GRB 090418A
GCN Circular 9162
Subject
GRB 090418A: ROTSE-III Refined Analysis
Date
2009-04-19T16:15:56Z (16 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 9175
Subject
GRB 090418A: Swift/UVOT Observations
Date
2009-04-20T19:47:16Z (16 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 9179
Subject
GRB 090418A: optical observations
Date
2009-04-20T22:23:53Z (16 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 9183
Subject
GRB 090418A: Swift/UVOT Detection of the Neighbouring Galaxy
Date
2009-04-21T21:52:49Z (16 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 9190
Subject
GRB 090418A: RTT150 optical observations
Date
2009-04-22T11:07:11Z (16 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 9196
Subject
GRB 090418A: Konus-Wind and Swift/BAT joint spectral analysis
Date
2009-04-22T20:08:42Z (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), 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 9199
Subject
GRB 090418A: R and I band observation
Date
2009-04-23T08:36:23Z (16 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 9211
Subject
GRB090418A Rc-band photometry
Date
2009-04-23T19:03:44Z (16 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 9293
Subject
GRB 090418A BVRcIc field calibration
Date
2009-04-29T14:49:54Z (16 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 9329
Subject
GRB 090418A: optical observation
Date
2009-05-09T20:15:43Z (16 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.