GRB 050820
GCN Circular 3860
Subject
VLT/UVES spectroscopy of GRB050820
Date
2005-08-23T10:29:02Z (20 years ago)
From
Paul Vreeswijk at ESO <pvreeswi@eso.org>
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 Circular 3838
Subject
Swift/UVOT photometry of GRB050820
Date
2005-08-20T21:04:12Z (20 years ago)
From
Margaret Chester at PSU <chester@astro.psu.edu>
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 Circular 3837
Subject
GRB050820: refined XRT analysis
Date
2005-08-20T19:51:24Z (20 years ago)
From
Kim Page at U.of Leicester,Swift SDC <kpa@star.le.ac.uk>
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 Circular 3836
Subject
GRB 050820: Early RAPTOR detections
Date
2005-08-20T18:49:51Z (20 years ago)
From
James Wren at LANL <jwren@nis.lanl.gov>
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 Circular 3835
Subject
GRB 050820 Swift-BAT refined analysis
Date
2005-08-20T14:11:03Z (20 years ago)
From
Jay R. Cummings at NASA/GSFC/Swift <jayc@milkyway.gsfc.nasa.gov>
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 Circular 3834
Subject
GRB 050820: P60 Temporal Decay Index
Date
2005-08-20T10:37:09Z (20 years ago)
From
S. Bradley Cenko at Caltech <cenko@srl.caltech.edu>
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 Circular 3833
Subject
GRB 050820: High Resolution Spectroscopy from Keck
Date
2005-08-20T09:51:16Z (20 years ago)
From
Jason Prochaska at UCO/Lick Obs <xavier@ucolick.org>
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 Circular 3830
Subject
GRB 050820: Swift detection of a GRB
Date
2005-08-20T07:29:30Z (20 years ago)
From
David Burrows at PSU/Swift <dxb15@psu.edu>
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 Circular 3829
Subject
GRB050820: Optical afterglow from P60
Date
2005-08-20T07:15:30Z (20 years ago)
From
Derek Fox at PSU <dfox@astro.psu.edu>
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."