GRB 080727C

A. M. Parsons (GSFC), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), S. T. Holland (CRESST/USRA/GSFC),
E. A. Hoversten (PSU), S. D. Hunsberger (PSU), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL),
D. Perez (U Leicester), T. Sakamoto (NASA/UMBC),
R. L. C. Starling (U Leicester), M. C. Stroh (PSU) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 23:07:35 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080727C (trigger=318170).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 32.645, +64.151 which is 
   RA(J2000)  = 02h 10m 35s
   Dec(J2000) = +64d 09' 05"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multiple peaks
with a duration of about 100 sec.  The peak count rate
was ~3500 counts/sec (15-350 keV), at ~25 sec after the trigger. 

The XRT began observing the field at 23:08:47.9 UT, 72.5 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
32.63384, 64.13771 which is equivalent to:
   RA(J2000)  = 02h 10m 32.12s
   Dec(J2000) = +64d 08' 15.8"
with an uncertainty of 2.8 arcseconds (radius, 90% containment). This
location is 50 arcseconds from the BAT onboard position, within the BAT
error circle. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (6.78e+21
cm^-2, Kalberla et al. 2005), with an excess column of 7.7
(+7.98/-6.22) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.30e-09 erg cm^-2 s^-1 (0.2-10
keV). 


UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 81 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
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the large, but uncertain extinction expected. 




We note that the Galactic latitude of this source is 2.6 deg,
but we believe this to be a GRB based on the BAT and XRT lightcurves
and the spectral information. 

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.)

I. Bikmaev (KSU/AST), I. Khamitov (TUG), N. Sakhibullin (KSU/AST),
Z. Eker (TUG), U. Kiziloglu (METU),  E. Gogus (Sabanci Uni.)
R. Burenin, M. Pavlinsky, R. Sunyaev (IKI),

report:

The field  of GRB 080727C (GCN 8035
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 , SWIFT trigger=318170) was observed 
with Russian-Turkish 1.5-m  telescope (RTT150, Bakirlitepe, TUBITAK
National Observatory, Turkey), starting at  28 July, 00:58 UT,
i.e. ~2 hours after the burst, using Andor CCD.

We made 2*900 sec exposures in the R band and 900 sec exposure in the I 
band. We found no new source within XRT error circle. Using USNO-B1 stars 
we estimated frame limits as R~23.0 mag, I~21.5 mag.


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J.P. Osborne, A.P. Beardmore, P.A. Evans and M.R. Goad (U. Leicester) 
report on behalf of the Swift-XRT team.

Using 1905 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 080727C, 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 = 32.63485, +64.13754 which is equivalent
to:

RA (J2000): 02h 10m 32.36s
Dec (J2000): +64d 08' 15.2"

with an uncertainty of 1.5 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.

C. Guidorzi (INAF-OAB), S. Kobayashi, M.J. Burgdorf (Liverpool JMU)
and N. Tanvir (U. Leicester) report on behalf of a larger collaboration:

On 2008 July 28 (01:35:55 UT) we began observing the field of GRB 080727C
(Parsons et al. GCN Circ. 8035
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 ) with the Liverpool Telescope.
Observations consisted of 6x300s exposures acquired using the SDSS-i'
filter.

In our coadded frame we do not detect any source inside the refined XRT
error box (Osborne et al. GCN Circ. 8038
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 ) down to the limiting magnitude
reported below.

Telescope   Filter  T_mid[s]   Exposure[s]    M_lim (3-sigma)

-------------------------------------------------------------
Liverpool   SDSS-i'  9830        6x300         22.8
-------------------------------------------------------------

The calibration was performed using the I magnitudes of several USNOB-1
catalogue field objects. The value derived by us is consistent with
that given by Bikmaev et al. (GCN Circ. 8036
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 ).

R.L.C. Starling (U. Leicester) and A.M. Parsons (GSFC) report on behalf of 
the Swift XRT team:

We have analysed the first five orbits of Swift XRT data for GRB 080727C 
(trigger=318170, Parsons et al. GCN Circ. 8035
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 ) beginning at T0+79 s until 
T0+22.6 ks. The enhanced XRT position is given in Osborne et al. 
(GCN Circ. 8038
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 ).

Up to approximately T0+110 s the light curve appears to be flat. 
Thereafter the light curve can be fitted with a broken power law with 
alpha1 = 1.5+/-0.1, breaking at Tbk = 740 +1880/-370 s to a slightly 
shallower decay of alpha2 = 1.2 +0.1/-0.3. 

The Photon Counting mode spectrum consisting of 502 s of data during the 
first orbit is well fitted with an absorbed power law of photon index 
Gamma = 1.4+/-0.3 and intrinsic absorption (assuming z=0) of N_H = (1.2 
+0.5/-0.2) e22 cm-2 in addition to the high Galactic absorption in this 
direction of N_H = 6.8e21 cm-2 (Kalberla et al. 2005). 
We measure an average observed (unabsorbed) 0.3-10 keV flux over this time 
of 1.1e-10 (1.7e-10) erg/cm2/s corresponding to an observed count rate to 
flux conversion of 1 count/s = 9.9e-11 erg/cm2/s.

The predicted count rate at T+24 hr is 0.001 count/s corresponding to an
observed 0.3-10 keV flux of 1.35e-13 erg/cm2/s, assuming the decay 
continues with alpha=1.2.

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

E. A. Hoversten (PSU) and A. M. Parsons (GSFC) report on behalf of the
Swift/UVOT team:

The Swift/UVOT began observing the field of GRB 080727C starting 82
seconds after the BAT trigger (Parsons, et al. GCN Circ. 8035
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 ).  We do
not detect any source in any of the filters at the UVOT-enhanced XRT
position (Osborne, et al., GCN Circ. 8038
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 ).  The 3-sigma upper limits
at this position for single exposures are:

Filter  T_start    T_stop   Exp(s)  Mag (3-sigma upper limit)
-----------------------------------------------------
white      82.1     181.0    97.3     > 20.81
white    3987.1    4186.8   196.6     > 21.58
v         187.4     587.2   393.5     > 19.89
v        4397.7    4597.5   196.6     > 19.93
b         668.8     673.4     4.6     > 17.79
u         643.0     662.8    19.5     > 18.32
uvw1      618.4     638.2    19.5     > 18.11
uvm2      593.5     613.3    19.5     > 17.61
uvw2     4192.9    4392.7   196.6     > 20.17


The quoted upper limits have not been corrected for the expected
Galactic extinction along the line of sight corresponding to a large
reddening of E_{B-V} = 1.1 mag.  All photometry is on the UVOT flight
system described in Poole et al. (2008, MNRAS, 383, 627).

E. Fenimore (LANL), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC),
J. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), K. McLean (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+843 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 080727C (trigger #318170)
(Parsons, et al., GCN Circ. 8035
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 ).  The BAT ground-calculated position is
RA, Dec = 32.638, 64.130 deg which is 
   RA(J2000)  =  02h 10m 33.2s 
   Dec(J2000) = +64d 07' 48.6" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 77%.
 
The mask-weighted light curve shows several overlapping peaks starting
at ~T-5 sec and ending at ~T+200 sec.  T90 (15-350 keV) is 79.7 +- 8.8 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-3.3 to T+116.3 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.87 +- 0.20, 
and Epeak of 143.2 +- 50.0 keV (chi squared 66 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 5.2 +- 0.2 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+15.23 sec in the 15-150 keV band is
2.3 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.30 +- 0.05 (chi squared 81 for 57 d.o.f.).  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/318170/BA/

Gendre, B. (LAM/CNRS), Klotz, A. (CESR-OMP), Boer M. (OHP), Atteia J.L. 
(LATT-OMP) report:

We imaged the field of GRB 080727 detected by SWIFT
(trigger 318170) with the TAROT robotic telescope (D=25cm)
located at the Calern observatory, France.

The observations started 790.7s after the GRB trigger
(765.8s after the notice). The elevation of the field increased from
from 38 degrees above horizon and weather conditions
were good.

The date of trigger : t0 = 2008-07-27T23:07:35.040

At the enhanced XRT position given by Osborne et al.
(GCN #8038
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 ) we do not detect any optical transient.

We co-added a series of exposures:
t0+857.5s to t0+1850.1s : R > 18.5

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

N.B. Galactic coordinates are lon=131.4275 lat= +2.5930
and the galactic extinction in R band is 2.8 magnitudes
estimated from D. Schlegel et al. 1998ApJ...500..525S.

This message may be cited.

K. Yamaoka, S. Sugita (Aoyama Gakuin U.), M. Ohno, M. Kokubun,
M. Suzuki, T. Takahashi (ISAS/JAXA), Y.E. Nakagawa, T. Tamagawa
(RIKEN), T. Uehara, T. Takahashi, Y. Fukazawa, C. Kira, Y. Hanabata 
(Hiroshima U.),  M. Tashiro, Y. Terada, Y. Urata, A. Endo, K. Onda, 
N. Kodaka, K. Morigami, T. Sugasahara, W. Iwakiri (Saitama U.), 
T. Enoto, K. Nakazawa, K. Makishima (Univ. of Tokyo), E. Sonoda, M. Yamauchi, 
H. Tanaka, R. Hara, N. Ohmori (Univ. of Miyazaki),  S. Hong (Nihon U.), 
on behalf of the Suzaku WAM team, report:

The long 080727C (Swift/BAT trigger #318170; Parsons et al., GCN 8035
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 )
triggered the Suzaku Wide-band All-sky Monitor (WAM) which
covers an energy range of 50 keV - 5 MeV at 23:07:51.558 UT (=T0).
The observed light curve shows two peaks, starting at T0-13s, ending
at T0+70s, with a duration (T90) of about 54 seconds. The fluence in 150 - 1000 keV 
was (6.0 +/- 0.7) x 10^-6 erg/cm^2. The 1-s peak flux measured from T0+9s was 
0.78 +/- 0.12 photons/cm^2/s in the same energy range.

Preliminary result shows that the time-averaged spectrum from T0-7s to T0+47s 
is fitted by a single power-law with a photon index of 1.83 +/- 0.18
in the 150 - 1000 keV range (chi^2/d.o.f = 6.1/11). All the quoted errors are at statistical 
90% confidence level, in which the systematic uncertainties are not included.

The light curves with 1/64 sec time resolution for this burst are now available at:
http://www.astro.isas.jaxa.jp/suzaku/HXD-WAM/WAM-GRB/grb/trig/grb_table.html