GRB 251112A

D. Sadaula (GSFC/UMBC), S. D. Barthelmy (GSFC), 
R. Gupta (GSFC), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa),
C. B. Markwardt (GSFC), A. Mei (INAF-OAB)
M. J. Moss (GSFC), D. M. Palmer (LANL),
T. Parsotan (GSFC), T. Sakamoto (AGU)
(i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 251112A (trigger #1413695)
(Mei, et al., GCN Circ. 42656
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 ).  The BAT ground-calculated position is
RA, Dec = 274.081, 24.158 deg which is 
   RA(J2000)  =  18h 16m 19.5s 
   Dec(J2000) = +24d 09' 28.8" 
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted BAT light curve shows multi-peaked emission starting ~T-28 sec.
T90 (15-350 keV) is 55.42 +- 6.65 sec (estimated error including systematics).
 
The time-averaged spectrum from T-28.30 to T+32.38 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.77 +- 0.75, 
and Epeak of 48.4 +- 11.9 keV (chi squared 86.37 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 7.6 +- 0.9 x 10^-07 erg/cm2
and the 1-sec peak flux measured from T+1.05 sec in the 15-150 keV band is
0.7 +- 0.1 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.86 +- 0.15 (chi squared 94.39 for 57 d.o.f.).  All the quoted errors
are at the 90% confidence level. 
 
The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1413695

A.A. Breeveld (UCL-MSSL) and A. Mei (INAF-OAB) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 251112A 304 s after the BAT trigger (Mei et al., GCN Circ. 42656
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 ).
No optical afterglow consistent with the XRT position (Lanava et al., GCN Circ. 42665
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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

u_FC               304          553          246         >19.9
white              856          944           86         >20.0
uvw1               683          697           14         >17.2
uvm2               658          849           39         >17.6
uvw2               609          801           39         >18.0

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.158 in the direction of the burst (Schlegel et al. 1998).

S. Lanava (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), A.
Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB) and
P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

We have analysed 847 s of XRT data for GRB 251112A, from 90 s to 939 s
after the  Swift trigger. The data comprise 64 s in Windowed Timing
(WT) mode with the remainder in Photon Counting (PC) mode. The refined
XRT position is RA, Dec = 274.0697, +24.1535 which is equivalent to:

RA (J2000): 18h 16m 16.72s
Dec(J2000): +24d 09' 12.5"

with an uncertainty of 4.1 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=3.14 (+0.34, -0.30).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 3.3 (+/-0.4). The
best-fitting absorption column is  4.9 (+1.3, -1.1) x 10^21 cm^-2, in
excess of the Galactic value of 1.8 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 2.2 x 10^-11 (1.1 x 10^-10) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     4.9 (+1.3, -1.1) x 10^21 cm^-2
Galactic foreground: 1.8 x 10^21 cm^-2
Excess significance: 4.6 sigma
Photon index:	     3.3 (+/-0.4)

If the light curve continues to decay with a power-law decay index of
3.14, the count rate at T+24 hours will be 7.8 x 10^-9 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x
10^-19 (8.4 x 10^-19) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/01413695.

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

A. Mei (INAF-OAB), J. J. DeLaunay (PSU), M. Ferro (INAF-OAB),
R. Gupta (NASA GSFC) and M. H. Siegel (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 21:28:56 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a possible GRB 251112A (trigger=1413695).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 274.019, +24.226 which is 
   RA(J2000) = 18h 16m 05s
   Dec(J2000) = 24d 13' 32"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 60 sec.  The peak count rate
was ~600 counts/sec (15-350 keV), at ~25 sec after the trigger.

The XRT began observing the field at 21:30:22.7 UT, 86.9 seconds after
the BAT trigger. No source was detected in 782 s of promptly downlinked
data. We are waiting for the full dataset to detect and localise the
XRT counterpart.

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 91 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 25% of
the BAT 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
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
0.161.

Due to no credible afterglow candidate in the initial XRT and UVOT
data, we for now call this a possible GRB while we wait for
additional data for further inspection.

Burst Advocate for this burst is A. Mei (alessio.mei AT inaf.it).
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/)