GRB 110428A
GCN Circular 11982
Subject
GRB 110428A: Fermi-LAT Detection
Date
2011-04-29T01:54:25Z (14 years ago)
From
Vlasios Vasileiou at LUPM/Fermi-LAT <Vlasios.Vasileiou@lupm.in2p3.fr>
V. Vasileiou (CNRS/IN2P3/LUPM), N. Omodei (Stanford University), D.
Kocevski (SLAC), F. Piron (CNRS/IN2P3/LUPM),
on behalf of the Fermi Large Area Telescope collaboration.
Based on an on-ground analysis, the Large Area Telescope (LAT),
on-board the Fermi Gamma-ray Space Telescope, detected high energy
emission extending up to ~3 GeV from the GBM-detected GRB 110428A
(trigger 325675112). The detected emission lasts up to ~200 seconds.
We obtain a localization of RA, DEC (J2000 deg) = 5.30, 64.80 (00h 21m
12s, 64d 47' 42.0"), (galactic l=119.71 deg, b=2.11 deg), with a
statistical error of 0.15 deg (68% CL), compatible with the GBM
localization. The burst was initially at an angle of ~34 degrees to the
LAT boresight and triggered an autonomous repoint of the spacecraft.
According to preliminary spectral fits, the spectral index of the
detected emission is -1.5+-0.1 (68% CL) at E>100MeV energies.
Further analysis is ongoing.
The Fermi LAT point of contact for this burst is Vlasios Vasileiou
(vlasios.vasileiou@lupm.in2p3.fr).
The Fermi LAT is a pair conversion telescope designed to cover the
energy band from 20 MeV to greater than 300 GeV. It is the product of an
international collaboration between NASA and DOE in the U.S. and many
scientific institutions across France, Italy, Japan and Sweden.
GCN Circular 11983
Subject
Konus-Wind observation of GRB 110428A
Date
2011-04-29T13:56:48Z (14 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@mail.ioffe.ru>
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks,
P. Oleynik, M. Ulanov, D. Svinkin, and
T. Cline on behalf of the Konus-Wind team, report:
The long bright GRB 110428A localized by Fermi-LAT (Vasileiou et al.,
GCN 11982) triggered Konus-Wind at T0=33509.450 s UT (09:18:29.450).
The burst light curve shows two pulses started at ~T0-9 s with a total
duration of ~15 s.
As observed by Konus-Wind the burst
had a fluence of 2.70(-0.16, +0.15)x10^-5 erg/cm2,
and a 64-ms peak flux measured from T0+1.296 s
of 8.47(-1.17, +1.18)x10^-6 erg/cm2/s
(both in the 20 keV - 2 MeV energy range).
The time-integrated spectrum of the burst
(from T0 to T0+13.568 s) can be fitted (in the 20 keV - 2 MeV
range) by the GRB (Band) model for which:
the low-energy photon index is alpha = -0.30(-0.11, +0.12),
the high energy photon index beta = -3.00(-0.58, +0.27),
the peak energy Ep = 184(-10, +12) keV (chi2 = 78.2/59 dof).
The spectrum at the maximum count rate
(measured from T0+0.256 to T0+1.536 s) can be fitted
(in the 20 keV - 2 MeV range) by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.19(-0.13, +0.14),
and Ep = 257(-16, +17) keV (chi2 = 63.1/52 dof).
Fitting by GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy
photon index: beta < -3.5 (chi2 = 63.1/51 dof).
All the quoted errors are at the 90% confidence level.
The Konus-Wind light curve of this GRB is available
at http://www.ioffe.ru/LEA/GRBs/GRB110428_T33509/
GCN Circular 11984
Subject
GRB 110428A : Swift-XRT observations
Date
2011-04-29T14:46:44Z (14 years ago)
From
Andrea Melandri at INAF-OAB <andrea.melandri@brera.inaf.it>
A. Melandri, P. D'Avanzo, R. Margutti (INAF-OAB), B. Sbarufatti (INAF-
OAB/IASFPA) and M. Stamatikos (OSU/NASA/GSFC) report on behalf of the
Swift Team:
At 00:47 UT, April 29th, 2011, Swift began a Target of Opportunity
observation of the Fermi GBM/LAT discovered burst GRB 110428A
(Vasileiou et al. GCN 11982), ~55.6 ks after the Fermi detection.
In 4.8 ks of Photon Counting mode data, we detect two sources within
the Fermi-LAT error circle (0.15 deg radius, 68% CL) at the following
positions:
Source 1:
RA(J2000): 00 21 50.47
Dec(J2000): +64 48 52.4
with an uncertainty of 4.6 arcsec.
Source 2:
RA(J2000): 00 22 22.22
Dec(J2000): +64:50:57.1
with an uncertainty of 7.1 arcsec.
Uncertainty radii are given at 90% containment.
We note that the position of Source 1 is consistent with a known
ROSAT source (1RXS J002150.5+644850) also present in the DSS. Source
2 is an uncatalogued object.
The two sources have a count rate of about (1.2e-2 +/- 1.8e-3) and
(2.9e-3 +/- 9.1e-4) cts/s, respectively. It is not possible to
determine whether these sources are fading given the current
statistics. Further Swift-XRT observations of the field are planned.
We encourage ground-based follow-up observations.
This circular is an official product of the Swift-XRT team.
GCN Circular 11988
Subject
GRB 110428A: Suzaku WAM observation of the prompt emission
Date
2011-05-02T10:21:42Z (14 years ago)
From
Makoto Tashiro at Saitama U/Swift <tashiro@phy.saitama-u.ac.jp>
W. Iwakiri, Y. Terada, M. Tashiro, K. Takahara, T. Yasuda (Saitama U.),
T. Uehara, Y. Hanabata, T. Takahashi, Y. Fukazawa (Hiroshima U.),
N. Vasquez (Tokyo Tech.) K. Yamaoka (Aoyama Gakuin U.),
M. Ohno, M. Kokubun, T. Takahashi (ISAS/JAXA),
S. Sugita (Nagoya U.), Y. E. Nakagawa (Waseda U.),
N. Ohmori, M. Akiyama, M. Yamauchi (Univ. of Miyazaki),
Y. Urata, P. Tsai (NCU), K. Nakazawa, K. Makishima (Univ. of Tokyo),
on behalf of the Suzaku WAM team, report:
The long bright GRB 110428A localized by Fermi-LAT (Vasileiou et al.,
GCN 11982) was observed the Suzaku Wide-band All-sky Monitor (WAM) which
covers an energy range of 50 keV - 5 MeV at 09:18:30 UT (=T0).
The observed light curve shows double-peaked structure starting at
T0-2s, ending at T0+10 s with a duration (T90) of about 5 seconds. The
fluence in 100 - 1000 keV was 1.31 (-0.43, +2.03) x 10^-5 erg/cm^2.
The 1-s peak flux measured from T0+4 s was
9.91 (-0.34, +1.19) photons/cm^2/s in the same energy range.
Preliminary result shows that the time-averaged spectrum from
T0-2s to T0+10s is well fitted by a power-law with exponential cutoff
model :
dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak) with
alpha 1.11 (-0.22, +0.19), and Epeak 195.5 (-14.4, +15.9) keV
(chi2/d.o.f. = 15.8/20).
All the quoted errors are at statistical 90% confidence level.
GCN Circular 11989
Subject
GRB 110428A : X-ray afterglow confirmation
Date
2011-05-02T19:15:40Z (14 years ago)
From
Andrea Melandri at Liverpool John Moores U <axm@astro.livjm.ac.uk>
A. Melandri, P. D'Avanzo, R. Margutti (INAF-OAB), B. Sbarufatti (INAF-
OAB/IASFPA) report on behalf of the Swift Team:
Swift continued to monitor the field of GRB 110428A (Vasileiou et
al., GCN 11982) in two different observations carried out on April
29th and May 1st, 2011.
In the final 18.49 ks of data (at a mean T-T0 = 2.07 days after the
burst event) we still detect Source #1 reported by Melandri et al.
(GCN 11984) with count rate of (1.6e-2 +/- 1.1e-3) cts/s, consistent
with a constant flux for this source.
Source #2 is no longer detected with a 3 sigma upper limit of 1.4e-3
cts/s. The probability for this source of having a constant flux is
8e-6. This is evidence of the fading of Source #2 with respect to the
XRT observation reported in Melandri et al. (GCN 11984). Therefore we
consider Source #2 as the X-ray afterglow of GRB 110428A.
This circular is an official product of the Swift-XRT team.
GCN Circular 12012
Subject
GRB 110428A: Fermi-GBM observation
Date
2011-05-06T18:25:50Z (14 years ago)
From
David Tierney at UCD <david.tierney@ucd.ie>
D. Tierney (UCD) and G. Fitzpatrick (UCD)
report on behalf of the Fermi GBM Team:
"At 09:18:30.41 UT on 28 April 2011, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 110428A (trigger 325675112 / 110428388)
which was also detected by the Fermi-LAT
(V. Vasileiou et al. 2011, GCN 11982),
Konus-Wind (S. Golenetskii et al. 2011, GCN 11983),
and Suzaku WAM (W. Iwakiri et al. 2011, GCN 11988).
The GBM on-ground location is consistent with the Swift-XRT position
(A. Melandri et al. 2011, GCN 11984).
The GBM light curve consists of a single pulse
with a duration (T90) of 5.6 +/- 0.2 s (50-300 keV).
The time-averaged spectrum from T0+1.8 s to T0+9 s is
best fit by a Band function with Epeak = 175.60 (+3.95/-3.82) keV,
alpha = -0.20 (+0.03/-0.03), and beta = -2.88 (+0.10/-0.12)
(C-Stat 559.66 for 482 d.o.f.).
The event fluence (10-1000 keV) in this time interval is
(2.27 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+7 s in the 10-1000 keV band
is 26.8 +/- 0.4 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."
GCN Circular 12017
Subject
Radio observations of GRB 110428A with the EVLA
Date
2011-05-19T19:33:20Z (14 years ago)
From
Poonam Chandra at Royal Mil. College Canada <Poonam.Chandra@rmc.ca>
"Poonam Chandra (RMC), Dale A. Frail (NRAO), S. Bradley Cenko
(Berkeley), Fiona Harrison (Caltech) and Srinivas Kulkarni (Caltech)
report:
We observed the Fermi burst GRB 110428A (Vasileiou et al. GCN 11982)
with the Expanded
Very Large Array (EVLA) at various radio frequencies between April 30
and May 13. We did not detect any significant radio source within the
7.1" error circle of source 2 (Melandri et al. GCN 11984). Below are the
details and 3-sigma upper limits from our observations:
Epoch Frequency 3-sigma upper limit
Apr 30.45 UT 4.5 GHz 93
uJy
Apr 30.45 UT 7.9 GHz 66
uJy
May 3.50 UT 4.5 GHz 66
uJy
May 3.50 UT 7.9 GHz 54
uJy
May 6.74 UT 4.5 GHz 87
uJy
May 6.74 UT 7.9 GHz 60
uJy
May 10.48 UT 22.45 GHz 240
uJy
May 13.41 UT 8.33 GHz 35
uJy
We thank the EVLA staff for scheduling our observations so promptly. The
National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."