broad depression around 3780 AA, which we
interpret as a DLA. We identify CIV 1548 and 1550, Si II 1304 and 1526,
SiII* 1533, FeII 1608, MgII 2798 and 2803, and several others, from
which we measure a redshift z=2.1062. We caution that the wavelength
solution is based on archival calibration data.
We thank the ESO observing staff, in particular Joel Vernet, Thomas
Bensby, and Stephane Brillant.
GCN Circular 9938
Subject
GRB 090926A: Swift/UVOT detection of an optical afterglow
Date
2009-09-27T02:10:34Z (16 years ago)
From
Caryl Gronwall at PSU/Swift-UVOT <caryl@astro.psu.edu>
C. Gronwall (PSU) and L. Vetere (PSU) report on behalf of the
Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 090926A
approximately 13 hours after the Fermi/GBM trigger (Bissaldi,
GCN Circ. 9933). In a 357 sec observation in the white filter, we
find a candidate optical afterglow within the XRT error circle (Vetere
et al., GCN Circ. 9936) at
RA(J2000) = 23:33:36.037 = 353.400154
Dec(J2000) = -66:19:26.64 = 66.324067
with a 90%-confidence error radius of about 0.11 arc sec. This position
is 0.99 arc sec. from the center of the XRT error circle and is
consistent
with the optical afterglow position found by Skynet/PROMPT (Haislip et
al., GCN Circ. 9937). The estimated magnitude is 18.78 +/- 0.04.
This value is not corrected for the Galactic extinction due to the
reddening of E(B-V) = 0.03 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 9937
Subject
GRB 090926A: Skynet/PROMPT Discovery of the Optical Afterglow
Date
2009-09-27T01:36:29Z (16 years ago)
From
Josh Haislip at U.North Carolina <haislip@physics.unc.edu>
J. Haislip, D. Reichart, K. Ivarsen, A. LaCluyze, A. Foster, J. Moore, A.
Oza, M. Schubel, J. Styblova, A. Trotter, J. A. Crain, and M. Nysewander
report:
Skynet observed the Fermi/LAT localization of GRB 090926A (Uehara et al.,
GCN 9934) with four of the 16" PROMPT telescopes at CTIO beginning 19.0
hours after the trigger in UBVRI.
We detect an optical source within the Swift/XRT localization (Vetre et
al., GCN 9936) that is not in the DSS (POSS-II Red), at
RA = 23:33:36.02
DEC = -66:19:26.5
Stacking only images that increase the limiting magnitude yields:
mean
time
since cal.
trig. tel. exp. fil. magnitude stars
(h) (# x s)
19.9 PROMPT-2 22 x 80 V 18.81 +0.10 -0.09 52 NOMAD
20.0 PROMPT-5 22 x 80 I 18.24 +0.04 -0.04 165 USNO B1
20.0 PROMPT-4 24 x 80 R 18.06 +0.03 -0.03 230 USNO B1
GCN Circular 9936
Subject
GRB090926A: UVOT-enhanced XRT position
Date
2009-09-27T00:26:28Z (16 years ago)
From
Loredana Vetere at PSU <vetere@astro.psu.edu>
L. Vetere (PSU), P.A. Evans and M.R. Goad (U. Leicester) report
on behalf of the Swift-XRT team:
Using 3190 s of XRT Photon Counting mode data and 4 UVOT
images, 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 =353.40070, -66.32390 which is equivalent to:
RA (J2000): 23 33 36.18
Dec (J2000): -66 19 25.9
with an uncertainty of 1.5 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, MNRAS, 397, 1177).
This circular is an official product of the Swift-XRT team.