- GCN Circular #5684
K. Hurley and T. Cline, on behalf of the Ulysses and Konus GRB teams,
S. Golenetskii, E. Mazets, V. Pal'shin, and D. Frederiks on behalf of
the Konus-Wind team,
D. M. Smith, R. P. Lin, J. McTiernan, E. Bellm, R. Schwartz, C. Wigger, W.
Hajdas, and A. Zehnder, on behalf of the RHESSI GRB team,
A. von Kienlin, G. Lichti, and A. Rau, on behalf of the
INTEGRAL SPI-ACS GRB team,
K.Yamaoka, M.Ohno, Y.Fukazawa, T.Takahashi, M.Tashiro, Y. Terada,
T.Murakami, and K.Makishima on behalf of the Suzaku WAM team, and
S. Barthelmy, J. Cummings, D. Palmer, N. Gehrels, and H. Krimm, on behalf of
the Swift-BAT team,
Ulysses, Konus-Wind, RHESSI, INTEGRAL (SPI-ACS), Suzaku (WAM), and
Swift (BAT) observed this hard-spectrum GRB starting around 04621
seconds. It had a duration of about 215 s in two distinct episodes,
and a fluence of about 3 x 10^-4 erg/cm^2. We have triangulated it to
a preliminary ~855 sq. arcmin. error box (3 sigma), whose coordinates are:
Center: 127.639, -42.210
Corners: 127.490, -42.705
127.737, -43.008
127.555, -41.399
127.774, -41.726
This error box may be improved. It was outside the Swift BAT field of
view for both episodes, and therefore Swift did not image the burst,
although it did detect it. However, in the course of a later,
preplanned observation beginning at T+10 minutes, BAT imaged a weak source
within the IPN error box, at RA, Dec= 127.630, -42.696, which could be
the gamma-ray afterglow. A ToO observation of this source has been
requested. Further details of the energy spectrum will be given in a
forthcoming GCN.
- GCN Circular #5685
E. Bellm, M. Bandstra, S. Boggs, C. Wigger, W. Hajdas,
D. M. Smith, and K. Hurley on behalf of the RHESSI team report:
As observed by RHESSI, GRB060928 (Hurley et al., GCN 5684) displayed two
periods of emission. The first had a duration of ~14s starting at about
T0 = 01:17:05 UT. The preliminary fit to the time-integrated RHESSI
spectrum from T0 - T0+14s between 500 keV and 10 MeV is simple power law with
alpha = -2.21 +0.85/-1.74
(90% confidence levels).
The 500 keV-10 MeV fluence is 1.5 E-5 erg/cm^2.
The second outburst began at T1 = 01:20:05 UT and had a duration of ~25s.
A spectral fit to the time-integrated RHESSI spectrum
from T1 - T1+25s between 30 keV and 10 MeV gives a cutoff power law with
alpha = -1.36 +0.05/-0.04
E0 = 2090 +480/-370 keV
Epeak = 1340 +/- 220 keV
The 30 keV-10 MeV fluence is 2.43 +/- 0.91 E-4 erg/cm^2.
- GCN Circular #5686
K.L. Page (U. Leicester), J. Cummings (GSFC/UMBC), K. Hurley
(UCBerkeley/SSL), D.N. Burrows, D.C. Morris, J.A. Kennea, P. Brown (PSU)
and D.M. Palmer (LANL) report on behalf of the Swift team:
Swift-BAT serendipitously observed the location of the IPN localised burst
GRB 060928 (GCN Circ. 5684, Hurley et al.; GCN Circ. 5685, Bellm et al.),
which was out of the BAT field of view when the burst itself happened,
during a 28-minute observation beginning 11 minutes after the burst
trigger. Ground analysis of BAT data shows a weak source at RA, Dec
127.613, -42.739 (J2000) with a 90% confidence error circle of 2.5 arcmin
radius. BAT detects emission for many minutes in the 15-50 keV energy
range starting 11 minutes after the original burst and 8 minutes after the
larger second burst. This is unusual, and, in fact, such late high energy
emission has been seen by BAT only in one previous burst, the extremely
energetic very high redshift GRB 050904.
Swift-XRT performed a Target of Opportunity observation, starting
approximately 5.5 days after the burst. UVOT could not observe the
position because of a bright star in the field.
Using 7.2 ks of XRT Photon Counting mode data, we detect an uncatalogued
source within the IPN error box and close to the weak BAT detection at a
position of:
RA(J2000) = 08 30 29.90
Dec(J2000) = -42 44 58.5
with an estimated radial uncertainty of 6 arcsec (90% containment,
including boresight uncertainties). This is 49 arcsec from the
ground-calculated BAT position.
The mean count rate of the X-ray source is (4.9 +/- 1.5)e-3 count s^-1
which, assuming a photon index of 2.1 and a Galactic absorbing column of
1.1e22 cm^-2, corresponds to an observed (unabsorbed) flux of 3.5e-13
(8.0e-13) erg cm^-2 s^-1.
At the present time it is not possible to determine whether the source is
fading. Further observations are needed to verify whether or not this
source is, indeed, the afterglow of GRB 060928.
This circular is an official product of the Swift team.
- GCN Circular #5688
M. Ohno, T. Takahashi, T. Asano, T. Uehara, Y. Fukazawa (Hiroshima U.),
M. Suzuki, Y. Terada, T. Tamagawa (RIKEN),
K. Yamaoka, S. Sugita (Aoyama Gakuin U.),
M. Tashiro, K. Abe, K. Onda, Y. Sato, M. Suzuki, Y. Urata (Saitama U.),
T. Enoto, R. Miyawaki, K. Kokubun, K. Makishima (Univ. of Tokyo),
K. Nakazawa, T. Takahashi (ISAS/JAXA), S. Hong (Nihon U.),
on behalf of the Suzaku WAM team report:
The bright, long burst, GRB 060928 (Hurley et al., GCN 5684),
triggered the Suzaku Wideband All-sky Monitor (WAM), which covers
the energy range of 50 keV - 5 MeV, at 01:17:01.74 (UT).
Two distinct strong bursts were seen in the light curve observed
with the WAM. The duration of the first and second burst was
about 14 seconds and 70 seconds, respectively. These two bursts
were separated by about 200 seconds.
Here we report the analysis result only for the first burst.
The fluence in 100 - 1000 keV was 2.18(-0.11, +0.11)x10-5 erg/cm2,
while the 1-s peak flux was 9.75(-0.47, +0.51) photons/cm2/s in the
same energy range.
Preliminary result shows that the time-averaged spectrum is
well described by a power law with an exponential
cutoff as follows.
dN/dE ~ E^{-alpha} * exp(-(2-alpha)*E/Epeak)
alpha 1.18 (-0.18, +0.17), and
Epeak 580 (-70, +112) keV.
All the quoted errors are at statistical 90% confidence level,
while systematic errors are not included.
- GCN Circular #5689
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, and
T. Cline on behalf of the Konus-Wind team report:
The long bright GRB 060928 (Hurley et al., GCN 5684)
triggered Konus-Wind at T0=4622.782 s UT (01:17:02.782).
As observed by Konus-Wind the burst shows
two main episodes of emission.
The first started at ~T0 and had a duration of ~15 s.
The second more intense episode started at T-T0 ~150 s
and had a duration of ~75 s.
Both episodes demonstrate strong spectral evolution.
The time-integrated spectrum of the first episode
(from T0 to T0+18.176 s)
can be fitted (in the 20 keV - 2 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ E^alpha * exp(-(2+alpha)*E/Ep)
with alpha = -1.00(+0.07, -0.06),
and Ep = 381(-34, +41) keV (chi2 = 76/59 dof).
The fluence of this part is 2.83(-0.25, +0.12)x10^-5 erg/cm2
(in the 20 keV - 2 MeV range).
The time-integrated spectrum of the second episode
(from T0+149.248 s to T0+221.184 s)
can be fitted (in the 20 keV - 8 MeV range)
by GRBM (Band) model for which:
the low-energy photon index is alpha = -1.28 +/- 0.02,
the high energy photon index beta = -2.27(-0.21, +0.14),
the peak energy Ep = 705(-68, +74) keV (chi2 = 99/81 dof).
The fluence of this part is 3.54(-0.14, +0.19)x10^-4 erg/cm2
(in the 20 keV - 8 MeV range).
The total burst fluence is 3.82(-0.14, +0.19)x10^-4 erg/cm2,
and the 256-ms peak flux measured from T0+198.912 s
2.93(-1.78, +1.38)x10^-5 erg/cm2/s
(both in the 20 keV - 8 MeV energy range).
We also analyzed several time-resolved spectra of this GRB.
The spectra can be fitted either by
by power law with exponential cutoff model
or GRBM (Band) model.
The preliminary results of this analysis
are summarized in the table below.
The chosen time intervals are shown on the K-W light curve
of this GRB available at
http://www.ioffe.rssi.ru/LEA/GRBs/GRB060928_T04622/
------------------------------------------------------------------------
Int Tstart dT alpha Epeak beta chi2/dof
s s keV
------------------------------------------------------------------------
A 0 1.792 -0.36 +/- 0.09 459(-30,+33) -- 82/57
B 1.792 8.192 -0.85(-0.14,+0.15) 150(-12,+14) -- 82/59
C 9.984 8.192 -1.06(-0.16,+0.19) 517(-123,+215) -- 73/75
D 149.248 24.576 -1.19(-0.12,+0.14) 443(-99,+176) -- 80/59
E 173.824 39.168 -1.25 +/- 0.02 757(-65,+71) -2.22(-0.15,+0.10) 103/79
F 212.992 8.192 -1.35(-0.42,+0.49) 91(-20,+39) -- 54/59
G* 185.088 2.816 -1.04+/-0.03 1260(-168,+160) -2.83(-1.18,+0.35) 103/85
---------------------------------------------------------------------------
* - this interval (G) has the hardest spectrum
All the quoted errors are at the 90% confidence level.
- GCN Circular #5690
A. Pelangeon & J-L. Atteia (LATT-OMP) report:
We have used the spectral parameters of GRB 060928
provided by Ohno et al. (GCNC 5688) and
Golenetskii et al. (GCNC 5689) to compute
the spectral pseudo-redshift** of this burst
localized by IPN (Hurley et al., GCNC 5684).
- With the parameters of Suzaku/WAM we find
a pseudo-redshift pz= 2.30 +/- 0.70
- With the parameters of Konus-Wind we find
a pseudo-redshift pz= 2.20 +/- 0.45
** cf. http://www.ast.obs-mip.fr/grb/pz
- GCN Circular #5692
The pseudo-redshifts of GRB 060928 given in GCN Circular 5690
have been erroneously computed with the spectral parameters
of the 1st peak of this GRB.
A computation based on a 15 sec long intervalle near the
maximum of the burst gives a smaller pseudo-redshift
pz = 1.3 +/- 0.2
We apologize for this mistake.
- GCN Circular #5721
K.L. Page (U. Leicester) and N. Gehrels (NASA/GSFC) report on behalf of
the Swift-XRT team:
Swift-XRT performed a second observation of the IPN-discovered burst GRB
060928 on 2006-10-07 starting at 01:17 (9 days after the trigger).
In a 10 ks observation, we no longer detect the source reported in GCN
Circ. 5686 (Page et al.) Thus, we confirm that this source [previously
reported to have a position of RA,Dec 08 30 29.90, -42 44 58.5 (J2000),
estimated uncertainty 6 arcsec radius] has faded from view.
During this second observation, the 3-sigma upper limit on the count rate
is about 3e-3 count s^-1, corresponding to an observed (unabsorbed) flux
of 2.1e-13 (4.9e-13) erg cm^-2 s^-1. Since the source has faded over time,
it is, indeed, believed to be the X-ray afterglow of GRB 060928.
This circular is an official product of the Swift-XRT team.
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