GRB 060825

J. Haislip, G. Spear, T. Graves, M. Nysewander, D. Reichart, K. Ivarsen, A.
Foster, A. LaCluyze, J. A. Crain report:

Skynet observed the localization of GRB 060825 (Sato et al., GCN 5471
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 ) with
the GLAST Optical Robotic Telescope (GORT) in California beginning 1.1
hours after the burst in BVRI.

No new source is detected within the XRT error circle to a 3-sigma limiting
magnitude of R > 21.0 at a mean time of 5.4 hours after the burst.

Gaug M. and Garczarczyk M., Bastieri D., Fagiolini M., Galante N.,
Longo F., Mizobuchi S., Picciolini A., Scampin V. and Stamerra A.
report for the MAGIC collaboration:

The MAGIC Imaging Atmospheric Cherenkov Telescope performed a follow-up
observation of the SWIFT-BAT burst GRB060825 (GCN circular 5478
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 , Fenimore
E. et al.). We received the GCN alert at T0+19s. The telescope slewed fast
to the GRB sky coordinates and started data taking 38s after the alert, at
T0+57s. In total 33min of data from the GRB sky coordinates were
accumulated. Due to the short duration of the burst (T90 = 8.8s), only the
early afterglow phase was observed. The observation overlapped with the
small x-ray flare detected by SWIFT-XRT (GCN circular 5479
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 , Beardmore A.P.
et al.), centered at T0+220s.

No evidence for VHE emission above the analysis threshold of 90GeV was
found. A preliminary analysis, for the hypothesis of steady emission and
assumption of a differential photon spectral index of -2.5, yields the
following 95% CL differential flux upper limits (inc. 30% systematic error
on the absolute flux level):

E(80-125 GeV)   : 1.8 x 10^(-10) erg/cm^2/s
E(125-175 GeV)  : 1.9 x 10^(-10) erg/cm^2/s
E(175-300 GeV)  : 1.2 x 10^(-10) erg/cm^2/s
E(300-1000 GeV) : 0.6 x 10^(-10) erg/cm^2/s

This message can be cited.

P. Chandra (UVA/NRAO) and  D. A. Frail (NRAO) report on behalf of the 
Caltech-NRAO-Carnegie GRB
Collaboration:

"We observed the field centered on the BAT position of the Swift burst GRB
060825 (GCN#5472
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 ) using the VLA at a frequency of 8.46 GHz at 2 epochs. 
There is no detection of the GRB at both the epochs.

Date        UT    rms(microJy)    2-sigma upper limit
2006-08-27    9.36    45        < 90 microJy
2006-08-29    8.23    47        < 94 microJy

The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc."

A. Pelangeon & J-L. Atteia (LATT-OMP) report:

We have used the spectral parameters of GRB 060825
provided by Fenimore et al. (GCNC 5478) to
compute the spectral pseudo-redshift** of this burst
detected by SWIFT-BAT (Sato et al., GCNC 5471).

We find a pseudo-redshift pz= 2.0 +/- 0.6


** cf. http://www.ast.obs-mip.fr/grb/pz

A.P. Beardmore, K.L. Page (U. Leicester) & G. Sato (GSFC/ISAS) report on 
behalf of the Swift-XRT team:

We have analysed the first 4 orbits of Swift-XRT data obtained for GRB 060825
(trigger 226382). From 3660 seconds of data, we find a refined position of:

RA(J2000)  =   01 12 29.00
Dec(J2000) =  +55 47 46.5

with an uncertainty of 4.1 arcsec (90% containment). This is 0.8 arcsec
from the XRT position reported in GCN Circ. 5471
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  (Sato et al.), and 18.6
arcsec from the refined BAT position in GCN Circ. 5478
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  (Fenimore et al.).

The X-ray afterglow is faint, initially only 0.8 count/s, 74s after
the BAT trigger, decaying with a slope of alpha = 0.87 +/- 0.09 out to 20ks.
There is, however, a small flare centred at 220s, where the count rate rises
to 1.2 count/s.

The X-ray spectrum from the first four orbits can be well fitted by an
absorbed power-law, with a photon index of Gamma = 1.64 +/- 0.29 absorbed
by the Galactic column density of 3.0e21 cm^-2. The early time unabsorbed
flux (between 74 - 189s after the trigger) was 3.57e-11 erg cm^-2 s^-1
over the 0.3-10 keV band.

Providing the source decays at the same rate then the count rate is
predicted to be ~0.002 count/s 24 hr after the trigger, which
corresponds to an observed 0.3-10keV flux of 1.20e-13 erg cm^-2 s^-1,
or an unabsorbed flux of 1.58e-13 erg cm^-2 s^-1.

This circular is an offical product of the Swift-XRT team.

E. Fenimore (LANL),  L. Barbier (GSFC),  S. Barthelmy (GSFC),
J. Cummings (GSFC/ORAU), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC),
on behalf of the Swift-BAT team:

Using the data set from T-240 to T+614 sec from the recent telemetry
downlink, we report further analysis of Swift GRB 060825
(trigger #226382)  (Sato, et al., GCN Circ. 5471
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 ).  The BAT ground-calculated
position is (RA,Dec) = 18.130, 55.796 deg {1h 12m 31.3s, 55d 47' 44.7"} (J2000)
+- 0.7 arcmin, (radius, sys+stat, 90% containment).  The partial 
coding was 90%.

The mask-weighted light curve shows a single broad peak from T-4 sec to T+7 sec
T90 (15-350 keV) is 8.1 +- 1 sec (estimated error including systematics).

The time-averaged spectrum from T-4.2 to T+7.0 is best fit by
a power law with an exponential cutoff.  This fit gives a photon index
1.11 +- 0.32, and Epeak of 73 +- 18 keV (chi squared 54.91 for 56 d.o.f.).
For this model the total fluence in the 15-150 keV band is
9.8 +- 0.5 x 10^-7 erg/cm2 and the 1-sec peak flux measured from
T+0.07 sec in the 15-150 keV band is 2.7 +- 0.2 ph/cm2/sec.
A fit to a simple power law gives a photon index of 1.71 +- 0.07
(chi squared 67.23 for 57 d.o.f.).  All the quoted errors are at the 90%
confidence level.

A. Gomboc reports on behalf of the Liverpool GRB group:

The 2-m Liverpool Telescope (La Palma, Canary Islands) robotically
followed-up GRB060825 (SWIFT trigger 226382, Sato et al. GCN
5471
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 ) starting 2.6 min after the GRB trigger time. We do not find an
optical counterpart in 6 x 10s co-added images at the mean time 5.7 min
after the trigger to a limiting magnitude of R~18.3.

Limiting magnitude has been derived with reference to USNOB1.

P. D'Avanzo, S. Covino (INAF-OABrera), L. A. Antonelli (INAF-OAR) on
behalf of a larger collaboration, A. Magazzu` and G. Tessicini (INAF-TNG)
report:

We observed the field of GRB 060825 (Sato et al., GCN 5471
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 ) with the
italian 3.6m TNG telescope, sited in Canary Island, Spain. A set of BVRI
images have been collected, with a seeing of 1.3". The mean epoch of
observations is Aug 25.22 UT. We clearly see the DSS object reported by
de Ugarte Postigo et al. (GCN 5472
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 ) and Cenko et al. (GCN 5473
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 ). 

No new object is seen inside the XRT error box , to a limiting magnitude
of R > 23.9 (3sigma level).

We thank TNG staff for their support.

This message can be cited

[(GCN OPS NOTE(28aug06): Per author's request, G. Tessicini was added
to the author list.]

Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. (LATT-OMP) report:

We imaged the field of GRB 060825 detected by SWIFT
(trigger 226382) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.

First image was acquired 25.7s after the GRB trigger
(7.1s after the notice). The field elevation decreased from
77 degrees above horizon and weather conditions
were good.

Date of trigger : t0 = 2006-08-25T02:59:57.408

First image is 60.0 exposure trailed. No OT is visible:
t0+25.7s to t0+85.7s : R > 14.9

Second image is 30.0 exposure. No OT is visible:
t0+93.5s to t0+123.5s : R > 15.8

We co-added a series of exposures. No OT is visible:
t0+93.5s to t0+377.7s : R > 18.4

We do not detect the candidate of de Ugarte Postigo et al.
(GCNC 5472).

Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.

N.B. Galactic coordinates are lon=125.8970 lat= -6.9459
and the galactic extinction in R band is 0.7 magnitudes
estimated from D. Schlegel et al. 1998ApJ...500..525S.

This message may be cited.

S. B. Cenko (Caltech) and D. B. Fox (Penn State) report on behalf of a
larger collaboration:

We have imaged the field of GRB 060825 (Sato et al., GCN 5471
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 ) with the
automated Palomar 60-inch telescope.  Images consisted of 6 x 180 s
exposures in the Kron R and Sloan i' filters taken at a mean epoch of
approximately August 25.2 UT (~ 2 hr after the burst).

We clearly detect the object identified by de Ugarte Postigo et al. (GCN
5472
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 ) in both filters.  The object has a magnitude R ~ 21.2, I ~ 19.5 in
our images (measured with respect to the USNO-B catalog).  However, as
noted already, the object appears to be present in the DSS2 red plates.

We find no other objects inside the XRT error circle, to a limiting
magnitude of approximately R > 22.0, I > 21.0.  No values in this circular
have been corrected for the large Galactic extinction along the line of
sight.

A. de Ugarte Postigo, J.Gorosabel, M. Jelinek, R. Cunniffe,
S. Vitek, A.J. Castro-Tirado (IAA-CSIC Granada),P. Kubanek (ASU AV CR
Ondrejov & ISDC Versoix) and L. Sabau-Graziati (INTA Torrejon de
Ardoz, Madrid) report

Main text:
"The BOOTES-IR 0.6m telescope, located at IAA-CSIC Observatorio de
Sierra  Nevada in Granada (Spain), observed the SWIFT error box for 
GRB 060825 (Sato et al. GCNC 5471) starting at 03:26 UT in R-band.

We detect an object on the edge of the XRT error box at coordinates 
R.A.= 01:12:29.58, Dec. = +55:47:43.8 (J2000) with estimated 
uncertanity of 0.7 arcsec  which might be present at the DSS2 
image.

A finding chart will be soon available at:
www.iaa.es/~deugarte/GRBs/060825/grb060825.gif

This message is quotable".

[GCN OPS NOTE(31aug06): Per author's request, "L.D. S-G" was changed
to "L. S-G".]

G. Sato (GSFC/ISAS), S. D. Barthelmy (GSFC), M. M. Chester (PSU),
N. Gehrels (NASA/GSFC), S. T. Holland (GSFC/USRA),
S. Immler (GSFC/USRA), J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA),
F. E. Marshall (NASA/GSFC), K. M. McLean (LANL/UTD),
K. L. Page (U Leicester) and D. M. Palmer (LANL) report on behalf of
the Swift Team:

At 02:59:57 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060825 (trigger=226382).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 18.102, +55.805 {01h 12m 24s, +55d 48' 18"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single bright peak
with some structure and a duration of about 15 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began taking data at 03:01:03 UT, 66 seconds after the BAT
trigger.  The XRT on-board centroid algorithm did not find a source in the
image, however ground analysis of quicklook data reveals a faint uncatalogued
point source at the following coordinates: RA(J2000) = 01h 12m 28.9s,
Dec(J2000) = +55d 47m 46.4s with an error of 5.4 arcseconds radius (90%
confidence). This position is 49 arcseconds from the BAT position. 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 72 seconds after the BAT trigger. No
afterglow candidate has been found in the initial data products. The
2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical
3-sigma upper limit has been about 18.5 mag. The 8'x8' region for the
list of sources generated on-board covers 100% of the BAT error
circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to
E(B-V) of  0.57.