- GCN/BACODINE POSITION NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Sat 20 Aug 05 06:35:15 UT
NOTICE_TYPE: Swift-BAT GRB Position
TRIGGER_NUM: 151207, Seg_Num: 0
GRB_RA: 337.400d {+22h 29m 36s} (J2000),
337.467d {+22h 29m 52s} (current),
336.797d {+22h 27m 11s} (1950)
GRB_DEC: +19.578d {+19d 34' 42"} (J2000),
+19.607d {+19d 36' 26"} (current),
+19.322d {+19d 19' 18"} (1950)
GRB_ERROR: 4.00 [arcmin radius, statistical only]
GRB_INTEN: 5590 [cnts] Image_Peak=234 [image_cnts]
TRIGGER_DUR: 1.024 [sec]
TRIGGER_INDEX: 146 E_range: 25-100 keV
BKG_INTEN: 34936 [cnts]
BKG_TIME: 23680.00 SOD {06:34:40.00} UT
BKG_DUR: 8 [sec]
GRB_DATE: 13602 TJD; 232 DOY; 05/08/20
GRB_TIME: 23693.11 SOD {06:34:53.11} UT
GRB_PHI: 128.38 [deg]
GRB_THETA: 20.44 [deg]
SOLN_STATUS: 0x3
RATE_SIGNIF: 15.62 [sigma]
IMAGE_SIGNIF: 8.38 [sigma]
MERIT_PARAMS: +1 +0 +0 +0 +2 +4 +0 +0 +84 +1
SUN_POSTN: 149.55d {+09h 58m 12s} +12.39d {+12d 23' 30"}
SUN_DIST: 147.06 [deg]
MOON_POSTN: 337.76d {+22h 31m 03s} -12.84d {-12d 50' 27"}
MOON_DIST: 32.45 [deg]
MOON_ILLUM: 100 [%]
GAL_COORDS: 82.79,-32.02 [deg] galactic lon,lat of the burst (or transient)
ECL_COORDS: 347.12, 26.84 [deg] ecliptic lon,lat of the burst (or transient)
COMMENTS: SWIFT-BAT GRB Coordinates.
COMMENTS: This is a rate trigger.
COMMENTS: A point_source was found.
COMMENTS: This does not match any source in the on-board catalog.
COMMENTS: This does not match any source in the ground catalog.
COMMENTS: This is a GRB.
- red DSS finding chart
ps-file
- GCN/SWIFT NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Sat 20 Aug 05 06:36:58 UT
NOTICE_TYPE: Swift-XRT Position
TRIGGER_NUM: 151207, Seg_Num: 0
GRB_RA: 337.4075d {+22h 29m 37.8s} (J2000),
337.4754d {+22h 29m 54.0s} (current),
336.8052d {+22h 27m 13.2s} (1950)
GRB_DEC: +19.5591d {+19d 33' 32.7"} (J2000),
+19.5881d {+19d 35' 17.0"} (current),
+19.3026d {+19d 18' 09.4"} (1950)
GRB_ERROR: 5.8 [arcsec radius, statistical plus systematic, 90% containment]
GRB_INTEN: 652.09 [arb]
GRB_SIGNIF: 7.28 [sigma]
GRB_DATE: 13602 TJD; 232 DOY; 05/08/20
GRB_TIME: 23773.10 SOD {06:36:13.10} UT [Start of CCD integration]
TAM[0-3]: 327.63 237.19 261.26 242.88
AMPLIFIER: 2
WAVEFORM: 134
SUN_POSTN: 149.55d {+09h 58m 12s} +12.39d {+12d 23' 29"}
SUN_DIST: 147.08 [deg]
MOON_POSTN: 337.77d {+22h 31m 06s} -12.84d {-12d 50' 05"}
MOON_DIST: 32.42 [deg]
MOON_ILLUM: 100 [%]
GAL_COORDS: 82.78,-32.04 [deg] galactic lon,lat of the burst
ECL_COORDS: 347.12, 26.82 [deg] ecliptic lon,lat of the burst
COMMENTS: SWIFT-XRT Coordinates.
COMMENTS: WARNING: XRT alignment calibration is on-going, and there may be
COMMENTS: residual systematic offsets of several arcseconds not accounted for yet
COMMENTS: by our on-board position determination algorithm. We have increased
COMMENTS: the estimated error circle radius to take this into account.
- GCN/SWIFT NOTICE
TITLE: GCN/SWIFT NOTICE
NOTICE_DATE: Sat 20 Aug 05 06:39:51 UT
NOTICE_TYPE: Swift-BAT GRB Lightcurve
TRIGGER_NUM: 151207, Seg_Num: 0
GRB_RA: 337.400d {+22h 29m 36s} (J2000),
337.467d {+22h 29m 52s} (current),
336.797d {+22h 27m 11s} (1950)
GRB_DEC: +19.578d {+19d 34' 42"} (J2000),
+19.607d {+19d 36' 26"} (current),
+19.322d {+19d 19' 18"} (1950)
GRB_DATE: 13602 TJD; 232 DOY; 05/08/20
GRB_TIME: 23693.11 SOD {06:34:53.11} UT
TRIGGER_INDEX: 146
GRB_PHI: 128.38 [deg]
GRB_THETA: 20.44 [deg]
DELTA_TIME: 0.00 [sec]
TRIGGER_DUR: 1.024 [sec]
LC_URL: sw00151207000msb.lc
SUN_POSTN: 149.55d {+09h 58m 12s} +12.39d {+12d 23' 30"}
SUN_DIST: 147.06 [deg]
MOON_POSTN: 337.76d {+22h 31m 03s} -12.84d {-12d 50' 27"}
MOON_DIST: 32.45 [deg]
MOON_ILLUM: 100 [%]
GAL_COORDS: 82.79,-32.02 [deg] galactic lon,lat of the pointing direction
ECL_COORDS: 347.12, 26.84 [deg] ecliptic lon,lat of the pointing direction
COMMENTS: SWIFT-BAT GRB Lightcurve.
COMMENTS:
COMMENTS: The next comments were copied from the BAT_POS Notice:
COMMENTS: This is a rate trigger.
COMMENTS: A point_source was found.
COMMENTS: This does not match any source in the on-board catalog.
COMMENTS: This does not match any source in the ground catalog.
COMMENTS: This is a GRB.
- GCN notice #3829
Derek B. Fox (Penn State) and S. Bradley Cenko (Caltech) report on
behalf of a larger collaboration:
"We have observed the BAT/XRT localization region of GRB050820 (Swift
Trigger #151207) with the robotic Palomar 60-inch telescope (P60), in
a series of automated exposures beginning at 06:37 UT, approximately 3
minutes after the burst.
We identify a bright, new, variable point source within the XRT (and
BAT) localization region at coordinates:
R.A. 22:29:38.11, Dec +19:33:37.1 (J2000)
with coordinate uncertainty <0.5 arcsec relative to USNO-B1.0 catalog
astrometry. Photometry of the source relative to the USNO-B1.0
catalog indicates that in the R-band it brightens to a peak magnitude
of R~14.7 mag at 7 minutes after the burst and has decayed by 0.4 mag
at 12 minutes after the burst.
We therefore identify the source as the optical afterglow of
GRB050820."
- GCN notice #3830
M. Page (UCL-MSSL), D. Burrows (PSU), A. Beardmore (U. Leicester), D.
Palmer (LANL),
J, Kennea (PSU), N. Gehrels (GSFC), C. Markwardt (GSFC/UMD), K. Page (U.
Leicester),
T. Sakamoto (GSFC/NRC), M. Chester (PSU), P. Boyd (GSFC) report on behalf
of the Swift team:
At 06:34:53 BAT triggered, located, and immediately slewed to GRB
050820 (trigger=151207). The BAT on-board calculated position is
RA,Dec 337.400d, +19.578d {22h 29m 36s, 19d 34' 42"} (J2000) with an
uncertainty of 2 arcmin (radius, 90% containment, stat+sys). The BAT
light curve shows a broad double-humped structure about 20 seconds
long, with peaks around T+1s and T+14 s, with a peak count rate
of ~1500 counts per second (15-350 keV) at ~1 second after the trigger.
XRT began observing at 06:36:13 UT, 80s after the BAT trigger. A bright
uncatalogued source was found in the field, which XRT was able to centroid
on. The on-board calculated coordinates of this source are:
RA(J2000): 22:29:37.8, Dec(J2000): 19:33:32.7, with an uncertainty of 7
arcseconds radius (90% containment). This position lies 73 arcseconds from
the center of the BAT error circle, and 6.2 arcseconds from the P60
position (GCN 3829).
The UVOT began observations at 06:36:13 UT, 80s after the BAT trigger.
There is no new source detected in the preliminary UVOT data in the XRT
error circle.
- GCN notice #3833
J. X. Prochaska (UCO/Lick), J. S. Bloom, J. T. Wright (UC Berkeley),
R. Paul Butler (DTM, Carnegie), H. W. Chen (MIT), S.S. Vogt (UCO/Lick),
and G.W. Marcy (UC Berkeley) report:
"Starting at 07h28m59s 20 Aug 2005 UTC, we began spectroscopic
observations
of the optical transient (Fox & Cenko GCN #3829) of GRB 050820
(Page et al. GCN #3830) with HIRES/Keck I. In a series of 900 sec
exposures
the continuum from the afterglow is well detected as are many absorption
lines. Based on the identification of a damped Ly alpha feature, SiII
1304, OI 1302, and numerous fine structure lines we measure the GRB
redshift to be
z=2.612 +/- 0.002."
We are grateful to Derek Fox for his assistance in helping us acquire
this data.
This message may be cited.
----------------------------------------------
Jason X. Prochaska
UCO/Lick Observatory
UC Santa Cruz
Santa Cruz, CA 95064
xavier@ucolick.org
http://www.ucolick.org/~xavier/
831-459-2135 (Direct)
831-459-2991 (UCO/Lick Main)
831-459-5244 (Fax)
- GCN notice #3834
S. Bradley Cenko (Caltech) and Derek B. Fox (Penn State) report on behalf
of a larger collaboration:
We have continued to image the afterglow (GCN 3829) of GRB 050820 (GCN
3830) with the automated Palomar 60-inch telescope. Using the USNO-B1
star located at RA=22:29:39.88, Dec=+19:32:47.5 (USNO-B1 1095-0581263, R =
15.21) as a reference, we find, after rising to a peak magnitude of R =
14.7 approximately 7 minutes after the burst, the afterglow has exhibited
a relatively smooth power-law decay with index alpha = -0.9. In an image
taken ~ 93 minutes after the burst, the afterglow has a magnitude of R ~
17.4.
Further observations are planned.
- GCN notice #3835
J. Cummings (GSFC/NRC), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cannizzo (GSFC-UMBC), L. Cominsky (Sonoma State U.),
D. Hullinger (GSFC/UMD), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS),
J. Tueller (GSFC)
on behalf of the Swift-BAT team:
Using the full data set from the recent telemetry downlink, we
report further analysis of Swift-BAT GRB 050820 (trigger #151207)
(Page, et al., GCN 3830). The ground-analysis position is
RA,Dec 337.418, +19.560 (J2000) with an uncertainty of 2 arcmin
(radius, 90%, stat+sys). This is 31 arcseconds from the optical
transient reported by Fox et al. in GCN Circ. 3829.
The light curve is multi-peaked and the spectrum clearly evolves
from hard to soft within each of the two main peaks. There is a
probable small precursor at ~ T-15 seconds, the largest peak at
T+0 seconds, and two other peaks at T+9 and T+13 seconds. T90 is
26 +- 2 seconds. Fitting a simple power law over the interval from
T-17 to T+22 seconds, the photon index is 1.7 +/- 0.1 with a fluence
of 1.9 +/- 0.2 x 10^-6 erg/cm^2 in the 15-350 keV band (90% c.l).
The peak flux in a 1-second wide window starting at T-0.25 seconds
is 1.3 +/- 0.2 ph/cm^2/sec (15-350 keV).
The isotropic-equivalent energy using the redshift of 2.612
(Prochaska, et al. GCN 3833) is 9.7 (-2.6/+3.5) x 10^51 ergs
in the 4.2-41.5 keV band in the GRB rest frame (15-150 keV band in
the observer's frame) using a simple power-law model.
- GCN notice #3836
J. Wren, W. T. Vestrand, P. Woznaik, S. Evans, R. White report
on behalf of the RAPTOR team at Los Alamos National Laboratory:
The RAPTOR system of robotic telescopes responded to GRB 050820
(Swift trigger 151207) beginning at 06:35:20.46 UT, 5.5 seconds
after the GCN notice was sent. We detect the object reported by
Fox and Cenko (GCN 3029). Our early images show the source
rising rapidly to a unfiltered peak magnitude of ~14.5. We confirm
the Fox and Cenko observation that the source reaches
a peak brightness approximately 8 minutes after the burst and
then begins a steady power law decline.
- GCN notice #3837
K.L. Page, A.P. Beardmore, M.R. Goad (U. Leicester), J.A. Kennea, D.N.
Burrows (PSU), F. Marshall (GSFC) and A. Smale (NASA HQ) report on behalf
of the Swift/XRT team:
We have analysed the first 6 orbits of XRT data for GRB050820, spanning 88
- 3e5 seconds after the burst. There is a bright, fading afterglow in the
field of view, with refined coordinates of
RA(J2000): 22:29:38.2
Dec(J2000): 19:33:31.1
with an uncertainty of 7 arcseconds radius (90% containment). This is 5.9
arcsec from the on-board XRT position given in GCN 3830 and 6.1 arcsec
from the optical afterglow reported in GCN 3829.
XRT observations began in Windowed Timing mode 88 seconds after the
trigger, followed by Photon Counting (PC) data from the start of the
second orbit (4660 seconds after the burst). The PC data show a smooth
decline with a decay slope of alpha = 1.13 +/- 0.04.
The PC spectrum can be well fitted by a power-law with Gamma = 1.94 +/-
0.07, and an excess absorbing column of ~6e21 cm^-2 in the rest-frame of
the GRB (taking the redshift of 2.612 from GCN 3833).
Assuming a smooth, unbroken decay, the predicted count-rate at 24 hours
(06.30 UT on 2005-08-21) is 0.085 count s^-1, corresponding to an
unabsorbed 0.3-10 keV flux of 3.4e-12 erg cm^-2 s^-1.
- GCN notice #3838
M. Chester (PSU), M. Page (UCL-MSSL), P. Roming (PSU),
F. Marshall (GSFC), P. Boyd (GSFC), L. Angelini (GSFC-JHU),
J. Greiner (MPE), N. Gehrels (GSFC), on behalf of the Swift UVOT team.
Swift/UVOT began observing GRB050820 at 06:36:13 UT.
The initial 100-second finding chart exposure in V was cut short
due to entry into the SAA; it was repeated on the second orbit.
The afterglow is detected in the V, B, U, and one UV band.
Similar to the ground-based observations (GCN #3829),
UVOT sees a rising, then falling, light curve in V.
Analysis in the other bands is continuing.
V-band Observations:
Time-Since-Trigger V
80 s 18.2 0.3
4635 s 17.6 0.2
12238 s 18.2 0.2
Other:
Time-Since-Trigger Mag Filter
5647 s 18.3 0.2 U
10423 s 19.0 0.1 B
4741 s 20.4 0.2 UVW1
11331 s >21.0 UVW2
The magnitudes have not been corrected for extinction.
Upper limits are given at the 5-sigma level.
- GCN notice #3843
Daryl Macomb, Jessica Elias (Boise State U.),
Jerry Bonnell, Alexander Kutyrev, Jay Norris (NASA/GSFC),
and Ron Canterna, Mike Pierce (U. Wyoming) report:
We observed the position reported by Fox and Cenko (GCN 3829)
of the afterglow for GRB 050820a (Swift trigger #151207, Page et al.,
GCN 3830) with the 2.3-meter WIRO telescope. Starting at 08:10 UT
(96 minutes after the GRB trigger) and continuing until 11:30 UT,
we detected the fading afterglow in the J band in each of 120 40-s
integrations. J magnitudes determined at the following times were
(relative to burst trigger):
Epoch T-Ttrig J mag
1 6240 s 16.0
2 9600 s 16.7
3 16020 s 16.9
Between epochs 1 and 2, the inferred average power-law decay index
is -1.5, steeper than the -0.9 index reported by Cenko and Fox
(GCN 3834) for the initial decay during the interval ~ 7 - 93 minutes
after the burst. Between epoches 2 and 3, the average decay index
flattens to -0.44, after which our observations ended due to twilight.
The times of the three reported epochs are arbitrary. Detailed
analysis to yield accurate break times and indices is in progress.
- GCN notice #3845
A. Henden (AAVSO/USNO) reports on behalf of the USNO GRB Team:
We have acquired BVRcIc all-sky photometry for a 23x23arcmin
field centered on the coordinates of the optical afterglow
(Fox and Cenko, GCN 3829) for the Swift burst GRB050820a
(Page et al., GCN 3830) with the USNOFS 1.0-m telescope
on one photometric night but with bright moonlight. Stars
brighter than V=12.0 are saturated and should be used with
care. We have placed the photometric data on our anonymous
ftp site:
ftp://ftp.nofs.navy.mil/pub/outgoing/aah/grb/grb050820.dat
The astrometry in this file is based on linear plate solutions
with respect to UCAC2. The external errors are about 100mas.
The estimated external photometric error is about 0.03mag.
As always, you should check the dates on the .dat file prior to
final publication to get the latest photometry. There is
a README file on the ftp directory to give you information
about the procedures used to calibrate these fields.
- GCN notice #3846
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks
and T. Cline on behalf of the Konus-Wind team,
and A. Rau, A. von Kienlin, G. Lichti on behalf of the INTEGRAL SPI-ACS
GRB team report:
A long soft GRB triggered Konus-Wind at T0=23954.512s UT (06:39:14.512).
It was also detected by INTEGRAL SPI-ACS. Because the burst was soft,
the SPI-ACS response was weak, and precise triangulation of this burst
is not possible. But the estimated time delay is consistent with the
position of GRB 050525a, detected by Swift-BAT ~260 sec before
Konus-Wind trigger (Page et al., GCN 3830; Cummings et al., GCN 3835).
The Konus-Wind GRB consists of two parts:
from ~T0-35s to ~T0+29s and ~T0+135s to ~T0+235s
and is much more intense than the Swift burst (precursor?),
which was weakly seen by Konus-Wind in background data.
The total burst duration is ~270 s.
The Konus-Wind light curve recorded in the background mode
is very similar to the light curve of the famous GRB 041219a
(Vestrand et al., Nature, 435, 178 (2005)):
weak precursor, main pulse at ~250 sec after it,
second pulse at ~150 s after main and then - weaker pulse(s).
The Konus-Wind light curve of this GRB can be seen
at
http://www.ioffe.rssi.ru/LEA/GRBs/GRB050825_T23954/
Based on these facts, we strongly suggest that this GRB is the main part
of the GRB 050525a.
In this case the optical trainsient reported by Fox and Cenko (GCN 3029)
and Wren et al. (GCN 3836) is in fact the prompt optical emission of
very long GRB 050525a (the total duration including Swift
precursor is ~500 sec).
We hope, that the further analysis of this event will clarify this issue.
- GCN notice #3847
P. B. Cameron (Caltech) and D. A. Frail (NRAO) report on behalf of a
larger collaboration:
"We have undertaken VLA observations at a frequency of 8.46 GHz toward
GRB 050820A (GCN 3830) on August 20.39 UT and 21.20 UT, about 2.9 hrs
and 22.3 hrs after the burst, respectively. On the first epoch no
significant radio emission was detected at the position of the optical
afterglow (GCN 3829), but on the second epoch a new radio source has
appeared with a flux density of 690+/- 41 microJy.
Further observations are planned.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."
- GCN notice #3848
T. Sakamoto (GSFC/NRC) on behalf of the Swift-BAT team:
The isotropic-equivalent energy of GRB050820A reported in GCN 3835
is not correctly represented. We want to correct the last paragraph
of GCN 3835 to the following.
"The isotropic-equivalent energy using the redshift of 2.612
(Prochaska, et al. GCN 3833) is (2.2 +- 0.13) x 10^52 ergs
in the 54-542 keV band in the GRB rest frame (15-150 keV band
in the observer's frame) using a simple power-law model."
We would like to thank Dr. Arnon Dar for reporting about this mistake.
- GCN notice #3852
V. Pal'shin and D.Frederiks on behalf of the Konus-Wind team:
There were several misprints in our GCN 3846.
The subject line should have read:
------------------------------------
"GRB 050820a - a long GRB like GRB041219a? (Konus-Wind observation)"
------------------------------------
The correct circular text should be:
------------------------------------
"S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks
and T. Cline on behalf of the Konus-Wind team,
and A. Rau, A. von Kienlin, G. Lichti on behalf of the INTEGRAL SPI-ACS
GRB team report:
A long soft GRB triggered Konus-Wind at T0=23954.512s UT (06:39:14.512)
on August 20. It was also detected by INTEGRAL SPI-ACS. Because the
burst was soft, the SPI-ACS response was weak, and precise triangulation
of this burst is not possible. But the estimated time delay is
consistent with the
position of GRB 050820a, detected by Swift-BAT ~260 sec before
Konus-Wind trigger (Page, et al., GCN 3830; Cummings, et al., GCN 3835).
The Konus-Wind GRB consists of two parts:
from ~T0-35s to ~T0+29s and from ~T0+135s to ~T0+235s
and is much more intense than the Swift burst (precursor?),
which was weakly seen by Konus-Wind in background data.
The total burst duration is ~270 s.
The Konus-Wind light curve recorded in the background mode
is very similar to the light curve of the famous GRB 041219a
(Vestrand et al., Nature, 435, 178 (2005)):
weak precursor, main pulse at ~250 sec after it,
second pulse at ~150 s after main and then - weaker pulse(s).
The Konus-Wind light curve of this GRB can be seen
at http://www.ioffe.rssi.ru/LEA/GRBs/GRB050820_T23954/
Based on these facts, we strongly suggest that this GRB is the main part
of the GRB 050820a.
In this case the optical transient reported by Fox and Cenko (GCN 3829)
and by Wren et al. (GCN 3836) is in fact the prompt optical emission of
very long GRB 050820a (the total burst duration including Swift
precursor is ~500 sec).
We hope, that the further analysis of this event will clarify this
issue."
We apologize for these misprints.
- GCN notice #3853
I. Bikmaev, A. Galeev, N. Sakhibullin (KSU/AST),
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI),
I. Khamitov, Z. Aslan (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.),
report:
We have observed the OT of GRB 050820A (GCN 3829) with the
Russian-Turkish 1.5-m telescope (Bakirlitepe, TUBITAK National
Observatory, Turkey) in two consequative nights .
We made a series of exposures in Rc between UT 18:35 - 22:15, August
20, 2005, and in BRcIc between UT 22:46-01:15, August 21/22, 2005.
Moonlight produced variable background in all images for both nights. The
afterglow is clearly detected in all bands. Using Henden's stars (GCN 3845)
present in the frames, we estimated the magnitudes as follow:
t-t0 Band mag merr exptime
(hours, midtime) (sec,total)
18.05 Rc 19.48 +/- 0.01 900
41.42 Rc 20.38 +/- 0.05 1800
40.93 B 21.00 +/- 0.06 1800
41.55 Ic 19.83 +/- 0.07 1800
On the basis of our Rc data, we estimeted an alpha index of power-law
decay for the observed period as ~ -1.0.
The JPG-images of BRcIc and color combined image are available at:
http://www.tug.tubitak.gov.tr/~irekk/grb/grb050820a/grb050820A_b.JPG
http://www.tug.tubitak.gov.tr/~irekk/grb/grb050820a/grb050820A_r.JPG
http://www.tug.tubitak.gov.tr/~irekk/grb/grb050820a/grb050820A_i.JPG
http://www.tug.tubitak.gov.tr/~irekk/grb/grb050820a/grb050820_bri.JPG
This message may be cited.
- GCN notice #3858
J. Cummings (GSFC/NRC), L. Barbier (GSFC), S. Barthelmy (GSFC),
D. Hullinger (GSFC/UMD), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS),
J. Tueller (GSFC)
on behalf of the Swift-BAT team:
A second, larger, harder episode of gamma rays from T+217 to T+270
sec was detected from GRB 050820A, as noted by Golenetskii et al.
in GCN circ. 3846, 3852. We confirm that this larger episode of
emission was from the same source as the first episode (from T-17
to T+22 sec), using BAT mask-weighting on a partial data set.
Swift was entering the SAA as the first episode of emission was
ending. We reported BAT refined analysis for the period covering
the first episode of emission in GCN circ. 3835, 3848. The BAT
entered SAA mode at T+241 sec. At this time data collection became
very limited. We use mask-weighted data prior to this time, and a
non-directional residual rate with a background model subtraction
after this time, for the following information on the second
episode:
There were two peaks at T+228 and T+259 sec. T90 was 50 +/- 5 sec
(for the second episode alone). In a simple power law fit, the
photon index for the first part of the second episode from T+217
to T+241 was 1.06 +/- 0.03. The 1-sec peak flux is estimated to
be 6 +/- 1 ph/cm^2/sec (15-350 keV) at T+259 sec. For reference,
the previously reported photon index for the first episode of
emission from T-17 to T+22 sec was 1.7 +/- 0.1 and the 1-sec peak
flux was 1.3 +/- 0.2 ph/cm^2/sec (15-350 keV).
We estimate the total fluence for the entire event including both
episodes to be 8.4 +/- 0.3 x 10^-6 erg/cm^2 in the 15-150 keV band.
The quoted uncertainty is statistical. Roughly 60% of the fluence
is in the period lacking mask-weighted data and having a very high
background rate, thus systematic errors may be large and we
estimate them to be +/- 0.6 x 10^-6 erg/cm^2. The fluence estimate
includes the assumption that the part of the second episode after
T+241 sec had the same spectrum as it did from T+217 to T+241 sec.
For the entire burst then, using the measured redshift of 2.612
(Prochaska, et al. GCN 3833), we calculate the isotropic-equivalent
energy in the 54-542 keV band in the GRB rest frame (15-150 keV
band in the observer's frame) as ~1.5 x 10^53 ergs.
Jay Cummings
- GCN notice #3860
C. Ledoux, P. Vreeswijk (ESO), S. Ellison (U. Victoria), A. Jaunsen
(ESO/U. Oslo), A. Smette (ESO), J. Fynbo (U. Copenhagen), P. Moller,
A. Kaufer (ESO), M. Andersen (AIP), R. Wijers (U. Amsterdam) &
J. Hjorth (U. Copenhagen) report:
We observed the afterglow (Fox & Cenko, GCN 3829) of GRB 050820 (Page
et al, GCN 3830) with UVES at VLT/UT2, starting at 7:08 UT (33 minutes
after the burst trigger). The spectra cover most of the optical
wavelength range (split into two observations of a total of 60min
using one dichroic beam splitter and 40min using the other), with an
approximate resolving power of 46,000 (6.5 km/s).
We obtain a redshift of z=2.6147 (and therefore confirm the redshift
reported by Prochaska et al., GCN 3833) from the detection of numerous
host-galaxy metal absorption lines (e.g., CII, CIV, NI, OI, AlII,
AlIII, SiII, SiIV, SII, ArI, CrII, FeII, NiII, ZnII) spread over a
velocity interval of ~400 km/s. Strong fine-structure lines of CII*
and SiII* are also detected. We measure a total neutral hydrogen
column density of log N(HI)=21.0 and metallicities of [Si/H]=-0.6 and
[Fe/H]=-1.1.
In addition, an intervening metal absorption line system with log
N(HI)=20.0 is observed at zabs=2.3597.
We acknowlegde the excellent support from the ESO staff, and in
particular the alertness of night astronomer Stefano Bagnulo.
- GCN notice #3863
C. MacLeod, M. Nysewander report on behalf of the UNC team of the FUN GRB
Collaboration:
We have observed the position of the GRB 050820a afterglow reported by Fox
et al. (GCN 3829). We detect the afterglow in RcIc:
Mean Time Integration Filter Magnitude Telescope
Since GRB Time
2.2 hr 39 x 40 sec Ic 17.40 +/- .08 PROMPT-3
2.2 hr 22 x 30 sec Rc 17.64 +/- .09 PROMPT-5
21.5 hr 136 x 40 sec Ic 18.42 +/- .11 PROMPT-3
21.7 hr 179 x 30 sec Rc 20.06 +/- .31 PROMPT-5
Rc and Ic calibrations were made relative to 7 calibration stars posted by
Henden (GCN 3845).
PROMPT is still being built and commissioned.
- GCN notice #3864
I. Khamitov, Z. Aslan (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.),
I. Bikmaev, A. Galeev, N. Sakhibullin (KSU/AST),
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI),
report:
We have continued observing the OT of GRB 050820A (GCN 3829) with
the Russian-Turkish 1.5-m telescope (Bakirlitepe, TUBITAK National
Observatory, Turkey) on the nights of August 22 and 23 in B,Rc,Ic bands.
We made a series of exposures between UT 20:23 - 01:33, August 22/23,
and between UT 20:09-00:34, August 23/24, 2005. The afterglow is still
clearly detected in all bands. Using Henden's stars (GCN 3845) present
in the frames, we estimated the magnitudes as follow:
t-t0 Band mag merr exptime
(hours) (sec,total)
64.39 B 22.24 -/+ 0.06 7860
64.43 Rc 21.02 -/+ 0.03 3900
64.53 Ic 20.46 -/+ 0.05 3900
87.57 B 22.57 +/- 0.08 5400
87.72 Rc 21.30 +/- 0.04 2700
87.82 Ic 20.87 +/- 0.09 2700
We note that, on re-examining the co-added image for 21 Aug in B-band
(GCN 3853), we noticed that it included a cosmic ray event close to OT.
More careful calculation has resulted in a fainter value of B magnitude:
21.47 +/- 0.06 (40.93h after the trigger).
This message may be cited.
- GCN notice #3896
Z. Aslan, I. Khamitov (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.),
I. Bikmaev, A. Galeev, N. Sakhibullin (KSU/AST),
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI),
report:
We have continued observing the OT of GRB 050820A (GCN 3829) with
the Russian-Turkish 1.5-m telescope (Bakirlitepe, TUBITAK National
Observatory, Turkey) using TFOSC in R band.
We made 5*300s exposures between UT 22:40 - 23:05, August 27. Using
Henden's stars (GCN 3845) present in the frames, we estimated the
magnitude of the co-added image as R=22.14+/-0.1 (184.25h after the
trigger).
The OT is fading with the same power-law decay. Using all the data
obtained at the RTT150 (GCN3864, GCN3853) we estimated an alpha index of
power-law decay of -1.06+/-0.03.
The JPG-image is available at:
http://www.tug.tubitak.gov.tr/~irekk/grb/grb050820a/grb050820A_050827r.JPG
This message may be cited.
- GCN notice #4045
F. Mannucci, S. Covino, D. Malesani, on behalf of the CIBO collaboration
report:
We observed the field of GRB 050820A (Page et al., GCN 3830) in the NIR
at the TNG equipped with NICS on the 21st of August at 05:00 UT, about
22.4 hours after the high-energy event. The OT identified by Fox et al.
(GCN 3829) is clearly visible with J magnitude:
J = 18.48 +/- 0.08
Calibration has been derived by comparison with a suitable number of
2MASS stars in the field.
This message can be cited.
- astro-ph/0608183 from 8 Aug 2006
Cenko: Multi-Wavelength Observations of GRB 050820A: An Exceptionally Energetic Event Followed from Start to Finish
We present observations of the unusually bright and long gamma-ray burst GRB
050820A, one of the best-sampled broadband data sets in the Swift era. The
gamma-ray light curve is marked by a soft precursor pulse some 200 s before the
main event; the lack of any intervening emission suggests that it is due to a
physical mechanism distinct from the GRB itself. The large time lag between the
precursor and the main emission enabled simultaneous observations in the
gamma-ray, X-ray, and optical band-passes, something only achieved for a
handful of events to date. While the contemporaneous X-rays are the low-energy
tail of the prompt emission, the optical does not directly track the gamma-ray
flux. Instead, the early-time optical data appear mostly consistent with the
forward shock synchrotron peak passing through the optical, and are therefore
likely the beginning of the afterglow. On hour time scales after the burst, the
X-ray and optical light curves are inconsistent with an adiabatic expansion of
the shock into the surrounding region, but rather indicate that there is a
period of energy injection. Observations at late times allow us to constrain
the collimation angle of the relativistic outflow to theta = 6.8 - 9.3 degrees.
Our estimates of both the kinetic energy of the afterglow and the prompt
gamma-ray energy release make GRB 050820A one of the most energetic events for
which such values could be determined.
- 0707.0952 from 6 Jul 2007
Genet: The rise of the afterglow in GRB 050820a
Abstract: The early optical afterglow of GRB 050820a recorded by the RAPTOR telescope
shows both a contribution from the prompt emission and the initial rise of the
afterglow. It is therefore well-suited for the study of the dynamical evolution
of the GRB ejecta when it first undergoes the decelerating effect of the
environment. This is a complex phase where the internal, reverse, and forward
shocks can all be present simultaneously. We have developed a simplified model
that can follow these different shocks in an approximate, but self-consistent
way. It is applied to the case of GRB 050820a to obtain the prompt and
afterglow light curves. We show that the rise of the afterglow during the
course of the prompt emission has some important consequences. The reverse
shock propagates back into the ejecta before internal shocks are completed,
which affects the shape of the gamma-ray profile. We get the best results when
the external medium has a uniform density, but obtaining a simultaneous fit of
the prompt and afterglow emission is not easy. We discuss a few possibilities
that could help to improve this situation.
- 1110.0487 from 5 Oct 11
Hsiao-Wen Chen: Near-infrared Spectroscopy of GRB Host Galaxies at z >~ 1.5: Insights into Host Galaxy Dynamics and Interpretations of Afterglow
Absorption Spectra
This paper presents near-infrared echellette spectra of faint galaxies in the fields around GRB 050820A at redshift z=2.613 and GRB 060418 at
z=1.490. The spectroscopic data show that both GRBs originate in a dynamic environment of interacting galaxies separated by < 15 h^{-1} kpc in
projected distance and |dv| <~ 60 km/s in line-of-sight velocity. The optical afterglows revealed in early-epoch Hubble Space Telescope images
are at least 2.5 h^{-1} kpc (or 0.4") away from the high surface brightness regions of the interacting members, indicating that the GRB events
occurred either in the outskirts of a compact star-forming galaxy or in a low surface brightness satellite. Comparisons of the systemic
redshifts of the host galaxies and the velocity distribution of absorbing clouds revealed in early-time afterglow spectra further show that the
majority of the absorbing clouds are redshifted from these compact star-forming galaxies. These include the gas producing fine-structure
absorption lines at physical distances d ~ a few x 100 pc from the GRB afterglow. The lack of blueshifted absorbing clouds and the spatial
offset of the GRB event from the star-forming regions make it difficult to attribute the observed large velocity spread (~ 200-400 km/s) of
absorbing gas in the GRB host to galactic-scale outflows. We consider a scenario in which the GRB event occurred in a dwarf satellite of the
interacting group and interpret the broad absorption signatures in the afterglow spectra as a collective effect of the turbulent halo gas and
the host star-forming ISM. We briefly discuss the implications for the absorption properties observed in the afterglow spectra.
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