GRB 090418, GRB 090418A
GCN Circular 9329
Subject
GRB 090418A: optical observation
Date
2009-05-09T20:15:43Z (17 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
V. Rumyantsev, E. Pavlenko(CrAO), A. Pozanenko (IKI) report on behalf of
larger GRB follow-up collaboration:
We observed the afterglow of the Swift GRB 090418A (Mangano et al., GCN
9149) in I-filter on Apr. 20 (UT) 02:34:12 - 04:08:27
and in R-filter on Apr. 20 (UT) 21:03:05 - 22:49:20 with Shajn telescope of
CrAO. We clearly detect afterglow in both epochs in stacked images.
Preliminary photometry of Apr. 20 as well a photometry in V-filter of Apr.
18 observations (Pavlenko et al. GCN 9179) is following:
T0+ Filter, Exposure, mag., err. UL Seeing
(d) (s)
0.5476 V 17x60 22.3 +/- 0.2 23.2 1.9"
2.4507 R 70x60 22.8 +/- 0.1 24.4 1.9"
Due to worse seeing (2.4") on Apr. 20 (UT) 02:34:12 - 04:08:27 the afterglow
is evidently contaminated with nearby galaxy and photometry will be reported
later. The photometry of Apr. 20 (UT) 21:03:05 - 22:49:20 also should be
treated with caution due to possible contamination.
GCN Circular 9293
Subject
GRB 090418A BVRcIc field calibration
Date
2009-04-29T14:49:54Z (17 years ago)
From
Arne A. Henden at AAVSO <arne@aavso.org>
A. Henden (AAVSO), J. Gross (SRO), B. Denny (DC-3),
D. Terrell (SwRI), and W. Cooney (SRO) report:
We have performed an all-sky calibration of the field
for the GRB090418A afterglow reported by Chornock,
et al. (GCN 9148) using the Sonoita Research
Observatory (SRO) 35cm telescope in southern
Arizona. Two photometric nights were used for the
calibration, with multiple Landolt fields observed
during each night along with an extinction
star for the calibration. The calibration file has
a limiting magnitude around V=18, with good standards
brighter than V=16. The file is available at
ftp://ftp.aavso.org/public/calib/grb/grb090418a.dat
We estimate the external zeropoint error of this calibration
to be about 0.02mag. In particular, the star used by
Henden, et al. (GCN 9211) as a comparison star:
17:57:42.53 +33:25:47.2 J2000
has an R magnitude of 12.82, so all of the photometry in
GCN 9211 should be adjusted 0.30mag brighter.
Our system is available for any other bright UBVRI
calibrations (4<V<19) for this field or any
other field; contact the first author for such requests.
The AAVSO thanks the Curry Foundation for their continued support of the
AAVSO International High Energy Network,
GCN Circular 9211
Subject
GRB090418A Rc-band photometry
Date
2009-04-23T19:03:44Z (17 years ago)
From
Arne A. Henden at AAVSO <arne@aavso.org>
A. Henden (AAVSO), J. Gross (SRO), B. Denny (DC-3),
D. Terrell (SwRI), and W. Cooney (SRO) report:
We obtained photometry of the GRB090418A afterglow
reported by Chornock et al. (GCN 9148) using the Sonoita
Research Observatory (SRO) 35cm telescope in southern
Arizona, utilizing an automatic VOevent trigger. The
Rc-band exposures began about 2 minutes after the burst
and continued until twilight. Ten 60-second and five
180-second exposures were acquired.
Astrometry of the afterglow from several images and
using UCAC as the reference catalog yields coordinates:
17:57:15.151 +33:24:20.93 J2000 (+/- 50mas)
Photometry, assuming that the star at
17:57:42.53 +33:25:47.2
has an R magnitude of 13.12
UT(mid) delT exp Rc err
11.1728 162 60 15.802 0.044
11.1919 231 60 16.185 0.048
11.2111 300 60 16.500 0.043
11.2303 369 60 16.818 0.058
11.2494 438 60 17.019 0.066
11.2686 507 60 17.249 0.067
11.2878 576 60 17.440 0.063
11.3069 645 60 17.605 0.105
11.3261 714 60 17.680 0.089
11.3450 782 60 17.855 0.115
11.3958 965 180 18.007 0.104
11.6522 1888 180 18.778 0.129
11.7067 2084 180 18.919 0.138
11.7592 2273 180 18.960 0.142
11.8114 2461 180 18.891 0.196
Where delT is the time in seconds from the burst (Mangano et al.,
GCN 9149), and the exposure is in seconds. The optical afterglow
candidate is in the filter reflection halo from HD163948,
a 6.9mag star about 2arcmin distant, so the last
few magnitudes may have a systematic bias.
We note that this field was not calibrated by SDSS through DR6.
We will perform a BVRI calibration over the next few nights.
GCN Circular 9199
Subject
GRB 090418A: R and I band observation
Date
2009-04-23T08:36:23Z (17 years ago)
From
Rupak Roy at ARIES <rupakroy1980@gmail.com>
Brajesh Kumar, Rupak Roy, Brijesh Kumar and S. B. Pandey (ARIES,
NainiTal, India, on behalf of larger Indian GRB collaboration).
We have imaged the field of swift GRB 090418A (GCN 9149) with the 104
cm Sampurnanand Optical telescope at ARIES Nainital on 18th April 2009
at 19.815 hrs UT.
We do not detect any afterglow candidate in our co-added R_c and I_c
band images (exp time 1400sec in each band) within the error circle of
XRT (GCN 9163).
The Photometry of the co-added frames put a 3 sigma upper limit of R ~
20.64 and I ~ 19.65 mag in comparison to the nearby USNO - B1 stars.
GCN Circular 9196
Subject
GRB 090418A: Konus-Wind and Swift/BAT joint spectral analysis
Date
2009-04-22T20:08:42Z (17 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), K. McLean (GSFC/UMD),
D. Palmer (LANL), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), and T. Ukwatta (GWU)
on behalf of the Swift-BAT team,
report:
We performed the Konus-Wind and the Swift/BAT joint spectral analysis
of GRB 090418A (Swift/BAT trigger #349510: Mangano et al., GCN Circ.
9149, Fenimore et al. GCN Circ. 9157).
Since the Konus-Wind observed this GRB in the waiting mode, we only
have 3 channel spectral data for the Konus-Wind which cover the energy
range from 20 keV to 1.2 MeV. Therefore, the joint spectral analysis of
the Konus-Wind and the Swift/BAT data enables to derive the broad-band
spectral parameters of this burst.
The time interval of the spectral data for each instrument is chosen
from T0(BAT)-6.7 to T0(BAT)+58.1 sec where T0(BAT) is the trigger time
of BAT at 11:07:40.2 UTC. The energy ranges which we used in the joint
spectral analysis are 20-1200 keV and 14-150 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 20%. No systematic residual from the
best fit model is seen in the spectral data of each instrument. The
best fit spectral parameters are: alpha = -1.30 +/- 0.09 and Epeak =
610(-164, +530) keV (chi2/dof = 37.0/57). The best fit spectral
parameters for the GRB (Band) model fixing beta = -2.5 are: alpha = -1.30
+/- 0.09, and Epeak = 601(-215, +554) keV (chi2/dof = 37.1/57). The
energy fluence in the 15-1200 keV band calculated by a power-law with
exponential cutoff model for this 64.8 sec interval is (1.79 +/-
0.21)x10^-5 erg/cm2.
All the quoted errors are at the 90% confidence level.
Assuming z = 1.6 (Chornock et al., GCN Circ. 9151) 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 ~2x10^53 erg in 1 keV to 10
MeV at the GRB rest frame extrapolating the best Band function fit
fixing beta = -2.5.
The Konus-Wind light curve of this GRB is available
at http://www.ioffe.ru/LEA/GRBs/GRB090418A/
GCN Circular 9190
Subject
GRB 090418A: RTT150 optical observations
Date
2009-04-22T11:07:11Z (17 years ago)
From
Rodion Burenin at IKI, Moscow <rodion@hea.iki.rssi.ru>
I. Bikmaev, R.Zhuchkov, N. Sakhibullin (KSU/AST),
I. Khamitov, Z. Eker (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.),
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI)
report:
The optical afterglow of GRB 090418A (Chornock et al., GCN 9148, Mangano et
al., GCN 9149) was observed with Russian-Turkish 1.5-m telescope (RTT150,
Bakirlitepe, TUBITAK National Observatory, Turkey) under moderate
transparences. We obtained series of 600s exposures in BVRc filters,
centered at April 18, 23:40 UT, i.e. 0.52 days after the burst.
The afterglow is clearly seen at combined R image, and marginally detected
at combined B,V frames.
Using the same calibration star USNO-B1.0 1234-0288651 as Pavlenko et
al. (GCN 9179), we estimate the following magnitudes of OT:
Filter, Exposure, mag., err.
(s)
B 3x600 23.5 limit
V 3x600 22.7 limit
R 4x600 22.1 +/- 0.1
We made also series of 3x900 sec exposures in Rc filter centered on April
20, 23:00, i.e. 2.5 days after the burst. The afterglow was not detected on
the combined frame with a limit R=23.3 mag
RTT150 finding chart (Rc) can be found at:
http://hea.iki.rssi.ru/grb/090418a/indexeng.html
GCN Circular 9183
Subject
GRB 090418A: Swift/UVOT Detection of the Neighbouring Galaxy
Date
2009-04-21T21:52:49Z (17 years ago)
From
Stephen Holland at USRA/NASA/GSFC/SSC <Stephen.T.Holland@nasa.gov>
S. T. Holland (CRESST/GSFC/USRA) reports on the behalf of the Swift
UVOT team:
Swift/UVOT observed the POSS2 galaxy (Pavlenko, et al., 2009,
GCNC 9179) located approximately 4 arcsec northwest of the afterglow
of GRB 090418A (Mangano, et al.,2009, GCNC 9149). We obtain the
following preliminary magnitudes and 1-sigma errors for this galaxy.
Filter Exposure Mag Err Sigma
-------------------------------------
v 6163 21.0 0.2 5.5
b 4361 22.2 0.5 2.3
u 6057 21.3 0.2 5.6
uvw1 6178 21.6 0.2 4.7
uvm2 2109 21.5 0.4 2.9
uvw2 1357 21.3 0.3 3.4
-------------------------------------
Exposure is the total exposure time in seconds. The quoted magnitudes
have not been corrected for the expected Galactic extinction along
the line of sight corresponding to a reddening of E_{B-V} = 0.04 mag
(Schlegel, et al., 1998, ApJS, 500, 525). All photometry is on the
UVOT photometric system described in Poole et al. (2008, MNRAS, 383,
627).
The detection of the galaxy in the uvw2 filter suggests that the
galaxy has a redshift of less than approximately 1.3. The redshift of
the afterglow is at least z = 1.608 (Chornock, et al., 2009, GCNC
9151). Therefore, we conclude that this galaxy is unlikely to be the
host galaxy of GRB 090418A, in agreement with Pavlenko, et al. (2009,
GCNC 9179).
GCN Circular 9179
Subject
GRB 090418A: optical observations
Date
2009-04-20T22:23:53Z (17 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
E. Pavlenko, V. Rumyantsev (CrAO), A. Pozanenko (IKI) report on behalf of
larger GRB follow-up collaboration:
We observed the error box of Swift GRB 090418A in series of BVRI
exposures on Apr. 18 with Shajn telescope of CrAO. We detect the afterglow
(Chornock et al., GCN 9148, Mangano et al., GCN 9149) in all filters in
stacked images. Astrometry of the afterglow is RA(J2000): 17 57 15.17
Dec(J2000): +33 24 21.14 with uncertainty of 0.3 arcsec is fully compatible
with reported one in GCNs 9148, 9149.
Preliminary photometry of combined images is based on USNO-B1.0
1234-0288651 star RA=17:57:13.29 Dec=+33:25:00.6 is following:
T0+ Filter, Exposure, mag., err.
(d) (s)
0.5484 B 36x60 23.30 +/- 0.20
0.5484 R 17x60 22.23 +/- 0.14
0.5491 I 17x60 22.40 +/- 0.24
We note, that OT is ~4" North-West of bright galaxy which is also visible
in POSS2.
Taking the redshift z=1.608 of the GRB source (Chornock et al., GCN 9151)
and the scale of ~8.6 kpc/" at that redshift it is unlikely that the galaxy
is related with OT.
A finding chart the combined image in I can be found at
http://grb.rssi.ru/GRB090418A/GRB090418_I_ZTSh_090418.gif
GCN Circular 9175
Subject
GRB 090418A: Swift/UVOT Observations
Date
2009-04-20T19:47:16Z (17 years ago)
From
Stephen Holland at USRA/NASA/GSFC/SSC <Stephen.T.Holland@nasa.gov>
S. T. Holland (CRESST/GSFC/USRA) and V. Mangano (INAF-IASFPA) report
on the behalf of the Swift UVOT team:
The Swift/UVOT observed the field of GRB 090418A starting 84 s
after the BAT trigger (Mangano, et al. 2009, GCN Circ. 9149).
Settled exposures started at T+160 s. The refined UVOT position for the
optical afterglow is
RA (J2000) = 17:57:15.17 = 269.31321 (deg)
Dec (J2000) = +33:24:21.1 = +33.40585 (deg)
with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence,
statistical + systematic). Preliminary 3-sigma magnitudes and upper
limits are
Filter T_start T_stop Exp(s) Mag Err
-------------------------------------------------------------
u (fc) 160 410 246 17.31 0.09
v 466 485 19 17.31 0.24
b 415 435 19 18.22 0.25
u 539 559 19 18.55 0.39
uvw1 515 835 19 >18.1 3-sigma UL
uvm2 490 510 19 >17.6 3-sigma UL
uvw2 441 461 19 >18.1 3-sigma UL
uvw1 515 11,831 1337 20.82 0.26
114,115 131,895 2064 >22.0 3-sigma UL
uvm2 490 18,413 2109 >21.8 3-sigma UL
uvw2 441 16,709 1357 >21.8 3-sigma UL
-------------------------------------------------------------
The quoted magnitudes have not been corrected for the expected
Galactic extinction along the line of sight corresponding to a
reddening of E_{B-V} = 0.04 mag (Schlegel, et al., 1998, ApJS, 500,
525). All photometry is on the UVOT flight system described in Poole
et al. (2008, MNRAS, 383, 627).
The detection in the uvw1 filter, combined with the lack of a
detection in the uvm2 filter, is consistent with this source having a
redshift of z = 1.608 (Charnock, et al., 2009, GCN Circ. 9151).
GCN Circular 9170
Subject
GRB 090418: Erratum in GCN 9168
Date
2009-04-20T08:33:35Z (17 years ago)
From
Michitoshi Yoshida at Okayama Astrophysical Obs <yoshida@oao.nao.ac.jp>
M. Yoshida on behalf of the MITSuME collaboration:
I made a typo in GCN 9168. We observed "GRB 090418 (Mangano et al.
GCN 9149)" instead of "GRB 090417B". I apologize for my carelessness.
GCN Circular 9168
Subject
GRB 090418: Optical observations with MITSuME Okayama and Ishigaki 1m telescope
Date
2009-04-20T07:23:37Z (17 years ago)
From
Michitoshi Yoshida at Okayama Astrophysical Obs <yoshida@oao.nao.ac.jp>
D. Kuroda, M. Yoshida, M. Isogai, K. Yanagisawa, Y. Shimizu,
S. Nagayama, H. Toda, M. Isogai (NAOJ) and N. Kawai (Tokyo Tech)
report on behalf of the MITSuME collaboration:
We observed the field of GRB 090417B (Mangano et al. GCN 9149)
with optical three color (g', Rc and Ic) CCD cameras attached to
the MITSuME 50cm telescope of Okayama Astrophysical Observatory
and the 1m telescope of Ishigaki-Jima Observatory.
We started the observation at 13:26:42 UT, 8342s after the burst
at Okayama. We could not find a new source at the position of the
afterglow (Chornock et al. GCN 9148; Mangano et al. GCN 9149;
Goad et al. GCN 9154). 3-sigma upper limits to our observations
are the following. We used GSC2.3 catalog for flux calibration.
Okayama MITSuME observation
Mid-UT Td(day) EXP-T g' Rc Ic
-------------------------------------------------------------
13:56:41 0.11736 2940s (49x60s) >19.2 >19.1 >19.0
16:27:25 0.22204 5880s (98x60s) >20.5 >20.3 >20.1
-------------------------------------------------------------
Ishigaki-Jima 1m telescope observation
Mid-UT Td(day) EXP-T g' Rc Ic
-------------------------------------------------------------
14:48:36 0.15342 3000s (10x300s) >20.6 >20.9 >19.9
-------------------------------------------------------------
GCN Circular 9166
Subject
VLA radio detection of GRB 090418
Date
2009-04-19T23:59:16Z (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 a larger collaboration:
"We used the Very Large Array to observe the field of view toward the
GRB 090418 (GCN 9149) at a frequency of 8.46 GHz on 2009 Apr.19.46 UT.
We observed the radio afterglow of the GRB at a position J2000
RA 17:57:15.156, Dec 33:24:20.78 which is 0.39" away from the KAIT
optical afterglow position reported by Chornock et al. (GCN 9148).
The GRB radio afterglow flux density is 219+/-44 uJy.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 9163
Subject
GRB 090418: Swift XRT refined analysis
Date
2009-04-19T16:55:19Z (17 years ago)
From
Vanessa Mangano at INAF-IASFPA <vanessa@ifc.inaf.it>
Mangano V., Sbarufatti B. (INAF-IASFPA) report on behalf of the
Swift XRT Team:
We have analysed the first four orbits of Swift-XRT data obtained from
GRB 090418 (trigger 349510; Mangano, et al., GCN Circ. 9149),
comprising 116 s taken in Windowed Timing (WT) mode, from T+102 s to
T+218 s, and a total exposure of 8.5 ks in Photon Counting (PC)
mode from T+219 s to the end of the observation at T+18 ks.
The best position of the X-ray afterglow is the UVOT enhanced XRT
position given in Goad, et al., GCN Circ. 9154, that is
RA, Dec = 269.31329, +33.40607 which is equivalent to:
RA (J2000): 17h 57m 15.19s
Dec (J2000): +33d 24' 21.8"
with an uncertainty of 1.7 arcsec (radius, 90% confidence).
The 0.3-10 keV X-ray light curve is well fitted by a doubly broken
pawer law, with a initial decay slope alpha1=1.7+/-0.1,
a first breal at about T+245 s, an intermediate decay slope
alpha2=0.35 -0.1+0.06, a second break at about T+2 ks and
a final decay slope alpha3=1.39+/-0.06
If decaying at this rate, the afterglow will reach a count-rate of
6.1E-3 counts/s at T+48h.
The average WT spectrum (corresponding to the initial steep decay phase)
is best fitted by an absorbed power-law model, with photon index 2.0+/-0.2,
and intrinsic NH=(6+/-3)E21 cm-2 (at the redshift z=1.608,
Chornock, et al., GCN circ. 9151) in excess with respect to the galactic
absorption value of 3.6E20 cm-2 (Kalberla et al. 2005).
The average observed(unabsorbed) flux in the 0.3-10 keV band is
3.5(4.6)E-10 ergs cm-2 s-1.
The average PC spectrum of the first orbit (covering the intermediate
slowly decaying phase) is well fitted by an absorbed power-law model,
with photon index 2.1+/-0.1, intrinsic NH=(1.2+/0.3)E22 cm-2
and average observed(unabsorbed) flux in the 0.3-10 keV band of
1.5(2.2)E-10 ergs cm-2 s-1.
Finally, the average PC spectrum from T+4.2 ks to T+18 ks (orbits 2-4)
is well fitted by an absorbed power-law model,
with photon index 2.0+/-0.1, intrinsic NH=(1.1+/0.2)E22 cm-2
and average observed(unabsorbed) flux in the 0.3-10 keV band of
1.3(1.8)E-11 ergs cm-2 s-1.
The average count-rate to observed(unabsorbed) flux conversion factor
is 4.5(6.5)E-11.
All quoted errors are at 90% confidence level.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00349510.
This circular is an official product of the Swift-XRT team.
GCN Circular 9162
Subject
GRB 090418A: ROTSE-III Refined Analysis
Date
2009-04-19T16:15:56Z (17 years ago)
From
Fang Yuan at ROTSE <yuanfang@umich.edu>
F. Yuan (U Mich) report on behalf of the ROTSE collaboration:
ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB
090418A (Swift trigger 349510; Mangano et al, GCN 9149) 19.0 s after
the burst, during the gamma-ray emission, and detected the optical
counterpart (Yuan et al, GCN 9150). We took 10 5-sec, 10 20-sec and 26
60-sec useful exposures before sunrise. Further analysis of single
images revealed an initially rising lightcurve with two subsequent
peaks at ~40s (~15.6 mag) and ~130s (~15.4 mag) before the OT dropped
below our detection limit.
GCN Circular 9157
Subject
GRB 090418: Swift-BAT refined analysis
Date
2009-04-18T17:54:33Z (17 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
E. E. Fenimore (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), V. Mangano (INAF-IASFPA), D. M. Palmer (LANL),
A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
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+705 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 090418 (trigger #349510)
(Mangano, et al., GCN Circ. 9149). The BAT ground-calculated position is
RA, Dec = 269.320, 33.407 deg, which is
RA(J2000) = 17h 57m 16.8s
Dec(J2000) = +33d 24' 24.4"
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 31%.
The mask-weighted light curve shows two clusters of peaks. The first
starts at ~T-8 sec, peaks at ~T+1 sec, and reaches a minimum at T+15 sec.
The second cluster peaks at around T+40 sec and returns to background
at ~T+70 sec. T90 (15-350 keV) is 56 +- 5 sec (estimated error
including systematics).
The time-averaged spectrum from T-8.5 to T+61.1 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.48 +- 0.07. The fluence in the 15-150 keV band is 4.6 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.06 sec in the 15-150 keV band
is 1.9 +- 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/349510/BA/
GCN Circular 9154
Subject
GRB 090418: Enhanced Swift-XRT position
Date
2009-04-18T16:00:43Z (17 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 2594 s of XRT Photon Counting mode data and 5 UVOT
images for GRB 090418, 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 = 269.31329, +33.40607 which is equivalent
to:
RA (J2000): 17h 57m 15.19s
Dec (J2000): +33d 24' 21.8"
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 9152
Subject
GRB 090418: PAIRITEL NIR detection
Date
2009-04-18T14:13:00Z (17 years ago)
From
Bethany Cobb at UC Berkeley <bcobb@astro.berkeley.edu>
B. E. Cobb and J. S. Bloom (UC Berkeley) report:
We observed the optical afterglow of GRB 090418 (Mangano et al., GCN 9149)
with the 1.3-m Peters Automated Infrared Imaging Telescope (PAIRITEL)
beginning at 2009-04-18 11:34 UT, 26 minutes after the Swift
Trigger. We detect the afterglow (Chornock et al., GCN 9148; Yuan et al.,
GCN 9150) in 651 sec mosaics of 7.8 sec simultaneous individual exposures
in the J, H, and Ks filters. Preliminary photometry for the afterglow in
these
mosaics, with midtime 2009-04-18 11:43 UT (35 minutes post-burst), yields
J = 17.7 +- 0.4, H = 17.5 +- 0.4, and Ks = 16.1 +- 0.4
(all magnitudes given in the Vega system), calibrated to the 2MASS system.
GCN Circular 9151
Subject
GRB 090418 Lick Redshift
Date
2009-04-18T12:34:39Z (17 years ago)
From
Ryan Chornock at UC Berkeley <chornock@astro.berkeley.edu>
R. Chornock, S. B. Cenko, C. V. Griffith, M. E. Kislak, I. K. W. Kleiser, and
A. V. Filippenko (UC Berkeley) report:
We obtained optical spectra of the afterglow of GRB 090418 (Chornock et al., GCN
9148; Mangano et al., GCN 9149; Yuan et al., GCN 9150) using the Kast
spectrograph on the Lick 3-meter telescope. Our first 900s exposure, starting
at 11:21:16 UT (only 816s after the burst trigger) reveals a smooth continuum
extending to the blue limit of our spectra (3450 Angs). Superposed on the
continuum are absorption lines of C IV, Mg II, Fe II, Al II, and Mg I at
z=1.608, which we suggest is the redshift of this burst. Further analysis is
ongoing.
GCN Circular 9150
Subject
GRB 090418: ROTSE-III Confirmation of Optical Counterpart
Date
2009-04-18T12:10:59Z (17 years ago)
From
Fang Yuan at ROTSE <yuanfang@umich.edu>
F. Yuan (U Mich), B. E. Schaefer (Louisiana State), W. Rujopakarn
(Steward), report on behalf of the ROTSE collaboration:
ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB
090418 (Swift trigger 349510; Mangano et al, GCN 9149) in twilight.
The first image was at 11:07:59.2 UT, 19.0 s after the burst (4.2 s
after the GCN notice time). The unfiltered images are calibrated
relative to USNO B1.0.
We detect the optical counterpart at the KAIT and UVOT position
(Chornock et al. GCN 9148; Mangano et al, GCN 9149) at the following
magnitude and limit:
start UT end UT mag magerr mlim(of image)
--------------------------------------------------------------------------------
11:07:59.2 11:09:06.3 15.9 0.1 17.0
11:09:19.6 11:14:02.1 15.9 0.1 16.8
11:14:11.3 11:25:31.5 - - 16.7
GCN Circular 9149
Subject
GRB 090418: Swift detection of a burst with optical afterglow
Date
2009-04-18T11:35:24Z (17 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
V. Mangano (INAF-IASFPA), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
P.A. Curran (MSSL-UCL), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU),
J. Mao (INAF-OAB), P. T. O'Brien (U Leicester), D. M. Palmer (LANL),
A. M. Parsons (GSFC), M. Perri (ASDC), B. A. Rowlinson (U Leicester),
B. Sbarufatti (INAF-IASFPA), G. Tagliaferri (INAF-OAB),
T. N. Ukwatta (GSFC/GWU), L. Vetere (PSU) and H. Ziaeepour (UCL-MSSL)
report on behalf of the Swift Team:
At 11:07:40 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090418 (trigger=349510). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 269.334, +33.409 which is
RA(J2000) = 17h 57m 20s
Dec(J2000) = +33d 24' 31"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows two main peaks
with a duration of about 70 sec. The peak count rate
was ~2000 counts/sec (15-350 keV), at ~45 sec after the trigger.
The XRT began observing the field at 11:09:16.3 UT, 96.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
269.3129, 33.4055 which is equivalent to:
RA(J2000) = 17h 57m 15.09s
Dec(J2000) = +33d 24' 19.9"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 64 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
3.55e+20 cm^-2 (Kalberla et al. 2005).
The initial flux in the 2.5 s image was 1.05e-09 erg cm^-2 s^-1 (0.2-10
keV).
UVOT took a finding chart exposure of 250 seconds with the u filter starting
859 seconds after the BAT trigger. An afterglow candidate has been
found in the initial data products at
RA(J2000) = 17:57:15.1 = 269.31458
Dec(J2000) = +33:24:21 = +33.40583
with an estimated uncertainty of 1.0 arcsec (radius, 90% confidence, statistical
+ systematic). This is 1.1 arcsec from the XRT position. The estimated
magnitude is u = 17.3 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.04.
Burst Advocate for this burst is V. Mangano (vanessa AT ifc.inaf.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 9148
Subject
GRB 090418 OA candidate
Date
2009-04-18T11:16:22Z (17 years ago)
From
Ryan Chornock at UC Berkeley <chornock@astro.berkeley.edu>
R. Chornock, S. B. Cenko, W. Li, and A. V. Filippenko (UC Berkeley) report on
behalf of the KAIT GRB team:
The Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory automatically
slewed to the position of GRB 090418 and discovered a new new point source not
present in the DSS at coordinates (J2000): 17:57:15.17 +33:24:21.1
at an unfiltered magnitude of approximately 15.8 at UT=11:10:57. Further
observations are in progress.