GRB 171212A

A. Tohuvavohu (PSU), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), P. D'Avanzo (INAF-OAB), A. Deich (PSU),
S. W. K Emery (UCL-MSSL), P. A. Evans (U Leicester), J.D. Gropp (PSU),
J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB),
K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Swift Team:

At 11:57:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 171212A (trigger=796778).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 293.900, +20.568 which is 
   RA(J2000) = 19h 35m 36s
   Dec(J2000) = +20d 34' 06"
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 120 sec.  The peak count rate
was ~800 counts/sec (15-350 keV), at ~90 sec after the trigger. 

The XRT began observing the field at 11:58:52.7 UT, 91.0 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 293.91826,
20.59159 which is equivalent to:
   RA(J2000)  = 19h 35m 40.38s
   Dec(J2000) = +20d 35' 29.7"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 104 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 1.23
x 10^22 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 1.28e-08 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 99 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 large, but uncertain, extinction expected. 

Because this event is very close to the Galactic plane (lat=0.03 degrees)
it is possibly a Galactic transient, in which case it takes the 
name 'Swift J1935.7+2036'. 

Burst Advocate for this burst is A. Tohuvavohu (aaronb AT swift.psu.edu). 
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.)

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

Using 1519 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 171212A, 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 = 293.91782, +20.59204 which is equivalent
to:

RA (J2000): 19h 35m 40.28s
Dec (J2000): +20d 35' 31.3"

with an uncertainty of 2.3 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.

E. Mazaeva (IKI), A. Pozanenko (IKI), I. Reva (FAPHI), M. Krugov 
(FAPHI), A. Kusakin (FAPHI), A. Volnova (IKI)   report on behalf of 
larger GRB follow-up collaboration:

We observed the field of GRB 171212A (Tohuvavohu  et al., GCN 22243
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 ) 
with Zeiss-1000 1-m telescope of Tien Shan Astronomical Observatory 
starting on Dec. 12 (UT) 12:21:15. We took several images in R-filter. 
Within enhanced Swift-XRT error circle   (Evans et al. GCN 22245
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 )  we do 
not detect any object. Preliminary photometry of initial combined images 
is following.

Date        UT start    t-T0  Filter Exp.   OT   Err. ULim
                      (mid, days)     (s)

2017-12-12  12:21:15 0.01896  R      3*120  n/d  n/d  20.0
2017-12-12  12:21:15 0.02728  R     13*120  n/d  n/d  21.1


The photometry is based on several nearby USNO-B1.0 stars

USNO-B.1_id  R2
1105-0415742 17.60
1105-0415769 17.54
1105-0415805 16.38
1106-0408959 17.07
1105-0415666 16.91

A. A. Breeveld (UCL-MSSL) and A. Tohuvavohu (PSU) report on behalf of 
the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 171212A 99 
s after the BAT trigger (Tohuvavohu et al., GCN Circ. 22243
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 ).
No optical afterglow consistent with the enhanced XRT position (Evans et 
al., GCN Circ. 22245
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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            99          249          147         >20.3
u_FC               257          507          246         >19.8
white               99         5510          383         >20.8
v                  588         5921          235         >19.0
b                  513         6581          275         >20.1
u                  257         6536          468         >20.1
w1                 638         6331          236         >19.5
m2                5926         6125          197         >19.3
w2                 738         5716          216         >19.5

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 7.95 in the direction of the 
burst (Schlegel et al. 1998).

A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), A. Melandri
(INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), S. J. LaPorte
(PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), S.L. Gibson (U.
Leicester) and A. Tohuvavohu report on behalf of the Swift-XRT team:

We have analysed 5.7 ks of XRT data for GRB 171212A (Tohuvavohu et al.
GCN Circ. 22243
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 ), from 81 s to 29.5 ks after the  BAT trigger. The data
comprise 347 s in Windowed Timing (WT) mode (the first 8 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Evans et
al. (GCN Circ. 22245
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 ).

The late-time light curve (from T0+5.1 ks) can be modelled with a
power-law decay with a decay index of alpha=1.2 (+0.4, -0.3).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.83 (+/-0.08). The
best-fitting absorption column is  4.73 (+0.23, -0.22) x 10^22 cm^-2,
in excess of the Galactic value of 1.2 x 10^22 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 8.1 x 10^-11 (1.9 x 10^-10) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     4.73 (+0.23, -0.22) x 10^22 cm^-2
Galactic foreground: 1.2 x 10^22 cm^-2
Excess significance: 26.2 sigma
Photon index:	     1.83 (+/-0.08)

If the light curve continues to decay with a power-law decay index of
1.2, the count rate at T+24 hours will be 1.5 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-13 (2.8 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00796778.

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

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF/USRA),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. Stamatikos (OSU),
A. Tohuvavohu (PSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):

Using the data set from T-240 to T+1004 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 171212A (trigger #796778)
(Tohuvavohu et al., GCN Circ. 22243
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 ).  The BAT ground-calculated position is
RA, Dec = 293.920, 20.597 deg which is
  RA(J2000)  =  19h 35m 40.8s
  Dec(J2000) = +20d 35' 49.6"
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 60%.

The mask-weighted light curve shows a multi-peaked structure that starts at
~ T-30 s and ends at ~T+100 s, with some weak emissions lasting till ~ T+370 s.
T90 (15-350 keV) is 320 +- 72 sec (estimated error including systematics).

The time-averaged spectrum from T-28.82 to T+371.18 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.23 +- 0.14.  The fluence in the 15-150 keV band is 3.4 +- 0.3 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+90.68 sec in the 15-150 keV band
is 0.7 +- 0.2 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/796778/BA/