GRB 090423
GCN Circular 9582
Subject
GRB 090423: Spitzer observations of the z~8.3 burst
Date
2009-06-26T21:12:05Z (16 years ago)
From
Edo Berger at Harvard <eberger@cfa.harvard.edu>
R. Chary, J. Surace, S. Carey (SSC/Caltech), E. Berger (Harvard), and G.
Fazio (SAO/Harvard) report on behalf of a larger collaboration:
"As part of the IRAC Warm Instrument Characterization Campaign (IWIC),
we observed the field of the z=8.3 GRB090423 (GCN 9198) for 72 hours
using Spitzer/IRAC at 3.6 microns. The observations took place between
2009 June 5.01 and 10.81 UT, corresponding to about 46 days after the
burst in the observer frame, or about 5 days in the rest-frame. We
detect a weak source at the location of the near-IR afterglow (Tanvir et
al. 2009 arXiv:0906.1577), confirmed through an astrometric tie to the
Gemini-North near-IR images. Aperture-corrected photometry of the
source results in a 3.6 micron flux density of 46+/-17 nJy (or
27.2+/-0.3 AB mag). The spectral energy distribution and power-law
decay of the afterglow presented in Tanvir et al. 2009 predicts a 3.6
micron flux density of ~27.3 AB mag at the time of our observations.
The detected source is thus consistent with being the afterglow.
An image of the region can be found at:
http://www.its.caltech.edu/~rchary/grb090423/
Light colors designate bright flux, dark colors are faint. The pixel
scale in the IRAC image (left) is 0.4"/pixel. The right-hand image is
the Gemini J-band image from Cucchiara et al. (GCN 9209). The red
circles are 1" radius and show the position of the afterglow.
Further analysis is ongoing, and a second epoch of observations is
planned for February 2010 to assess the contribution of an
underlying host galaxy to the measured flux."
GCN Circular 9503
Subject
GRB 090423: WSRT Radio Observations
Date
2009-06-11T23:45:46Z (16 years ago)
From
Alexander van der Horst at NASA/MSFC <Alexander.J.VanDerHorst@nasa.gov>
A.J. van der Horst (NASA/MSFC/ORAU) reports on behalf of a large
collaboration:
"We observed the position of the high redshift GRB 090423 afterglow
at 4.9 GHz with the Westerbork Synthesis Radio Telescope at May 22
11.47 UT to 23.46 UT, i.e. 29.15 - 29.65 days after the burst (GCN 9198).
We do not detect a radio source at the position of the infrared counterpart
(GCN 9202). The three-sigma rms noise in the map around that position is
75 microJy per beam. The formal flux measurement for a point source at the
position of the optical counterpart is 44 +/- 25 microJy.
We would like to thank the WSRT staff for scheduling and obtaining these
observations."
GCN Circular 9416
Subject
GRB 090423: Fermi GBM T90 follow-up analysis results
Date
2009-05-21T14:26:47Z (16 years ago)
From
Andreas von Kienlin at MPE <azk@mpe.mpg.de>
A. von Kienlin (MPE), C. Kouveliotou (NASA/MSFC) and V. Connaughton (UAH)
report on behalf of the Fermi GBM Team:
"We performed a detailed follow-up analysis of the T90 of the high redshift
GRB 090423 (H. Krimm et al., GCN Circ. # 9198) to determine the nature of
the extended pulse centered at T+30s as reported earlier (A. von Kienlin,
GCN # 9229). Due to the low significance of the detection, we were not able
to accurately locate this later pulse (the emission was only significantly
seen with one of the two triggered detectors). We conclude, therefore, that
this pulse is most probably due to background fluctuations.
The final GBM T90 derived between 10-300 keV is 11.5 +/- 2.0 sec. This
duration agrees within the error with the value of 10.3 +/- 1.1 sec reported
by the Swift team (H. Krimm et al., GCN Report 211.2)"
GCN Circular 9323
Subject
GRB 090423: optical limit
Date
2009-05-05T00:21:38Z (16 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
V. Rumyantsev, E. Pavlenko, O. Antoniuk (CrAO), A. Pozanenko (IKI) report on
behalf of larger GRB follow-up collaboration:
We observed the error box of Swift GRB 090423 (Krimm et al. GCN 9198) on
Apr. 23 between (UT) 090423 23:34:46 -- 090424 01:13:20 in R -filter with
Shajn telescope of CrAO. The observation was planning and performed before
the redshift z ~ 8 of GRB 090423 was confirmed (Cucchiara et al. GCN 9213;
Olivares et al. GCN 9215; Thoene et al. GCN 9216; Tanvir et al. GCN
9219). Indeed we do not detect optical afterglow at the place of IR
afterglow detection (Tanvir et al. GCN 9202; Levan et al. GCN 9206;
Cucchiara et al. GCN 9209). Limiting magnitude of the combined image is
following :
T0+ Filter, Exposure, mag., err.
(d) (s)
0.6877 R 93x60 >24.0 (3 sigma)
The combined R-image can be found at
http://grb.rssi.ru/GRB090423/GRB090423_ZTSh_a.gif
GCN Circular 9322
Subject
GRB 090423: 250 GHz upper limit for a z=8.2 GRB with MAMBO-2 at the IRAM 30m
Date
2009-05-04T18:21:20Z (16 years ago)
From
Dominik A. Riechers at Caltech <dr@caltech.edu>
D. A. Riechers (Caltech), F. Walter (MPIA Heidelberg), F. Bertoldi
(AIfA Bonn), C. L. Carilli (NRAO), P. Cox (IRAM), C. Kramer (IRAM),
D. Riquelme (IRAM) report:
"We used the Max-Planck-Millimeter Bolometer (MAMBO-2) array at the
IRAM 30-m telescope to observe the field of view toward the host
galaxy of GRB 090423 (GCN 9198) at redshift z=8.2 (GCN 9219), RA
09:55:33.19, Dec +18:08:57.7 (J2000) at 250 GHz. Observations were
carried out for 4.5 hr on 2009 April 25, centered at UT 18.5. We
obtained a non-detection of
S_nu(250 GHz,1.20 mm) = 0.23 +/- 0.32 mJy
(1 sigma error), i.e. a 3 sigma upper flux density limit of 0.96 mJy
on the GRB afterglow and the dust continuum in the host galaxy at 1.2
mm (rest-frame 130 um). Together with the 3 mm observations carried
out at the Plateau de Bure Interferometer (GCN 9273), this indicates a
flat spectral slope at millimeter wavelengths. The 117-element MAMBO-2
bolometer detectors cover 210-290 GHz (half power). The bolometers
have a FWHM beam size of 10.7 arcsec, at a pixel spacing of 20
arcsec. Observations were carried out in ON-OFF observing mode under
good weather conditions, with low sky noise and opactities of
tau=0.1-0.26 (derived from skydips). Calibrations were performed on
CW-LEO.
We acknowledge the excellent support of the staff at IRAM. IRAM is
supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). This
message may be cited."
GCN Circular 9279
Subject
GRB 090423: pseudo burst at z=1 and its relation to GRB 080913
Date
2009-04-29T00:10:01Z (16 years ago)
From
Binbin Zhang at UNLV <zbb@physics.unlv.edu>
Bin-Bin Zhang and Bing Zhang (University of Nevada Las Vegas) report:
GRB 090423 is a second, high-z, intrinsically short GRB after GRB
080913. Following the similar procedure discussed in Zhang, B et al
2009, http://arxiv.org/abs/0902.2419 , we have simulated a pseudo GRB
by shifting GRB 090423 to z=1. The following three factors, i.e,
specific flux (f_\nu) amplification due to a smaller luminosity
distance, blue-shift of spectrum, and temporal compression of the
lightcurve (de-dilation), have been considered. We notice that there is
an early X-ray flare in GRB 090423 (again similar to GRB 080913), which
should be harder and observable by BAT if it were at z=1. Following the
similar procedure described in Zhang et al. (2009), we manipulate the
XRT data of GRB 090423 to simulate the BAT band extended emission of the
pseudo burst. The constructed BAT band lightcurve of the pseudo GRB at
z=1 is shown in the figure at
http://grb.physics.unlv.edu/gcns/090423/pseudo.jpg . This psuedo burst
appears as a short duration GRB with extended emission.
On the other hand, both high-z GRBs have high isotropic luminosity and
energy, which make them following the Amati/Yonetoku correlation defined
by GRBs that are of the massive star origin (Type II or long
population). Although it is possible to have NS-NS and NS-BH mergers
(Type I or short population) at such a high-z (Belczynski et al. 2009),
the difficulty is to have two such energetic merger events at high-z.
The Type I model has difficulty to accommodate both low-z, low-L Type I
events and these events in terms of luminosity function (Zhang et al.
2009). Based on the multiple criteria analysis, we cannot address the
physical category of GRB 090423 and GRB 080913 using more definite
criteria (e.g. SN association, host galaxy property, etc). On the other
hand, one can use less definite criteria (Amati/Yonetoku relation and
energetics) to judge that both bursts are Type II (massive star
collapse) candidates. A judging flow chart using Fig. 8 of Zhang et al.
(2009) is posted at
http://grb.physics.unlv.edu/gcns/090423/flowchart.jpeg . We also
noticed the interesting discussions by Krimm et al. (GCN 9241) and Nava
et al. (GCN 9235), which are broadly consistent with our conclusion here.
Finally, using the three samples (Type II Gold, Type I Gold, and Other
Short/Hard) defined in Zhang et al. (2009), we plot the intrinsic
duration (T_{90}/(1+z)) as a function of z (see
http://grb.physics.unlv.edu/gcns/090423/t90z.png ). It is interesting to
note that the two high-z bursts are intrinsically shorter than the
majority of Type II GRBs. If these observations persist in the future,
it may suggest an intrinsic trend of short duration for Type II GRBs at
high-z.
This message can be cited.
GCN Circular 9274
Subject
GRB 090423: CARMA mm observations
Date
2009-04-28T01:57:49Z (16 years ago)
From
Poonam Chandra at U Virginia/NRAO <pc8s@virginia.edu>
D. C.-J. Bock (CARMA), P. Chandra (RMC), D. A. Frail (NRAO), and S. R.
Kulkarni (Caltech) report on behalf of a larger collaboration:
"We observed the field of view of GRB 090423 (GCN 9198) with the Combined
Array for Research in Millimeter-Wave Astronomy (CARMA) at a frequency of
92.5 GHz at the mean observation time of 2009 April 25, 0440 UT. We do not
detect mm emission either within the Swift-XRT error circle (GCN 9205) or
at the UKIRT K-band position (GCN 9202). The 3-sigma upper limit on the
flux density of GRB afterglow is 0.7 mJy.
We acknowledge excellent support from the staff and observers at CARMA."
GCN Circular 9273
Subject
GRB 090423: millimeter detection
Date
2009-04-28T00:29:21Z (16 years ago)
Edited On
2024-11-18T09:45:43Z (a year ago)
From
Alberto Castro-Tirado at Inst.de Astro. de Andalucia <ajct@iaa.es>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Leo P. Singer at NASA/GSFC <leo.p.singer@nasa.gov>
A. J. Castro-Tirado (IAA-CSIC Granada), M. Bremer and J.-M. Winters
(IRAM Grenoble), J. Gorosabel, S. Guziy, M. Jelínek (IAA-CSIC), P.
Kubánek (GACE, Univ. de Valencia), A. de Ugarte Postigo (ESO Santiago)
and D. Pérez-Ramírez (Univ. de Jaén), report:
"Following the detection by Swift of GRB 090423 (Krimn et al. GCNC
9198), millimeter observations were conducted on Apr 23 & 24 at the
Plateau de Bure Interferometer. Consistent with the nIR afterglow
(Tanvir et al. GCNC 9202) we clearly detect a source at 3-mm with a flux
density of ~0.2 mJy (preliminary) on the combined dataset. Pending of
confirming its variability we propose this as the likely millimeter
afterglow to GRB 090423. Considering the reported redshift values
around z ~ 8, this is the most distant radio source detected to date.
Further observations are scheduled. We acknowledge the Bure staff for
its excellent support."
GCN Circular 9261
Subject
GRB 090423: GROND second epoch imaging and refined SED
Date
2009-04-26T18:38:40Z (16 years ago)
From
Thomas Kruehler at MPE/MPI <kruehler@mpe.mpg.de>
T. Kruehler, J. Greiner and F. Olivares (all MPE Garching) report on behalf
of the GROND team:
We obtained a second epoch of imaging of the field of GRB 090423 (Swift
trigger 350184, H. Krimm et al., GCN #9198), which started on 25 Apr. 2009
at 00:44 UT, 40.8 h after the trigger.
In the second epoch, the NIR afterglow (Tanvir et al. GCN #9202) is
undetected in stacked images with a total integration time of 4800~s in
each of J, H and K down to limiting AB magnitudes of J_AB > 22.7, H_AB >
22.3 and K_AB > 21.6.
Together with the magnitudes reported in Olivares et al. (GCN #9215) this
implies a fading with a power law index faster than 1.2. This lower limit
on the temporal decay index is consistent with that found for the X-ray
afterglow at a similar time interval (G. Stratta & M. Perri, GCN #9212).
In addition we report on a refined analysis of the GROND photo-z from
Olivares et al. (GCN #9215). Using an improved photometric calibration and
including the deep z' band upper limit from Perley et al. (GCN #9217) which
is contemporaneous to our GROND imaging, we find a refined photometric
redshift of 8.0+0.4-0.8 (90% confidence level). The error range is unlikely
to improve due to the gap between the z' and J bands (for the negative
error), and the width of the J filter band (for the positive error).
This range covers the previous claims from photometric (GCNs #9213, #9215,
#9217) and spectroscopic observations (GCNs #9219, #9222). The SED is well
described with a power law of index ~1. No signatures of intrinsic dust are
evident with an upper limit of A_V < 0.5, assuming a SMC dust reddening
template.
GCN Circular 9251
Subject
GRB 090423: Fermi GBM observation (correction of isotropic equivalent energy)
Date
2009-04-25T20:05:22Z (16 years ago)
From
Andreas von Kienlin at MPE <azk@mpe.mpg.de>
A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team:
"The isotropic equivalent energy of GRB 090423 given in
GCN Circular 9229 has been erroneously computed.
At a redshift of about 8 the correct value for the isotropic
equivalent energy is E_iso = (1.0 +/- 0.3)E+53 ergs.
This value was determined from the observed event fluence of
(1.1 +/- 0.3)E-06 erg/cm^2 in the 8 to 1000 keV energy range
(observer's frame!).
We apologize for this mistake."
GCN Circular 9249
Subject
VLA radio observation of high-z GRB 090423
Date
2009-04-25T10:41:23Z (16 years ago)
From
Poonam Chandra at U Virginia/NRAO <pc8s@virginia.edu>
"Poonam Chandra (RMC), Dale A. Frail (NRAO) and S. R. Kulkarni (Caltech)
report on behalf of a larger collaboration:
"We used the Very Large Array to observe the field of view toward the
high redshift GRB 090423 (GCN 9198) at a frequency of 8.46 GHz on 2009
Apr. 25.00 UT. We do not detect any radio emission either within the
Swift-XRT error circle (GCN 9205) or at the UKIRT K-band position (GCN
9202). The 3-sigma upper limit on the radio flux density of GRB
afterglow is 135 uJy (map rms 45 uJy).
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
GCN Circular 9244
Subject
GRB090423: Y-band limit
Date
2009-04-25T04:12:16Z (16 years ago)
From
Myungshin Im at Seoul Nat U <mim@astro.snu.ac.kr>
M. Im, C. Choi, Y. Jeon, W. Park, I. Lee (Seoul National Univ),
Y.-B. Jeon (KASI) and Y. Urata (NCU) on behalf of EAFON team.
We took a series of Y-band images of GRB090423 using the 1.0m
telescope at Mt. Lemmon (Arizona, US) operated by the Korea Astronomy
Space Science Institute.
We do not detect the afterglow in a stacked image with the
total exposure time of 78 min, placing an upper limit of Y < 19.8 (Vega)
at 3-sigma at the mid point of UT April 24, 06:16. The photometry
calibration was done using the calibration data reported
in Im et al. (GCN 9242, 9221).
We thank the LOAO operator, J. Yoon for his assistance for this
observation.
GCN Circular 9242
Subject
GRB 090423: Y-band field calibration update/correction
Date
2009-04-25T02:31:03Z (16 years ago)
From
Myungshin Im at Seoul Nat U <mim@astro.snu.ac.kr>
M. Im, Y. Jeon, C. Choi, W. Park, I. Lee Seoul National Univ),
Y.-B. Jeon (KASI) and Y. Urata (NCU) on behalf of EAFON team.
The Y-band calibration data reported earlier by Im et al.
(GCN 9221) have been updated with a revised zero point,
and the catalog now includes more objects.
The updated field calibration data are available
at the same location as before:
http://astro.snu.ac.kr/~mim/grb/readme
http://astro.snu.ac.kr/~mim/grb/grb090423_ycal.dat
http://astro.snu.ac.kr/~mim/grb/yobj.reg
http://astro.snu.ac.kr/~mim/grb/chart.gif
We thank the LOAO operator, J. Yoon for his assistance for this
observation.
GCN Circular 9241
Subject
GRB 090423: Swift/BAT spectral lag results
Date
2009-04-25T01:47:05Z (16 years ago)
From
Hans Krimm at NASA-GSFC <hans.a.krimm@nasa.gov>
H. A. Krimm (CRESST/GSFC/USRA), J. P. Norris (U. Denver), T. N. Ukwatta (GSFC/GWU),
S. D. Barthelmy (GSFC), P. A. Evans (U. Leicester), N. Gehrels (GSFC),
M. Stamatikos (GSFC/ORAU)
Using the Swift/BAT data we have completed spectral lag analysis for
the high redshift burst, GRB 090423 (Krimm et al., GCN 9198). Using
16-ms binning on the event data, for the "whole" burst (15 seconds),
we obtain:
chans 3->1: 0.046 +0.085 -0.058 seconds
chans 3->2: 0.044 +0.070 -0.052 seconds
For the peak 3 seconds of the burst we obtain:
chans 3->1: 0.021 +0.054 -0.032 seconds
chans 3->2: 0.006 +0.046 -0.071 seconds
where the channels are 15-25 keV, 25-50 keV, and 50-100 keV. The lag
in each case is consistent with zero, but the 1-sigma error bars are
roughly as large as the median lag values for long bursts. Thus this
burst is too dim for us to utilize lags as a discriminant for long vs.
short.
Given the relatively short duration of this burst, it is informative to
look at other possible indicators of whether the burst is in fact a
short burst seen at a large distance.
The calculations below use z=8, which is roughly the average of the
photometric and spectroscopic redshifts determined for this burst
(Cucchiara et al., GCN 9213; Olivares et al., GCN 9215; Thoene et al.,
GCN 9216; Perley et al., GCN 9217; Tanvir et al., GCN 9219;
Fernandez-Soto et al., GRB 9222).
When converted to the rest frame, the T90 values (10.3 � 1.1 sec,
Swift/BAT 15-350 keV, Palmer et al., GCN 9204) and (12 sec, Fermi/GBM
8-1000 keV, Kienlin, GCN Circ. 9229) transform to 1.1 � 0.1 sec and
1.3 sec, respectively. However, one must be careful in comparing these
numbers to the BATSE short-hard burst divide (Kouveliotou et al.,
ApJ 413, L101, 1993). The BATSE duration distribution is in the observer frame. With a typical redshift of z = 1-2 for BATSE bursts, the dividing
line between long and short in the rest frame is 0.7 to 1.0 seconds.
Thus this burst is on the boundary and toward the long side.
While the duration and lag are consistent with short bursts (with large
errors), there are other observations which are more consistent with
GRB 090423 being a long burst in the source frame.
The spectral fits to the BAT data (Palmer et al., GCN 9204) are
inconclusive as to whether this is a long or short burst. Both the photon
index, alpha = 0.8 +/- 0.5, and Epeak = 440 keV in the source frame, from
a cut-off power-law model fit, are consistent with the results for other
short bursts detected by Swift/BAT. However, these numbers also fall
within the distributions for long bursts (Krimm et al., in preparation).
The main argument against this being a short burst is the isotopic energy.
The analysis performed by Amati et al. (GCN 9227) gives the burst
Eiso=1053 erg and shows that the burst is consistent with the Epeak-Eiso relation for long bursts. All previously known short bursts are outliers
to this relation. The calculated value of Eiso is a factor of > 50 greater than that for most other short bursts.
Furthermore it is questionable whether there would be sufficient time for
a binary neutron star system to form and inspiral to a merger given the
very early time interval since the Big Bang implied by z=8 (lookback time
of ~13 Gyr, corresponding to an age of the universe of 0.6 Gyr).
In conclusion, we can not say if GRB 090423 is short or long. Its
duration in the source frame is at the boundary between the two
classes, the lag analysis is inconclusive, the BAT spectral shape is
inconclusive, the Amati relationship favors long burst and the merger
time at such high redshift could be problematic for a short burst
interpretation.
GCN Circular 9235
Subject
GRB 090423: energetic, luminosity and jet break
Date
2009-04-24T21:57:44Z (16 years ago)
From
Giancarlo Ghirlanda at INAF/Brera <giancarlo.ghirlanda@brera.inaf.it>
L. Nava (INAF-OAB/Univ.Insubria); D. Burlon (MPE-Garching);
G. Ghirlanda (INAF-OAB); G. Ghisellini (INAF-OAB); M. Nardini (SISSA)
With the spectral parameters and fluence of GRB090423 as measured by
Fermi (von Kienlin et al., GCN 9229)
and given its redshift z=8.1 (Fernandez-Soto et al., GCN 9222), we
estimate the isotropic equivalent energy
Eiso = 1.03E53 and the isotropic equivalent peak luminosity Liso =
1.88E53 (the value of Eiso is consistent
with that obtained with the Swift spectral results given in Palmer et
al. GCN 9204).
Given the rest frame peak energy Ep= 746 keV, we show ( http://www.brera.inaf.it/utenti/ghirla/GRB/090423.html
)
that GRB090423 is consistent both with the Ep-Liso correlation
(Yonetoku et al. 2004) and with the Ep-Eiso
correlation (Amati et al. 2002, Ghirlanda et al. 2008, Nava et al.
2008; see also GCN 9227).
Noteworthly, GRB090423 is remarkably similar to GRB 080913 and GRB
071020 with respect to the Amati and
Yonetoku correlations. It is worth mentioning that these three GRBs
are long bursts according to their observed
T90 (12 s, 8 s and 4 s respectively) although, given their redshifts,
T90 ~ 1 sec in the rest frame.
Finally, considering the collimation corrected Ep-Egamma correlation
(e.g. Ghirlanda et al. 2007), we estimate that a
jet break should occur in the afterglow light curve between ~22 and 54
days (1 sigma consistency) or between ~10 and 130 days
(3 sigma consistency) assuming a homogeneous circum-burst environment
with standard parameters
(see Nava et al. 2006, Ghirlanda et al. 2007). However, this break may
not be observed in the
X-ray which, given the typical steep-flat-steep decay already observed
for this burst
( http://www.swift.ac.uk/xrt_curves/00350184/ ), could likely be due
to another emission component (e.g. Ghisellini et al. 2009).
This message may be cited.
GCN Circular 9229
Subject
GRB 090423: Fermi GBM observation
Date
2009-04-24T17:04:54Z (16 years ago)
From
Andreas von Kienlin at MPE <azk@mpe.mpg.de>
A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team:
"At 07:55:25.39 UT on 23 April 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090423 (trigger 262166127 / 090423330)
which was also detected by the Swift (H. A. Krimm et al. 2008, GCN 9198)
The GBM on-ground location is consistent with the Swift position.
The angle from the Fermi LAT boresight is 75.6 degrees.
The GBM light curve shows a single structured peak
with a duration (T90) of about 12 s (8-1000 keV). There is an
indication for extended emission until 30 s after the burst onset.
The time-averaged spectrum from T0-7.040 s to T0+5.248 s is
well fit by a power law function with an exponential
high energy cutoff. The power law index is -0.77 +/- 0.35 and
the cutoff energy, parameterized as Epeak, is 82 +/- 15 keV
(chi squared 275 for 238 d.o.f.). At a redshift of about 8
(F. Olivares et al. 2008, GCN 9215; C. Thoene et al. 2008, GCN 9216;
N. Tanvir et al. 2008, GCN 9219), the Epeak in the GRB rest frame,
Epeak_rest, is 738 +/- 135 keV.
The event fluence (8-1000 keV) in this time interval is
(1.1 +/- 0.3)E-06 erg/cm^2. Using standard cosmology
(Omega_matter = 0.27, Omega_lambda = 0.73, H0=71) the
isotropic equivalent energy in the 8-1000 keV band is
E_iso = (8.9 +/- 2.4)E+53 ergs. The 1-sec peak photon
flux measured starting from T0-1.920 s in the 8-1000 keV
band is 3.3 +/- 0.5 ph/s/cm^2.
The spectrum can also be fit by using a Band function with
Epeak = 54 +/- 22 keV and beta = -2.1 +/- 0.3. However alpha
is poorly constrained.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
GCN Circular 9227
Subject
GRB 090423: Ep,i - Eiso correlation
Date
2009-04-24T15:40:24Z (16 years ago)
From
Lorenzo Amati at INAF-IASF/Bologna <amati@iasfbo.inaf.it>
L. Amati (INAF/IASF Bologna, Italy), F. Frontera (Univ. Ferrara and INAF/IASF
Bologna, Italy), C. Guidorzi (Univ. Ferrara, Italy), E. Palazzi (INAF/IASF
Bologna, Italy) report:
On the basis of the spectral parameters and fluence measured by Swift/BAT
(Palmer et al., GCN 9204) and the redshift of ~7.5 - 8.5 suggested by
photometry and spectroscopy of the optical counterpart (Cucchiara et al.,
GCN 9213; Olivares et al., GCN 9215; Thoene et al., GCN 9216; Perley et
al., GCN 9217; Tanvir et al., GCN 9219; Fernandez-Soto et al., GRB 9222)
we find that GRB 090423 is fully consistent with the Ep,i - Eiso
correlation (Ep,i ~ 440 keV and Eiso ~10^53 erg for z = 8, assuming
a flat LambdaCDM cosmology with H0=70 km/s/Mpc and Omega_M = 0.27).
In addition, the track of this GRB in the Ep,i - Eiso plane
(http://www.iasfbo.inaf.it/~amati/grb090423.ps) implies a lower limit to
the redshift of 1.4 (68% c.l.) and 0.9 (90% c.l.) in order to be
consistent with the correlation. This further suggests that the event is
not a local very reddened GRB.
This message may be cited.
GCN Circular 9222
Subject
GRB 090423: Refined TNG analysis
Date
2009-04-24T14:16:29Z (16 years ago)
From
Cristiano Guidorzi at Ferrara U,Italy <guidorzi@fe.infn.it>
A. Fernandez-Soto (IFCA-Santander), F. Mannucci (INAF-OAA), D. Fugazza
(INAF-OAB), L.A. Antonelli (INAF-OAR), S. Campana (INAF-OAB), G.
Chincarini (Univ. Bicocca), S. Covino (INAF-OAB), P. D'Avanzo
(INAF-OAB/U. Bicocca), V. D'Elia (INAF-OAR), M. Della Valle
(INAF-OACa/ESO), A. Fiorenzano (TNG), C. Guidorzi (Univ. Ferrara), E.
Maiorano (IASF-Bo), J. Mao (INAF-OAB), R. Margutti (INAF-OAB/Univ.
Bicocca), S. Marinoni (TNG), E. Palazzi (IASF-Bo), C. C. Thoene (INAF-OAB)
report, on behalf of a larger collaboration (CIBO):
We have performed an in-depth analysis of the TNG spectrum of GRB090423
taken on Apr 23 at 22:16 UT with the NICS/Amici combination (Thoene et
al, GCN 9216). We have corrected the wavelength calibration, now based
both on the observation of sky features and a fit to the instrument
sensitivity.
We detect in the spectrum flux at wavelengths lambda>1.1 microns, and a
flux compatible with zero below that limit. Interpreting this wavelength
as the onset of Lyman alpha absorption in the IGM, this leads us to
deduce a value of z~8.1.
We have also analysed all the available photometry (GCNs 9200, 9201,
9202, 9206, 9209, 9210, 9213, 9214, 9215, 9217, 9218 and 9220) and find
that the data are well fit by an afterglow without intrinsic dust
obscuration, a photometric redshift 7.6<z<8.5, and a temporal decay
index 0.50.
[GCN OPS NOTE(24apr09): Per author's request, Marinoni was added
to the author list.]
GCN Circular 9221
Subject
GRB090423: Y-band field calibration
Date
2009-04-24T12:43:12Z (16 years ago)
From
Myungshin Im at Seoul Nat U <mim@astro.snu.ac.kr>
M. Im, Y. Jeon, C. Choi, W. Park, I. Lee Seoul National Univ),
Y.-B. Jeon (KASI) and Y. Urata (NCU) on behalf of EAFON team.
We took a series of Y-band photometry calibration data
for the field of GRB090423 using the 1.0m telescope at
Mt. Lemmon (Arizona, US) operated by the Korea Astronomy
Space Science Institute.
For the Y-band photometry standards, we used P239-C and
GD140 from UKIRT faint standards, and HIP 50459, a A0V star
from Hipparcos catalog. The zero points obtained for
these standards are applied to our observation of
the GRB090423 field, yielding Y-band photometry (Vega) for
objects in the GRB field down to Y(MKO) ~ 17.5 magnitude at 10-sigma.
The expected zero point accuracy is ~0.1mag.
To derive AB mag, add 0.63 mag to the values listed in
the catalog.
The calibration data and finding charts are available at
http://astro.snu.ac.kr/~mim/grb/readme
http://astro.snu.ac.kr/~mim/grb/grb090423_ycal.dat
http://astro.snu.ac.kr/~mim/grb/yobj.reg
http://astro.snu.ac.kr/~mim/grb/chart.gif
We thank the LOAO operator, J. Yoon for his assistance for this
observation.
GCN Circular 9220
Subject
GRB 090423 limiting magnitudes
Date
2009-04-24T11:36:15Z (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 observed the field of GRB 090423 (Krimm et al., GCN 9198)
using the 35cm telescope of Sonoita Research Observatory
with an automated VOevent trigger for an R-band image
sequence. Images began at 07:58:09UT on 2009-04-23,
170 seconds after the burst, under good conditions.
The afterglow candidate reported by Tanvir et al. (GCN 9202),
Levan et al. (GCN 9206), Cucchiara et al. (GCN 9209),
and shown by Olivares et al. (GCN 9215) to have both faded
and to have a photo-z of 8.0, is not detected in our images.
We place 3-sigma constraints of
200 seconds midpoint (1min image) Rc < 18
350 seconds midpoint (6min stack) Rc < 20
using USNO-A red magnitudes. The 19 total images, covering
the period 07:58:09 through 08:47:34, can be obtained from
ftp://ftp.aavso.org/public/sro/grb090423/
GCN Circular 9219
Subject
GRB 090423: VLT/ISAAC spectroscopy
Date
2009-04-24T07:20:35Z (16 years ago)
From
Nial Tanvir at IofA U.Cambridge <nrt@ast.cam.ac.uk>
N. Tanvir (U. Leicester), A. Levan (U. Warwick), K. Wiersema (U.
Leicester), J. Fynbo, J. Hjorth (DARK/NBI), P. Jakobsson (Reykjavik)
report on behalf of a larger collaboration:
We observed the afterglow of GRB 090423 with ISAAC on the VLT,
beginning about 01:30 (UT), approximately 17.5 hours post-burst.
Our provisional analysis shows a clear continuum at red wavelengths,
but no flux below about 11200A, consistent with a break due to
Lyman-alpha at a redshift z~8.2. However, we caution that we have not
yet carefully calibrated the instrumental response, and further work
is required to confirm this result.
We thank the VLT observers for their excellent support in obtaining
these data, particularly Valentin Ivanov and Giovanni Carraro.
GCN Circular 9218
Subject
GRB 090423: Near infrared observation at Okayama Observatory
Date
2009-04-24T04:03:34Z (16 years ago)
From
Michitoshi Yoshida at Okayama Astrophysical Obs <yoshida@oao.nao.ac.jp>
M. Yoshida, K. Yanagisawa, D. Kuroda, Y. Shimizu, S. Nagayama,
H. Toda (OAO, NAOJ) and N. Kawai (Tokyo Tech) report on behalf
of the MITSuME collaboration:
We observed the field of GRB 090423 (Krimm et al. GCN 9198) with a
near-infrared camera ISLE attached to the 188cm telescope of Okayama
Astrophysical Observatory. We also obtained optical data using the
optical three color CCD camera attached to the MITSuME 50cm
telescope.
We started the observation at 2009-04-23 10:32:27 UT, 2hr 37m after
the burst. We detected a very faint source close to the position of
the afterglow candidate reported by Tanvir et al. (GCN 9202) in our
J band image. The coordinate of the source is
J2000.0 9h 55m 33.3s +18d 08m 57.1s .
J band magnitude of the source is 20.1 mag, which is much fainter
than the previous report (Cucchiara et al. GCN 9213).
We could not find any new source in the optical bands and the other
near-infrared bands (H and Ks). The results of our photometry are
listed below. We used three 2MASS stars near the burst for near-
infrared flux calibration and GSC2.3 catalog for optical flux
calibration.
Near-infrared observation
Band Mid-UT Td(day) EXP-T mag
------------------------------------------------------
J 10:53:33 0.12377 720s 20.1 $B!^(B 0.3
H 11:04:30 0.13138 960s > 19.3
Ks 10:56:31 0.12584 480s > 18.7
------------------------------------------------------
Optical observation
Mid-UT Td(day) EXP-T g' Rc Ic
------------------------------------------------------------
11:43:56 0.15876 5940s >20.4 >20.2 >19.5
------------------------------------------------------------
GCN Circular 9217
Subject
GRB 090423: Deep z-band upper limit and confirmation of photo-z
Date
2009-04-24T03:51:52Z (16 years ago)
From
Daniel Perley at U.C. Berkeley <dperley@astro.berkeley.edu>
D. A. Perley, S. B. Cenko, and J. S. Bloom (UC Berkeley) report on
behalf of GRAASP:
We initiated a series of 15 x 200 second exposures of the field of GRB
090423 (Krimm et al, GCN 9198) in z-band using GMOS on Gemini-South
starting at 23:38 UT on 2009-04-23, 15.71 hours after the trigger. No
source is visible in the XRT error circle (Evans et al., GCN 9205) or
the NIR position (Tanvir et al., GCN 9202) in the co-added image. We
estimate a limiting magnitude (3-sigma) of:
z > 26.0 mag (t_mid = 16.25 hr)
This observation is nearly co-eval with the GROND photometry (Olivares
et al., GCN 9215) which detects the counterpart with a magnitude of J_AB
= 21.6, implying a color of J-z > 4.4 (AB). This, along with the
non-detection of a lower-redshift host galaxy candidate, the TNG
spectrum (Thoene at al., GCN 9216), and the nearly flat JHK SED,
confirms the very high redshift (z > 7) of this event.
We thank Eleazar Carrasco and the Gemini observing staff for acquiring
these observations.
GCN Circular 9216
Subject
GRB 090423: TNG Amici spectrum
Date
2009-04-24T03:17:30Z (16 years ago)
From
Paolo D'Avanzo at INAF-OAB <paolo.davanzo@brera.inaf.it>
C. C. Thoene (INAF-OAB), P. D'Avanzo (INAF-OAB/U. Bicocca), A.
Fernandez-Soto (IFCA-Santander), S. Campana, D. Fugazza (INAF-OAB),
L.A. Antonelli (INAF-OAR), G. Chincarini (Univ. Bicocca), S. Covino
(INAF-OAB), V. D'Elia (INAF-OAR), A. De Ugarte-Postigo (ESO), D.
Malesani (Dark/NBI), E. Palazzi (IASF-Bo), R. Salvaterra (INAF-OAB), A.
Fiorenzano (TNG) report, on behalf of a larger collaboration:
We observed the afterglow of GRB 090423 (Krimm et al. GCN 9198; Tanvir
et al. GCN 9202; Levan et al., GCN 9206; Cucchiara et al., GCN 9209)
with the Italian TNG 3.6m telescope located in the Canary Islands
(Spain). The observations were performed using the Amici grism. We took
a 2 hrs spectrum starting around Apr 23 at 22:16 UT (about 14.35 hours
after the burst) and covering the range 600-2700 nm with a resolution of
R ~ 50.
A preliminary analysis of the combined spectrum shows a very weak signal
at the position of the NIR afterglow. No signal is observed below
observed lambda ~ 10500 Angstrom. Assuming that the lack of signal at
bluer wavelengths is due to Ly-alpha absorption in the IGM this gives a
redshift of z ~ 7.6 (in agreement with the estimate of Olivares et al.,
GCN 9215). We point out that our wavelength calibration is based on an
archival wavelength table.
We are very grateful for the excellent support of the TNG staff.
[GCN OPS NOTE(24apr09): Per author's request, the author list was revised.]
GCN Circular 9215
Subject
GRB 090423: GROND detection and preliminary photo-z
Date
2009-04-24T03:05:49Z (16 years ago)
From
Jochen Greiner at MPI <jcg@mpe.mpg.de>
F. Olivares, T. Kruehler, J. Greiner, R. Filgas (all MPE Garching) report on
behalf of the GROND team:
We observed the field of GRB 090423 (Swift trigger 350184, H. Krimm et
al., GCN #9198) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m
MPI/ESO telescope at La Silla Observatory (Chile). Observations started on
23 Apr. 2009 at 23:08 UT, 15.2 h after the burst.
We detect the source within the XRT error circle (Evans et al. 2009, GCN #9205)
reported by Tanvir et al. (GCN #9202), Levan et al. (GCN #9206) and Cucchiara
et al. (GCN# 9209) in the NIR channels.
Preliminary photometry yields the following magnitudes and upper limits in
stacked images at a midtime of 16.7 h after the burst, obtained using
SDSS/2MASS stars as reference:
Filter Exp [s] AB Mag MagErr
----------------------------------
g' 16 x 369 > 25.0
r' 16 x 369 > 25.1
i' 16 x 369 > 24.2
z' 16 x 369 > 24.0
J 480 x 10 21.6 0.1
H 480 x 10 21.2 0.1
K 480 x 10 20.9 0.1
These magnitudes imply a significant fading to what was reported earlier
(GCNs #9202, #9213) and confirm this source to be the afterglow of GRB
090423. Furthermore, we confirm the red z-J color, and thus the probable
high redshift nature of this event. After correcting for the foreground
galactic extinction of E(B-V)=0.029 (Schlegel et al. 1998) and assuming no
intrinisic extinction, a fit with Hyper-z (Bolzonella et al. 2000) results
in a spectral index of 1.0 (+0.4,-0.5), comparable to that observed in
X-rays (Stratta & Perri, GCN #9212), and a preliminary photometric redshift
of z = 8.0+0.5-1.2.
GCN Circular 9214
Subject
GRB 090423: NOT z-band limit
Date
2009-04-23T23:17:44Z (16 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@astro.ku.dk>
D. Malesani (DARK/NBI), H. Dahle, I. Skorbakk (ITA, Oslo), E. Wuyts
(Univ. Chicago), P. Jakobsson (Univ. Iceland), J. P. U. Fynbo, J. Hjorth
(DARK/NBI), report on behalf of a larger collaboration:
We observed the field of GRB 090423 (Krimm et al., GCN 9198) with the
Nordic Optical Telescope equipped with the MOSCA camera. Observations
were carried out using the SDSS z' filter, starting on Apr 23.874 UT
(13.0 hr after the GRB trigger) and with a total exposure time of 1 hr.
At the position of the NIR candidate afterglow (Tanvir et al., GCN 9202;
Levan et al., GCN 9206; Cucchiara et al., GCN 9209), we do not detect
any source down to a limiting magnitude z(AB) > 23.7, calibrated using
the SDSS catalog.
We acknowledge excellent support from the NOT visiting observers.
GCN Circular 9213
Subject
GRB 090423: Correction to NIR photometry
Date
2009-04-23T20:36:32Z (16 years ago)
From
Antonino Cucchiara at PSU <cucchiara@astro.psu.edu>
A. Cucchiara, D. B. Fox (PSU), and E. Berger (Harvard) report:
"Further analysis of our Gemini+NIRI H-band imaging (Cucchiara, Fox &
Berger, GCN 9209) has led to a significant correction in the H-band
magnitudes for the afterglow/host (Tanvir et al., GCN 9202) of GRB
090423 (Kimm et al., GCN 9198). Our revised magnitudes for this
object are:
J mag: 19.29 +- 0.07
H mag: 18.57 +- 0.07
The revision to the H-band magnitude, in addition to the absence of
any detection in our Y-band images, suggests a break in the spectrum
below or within the J-band and above the Y-band, yielding, e.g., 7<~z<~9
in a Lyman-alpha interpretation.
Further analysis is in progress and additional observations are planned.
We apologize for any inconvenience."
GCN Circular 9212
Subject
GRB 090423: Swift-XRT refined analysis
Date
2009-04-23T20:06:55Z (16 years ago)
From
Matteo Perri at ISAC/ASDC <perri@asdc.asi.it>
G. Stratta and M. Perri (ASDC) report on behalf of the Swift-XRT Team:
We have analysed the first 8.4 ks of Swift-XRT data obtained from
GRB 090423 (trigger 350184; Krimm et al., GCN Circ. 9198), starting
from T+110 s and ending at T+18 ks.
The best position of the X-ray afterglow is the UVOT-enhanced XRT
position given in Evans et al. (GCN Circ. 9205).
The 0.3-10 keV X-ray light curve during the first Swift orbit shows a
flare peaking at T+170s. Starting from the second orbit (T+3.9 ks) the
curve is well described by a power-law model with index alpha=-1.3+/-0.1.
The X-ray spectrum during the power-law decay is well fit by an
absorbed power-law model with a photon index of 2.0+/-0.1 and a
total column density of (8.7+/-2.5)e20 cm**-2. The Galactic column
density in the direction of the source is 2.9e20 cm**-2
(Kalberla et al. 2005). The count-rate to observed (unabsorbed)
0.3-10 keV flux conversion factor deduced from this spectrum is
3.7(4.6)E-11 erg cm**-2 count**-1. Errors are given at the
1-sigma level.
We note that the X-ray column density is consistent, within 3 sigma,
with the Galactic value, consistent with the possibility that the burst
is at high redshift, as reported by Cucchiara et al. (GCN Circ. 9209).
Assuming the X-ray emission continues to decline at the same rate, we
predict a 0.3-10 keV XRT count rate of 5e-3 count/s at T+24 hr, which
corresponds to an observed 0.3-10 keV flux of ~2e-13 erg/cm**2/s.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00350184.
This circular is an official product of the Swift-XRT team.
GCN Circular 9210
Subject
GRB090423 - Swift/UVOT upper limits.
Date
2009-04-23T17:06:23Z (16 years ago)
From
Massimiliano de Pasquale at MSSL-UCL <mdp@mssl.ucl.ac.uk>
M. De Pasquale (MSSL/UCL) and H. Krimm (GSFC/GWU) report on
behalf of the Swift UVOT team:
The Swift/UVOT took the first settled exposure of GRB 090423 starting
77 s after the BAT trigger (Krimm, et al., 2009, GCN Circ. 9198) in the
white filter. We do not find any new source, at the enhanced position of
the XRT afterglow (Evans, et al. 2009, GCN Circ. 9205) nor at the
position of the K band candidate found by UKIRT (Tanvir,
et al. 2009, GCN Circ. 9206). No source is detected even when all
the images of all filters are summed. The 3-sigma upper limits for
detecting a source in the white and u band first exposures, and
subsequent co-added images in all filters are:
Filter T_start T_stop Exp(s) Mag
----------------------------------------------------------
white 77 227 147 >20.7
u 290 540 246 >20.0
v 619 6162 413 >19.6
b 545 5497 413 >20.2
u 290 5342 462 >20.4
uvw1 668 6503 344 >20.1
uvm2 644 6367 413 >20.1
uvw2 594 5958 412 >20.5
white 77 5752 560 >21.3
---------------------------------------------------------
The quoted upper limits have not been corrected for the expected
modest Galactic extinction along the line of sight corresponding to a
reddening of E_{B-V} = 0.03 mag (Schlegel, et al., 1998, ApJS, 500,
525). All photometry is on the UVOT photometry system described in
Poole et al. (2008, MNRAS, 383, 627).
GCN Circular 9209
Subject
GRB 090423: NIR photometry and evidence for spectral break
Date
2009-04-23T15:02:30Z (16 years ago)
From
Derek Fox at PSU <dfox@astro.psu.edu>
A. Cucchiara (PSU), D. B. Fox (PSU), and E. Berger (Harvard) report:
"On April 23.33 UT we imaged the field of Swift GRB 090423 (Krimm et
al., GCN 9198) with NIRI on the Gemini-North telescope. We obtained
9x60 sec exposures in Y,J,H. In the coadded J and H images we clearly
identify the object noted by Tanvir et al. (GCN 9202) and it appears
point-like (see also Levan et al., GCN 9206). The object is not
detected in Y-band.
We derive the following magnitudes, calibrated using three 2MASS stars
in the field:
J mag: 19.29 +- 0.07
H mag: 17.71 +- 0.14
The resulting J-H color of 1.1 AB mag is very red, corresponding to a
steep spectral slope of beta=3.8. Taken in conjunction with a flat
H-K color (see GCN 9202), our non-detection in Y-band, and a red I-J
color of 1.7 AB mag in comparison to P60 limits (GCN 9201), we suggest
that there is a likely break in the spectrum at about 1.2 microns,
with extinction an unlikely explanation due to the sharpness of the
feature and the shallow slope to redder wavelengths. If this is due
to Ly-alpha absorption, then the resulting redshift for GRB 090423 is
z~9.
Further analysis is in progress and additional observations are
planned."
GCN Circular 9207
Subject
GRB090423, RIMOTS optical upper limits
Date
2009-04-23T14:00:54Z (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
GRB090423 (Swift trigger 350184, GCN 9198, H. A. Krimm et al.)
with the unfiltered CCD camera on the 30-cm telescope
at University of Miyazaki.
The observation was started 10:49:54 UT, about 3.0 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 9198, H. A. Krimm et al. GCN 9202, N. Tanvir et al.
GCN 9204, D. M. Palmer et al. GCN 9205, P. A. Evans et al. )
the upper limits are as follows:
--------------------------------------------------------------
Start(UT) End(UT) Num. of frames Limit (mag.)
--------------------------------------------------------------
10:49:54 10:50:24 1 16.5
10:49:54 11:45:01 45 19.4
---------------------------------------------------------------
GCN Circular 9206
Subject
GRB 090423: UKIRT data further analysis
Date
2009-04-23T13:05:45Z (16 years ago)
From
Nial Tanvir at IofA U.Cambridge <nrt@ast.cam.ac.uk>
A. Levan (U. Warwick), N. Tanvir (U. Leicester),
K. Wiersema (U. Leicester)
Further analysis of the data reported in GCN 9202 reveals that the
source did not fade appreciably (i.e. by more than ~0.15 mag) between
observations with mid-times 25 and 41 minutes post-burst. However, we
do believe that the extension of the image is consistent with it
being a point source.
We note that the revised XRT error circle (GCN 9205) now contains this
source, making it likely the counterpart or host of this GRB.
GCN Circular 9205
Subject
GRB 090423: Enhanced Swift-XRT position
Date
2009-04-23T12:52:20Z (16 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester)
report on behalf of the Swift-XRT team.
Using 3221 s of XRT Photon Counting mode data and 7 UVOT
images for GRB 090423, 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 = 148.88830, +18.14937 which is equivalent
to:
RA (J2000): 09h 55m 33.19s
Dec (J2000): +18d 08' 57.7"
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 9204
Subject
GRB 090423: Swift-BAT refined analysis
Date
2009-04-23T12:45:50Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
D. M. Palmer (LANL), 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), 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-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090423 (trigger #350184)
(Krimm, et al., GCN Circ. 9198). The BAT ground-calculated position is
RA, Dec = 148.891, 18.165 deg, which is
RA(J2000) = 09h 55m 33.8s
Dec(J2000) = +18d 09' 55.7"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 92%.
The mask-weighted light curve shows a couple overlapping peaks starting
at ~T-2 sec, peaking at T+4 sec, and ending at ~T+15 sec.
T90 (15-350 keV) is 10.3 +- 1.1 sec (estimated error including systematics).
The time-averaged spectrum from T-0.7 to T+11.7 sec is best fit by a power law
with an exponential cutoff. This fit gives a photon index 0.80 +- 0.50,
and Epeak of 48.6 +- 6.2 keV (chi squared 41.4 for 56 d.o.f.). For this
model the total fluence in the 15-150 keV band is 5.9 +- 0.4 x 10^-7 erg/cm2
and the 1-sec peak flux measured from T+3.50 sec in the 15-150 keV band is
1.7 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index
of 1.90 +- 0.10 (chi squared 59.9 for 57 d.o.f.). 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/350184/BA/
GCN Circular 9202
Subject
GRB 090423: UKIRT K-band observations
Date
2009-04-23T10:51:23Z (16 years ago)
From
Nial Tanvir at IofA U.Cambridge <nrt@ast.cam.ac.uk>
N. Tanvir (U. Leicester), A. Levan (U. Warwick), T. Kerr (JACH),
T. Wold (JACH)
We observed the field of GRB 090423 with WFCAM on UKIRT, beginning at
08:16 (UT), approximately 20 minutes post-burst. We detect a faint
source in the K-band image just outside the revised XRT error circle,
at coordinate:
09 55 33.29 +18 08 57.8 (J2000, estimated uncertainty 0.3 arcsec)
The source has a magnitude K~17.5, but does not appear in SDSS images,
and therefore is very red. The image is also extended in the E-W
direction, and so might be (or include) a dusty host galaxy. However,
we caution that the images are slightly trailed and so further work is
required to determine whether this source is a point source or not.
GCN Circular 9201
Subject
GRB 090423: P60 Observations
Date
2009-04-23T09:46:20Z (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 GRB090423 (GCN 9198, Krimm et al.) with the
automated Palomar 60-inch telescope beginning at 2009 23 April 7:58 UT (~
3 minutes after the burst) in the Sloan r', i', and z' filters. In
coadded images we find no sources inside the XRT error circle to the
following limiting magnitudes (calculated with respect to several SDSS
stars in the field):
Mean UT t_b (min) Filter Magnitude
---------------------------------------------------------------------
23 Apr 08:11 16 r' > 21.5
23 Apr 08:15 20 i' > 21.5
23 Apr 08:17 22 z' > 20.5
The lack of an optical afterglow, together with the fact that the X-ray
column density is consistent with the Galactic value (Krimm et al., GCN
9198), make GRB090423 an interesting candidate high-redshift event. We
encourage observations at longer wavelengths to search for a NIR
counterpart.
GCN Circular 9200
Subject
GRB 090423: Faulkes Telescope South observations
Date
2009-04-23T09:42:02Z (16 years ago)
From
Andrea Melandri at Liverpool John Moores U <axm@astro.livjm.ac.uk>
A. Melandri (Liverpool JMU), C. Guidorzi (U. Ferrara), C.G. Mundell,
D. Bersier (Liverpool JMU), P. O'Brien, N. Tanvir (U. Leicester) on
behalf of a large collaboration report:
On 2009 April 23 at 07:57:07 UT we observed the Swift-BAT GRB 090423
(Krimm et al., GCN Circ. 9198) with the 2-m Faulkes Telescope South.
Observations started 108 seconds after the BAT trigger time and were
performed using the B, R and i' filters. We could not find any
uncatalogued object inside the XRT error circle down to the following
limiting magnitudes:
For single frames:
Mid Time Exposure Filter Limit
(min) (s) (mag)
-------------------------------------
16.05 60 i' > 18.0
21.30 120 r' > 20.0
24.29 120 i' > 19.0
-------------------------------------
For coadded frames:
Time Range Exposure Filter Limit
(min) (s) (mag)
-------------------------------------
13.58-53.82 660 r' > 20.8
15.55-45.95 420 i' > 20.5
-------------------------------------
Calibration was performed using few SDSS nearby stars on both filters.
GCN Circular 9198
Subject
GRB 090423: Swift detection of a burst
Date
2009-04-23T08:14:38Z (16 years ago)
From
Hans Krimm at NASA-GSFC <krimm@milkyway.gsfc.nasa.gov>
H. A. Krimm (CRESST/GSFC/USRA), A. P. Beardmore (U Leicester),
P. A. Evans (U Leicester), O. Godet (U Leicester), C. Gronwall (PSU),
C. Guidorzi (U Ferrara), P. T. O'Brien (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL), M. Perri (ASDC),
B. Sbarufatti (INAF-IASFPA), P. Schady (MSSL-UCL), G. Stratta (ASDC),
G. Tagliaferri (INAF-OAB) and T. N. Ukwatta (GSFC/GWU) report on
behalf of the Swift Team:
At 07:55:19 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090423 (trigger=350184). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 148.895, +18.160 which is
RA(J2000) = 09h 55m 35s
Dec(J2000) = +18d 09' 37"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a double-peaked
structure with a duration of about 20 sec. The peak count rate
was ~2000 counts/sec (15-350 keV), at ~5 sec after the trigger.
The XRT began observing the field at 07:56:31.8 UT, 72.5 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 148.8879,
18.1497 which is equivalent to:
RA(J2000) = 09h 55m 33.08s
Dec(J2000) = +18d 08' 58.9"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 44 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
2.89e+20 cm^-2 (Kalberla et al. 2005).
UVOT took a finding chart exposure of 150 seconds with the White filter
starting 77 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of
the BAT error circle. The typical 3-sigma upper limit has been about 19.6 mag.
The 8'x8' region for the list of sources generated on-board covers 100% of the
BAT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.03.
Burst Advocate for this burst is H. A. Krimm (krimm 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.)