GRB 130821A
GCN Circular 15127
Subject
IPN triangulation of GRB130821A
Date
2013-08-28T17:00:07Z (12 years ago)
From
Kevin Hurley at UCBerkeley/SSL <khurley@ssl.berkeley.edu>
K. Hurley on behalf of the Mars Odyssey GRB team,
S. Golenetskii, R. Aptekar, E. Mazets, V. Pal'shin, D. Frederiks,
D. Svinkin, and T. Cline on behalf of the Konus-Wind team,
I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin,
on behalf of the HEND-Odyssey GRB team,
W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr, on
behalf of the GRS-Odyssey GRB team,
D. M. Smith, J. McTiernan, R. Schwartz, and W.
Hajdas, on behalf of the RHESSI GRB team,
A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C.
Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
and
V. Connaughton, M. S. Briggs, C. Meegan, and V. Pelassa, on behalf of the Fermi
GBM team, report:
GRB 130821A, observed by the Fermi GBM (GCN 15113) and LAT (GCN 15115),
was also observed by Konus-Wind (GCN 15125), RHESSI, INTEGRAL SPI-ACS,
and Mars Odyssey-HEND. We have triangulated it to an annulus centered
at RA(2000)=297.840 deg (19h 51m 22s) Dec(2000)=-21.890 deg (-21d 53'
24"), whose radius is 18.673 +/- 0.049 deg (3 sigma). The minimum
distance between the center of the LAT one sigma error circle (GCN
15115) and the IPN annulus center line is 0.266 degrees; the circle lies
entirely outside the annulus. The two Swift XRT sources reported by
Page et al. (GCN 15123) also lie outside the IPN annulus, and are
therefore unlikely to be associated with the GRB. A map has been posted at
ssl.berkeley.edu/ipn3/130821.
Only minor improvement in the IPN localization is possible.
GCN Circular 15125
Subject
Konus-Wind observation of GRB 130821A
Date
2013-08-26T16:46:37Z (12 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:
The long-duration intense GRB 130821A
(Fermi-GBM detection: Jenke, GCN 15113;
Fermi-LAT detection: Kocevski, et al., GCN 15115)
triggered Konus-Wind at T0=58258.022 s UT (16:10:58.022).
The light curve shows multiple pulses from ~T0-40 to ~T0+80 s.
The emission is seen up to ~9 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB130821_T58258/
As observed by Konus-Wind, the burst
had a fluence of (9.9 � 0.9)x10-5 erg/cm2,
and a 64-ms peak flux, measured from T0+6.784 s,
of (1.3 � 0.1)x10-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum (measured from T0 to T0+78.080 s)
is best fit in the 20 keV - 18 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.33 � 0.11,
the high energy photon index beta = -2.25 � 0.19,
the peak energy Ep = 260 � 47 keV,
chi2 = 84.6/97 dof.
The spectrum at the maximum count rate
(measured from T0 to T0+12.544 s)
is best fit in the 20 keV - 18 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.11 � 0.07,
the high energy photon index beta = -2.33 � 0.10,
the peak energy Ep = 255 � 22 keV,
chi2 = 96.9/97 dof.
All the quoted results are preliminary.
GCN Circular 15124
Subject
GRB 130821A: Weihai optical upper limit
Date
2013-08-24T15:56:19Z (12 years ago)
From
Dong Xu at DARK/NBI <dong.dark@gmail.com>
D. Xu (DARK/NBI), D.-Y. Ren, C. Cao, S.-M. Hu (SDU) report:
We observed the XRT field of GRB 130821A (Jenke et al., GCN 15113;
Kocevski et al., GCN 15115; Page et al., GCN 15123) centered at
RA(J2000) = 20h 56m 38.44s and Dec(J2000) = -12d 02' 36.53", using
the 1m telescope located in Weihai, Shandong, China. We obtained
9x300s SDSS r'-band frames under cloudy conditions at a mean time of
14:20 UT on 2013-08-24 (i.e., 2.997 days after the burst).
No optical source is detected within the XRT error circle in the
stacked image, down to r'>20.8 mag, calibrated with nearby SDSS field.
GCN Circular 15123
Subject
GRB 130821A: Swift-XRT observation
Date
2013-08-24T09:04:45Z (12 years ago)
From
Kim Page at U.of Leicester <klp5@leicester.ac.uk>
K.L. Page, P.A. Evans (U. Leicester), V. D'Elia (ASDC), J. Gelbord (Eureka
Scientific) and J.L. Racusin (NASA/GSFC) report on behalf of the Swift-XRT
team:
Swift perfomed a Target of Opportunity observation of the Fermi GBM and
LAT-detected GRB 130821A (GCN Circ. 15113, 15115), between 100.7 and 136.5
ks after the trigger. Within the LAT error circle (0.1 degrees at 1-sigma;
statistical error only), in 9.9 ks of data there is a weak source with a
count rate of (1.3 +0.4/-0.3) x 10^-3 count s^-1 with a position of RA,
Dec 314.1601, -12.043481, which is equivalent to
RA(J2000) = 20h 56m 38.44s
Dec(J2000) = -12d 02' 36.53"
(5.5 arcsec uncertainty, 90% containment). We cannot determine whether the
source is fading.
We note, however, that in a ~10 ks observation faint background sources
are expected, and there are two other detections (one uncatalogued, one a
possible quasar) of a similar count rate outside the LAT 1-sigma error
circle. The logN-logS work by Mateos et al. (2008, A&A, 492, 51) indicate
we would expect to find around one source of this brightness within the
~0.03 deg^2 of the LAT error circle, while Elvis et al. (2009, ApJS, 184,
158) provide a slightly higher sky density, suggesting up to 3 sources
might be expected. It is therefore likely that the source detected in this
XRT observation is a serendipitous background object.
Excluding this possible, weak source, the 3-sigma upper limit on the XRT
count rate within the LAT error circle is 1.8 x 10^-3 count s^-1
(equivalent to an observed flux of 7.3 x 10^-14 erg cm^-2 s^-1 over 0.3-10
keV, assuming a typical counts to flux conversion factor of 4 x 10^-11 erg
cm^-2 count^-1).
We also note that, within the XRT field of view, although outside the LAT
1-sigma error circle, there is an X-ray source with a UVOT-enhanced
position of RA, Dec 313.92706, -11.96634, which is equivalent to
RA(J2000) = 20h 55m 42.49s
Dec(J2000) = -11d 57' 58.8"
(2.3 arcsec uncertainty, 90% containment). This position is 4 arcsec away
from the catalogued XMM Slew Survey object XMMSL1 J205542.2-115756. The
1-sigma uncertainty on the positions in the slew catalogue is 8 arcsec;
thus, this X-ray source is consistent with being XMMSL1 J205542.2-115756
and is unrelated to GRB 130821A.
This circular is an official product of the Swift-XRT team.
GCN Circular 15115
Subject
GRB 130821A: Fermi-LAT detection of a burst
Date
2013-08-22T18:34:02Z (12 years ago)
From
Daniel Kocevski at SLAC <dankocevski@gmail.com>
D. Kocevski (NASA/GSFC), N. Omodei (Stanford), J. Racusin (NASA/GSFC), S. Zhu (U. of Maryland), S. Guiriec (NASA/GSFC), Eleonora Troja (NASA/GSGC/UMCP) report on behalf of the Fermi-LAT team:
At 16:10:28.011 UT on 21 Aug 2013, Fermi-LAT detected high energy emission from GRB 130821A, which was also detected by Fermi-GBM (trigger 398794231/130821674 -- GCN 15113). The GBM detection triggered an autonomous repoint of the spacecraft.
The best LAT on-ground location is found to be RA=314.1, DEC=-12.0 (J2000) with an error radius of 0.1 deg (68% containment, statistical error only).
The burst was about 37 deg from the LAT boresight at the time of the trigger and the spacecraft slew brought the source within the LAT field of view for the next 2400 seconds. The data from the Fermi-LAT show long lasting emission with >40 photons above 100 MeV observed out to 2000s seconds with a TS of >170. Multi-peaked emission lasting roughly 40 seconds can be seen using the non-standard LAT Low Energy (LLE) with a significance of ~13 sigma. The highest energy LAT photon has an energy of ~6 GeV arriving 219 seconds after the trigger.
A Swift TOO request has been submitted.
The Fermi LAT point of contact for this burst is Daniel Kocevski (daniel.kocevski@nasa.gov).
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 15113
Subject
GRB 130821A: Fermi GBM Detection
Date
2013-08-22T16:51:18Z (12 years ago)
From
Peter Jenke at MSFC <peter.a.jenke@nasa.gov>
P. Jenke (UAH) reports on behalf of the Fermi GBM Team:
"At 16:10:28.011 UT on August 21 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 130821A (trigger 398794231/130821674),
which resulted in an Autonomous Repoint Request (ARR) that was accepted and
the LAT slewed to the GBM position.
The GBM on-ground location, using the Fermi GBM trigger
data, is RA = 308.2, Dec = -15.5 (J2000 degrees, equivalent to
J2000 20h 32m, -15d 30'), with a statistical uncertainty of 1 degree
(radius, 1-sigma containment, statistical only; there is additionally
a systematic error which is currently estimated to be 2 to 3 degrees).
The angle of the burst direction to the Fermi LAT boresight is 37 degrees.
The GBM light curve consists of multiple peaks
with a duration (T90) of about 84 s (50-300 keV).
The time-averaged spectrum from T0-3 s to T0+49 s is
well fit by a Band function with Epeak of 165 +/- 5 keV,
Alpha = -0.54 +/- 0.03 and Beta = -2.01 +/- 0.02.
The event fluence (10-1000 keV) in this time interval is
(6.60 +/- 0.08)E-05 erg/cm^2. The 1.0-sec peak photon flux measured
starting from T0+32 s in the 10-1000 keV band
is 27.6 +/- 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 OPS NOTE(25aug13); Per operator's request, the "A" suffix
was added to the GRB name.]