GRB 131024A

J. L. Racusin (NASA/GSFC), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), H. A. Krimm (CRESST/GSFC/USRA),
A. Maselli (INAF-IASFPA), K. L. Page (U Leicester),
D. M. Palmer (LANL), P. Romano (INAF-IASFPA), M. H. Siegel (PSU),
E. Troja (NASA/GSFC/UMCP) and T. N. Ukwatta (MSU) report on behalf of
the Swift Team:

At 12:26:20 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 131024A (trigger=575707).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 290.464, -64.603 which is 
   RA(J2000) = 19h 21m 51s
   Dec(J2000) = -64d 36' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual with an image trigger, the available
BAT light curve shows no significant structure. 

The XRT began observing the field at 12:28:34.2 UT, 133.5 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 290.48228, -64.60181 which
is equivalent to:
   RA(J2000)  = 19h 21m 55.75s
   Dec(J2000) = -64d 36' 06.5"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This
location is 28 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 4.45
x 10^20 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 136 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 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 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
0.05. 

Burst Advocate for this burst is J. L. Racusin (judith.racusin AT 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.)

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

Using 1446 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 131024A, 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 = 290.48247, -64.60275 which is equivalent
to:

RA (J2000): 19h 21m 55.79s
Dec (J2000): -64d 36' 09.9"

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.

A. Trotter, J. Haislip, D. Reichart, A. Verveer, T. Spuck, A. LaCluyze, 
N. Frank, J. Moore, T. Berger, H. T. Cromartie, R. Egger, A. Foster, K. 
Ivarsen, M. Maples, M. Nysewander, E. Speckhard, and J. A. Crain report:

Skynet observed the Swift/XRT localization of the field of GRB 131024A 
(Racusin et al., GCN 15365
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 , Swift trigger # 575707) with the 14-inch 
R-COP telescope at Perth Observatory, Australia, starting at 2013-10-24, 
12:28:14 UT and continuing until 14:25 UT (t=1.9-118m post trigger). 
R-COP took a total of 44x20-80s exposures simultaneously in the BRI bands.

In a stack of 2 early R-band images at a mean time t=6.9m we marginally 
detect (S/N~3.5 sigma) an uncataloged source in the R band within the 
XRT error circle, with R~18.9 mag. In later stacks at mean times 
~70-80m, we obtain only 3-sigma upper limits in all three bands:

band    t(mean) exp     mag
B       69m      9x80s  >19.2
R       80m     12x80s  >19.8
I       83m     16x80s  >18.9

Magnitudes are in the Vega system, calibrated to four APASS-DR7 stars in 
the field, and have not been corrected for line-of-sight Milky Way dust 
extinction, with expected E(B-V)=0.05 (Schlegel et al. 1998).

No further Skynet observations are scheduled.

S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
A. Y. Lien (NASA/GSFC/ORAU), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
J. L. Racusin (NASA/GSFC), T. Sakamoto (AGU), M. Stamatikos (OSU),
J. Tueller (GSFC), T. N. Ukwatta (MSU) (i.e. the Swift-BAT team):

Using the data set from T-239 to T+303 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 131024A (trigger #575707)
(Racusin, et al., GCN Circ. 15365
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 ).  The BAT ground-calculated position is
RA, Dec = 290.544, -64.599 deg which is
    RA(J2000)  =  19h 22m 10.5s
    Dec(J2000) = -64d 35' 54.8"
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 78%. The burst started during a pre-planned slew. 
Low-level emission begins around T-150 sec. Then there is a first peak from T-70 
to T-50 sec, a second peak from T-15 to T-4 sec and a third peak from T-2 to 
T+20 sec.  We note that there is a gap in the currently available data from 
~T-140 to T-120 sec. T90 (15-350 keV) is 112.00 +- 36 sec (estimated error 
including systematics).

The time-averaged spectrum from T-111.00 to T+17.00 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.85 +- 0.18.  The fluence in the 15-150 keV band is 1.2 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-55.50 sec in the 15-150 keV band
is 0.3 +- 0.1 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/575707/BA/

A. Maselli  (INAF-IASFPA), A. Melandri (INAF-OAB), V. Mangano (PSU),
M.C. Stroh (PSU), D.N. Burrows (PSU), P.A. Evans (U. Leicester), B.P.
Gompertz (U. Leicester), J.P. Osborne (U. Leicester), B. Sbarufatti
(INAF-OAB/PSU) and J.L. Racusin report on behalf of the Swift-XRT team:

We have analysed 6.5 ks of XRT data for GRB 131024A (Racusin  et al.
GCN Circ. 15365
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 ),  from 151 s to 24.0 ks after the  BAT trigger. The
data comprise 20 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Osborne et al. (GCN. Circ 15367).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=0.46 (+/-0.05).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.08 (+0.18, -0.17). The
best-fitting absorption column is  7.7 (+3.7, -3.2) x 10^20 cm^-2,
consistent with the Galactic value of 4.4 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 3.4 x 10^-11 (4.3 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.7 (+3.7, -3.2) x 10^20 cm^-2
Galactic foreground: 4.4 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.08 (+0.18, -0.17)

If the light curve continues to decay with a power-law decay index of
0.46, the count rate at T+24 hours will be 0.036 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-12 (1.6 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/00575707.

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

V. Sudilovsky, K. Varela, D. A. Kann and J. Greiner
(all MPE Garching) report on behalf of the GROND team:

We observed the field of the GRB 131024A (Racusin et al., GCN #15365
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 )
simultaneously in g'r'i'z'JHKs with GROND (Greiner et
al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at La Silla
Observatory (Chile).

Observations started at 00:20 UT on 25 October 2013, 12 hours after the
GRB. They were performed at an average seeing of 1.6" and at an average
airmass of 1.4.

Based on two co-added observations with individual exposure times of 1500s
in g'r'i'z' and 1200s in JHK, we do not detect any source with the
enhanced XRT circle (Osborne et al., GCN #15367
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 ) down to preliminary
limiting magnitudes (all in the AB system):

g' > 25.1 mag,
r' > 24.7 mag,
i' > 23.9 mag,
z' > 23.8 mag,
J > 21.6 mag,
H > 21.0 mag,
K > 20.0 mag.

We do note there is a marginally detected source in r' at roughly 1.6"
north-east of the center of the error circle.

Magnitudes are calibrated against GROND zeropoints (griz) and 2MASS stars
(JHK), and
are not corrected for the Galactic foreground extinction corresponding to
a reddening of E_(B-V)=0.04 mag in the direction of the burst (Schlegel
et al. 1998).

M. H. Siegel (PSU) and J. L. Racusin (NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 131024A
137 s after the BAT trigger (Racusin et al., GCN Circ. 15365
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 ).
No optical afterglow consistent with the enhanced XRT position
(Osborne et al., GCN Circ. 15367
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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) exposure and subsequent exposures are:

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

white (fc)         136          286          147         >20.63
white              136         1542          392         >21.69
v                  624         1592          116         >18.91
b                  550         1517           97         >19.75
u (fc)             294          544          245         >19.99
u                  294         1492          569         >20.49
uvw1               673         1468           97         >19.15
uvm2               648         1606          106         >18.99
uvw2               600         1567          116         >19.48

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
(Schlegel et al. 1998).