GRB 130803A

K. L. Page (U Leicester), F. E. Marshall (NASA/GSFC),
C. J. Mountford (U Leicester), D. M. Palmer (LANL) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 10:02:52 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130803A (trigger=565263).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 220.241, -2.467 which is 
   RA(J2000) = 14h 40m 58s
   Dec(J2000) = -02d 28' 01"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 50 sec.  The peak count rate
was ~4750 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 10:04:22.8 UT, 90.3 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 220.25472, -2.49296 which is equivalent
to:
   RA(J2000)  = 14h 41m 01.13s
   Dec(J2000) = -02d 29' 34.7"
with an uncertainty of 4.7 arcseconds (radius, 90% containment). This
location is 105 arcseconds from the BAT onboard position, within the
BAT error circle. This position may be improved as more data are
received; the latest position is available at
http://www.swift.ac.uk/sper.  We cannot determine whether the source is
fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (4.16 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 7
(+6.70/-4.79) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 93 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers none of
the XRT error circle. 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 0.05. 

Burst Advocate for this burst is K. L. Page (kpa AT star.le.ac.uk). 
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.)

A. Melandri (INAF/OAB), C. Guidorzi (U. Ferrara) and C. G. Mundell  
(LJMU) report on behalf of a large collaboration:

Tha Faulkes Telescope South robotically observed the field of GRB  
130803A starting ~ 2.9 minutes after the Swift trigger (Page et al.,  
GCN 15059
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 ). We find no credible afterglow candidate in the XRT error  
circle.

We estimate a 3 sigma upper limit of R>20.0 (texp=30s) ~3.5 minutes  
and I>21.9 (texp=700s) ~40 minutes after the burst.

Magnitudes are calibrated against nearby USNOB-1 stars.

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

Using 2053 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 130803A, 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 = 220.25273, -2.49195 which is equivalent
to:

RA (J2000): 14h 41m 0.66s
Dec (J2000): -02d 29' 31.0"

with an uncertainty of 1.8 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) and Evans
et al. (2009, MNRAS, 397, 1177).

This circular was automatically generated, and is an official product of the
Swift-XRT team.

GRB 130803A, Swift-BAT refined analysis
  
J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC),  W. H. Baumgartner (GSFC/UMBC),
E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
A. Y. Lien (NASA/GSFC/ORAU), C. B. Markwardt (GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL), T. Sakamoto (AGU), G. Sato (ISAS), M. Stamatikos (OSU),
J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
  
Using the data set from T-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 130803A (trigger #565263) (Page, et al.,
GCN Circ. 15059
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 ).  The BAT ground-calculated position is
RA, Dec = 220.256, -2.499 deg which is
    RA(J2000)  =  14h 41m 01.4s
    Dec(J2000) = -02d 29' 58"
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 30%.
  
The mask-weighted light curve shows two well-separated symmetrical peaks.  The
first, larger peak starts at about T0-2 seconds and lasts until about T+8 seconds.
The second peak, which was softer, starts about T0+41 seconds and lasts until about
T0+48 seconds.  T90 (15-350 keV) is 44 +- 2 sec (estimated error including
systematics).
  
The time-averaged spectrum from T-1.24 to T+45.76 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.69 +- 0.14.  The fluence in the 15-150 keV band is 1.5 +- 0.1 x 10^-06 erg/cm2.
The 1-sec peak photon flux measured from T+2.09 sec in the 15-150 keV band
is 5.1 +- 0.4 ph/cm2/sec.  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/565263/BA/

Subject: GRB 130803A: Fermi GBM observation

Hoi-Fung Yu (MPE) report on behalf of the Fermi GBM Team:

"At 10:02:53.75 UT on 03 Aug 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 130803A (trigger 397216976 / 130803419),
which was also detected by the Swift BAT and XRT (Page et al. 2013,
GCN 15059
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 ). The GBM on-ground location is consistent with the Swift
position. The angle from the Fermi LAT boresight is 86 degrees.

The GBM light curve consists of a single pulse,
with a duration (T90) of about 7.6 s (50-300 keV).
The time-averaged spectrum from T0-1.0 s to T0+4.9 s is
adequately fit by a power law function with an exponential
high-energy cutoff.  The power-law index is -0.85 +/- 0.09 and
the cutoff energy, parameterized as Epeak, is 141.6 +/- 12.2 keV.

The event fluence (10-1000 keV) in this time interval is
(2.5 +/- 0.1)E-6 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.6 s in the 10-1000 keV band
is 7.1 +/- 0.3 ph/s/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."

F. E. Marshall (NASA/GSFC) and K. L. Page (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 130803A
93 s after the BAT trigger (Page et al., GCN Circ. 15059
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 ).
No optical afterglow consistent with the enhanced XRT position
(Osborne et al. GCN Circ. 15062
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 )
is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first
finding chart (FC) exposures and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC            93          243          147         >21.0
u_FC               305          555          246         >20.3
white               93         6186          560         >21.7
v                  636        11010         1142         >20.8
b                  561         5981          413         >21.0
u                  305         5776          639         >20.7
w1                3936        16308          788         >21.4
m2                5167        11916         1082         >21.2
w2                4757         6392          393         >20.9

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.05 in the direction of the burst

K.Varela (MPE Garching), P.Afonso (American River College) and J.Greiner
(MPE Garching)report on behalf of the GROND team :

We observed the field GRB 130803A (Swift trigger 565263; Page et al.,
GCN 15059
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 ) simultaneously in g'r'i'z'JHKs with GROND (Greiner et al.2008,
PASP 120, 405) mounted at the 2.2m MPG/ESO telescope at La Silla
Observatory (Chile).

Observations started at 23:13 UT on August 3, about 13.2 hours after
the trigger at a mean seeing of 1.8 arcsec and a mean airmass of 1.3. We
detect an extended source inside the enhanced 1.4'' XRT error circle
(Swift webpage). This could be the GRB host, though at the moment no
statement about variability can be made.

For stacked integration times of 100 min. in JHK and ~ 125min in griz, we
present the following preliminary magnitudes and ULs at the 3 sigma level:

g' = 25.6 +/- 0.4 mag,
r' = 24.4 +/- 0.3 mag,
i' = 23.8 +/- 0.2 mag,
z' = 23.4 +/- 0.3 mag,
J > 23.2 mag,
H > 22.5 mag, and
K > 22.2 mag.

Given magnitudes are calibrated against GROND zeropoints as well as 2MASS
field stars and are not corrected for the expected Galactic foreground
extinction corresponding to a reddening of E(B-V) = 0.05 mag in the
direction of the burst (Schlegel et al. 1998).

Owen Littlejohns (ASU), Nat Butler (ASU), Alan M. Watson (UNAM),
Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM),
Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh
Bloom (UCB), Antonino Cucchiara (UCSC), Eleonora Troja (GSFC), Enrico
Ramirez-Ruiz (UCSC), José A. de Diego (UNAM), Leonid Georgiev (UNAM),
Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC),
and Harvey Moseley (GSFC) report:

We observed the field of GRB 130803A (Page, et al., GCN 15059
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 ) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the
1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on
Sierra San Pedro Mártir from 2013/08 4.15 to 2013/08 4.25 UTC (17.51
to 19.98 hours after the BAT trigger), obtaining a total of 1.53 hours
exposure in the r' and i' bands and 0.63 hours exposure in the Z,
Y, J, and H bands.

For a source within the Swift-XRT error circle, in comparison with SDSS DR9
and 2MASS, we obtain the following upper limits (3-sigma):

  r'    > 23.29
  i'    > 23.24
  Z     > 22.27
  Y     > 21.70
  J     > 20.90
  H     > 20.24

These magnitudes are in the AB system and not corrected for Galactic
extinction in the direction of the GRB. Our upper limits are consistent
with the detections and upper limits reported by Varela, et al. (GCN 15066
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 ).

We thank the staff of the Observatorio Astronómico Nacional in San Pedro
Mártir.

A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), B.P. Gompertz
(U. Leicester), B. Sbarufatti (INAF-OAB/PSU), P. D'Avanzo (INAF-OAB),
V. D'Elia (ASDC), J.A. Kennea (PSU), V. Mangano (PSU), M.C. Stroh (PSU)
and K.L. Page report on behalf of the Swift-XRT team:

We have analysed 10 ks of XRT data for GRB 130803A (Page  et al. GCN
Circ. 15059
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 ),  from 75 s to 61.7 ks after the  BAT trigger. The data
comprise 7 s in Windowed Timing (WT) mode (taken while Swift was
slewing), with the remainder in Photon Counting (PC) mode. The enhanced
XRT position for this burst was given by Osborne et al. (GCN. Circ
15062).

The late-time light curve (from T0+3.9 ks) can be modelled with  a
power-law decay with a decay index of alpha=0.87 (+/-0.09).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.40 (+0.24, -0.23). The
best-fitting absorption column is  8.7 (+1.6, -1.4) x 10^21 cm^-2, in
excess of the Galactic value of 4.2 x 10^20 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.5 x 10^-11 (1.3 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.7 (+1.6, -1.4) x 10^21 cm^-2
Galactic foreground: 4.2 x 10^20 cm^-2
Excess significance: 9.7 sigma
Photon index:	     2.40 (+0.24, -0.23)

If the light curve continues to decay with a power-law decay index of
0.87, the count rate at T+24 hours will be 9.6 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.3 x
10^-13 (1.2 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00565263.

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

K. Varela (MPE Garching), M. Tanga (MPE Garching), P. Afonso (American
River College) and J. Greiner (MPE Garching) report on behalf of the
GROND team:

We observed a second epoch of the field of GRB 130803A (Swift trigger
565263; Page et al., GCN 15059
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 ) simultaneously in g'r'i'z'JHKs with GROND
(Greiner et al.2008, PASP 120, 405) mounted at the 2.2m MPG/ESO telescope
at La Silla Observatory (Chile).

Observations started at 23:34 UT on August 5, about 61.7 hours after
the trigger at a mean seeing of 1.5 arcsec and a mean airmass of 1.3. We
confirm the detection of the source inside the enhanced 1.4'' XRT error
circle (Swift webpage) reported in a previous GCN (Varela et al.,
GCN15066
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 ),
and measure consistent magnitudes as compared to the first epoch
(the g'-band magnitude contained an error and should read g' = 24.6 +/- 0.4).
Thus, we consider this source as the potential host of GRB 130803A.