GRB 060807

M. De Pasquale (UCL-MSSL), S. D. Barthelmy (GSFC),
S. Campana (INAF-OAB), J. R. Cummings (NASA/UMD),
O. Godet (U Leicester), C. Guidorzi (Univ Bicocca&INAF-OAB),
J. E. Hill (GSFC/USRA), S. T. Holland (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), D. M. Palmer (LANL), S. B. Pandey (UCL-MSSL),
A. M. Parsons (GSFC), T. Sakamoto (NASA/ORAU) and
D. E. Vanden Berk (PSU) report on behalf of the Swift Team:

At 14:41:35 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060807 (trigger=223217).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is RA,Dec 252.527, +31.590
{16h 50m 07s, +31d 35' 25"} (J2000) with an uncertainty of 3 arcmin
(radius, 90% containment, including systematic uncertainty). 
The BAT light curve shows 1, possibly 2, peaks  with a duration
of about 15 sec.  The peak count rate was ~1000 counts/sec (15-350 keV),
at ~1 sec after the trigger. 

The XRT began taking data at 14:43:21 UT, 106 seconds after the BAT
trigger. The XRT on-board centroid algorithm did not find a source in
the image, however analysis of downlinked data finds an uncatalogued,
variable point source at the following location:  
RA(J2000): 16h 50m 02.77s, Dec(J2000) 31d 35m 31.1s with an estimated  
uncertainty of 4.2 arcseconds radius (90% containment). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 110 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
3-sigma upper limit is about 19.7 mag. The 8'x8' region for the
list of sources generated on-board covers 100% of the XRT 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  0.03. 

The Malindi telemetry downlink gap has just started, so we will not get
the full data set until ~22:30 UT. 

[GCN OPS NOTE(07aug06): Per author's request, the affilation of S.B.Pandey
was changed.]

K. Torii (Osaka U.) reports on behalf of the ART collaboration:

 The error region of GRB 060807 (De Pasquale et al. GCN 5409
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 ) was
observed with the 0.35m ART-3b in Toyonaka, Osaka. Under the bright
moon, 60 s exposures in Ic band were repeated.

 Preliminary analysis does not reveal a new object within the XRT
error region and the following upper limit is derived relative to
USNO-B1.0 I magnitude.

--------------------------------
StartUT		Limit	Exposure
================================
14:44:37	>17.7	60s x 10
================================

S.Okuno, S.Tanabe, T.Kidamura, D.Yonetoku, T.Murakami, 
H.Kodaira, S.Yoshinari, S.Yokota, R.Kozaka, Y.Kodama,
N.Emura, T.Asai, T.Nashimoto 
report on behalf of the Kanazawa GRB team:

We have imaged the field of GRB 060807 (M. De Pasquale et al. GCN 5409
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 )
in R band with 0.3m telescope at Kanazawa Japan.
The automated system took the first image at 300 s after the trigger
(under poor conditions).  Compared with the USNO-A2.0 catalog, no new
source was detected brighter than the limiting magnitude of R>15.6 mag
in the XRT error circle.  Further observations and analysis are 
in progress.

E.Sonoda, S.Maeno, M.Yamauchi
(University of Miyazaki)


"We have observed the field covering the error circle of
GRB060807 (GCN 5409
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 ) with the unfiltered CCD camera on
the 30-cm telescope at University of Miyazaki.
The observation was started 14:44:19 UT on Aug. 8.
After co-adding a set of 44 images (14:44:19 - 15:52:33 UT,
164s after the trigger) of 30 sec exposures,
we have compared with the USNO A2.0 catalog.

Preliminary analysis shows there is no new source brighter
than 17.6 mag. "

Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona),
David W. Hogg (NYU), Michael R. Blanton (NYU), David J. Schlegel
(LBNL), J. Brinkmann (APO), Donald Q. Lamb (Chicago), Donald
P. Schneider (PSU), and Daniel E. Vanden Berk (PSU) report:

The Sloan Digital Sky Survey (SDSS) imaged the field of burst
GRB060807 prior to the burst.  As these data should be useful
as a pre-burst comparison and for calibrating photometry,
we are supplying the images and photometry measurements for
this GRB field to the community.

Data from the SDSS, including 5 FITS images, 3 JPGS, and
3 files of photometry and astrometry, are being placed at
http://mizar.as.arizona.edu/~grb/public/GRB060807

We supply FITS images in each of the 5 SDSS bands of a 8'x8'
region centered on the GRB position (ra=252.527 (16:50:06.5),
dec=31.5900 (31:35:24.0); Swift-BAT TRIGGER 223217), as well
as 3 gri color-composite JPGs (with different stretches). The
units in the FITS images are nanomaggies per pixel.  A pixel
is 0.396 arcsec on a side. A nanomaggie is a flux-density unit
equal to 10^-9 of a magnitude 0 source or, to the extent that
SDSS is an AB system, 3.631e-6 Jy.  The FITS images have WCS
astrometric information.

In the file GRB060807_sdss.calstar.dat, we report photometry
and astrometry of 676 bright stars (r<20.5) within 15' of the
burst location.  The magnitudes presented in this file are asinh
magnitudes as are standard in the SDSS (Lupton 1999, AJ, 118,
1406). Beware that some of these stars are not well-detected
in the u-band; use the errors and object flags to monitor
data quality.

In the files GRB060807_sdss.objects_flux.dat and
GRB060807_sdss.objects_magnitudes.dat, we report photometry
of 825 objects detected within 6' of the GRB position.
We have removed saturated objects and objects with model
magnitudes fainter than 23.0 in the r-band.  The fluxes listed
in GRB060807_sdss.objects_flux.dat are in nanomaggies while
the magnitudes listed in GRB060807_sdss.objects_magnitudes.dat
are asinh magnitudes.

All quantities reported are standard SDSS photometry, meaning
that they are very close to AB zeropoints and magnitudes are
quoted in asinh magnitudes.  Photometric zeropoints are known
to about 2% rms.  None of the photometry is corrected for
dust extinction.  The Schlegel, Finkbeiner, and Davis (1998)
predictions for this region are A_U=0.148 mag, A_g=0.109 mag,
A_r = 0.079 mag, A_i=0.060 mag, and A_z=0.042 mag.

The file GRB060807_sdss.spectro.dat contains a list of the
3 objects with SDSS spectroscopy within 6 arcminutes of the
GRB position.  In addition to the redshift and 1-sigma error
for each object, this file also lists the object spectroscopic
classification.

SDSS astrometry is generally better than 0.1 arcsecond per
coordinate.  Users requiring high precision astrometry should
take note that the SDSS astrometric system can differ from
other systems such as those used in other notices; we have
not checked the offsets in this region.

More detailed information pertaining to our SDSS GRB releases
can be found in our initial data release paper (Cool et
al. 2006, astro-ph/0601218).  See the SDSS DR4 documentation
for more details: http://www.sdss.org/dr5.

These data have been reduced using a slightly different
pipeline than that used for SDSS public data releases.
We cannot guarantee that the values here will exactly match
those in the data release in which these data are included.
In particular, we expect the photometric calibrations to differ
by of order 0.01 mag.

This note may be cited, but please also cite the SDSS data
release paper, Adelman-McCarthy et al. (2006, ApJS, in press,
astro-ph/0507711), when using the data or referring to the
technical documentation.

S. Duscha M. Muehlegger A. Stefanescu G. Kanbach,N. Prymak, F. Schrey H. 
Steinle (MPE Garching) of the OPTIMA-Burst team report from the 1.3m Skinakas 
Observatory (University of Crete Heraklion Greece):


We observed the position of the XRT errorcircle of GRB 060807 (trigger 
#223217 De Pasquale et al. GCN Circ. 5409
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 ) on 2006 Aug 07 19:25 UT 
(mid-exposure; about 5 hours post burst): In a 20 min white light exposure we 
do not detect a counterpart candidate brighter than mag 20.

Johan P. U. Fynbo (DARK/NBI), Amanda Djupvik (NOT), Evert Rol (Leicester),
Andreas Jaunsen (Oslo) report on behalf of a larger collaboration:

"We have observed the field of GRB 060807 (De Pasquale et al., GCN5409
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 )
around Aug 7.9 with the Nordic Optical Telescope on La Palma. In the XRT
error circle we detect a faint source at the position:

(RA, Dec) = 16:50:02.6,  +31:35:30.7 (J2000.0)

with an uncertainty of about 0.5". The source is detected in the V, R and
i bands and is not detected in the SDSS (Cool et al., GCN5415
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 )."

S.D. Barthelmy (GSFC), L. Barbier (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), M. De Pasquale (UCL-MSSL),
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-120 to T+302 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 060807 (trigger #223217)
(De Pasquale, et al., GCN Circ. 5409
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 ).  The BAT ground-calculated position
is (RA,Dec) = 252.505, 31.597 deg {16h 50m 1.3s, 31d 35' 48.0"} (J2000)
+- 1.7 arcmin, (radius, sys+stat, 90% containment).  The partial coding was 69%.
 
The mask-weighted lightcurve shows a roughly triangular shaped peak
starting at T-50, peaking at T+0, and ending at T+30 sec.
T90 (15-350 keV) is 34 +- 4 sec (estimated error including systematics).
 
The time-averaged spectrum from T-16.5 to T+24.7 is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum
is 1.57 +- 0.20.  The fluence in the 15-150 keV band is
7.3 +- 0.9 x 10^-7 erg/cm2.  The 1-sec peak photon flux measured
from T-0.14 sec in the 15-150 keV band is 0.8 +- 0.2 ph/cm2/sec.
All the quoted errors are at the 90% confidence level.

D. Malesani (SISSA) & S. Piranomonte (INAF/Roma) report on behalf of the 
MISTICI collaboration:

We observed the candidate optical counterpart (Fynbo et al., GCN 5420
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 ) 
of GRB 060807 (De Pasquale et al., GCN 5409
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 ; Barthelmy et al., GCN 
5421
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 ). Observations were carried out in the K and R filters, with 
NTT+SofI and VLT+FORS1, respectively. The mean times were 8.46 and 8.72 
hr after the burst.

The candidate is well detected in both filters, and shows a very red 
color. Preliminary calibrations against 2MASS and USNO-B1 (R1 
magnitudes) shows R-K ~ 5 (assuming negligible time variations between 
the two epochs). We warn that there is some scatter (by ~0.2 mag) in the 
calibration for both the R- and K bands, so this value should be still 
considered as preliminary.

We acknowledge prompt support from the VLT and NTT observing staffs, in 
particular Claudio Melo and Valentin Ivanov.

This message can be cited.

K.L. Page, O. Godet (U. Leicester) & Max De Pasquale (UCL-MSSL) report on 
behalf of the Swift-XRT team:

We have analysed the first 4 orbits of Swift-XRT data obtained for GRB 
060807 (trigger number 223217). All useful data were collected in Photon 
Counting mode, starting 117 seconds after the BAT trigger. Using these 
first 8.6 ks of data, we obtain a refined position of:

RA(J2000) =   16 50 02.97
Dec(J2000) = +31 35 30.5

with an estimated uncertainty radius of 3.5 arcsec (90% containment).

Analysis of the light-curve implies that there was a steep decay at the 
start of the observation, followed by a period of almost constant 
emission until the end of the first orbit. The data obtained for orbits 
2-4 show a decline with alpha = 1.18 +/- 0.10. 

A spectrum formed from all the PC data for the first 4 orbits (117 s - 18
ks after the trigger), can be modelled with a power-law of photon index
Gamma = 2.15 +/- 0.12, with an excess absorbing column of NH = (1.3 +/-
0.3)e21 cm^-2 in addition to the Galactic value of 2.44e20 cm^-2. The mean
0.3-10 keV observed flux for this time period is 1.02e-11 erg cm^-2 
s^-1; the unabsorbed flux is 1.50e-11 erg cm^-2 s^-1.

Assuming the light-curve continues to decay with alpha ~ 1.18, the count 
rate at 24 hours is predicted to be 0.016 count s^-1. This corresponds to 
an observed (unabsorbed) flux of 6.81e-13 (1.00e-12) erg cm^-2 s^-1.

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

D. Malesani (SISSA), J. Fynbo (DARK/NBI), S. Piranomonte (INAF/OAR), & 
A. Djupvik (NOT), report:

We have performed relative photometry between the NOT (Fynbo et al., GCN 
5420
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 ) and VLT (Malesani et al., GCN 5422
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 ) R-band images of GRB 060807 
(De Pasquale et al., GCN 5409
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 ).

We find that the object indicated by Fynbo et al. (GCN 5420
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 ) dimmed by 
0.61 +- 0.06 mag between 6.69 and 8.93 hr after the GRB. This confirms 
that the object was indeed the optical afterglow of GRB 060807. Assuming 
a power-law time dependence F(t) propto t^-alpha, the inferred decay 
index is quite steep: alpha = 1.9 +- 0.2.

This message can be cited.

S. B. Pandey and M. De Pasquale (UCL-MSSL) report on behalf of the 
Swift/UVOT
team:

The Swift UVOT began observing GRB 060807 (trigger #223217,
M. De Pasquale et al., GCN Circular 5409
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 ) 110 seconds after the BAT
trigger. No optical afterglow is detected in the XRT refined error
circle (Page et al, GCN Circular 5423
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 ) and at location of the
afterglow reported by Fynbo et al. 2006 (GCN Circular 5420
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 ).

The 3-sigma limiting magnitudes for the coadded images for the
UVOT filters are listed below:

Filter            T_range(s)      Exposure(s)     3sig_Upper limit

WHITE        110-6965          599                20.5
V                  215-12151        1796              20.7
B                  693-18617        1079              21.4
U                  669-17927        1317              21.2
W1               645-17012        1318              20.4
M2               621-12834        1099              20.7
W2               721-11238        1102              20.8

T_range is calculated from the time of the burst. No correction has
been made for the Galactic reddening of to E(B-V) = 0.03 mag
(Schlegel et al. 1998) along the line of sight to the burst.

D. T. Durig (Cordell-Lorenz Observatory, University of the South) and S. 
Sposetti (Gnosca, Switzerland) report on behalf of the AAVSO International 
High Energy Network on optical observations of GRB060807 (GCN #5409
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 , De 
Pasquale et al.):

D. T. Durig reports the following unfiltered (CR) limiting magnitude:
2006 Aug 08, 03:41:45 UT, CR < 20.0 (15 hours, post-burst)

S. Sposetti reports the following R-band limiting magnitude:
2006 Aug 08, 19:45:00 UT, R < 20 (29 hours, post-burst)

Details of these observations follow at the end of this report.

FITS images of these observations are available from the AAVSO at
ftp://ftp.aavso.org/grb , and full details of these observations
are available at the following URLs:

Durig: http://www.aavso.org/pipermail/aavso-hen/2006-August/006238.html
Sposetti: http://www.aavso.org/pipermail/aavso-hen/2006-August/006240.html

The AAVSO thanks the Curry Foundation for their continued support of the
AAVSO International High Energy Network.

--------------------------

Observer: D. T. Durig  ( CLW01 )
Report: Started 2 hours of 30 second unguided exposures and got a few
thicker clouds near the end. So I added the first 150 good frames, total
exposure 75 minutes. No OT observed, but there is a dim background
variation at S/N~2 near reported position. Two accumulated hot pixels
nearby center at 1 oclock position and one near top center of frame are
artifacts. Gif image at http://arthur.sewanee.edu/obsv/view.php
Bright moonlight made background very bad and limited depth of
coverage.

Observer: Stefano Sposetti
Report: Observations begun at 19:45UT, aug 8th, about 29h later the
Swift-BAT trigger, under good sky conditions affected by moonlight. A
90min stacked R-filtered image centred at 20:45UT doesn't show any OT
brighter than 20mag (USNO A2.0 catalog).

N. Butler (UC Berkeley) reports:

We have analyzed the XRT PC mode data for GRB060807 (De Pasquale et al. 2006;
GCN5409
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 ), also analyzed carefully by Page et al. (2006; GCN5423
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 ).  We find 
identical spectral parameters (within errors) for the absorbed powerlaw model.
However, we note that the fit goodness for the data in the 0.3-10 keV band from 
0.1-250 ksec after the BAT trigger is marginal (chi^2/nu=138.8/103), rejectable 
at 99% confidence.

The spectrum exhibits rare (see, e.g., Butler 2006, astro-ph/0604083, for a 
few additional possible cases) and narrow modulations about the best fit 
model.  We can fit these modulations with 3 unresolved emission lines (giving 
a delta_chi^2 fit improvement of 39.0, for 6 additional degrees of freedom).  
We estimate a significance for the 3 line set of 5.0 sigma, including a 
decrease in the estimated significance due to the search for lines at many 
possible centroid energies in the 0.3-5.0 keV band.  Plots of the spectrum 
with and without the 3 most significant lines can be found at:

http://astro.berkeley.edu/~nat/GRB060807/xrt_060807_nolines.jpg , and
http://astro.berkeley.edu/~nat/GRB060807/xrt_060807_lines.jpg .

The centroid energies of the lines are 0.73, 0.90, and 1.24 keV, 
with uncertainties ~0.05 keV.  The brightest line at 0.73 keV has a flux 
~5 x 10^-14 erg cm^-2 s^-1 for the time period 0.1-250 ksec after the
BAT trigger, or 3% of the 0.3-10 keV afterglow flux.

Allowing associations for the lines with K-alpha transitions in H- or He-like 
species of common light metals or any ionization state in the Fe group 
elements, the 3-line set allows several redshift solutions.  The highest 
probability peaks have dz/z~0.2 and occur at z=0.4, 1.0, 1.6, and 4.5.  
The large X-ray absorbing column (e.g., GCN5423
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 ) suggests that the source is 
not at high-z.  An optical spectrum of the host galaxy or optical transient
could resolve the redshift degeneracy and would provide important insight 
into the nature of the X-ray emission.

Christina C. Thoene (DARK Cosmology Centre), Christina Henriksen (DARK,
NOT) and Klaas Wiersema (Univ. of Amsterdam) report:

We observed the field of GRB060807 on Sep. 20 and 22 with ALFOSC at the
NOT on La Palma in V, R and i.
At the position of the afterglow (GCN 5420
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 ), we detect an extended source,
clearly visible in stacked images from all three filters (8x600s in V and
R, 9x600s in I). We therefore conclude that the source is very likely the
host galaxy of GRB060807.
Photometry of the source gives values of V=24.9 +-0.1, R=24.26 +-0.05 and
i=22.1 +-0.2 using photometric zeropoints from the NOT/ALFOSC webpage.
This is a very red color as it was found for the color of the OT (GCN
5422
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 ) and might indicate a high redshift for this GRB.  More bands however
are required for a final conclusion.

An image of the host in the R-band can be found at
www.astro.ku.dk/~cthoene/GRBs/