GRB 070810A
GCN Circular 6748
Subject
GRB 070810A: Swift-BAT refined analysis
Date
2007-08-10T19:13:07Z (18 years ago)
From
Jay R. Cummings at NASA/GSFC/Swift <jayc@milkyway.gsfc.nasa.gov>
C. Markwardt (GSFC/UMD), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), D. Palmer (LANL), A. Parsons (GSFC),
T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. Ukwatta (GWU)
Using the data set from T-240 to T+804 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 070810A (trigger #287364) (Cummings,
et al., GCN Circ. 6733). The BAT ground-calculated position is
RA, Dec = 189.947, 10.747 deg which is
RA(J2000) = 12h 39m 47.2s
Dec(J2000) = 10d 44' 48"
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment). This
is 1.0 arcmin from the optical and refined XRT positions (Chester et al.
GCN circ. 6735 and Evans et al. GCN circ. 6736). The partial coding was 53%.
The mask-weighted light curve shows a single peak with softening spectral
evolution. T90 (15-350 keV) is 11.0 +- 1 sec (estimated error including
systematics).
The time-averaged spectrum from T-3.1 to T+14.3 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
2.04 +- 0.14. The fluence in the 15-150 keV band is
6.9 +- 0.6 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from
T-0.11 sec in the 15-150 keV band is 1.9 +- 0.2 ph/cm2/sec. All the quoted
errors are at the 90% confidence level.
GCN Circular 6757
Subject
GRB 070810A: Continued Keck Imaging
Date
2007-08-12T05:08:12Z (18 years ago)
From
Daniel Perley at U.C. Berkeley <dperley@astro.berkeley.edu>
D. A. Perley, J. S. Bloom (UC Berkeley), and C. C. Thoene (DARK, UCB)
report:
Beginning at 06:48:00 UT (2007-08-11) we began a second series of imaging
exposures on the field of GRB 070810A (GCN 7433) using the Keck I
telescope (+LRIS). We acquired a total of 390s in R band and 480s in g
band through high airmass.
The optical afterglow (GCN 6734) is still detected, but has faded
significantly since our previous imaging epoch (GCN 6741) and appears
marginally extended. Aperture photometry of the source indicates that it
has has faded by 3.2 +/- 0.1 magnitudes since the observations the first
night, corresponding to a decay index of alpha >= 1.5 between 4 hours and
28.6 hours including a possible contribution from a host galaxy or other
extended source.
Using the same calibration system as in our previous circular, we estimate
a preliminary magnitude of R=23.7.
GCN Circular 6761
Subject
GRB 070810A: ROTSE-III Refined Analysis
Date
2007-08-17T00:24:27Z (18 years ago)
From
Fang Yuan at ROTSE <yuanfang@umich.edu>
F. Yuan, E.S. Rykoff (U Mich), report on behalf of the ROTSE collaboration:
ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB
070810A (Swift trigger 287364; Cummings, et al., GCN 6733), and
detected the optical counterpart (Swan, et al., GCN 6734).
The initial aperture photometry reported in GCN 6734 was biased due to
contamination from the nearby star.
With a reference image taken 6 days after the burst, we were able to
subtract the nearby star and obtain better estimate of the OT
brightness with PSF fitting. Our refined analysis shows the OT at 18.0
� 0.2 mag (unfiltered images, calibrated relative to USNO-B1.0 R)
between 1607s and 2290s after the burst.
start UT end UT mag
-------------------------------------
02:38:39.5 02:50:02.3 18.0+/-0.2
03:13:15.7 03:24:39.0 18.5+/-0.2
The OT faded with a decay index 0.7 �0.2 in the next 40 minutes before
dropping below our detection threshold. This decay index is
significantly shallower than seen at later time in Keck photometry
(Perley, et al., GCN 6757), implying a light curve break between 1.2 hr
and 4 hr after the burst.