GRB 060804
GCN Circular 5394
Subject
GRB 060804: Swift detection of a burst with a possible UVOT counterpart
Date
2006-08-04T08:10:13Z (19 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
H. Z. Ziaeepour (UCL-MSSL), S. D. Barthelmy (GSFC),
D. N. Burrows (PSU), J. R. Cummings (NASA/UMD),
N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB),
J. A. Kennea (PSU), C. B. Markwardt (GSFC/UMD),
M. J. Page (UCL-MSSL), K. L. Page (U Leicester), D. M. Palmer (LANL),
G. Sato (GSFC/ISAS), M. Stamatikos (NASA/ORAU) and
G. Tagliaferri (INAF-OAB) report on behalf of the Swift Team:
At 07:28:19 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060804 (trigger=222546). Swift slewed immediately to the burst.
The BAT on-board calculated location is RA,Dec 112.201, -27.231
{07h 28m 48s, -27d 13' 52"} (J2000) with an uncertainty of 3 arcmin
(radius, 90% containment, including systematic uncertainty).
The BAT light curve shows a single peak with a duration of about 10 sec.
The peak count rate was ~600 counts/sec (15-350 keV), at ~5 sec
after the trigger.
The XRT began taking data at 07:30:21 UT, 121 seconds after the BAT
trigger. Although the XRT on-board centroid algorithm did not find a
source in the image, ground analysis revealed an uncatalogued point
source at a position of RA(J2000) = 07h 28m 49.40s, Dec(J2000) = -27d
12' 58.9", with an estimated error of 3.9 arcsec radius (90%
containment).
UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 128 seconds after the BAT trigger. A
possible afterglow candidate is seen in the 2.7'x2.7' sub-image
with an estimated magnitude of V=17 at position RA(J2000) =
07h 28m 49.36s Dec(J2000) = -27d 12' 56.7" with an estimated error of 1".
The Be star SPH 10 is in the BAT error circle. However, it is
inconsistent with the XRT and UVOT source location (2 arcminutes)
and is therefore unlikely to be associated with the burst.
GCN Circular 5395
Subject
GRB 060804: Refined analysis of the Swift-BAT burst
Date
2006-08-04T18:00:12Z (19 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. Tueller (GSFC), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/ORAU), E. Fenimore (LANL), N. Gehrels (GSFC),
D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), M. Koss (GSFC/UMD),
C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU),
H. Z. Ziaeepour (UCL-MSSL)
on behalf of the Swift-BAT team:
Using the data set from T-240 to T+800 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 060804 (trigger #222546)
(Ziaeepour, et al., GCN Circ. 5394). The BAT ground-calculated position
is RA,Dec = 112.216, -27.228 deg {7h 28m 51.8s, -27d 13' 41.8"} (J2000)
+- 2.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 18%.
The mask-weighted lightcurve shows two overlapping peaks. The first starts
at T-14 sec and peaking at T-10 sec. The second peaks at T+4 sec.
T90 (15-350 keV) is 16 +- 2 sec (estimated error including systematics).
The time-averaged spectrum from T-12.3 to T+5.5 is best fit by a simple
power-law model. The power law index of the time-averaged spectrum
is 1.78 +- 0.28. The fluence in the 15-150 keV band is
5.1 +- 0.9 x 10^-7 erg/cm2. The 1-sec peak photon flux measured
from T+4.46 sec in the 15-150 keV band is 1.2 +- 0.3 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.
GCN Circular 5396
Subject
GRB 060804: Swift-XRT Team Refined Analysis
Date
2006-08-04T19:29:01Z (19 years ago)
From
Kim Page at U.of Leicester <kpa@star.le.ac.uk>
K.L. Page (U. Leicester) & H.Z. Ziaeepour (UCL-MSSL) report on behalf of
the Swift-XRT team:
We have analysed the first 6 orbits of the XRT data obtained for GRB
060804 (trigger 222546). Using these 4340 seconds of data, we find a
refined position of:
RA(J2000) = 07 28 49.40
Dec(J2000) = -27 12 58.7
with an uncertainty of 3.6 arcsec (90% containment). This is 0.2 arcsec
from the initial XRT position stated in GCN 5394 (Ziaeepour et al.) and
53.8 arcsec from the refined BAT position in GCN 5395 (Tueller et al.)
The X-ray afterglow was sufficiently faint for the XRT to collect data
only in Photon Counting mode. During the first orbit, the count rate
remained close to constant, at ~1.5 count s^-1. Orbits 2-6, however, show
a power-law decay, with a slope alpha = 0.86 +/- 0.22.
There is no evidence for spectral evolution between the first orbit (where
the light-curve is flat) and the later decay, with the spectrum being well
fitted with a simple power-law of Gamma = 2.24 +/- 0.22, with the Galactic
absorbing column of 5.34e21 cm^-2; no excess NH is required. Between 130
and 700 seconds after the burst, the 0.3-10 keV observed (unabsorbed) flux
was 6.95e-11 (1.44e-10) erg cm^-2 s^-1.
If the afterglow continues to decay at the same rate, the count rate at 24
hours is predicted to be 0.012 count s^-1, corresponding to an observed
(unabsorbed) flux of 6.02e-13 (1.25e-12).
This circular is an official product of the Swift-XRT team.
GCN Circular 5397
Subject
GRB 060804: Swift UVOT observations
Date
2006-08-04T21:44:33Z (19 years ago)
From
Mat Page at MSSL/Swift <mjp@mssl.ucl.ac.uk>
S. B. Pandey, M. De Pasquale, M. J. Page and
H.Z. Ziaeepour (UCL-MSSL) report on behalf of the
Swift/UVOT team:
The Swift UVOT began taking settled exposures
on the field of the long duration GRB 060804
(BAT Trigger #222546), 128s after the BAT trigger
(Ziaeepour et al., GCN Circ. 5394). The optical
afterglow candidate (RA(J2000) = 07h 28m 49.36s
Dec(J2000) = -27d 12' 56.7") reported by Ziaeepour
et al. 2006 (GCN Circ. 5394) is clearly detected in
early frames. The fading behaviour of the candidate
before the later frames confirms that it is the
afterglow of GRB 060804. Detections in the initial
V and White images, and 3-sigma upper limits in the
later, coadded images are listed below.
Filter T_range(s) Exposure (s) Magnitude
White 126-225 98 17.9+-0.1
V 231-631 393 17.7+-0.1
Filter T_range(s) Exposure (s) 3-sigma UL
White 5211-12280 253 > 20.1
V 5621-5820 197 > 19.4
B 709-12219 944 > 20.5
U 685-18065 896 > 19.9
UVW1 661-15696 408 > 19.8
UVM2 637-6025 216 > 19.5
UVW2 5417-21845 747 > 19.7
T_range is calculated from the time of the trigger.
We caution that photometry of this afterglow
is complicated by the presence of a nearby source.
These measurements have not been corrected for the
estimated Galactic reddening of E_(B-V) = 0.657 mag
(Schlegel et al. 1998). We caution that the
extinction estimate for this burst, which has
|Galactic latitude| < 5 deg, is unreliable.