GRB 170206B

A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC),
A. Cholden-Brown (PSU), J. A. Kennea (PSU),
F. E. Marshall (NASA/GSFC), B. Mingo (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL), P. Romano (INAF-OAB),
B. Sbarufatti (INAF-OAB/PSU) and E. Troja (NASA/GSFC/UMCP) report on
behalf of the Swift Team:

At 21:57:25 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170206B (trigger=737125).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 271.786, +11.223, which is 
  RA(J2000) = 18h 07m 09s
  Dec(J2000) = +11d 13' 23"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  Due to a processing outage, the real-time light curve
is not available at this time. 

Using promptly downlinked data we find an uncatalogued X-ray source
with an enhanced position: RA, Dec 271.7708, 11.1943 which is
equivalent to:
   RA(J2000)  = 18h 07m 04.98s
   Dec(J2000) = +11d 11' 39.4"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). 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 in excess of the Galactic value (1.13 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 2.8
(+2.82/-2.42) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 250 seconds with the U filter. 
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 18.0 mag. No correction has been made 
for the expected extinction of E(B-V) = 0.146. 

Burst Advocate for this burst is A. Y. Lien (amy.y.lien 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.)

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Using 1338 s of XRT Photon Counting mode data and 1 UVOT  image, 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 = 271.77061, 11.19366 which is equivalent to:

RA (J2000):  18 07 04.95
Dec (J2000): +11 11 37.2

with an uncertainty of 1.9 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 is an official product of the Swift-XRT team.

S. J. LaPorte (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU),
S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo
(INAF-OAB) and A.Y. Lien report on behalf of the Swift-XRT team:

We have analysed 7.4 ks of XRT data for GRB 170206B (Lien et al. GCN
Circ. 20618
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 ), from 88 s to 24.5 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. Using 2057 s
of PC mode data and 3 UVOT images, we find an enhanced XRT position
(using the XRT-UVOT alignment and matching UVOT field sources to the
USNO-B1 catalogue): RA, Dec = 271.77062, +11.19383 which is equivalent
to:

RA (J2000): 18h 07m 04.95s
Dec(J2000): +11d 11' 37.8"

with an uncertainty of 1.6 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=2.48 (+0.19, -0.20).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.46 (+0.18, -0.17). The
best-fitting absorption column is  4.9 (+0.8, -0.7) x 10^21 cm^-2, in
excess of the Galactic value of 1.1 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 3.1 x 10^-11 (6.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     4.9 (+0.8, -0.7) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^21 cm^-2
Excess significance: 8.5 sigma
Photon index:	     2.46 (+0.18, -0.17)

If the light curve continues to decay with a power-law decay index of
2.48, the count rate at T+24 hours will be 2.5 x 10^-7 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.8 x
10^-18 (1.8 x 10^-17) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00737125.

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

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

Using the data set from T-239 to T+359 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 170206B (trigger #737125)
(Lien et al., GCN Circ. 20618
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 ).  The BAT ground-calculated position is
RA, Dec = 271.784, 11.175 deg which is
   RA(J2000)  =  18h 07m 08.2s
   Dec(J2000) = +11d 10' 28.3"
with an uncertainty of 2.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 78%.

The mask-weighted light curve shows a weak pulse that starts at ~T0 and
ends at ~T+15 s. T90 (15-350 keV) is 13.36 +- 2.67 sec (estimated error
including systematics).

The time-averaged spectrum from T-0.33 to T+15.53 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.42 +- 0.27.  The fluence in the 15-150 keV band is 3.2 +- 0.6 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.32 sec in the 15-150 keV band
is 0.4 +- 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/737125/BA/

S.W.K. Emery (UCL-MSSL) and A. Y. Lien (GSFC/UMBC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170206B
106 s after the BAT trigger (Lien et al., GCN Circ. 20618
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 ).
No optical afterglow consistent with the XRT position
(Evans et al. GCN Circ. 20619
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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           106          255          147         >20.3
u_FC               264          513          246         >19.6
white              106         1534          392         >20.7
v                  594         1411           97         >18.2
b                  519         1510           97         >19.1
u                  226         1484          343         >19.7
w1                 643         1460           97         >18.6
w2                 569         1386           97         >19.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.146 in the direction of the burst
(Schlegel et al. 1998).

K. P. Mooley (Hintze Fellow, Oxford), T. D. Staley, R. P. Fender 
(Oxford), G. E. Anderson (Curtin), T. Cantwell (Manchester), D. 
Titterington, S. H. Carey, J. Hickish, Y. C. Perrott, N. Razavi-Ghods, 
P. Scott (Cambridge), K. Grainge, A. Scaife (Manchester)

The AMI Large Array observed the Swift GRB 170206B (Lien et al., GCN 
20618
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 ) as part of the 4pisky program; follow up observations were 
obtained up to 10 days post-burst. Our observations at 15 GHz on 2016 
Feb 08.37, Feb 09.38, Feb 14.43 and Feb 15.46 (UT) do not reveal any 
radio source at the XRT location (Evans et al., GCN 20619
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 ), with 3sigma 
upper limits of 123 uJy, 108 uJy, 108 uJy and 108 uJy respectively.

We thank the AMI staff for scheduling these observations. The AMI-GRB 
database is a log of all GRB follow up observations with the AMI, and is 
available at http://4pisky.org/ami-grb/.