GRB 080727A
GCN Circular 8025
Subject
GRB 080727A: Enhanced Swift-XRT position
Date
2008-07-27T10:30:36Z (17 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester)
report on behalf of the Swift-XRT team.
Using 2786 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 080727A, we find an astrometrically corrected X-ray
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 208.39050, -18.54479 which is equivalent
to:
RA (J2000): 13h 53m 33.72s
Dec (J2000): -18d 32' 41.2"
with an uncertainty of 1.9 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest position
can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is
described by Goad et al. (2007, A&A, 476, 1401
http://www.swift.ac.uk/xrt_positions/Goad.pdf), the current algorithm is an
extension of this method.
This circular was automatically generated, and is an official product of the
Swift-XRT team.
GCN Circular 8027
Subject
GRB080727A: Swift/UVOT Upper Limits
Date
2008-07-27T14:38:23Z (17 years ago)
From
Wayne Landsman at GSFC/SSAI <wayne.b.landsman@nasa.gov>
W.B. Landsman (NASA/GSFC/Adnet) and S. Immler (PSU) report on behalf of
the Swift/UVOT team:
The Swift/UVOT observed the field of GRB080727A starting 113s after the
BAT trigger (Immler et al., GCN Circ. 8021). We do not find any
source, in any of the UVOT observations, at the UVOT-enhanced XRT
position of the afterglow (Evans et al. GCN Circ. 8025). The 3-sigma
upper limits for detecting a
source at this location in the co-added images are:
Filter T_start T_stop Exp(s) Mag (3-sigma upper limit)
-----------------------------------------------------------------
v 219 7675 1165 >20.6
b 700 7083 471 >20.9
u 675 6878 490 >20.6
uvw1 650 6673 491 >20.5
uvm2 1541 6468 236 >20.0
uvw2 730 7486 471 >20.8
white 113 7284 623 >21.8
-----------------------------------------------------------------
The quoted upper limits have not been corrected for the expected
Galactic extinction along the line of sight corresponding to a
reddening of E_{B-V} = 0.07 mag. All photometry is on the UVOT flight
system described in Poole et al. (2008, MNRAS, 383, 627).
GCN Circular 8028
Subject
GRB 080727A: Swift-XRT refined analysis
Date
2008-07-27T15:30:20Z (17 years ago)
From
Kim Page at U.of Leicester <kpa@star.le.ac.uk>
K.L. Page, J.P. Osborne (U. Leicester) and S. Immler (CRESST/GSFC/UMD)
report on behalf of the Swift-XRT team:
We have analysed the first three orbits of data obtained for GRB 080727A
(Immler et al., GCN Circ. 8021), covering 7 ks of Photon Counting mode
data. The UVOT-enhanced position has been given by Evans et al. (GCM Circ.
8025).
During the first orbit (117s - 1.9 ks after the trigger), the light-curve
shows a number of small flares, superimposed on a power-law decay of
alpha= 2.01 +0.18/-0.17. The source is no longer detected in the combined
second and third orbits of data (5.3 ks of exposure time, starting 5 ks
after the trigger). Although the upper limit is consistent with the
continued decay of alpha = 2.01, it is not possible to determine whether a
break has occurred.
The spectrum from the first orbit of data can be fitted with a power-law
of Gamma = 1.43 +0.20/-0.19, absorbed by the Galactic column in this
direction (6.75x10^20 cm^-2). The average observed (unabsorbed) flux over
this time is 5.56 (6.02) x 10^-12 erg cm^-2 s^-1. The counts to observed
flux conversion is 5.3 x 10^-11 erg cm^-2 count^-1.
With the limited information available from a detection only in the first
orbit, we are unable confidently to predict the flux at 24 hours.
This is an official product of the Swift-XRT team.
GCN Circular 8029
Subject
GRB 080727A, Swift-BAT refined analysis
Date
2008-07-27T16:47:32Z (17 years ago)
From
Takanori Sakamoto at NASA/GSFC <takanori.sakamoto-1@nasa.gov>
K. McLean (GSFC/UMD), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 080727A (trigger #318094)
(Immler, et al., GCN Circ. 8021). The BAT ground-calculated position is
RA, Dec = 208.416, -18.572 deg which is
RA(J2000) = 13h 53m 39.9s
Dec(J2000) = -18d 34' 18.6"
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 97%.
The mask-weighted light curve shows a single weak pulse starting
at T+~0 and ending a T+~5 sec.
T90 (15-350 keV) is 4.9 +- 1.0 sec (estimated error including systematics).
The time-averaged spectrum from T-0.1 to T+5.1 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.25 +- 0.34. The fluence in the 15-150 keV band is 1.3 +- 0.3 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+1.20 sec in the 15-150 keV band
is 0.3 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/318094/BA/
GCN Circular 8039
Subject
GRB 080727A: VLT upper limits
Date
2008-07-28T08:05:37Z (17 years ago)
From
Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst <malesani@astro.ku.dk>
D. Malesani (DARK), P. Jakobsson (Univ. Hertfordshire), A. J. Levan
(Univ. Warwick), E. Rol (Univ. Leicester), J. P. U. Fynbo (DARK), report
on behalf of a larger collaboration.
We observed the field of GRB 080727A (Immler et al., GCN 8021) with the
ESO VLT equipped with FORS1. Observations started on 2008 Jul 27.979 UT,
17.5 hr after the burst, for a total exposure time of 900 s in the R filter.
Inside the refined XRT error circle (Evans et al., GCN 8025), we detect
no new source down to a limiting magnitude R~26. Calibration was based
on tabulated zeropoints and is in rough agreement with USNO-B1 stars.
We acknowledge kind support from the observing staff at Paranal,
particularly Suzanna Randall, Karla Aubel, and Alain Smette.
GCN Circular 8048
Subject
GRB 080727A: Early IR observations
Date
2008-07-29T15:12:05Z (17 years ago)
From
Andrew Levan at U.of Leicester <anl@star.le.ac.uk>
A.J. Levan (U. Warwick) and K. Wiersema (U. Leicester) report for a
larger collaboration:
We observed the location of GRB 080727A (Immler et al. GCN
8021) using UKIRT. A series of K-band exposures were taken beginning at
06:24:51 UT, roughly 30 minutes after the burst, a total of 720s
of observtions were taken (36x20s). We find no evidence for any
source within the XRT error circle (Evans et al. GCN 8025) for GRB
080727A, down to a limit of K=19.8 mag (3-sigma).
Comparing this limit to the extrapolated X-ray flux 30 minutes
post-burst implies that the observed X-ray to optical/IR spectral
slope was beta_KX < ~0.8, thus the non-detection in the IR is likely
down to the rapid fading of the afterglow, rather than suppression
of the optical/IR flux.
We thank the staff of UKIRT for their rapid response to these alerts.