GRB 070805

P. Schady and A.M. Parsons report on behalf of the Swift UVOT team

The Swift/UVOT re-observed the field of GRB070805 on 2007-08-07 at 
14:36 UT, 1.8 days after the BAT trigger (GCN Circ. 6708
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 ). The 
uncatalogued source detected by UVOT in previous white band 
observations (GCN Circ. 6716
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 ) is detected and does not show any sign of 
decay. It is therefore unlikely that this source is the afterglow of 
GRB070805.

V. La Parola, P. Schady, F.E. Marshall, S. T. Holland and 
A. M. Parsons, E. Troja, J. Kennea
report on behalf of the Swift team

We have analysed the XRT and UVOT observations of 
GRB070805 (Parsons et al., GCN 6708
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 ).

The XRT observed the BAT position twice, with 2.3 and 7.7 
ksec exposure times.
We find a faint source (estimated unabsorbed flux: 3.4e-13 
erg/s/cm2) within the BAT error circle, at
RA= 16 20 02.8 (245.01175)
Dec= -59 57 34.8 (-59.959657)
(4 arcsec error radius, 90% confidence)
that is 82 arcsec from the BAT position (Stamatikos et al, 
GCN 6711
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 )
This source does not show any sign of decay, its count 
rate being consistent between the two observations.
The source is too faint to allow for any detailed spectral 
or temporal analysis.

A second, fainter source is detected only in the second 
observation, at
RA= 16 20 16.8 (245.069937)
Dec= -59 57 12.7 (-59.95352)
(4.7 arcsec error radius, 90% confidence)
The estimated unabsorbed flux is 1.13e-13 erg/s/cm2.

At present, neither of these sources can be confidently 
associated with the GRB afterglow.

On further inspection of the UVOT observations, an 
uncatalogued source is detected at the position of the 
first XRT source. This source was initially unidentified 
(GCN Circ. 6712
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 ) due to the density of the field and size 
of the BAT error circle. The source is detected in the 
white band filter at more than 3 sigma with an estimated 
magnitude of 20.1+/-0.2, and is marginally detected in the 
V, B and U filters. The refined UVOT coordinates of this 
source are
RA = 16 20 03.11 (245.0131)
Dec = -59 57 34.9 (-59.9597)
with an uncertainty of 0.7 arcseconds. There is little 
evidence for variability in the limited data currently 
available. Observations are ongoing.

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P. Schady and A.M. Parsons (GSFC) report on behalf of the Swift UVOT team

The Swift/UVOT observed the field of GRB070805 (trigger=287088) starting 
33 minutes after the BAT trigger (Parsons et al. 2007, GCN Circ.6708
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 ). We 
do not find any new source in the UVOT observations within the BAT error 
circle or in the whole of the UVOT field of view, which we note is a very 
crowded field.

The 5-sigma upper limits in the co-added frames are listed below:

Filter   Tmid   Exposure   Magnitude
          (s)    (s)        (5-sigma UL)
white    3267   333         > 20.2
v        2825   274         > 18.5
b        3441   274         > 19.5
u        3287   274         > 19.2
uvw1     3133   274         > 19.0
uvm2     2979   274         > 18.8
uvw2     3384   452         > 19.4

where Tmid is the weighted mean team of the coadded exposure. The values 
quoted above are not corrected for the expected Galactic extinction 
corresponding to a reddening of E(B-V) = 0.202 mag in the direction of the 
burst (Schlegel et al. 1998).

M. Stamatikos (GSFC/ORAU), L. Barbier (GSFC), S. D. Barthelmy (GSFC),
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/ORAU), G. Sato (GSFC/ISAS),
J. Tueller (GSFC), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-120 to T+182 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 070805 (trigger #287088)
(Parsons, et al., GCN Circ. 6708
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 ).  The BAT ground-calculated position is
RA, Dec = 245.057, -59.957 deg, which is 
   RA(J2000)  =  16h 20m 13.8s 
   Dec(J2000) = -59d 57' 26" 
with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 60%.
 
The mask-weighted light curve shows two overlapping FRED-like peaks,
the first starting at ~T_zero and the second ending at ~T+35 sec.
We note that the spacecraft slewed to a pre-planned target at T+135 sec.
During the slew the burst location left the BAT FOV at T+182 sec, and as such,
we can not determine if there as any burst activity beyond T+182 sec.
T90 (15-350 keV) is 31.0 +- 1.0 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.6 to T+35.7 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.84 +- 0.20.  The fluence in the 15-150 keV band is 7.2 +- 0.8 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+3.23 sec in the 15-150 keV band
is 0.7 +- 0.2 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

V. La Parola, J. Kennea, E. Troja, V. Mangano, B. 
Sbarufatti on behalf of the
Swift team.

We have analysed the first 2.3 ks of the XRT observation 
of GRB070805 (Parsons et al., GCN 6708
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 ).
Due to Earth limb constraint the XRT began observing the 
GRB location 33 min after the trigger, at 20:28:48 UT.
No sources are visible in this first orbit of data, with 
an upper limit to the unabsorbed flux of 2.4e-13 
erg/s/cm2.
We are waiting for more data for further analysis.

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D. E. Vanden Berk (PSU), P. Kuin (MSSL), F. E. Marshall (NASA/GSFC),
and A. M. Parsons (GSFC) report on behalf of the Swift-UVOT team:

UVOT took a finding chart exposure of 100 seconds with the White (160-650
nm) filter starting 1977 seconds after the BAT trigger.  No afterglow
candidate has been found in the initial data products. The overlap of the
sub-image and the BAT error circle is uncertain at this time. The 8'x8'
region for the list of sources generated on-board covers 100% of the
BAT error circle.  Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
region. No correction has been made for the extinction of E(B-V)=0.202.

A. M. Parsons (GSFC), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC),
J. A. Kennea (PSU), V. La Parola (INAF-IASFPA),
C. B. Markwardt (CRESST/GSFC/UMD), D. M. Palmer (LANL),
M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester),
E. Troja (INAF-IASFPA), T. N. Ukwatta (GSFC/GWU),
D. E. Vanden Berk (PSU), S. D. Vergani (DIAS-DCU) and
H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team:

At 19:55:45 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070805 (trigger=287088). 
The BAT on-board calculated location is 
RA, Dec 245.043, -59.945 which is 
   RA(J2000)  =  16h 20m 10s
   Dec(J2000) = -59d 56' 40"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows two peaks, the first
is ~5 sec in duration and the second peak is broader and weaker
ending around T+40 sec.  The peak count rate
was ~500 counts/sec (15-350 keV), at ~2 sec after the trigger. 

Because of an Earth limb constraint, the spacecraft did not slew promptly
to the BAT position, and so there are no immediate XRT or UVOT data products
to analyze.  The burst will come out of constraint at T+31 minutes. 

Burst Advocate for this burst is A. M. Parsons (parsons AT milkyway.gsfc.nasa.gov). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)