GRB 170208A

A. Cholden-Brown (PSU), D. N. Burrows (PSU), J. A. Kennea (PSU),
A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester),
B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf
of the Swift Team:

At 18:11:16 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170208A (trigger=737438).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 166.563, -46.779 which is 
   RA(J2000) = 11h 06m 15s
   Dec(J2000) = -46d 46' 43"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 10 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 18:13:16.4 UT, 120.2 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source with an enhanced position: RA, Dec 166.5643,
-46.7674 which is equivalent to:
   RA(J2000)  = 11h 06m 15.44s
   Dec(J2000) = -46d 46' 02.6"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 41 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 in excess of the Galactic value (1.25 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 2.4
(+2.01/-1.79) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 124 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 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 0.13. 

Burst Advocate for this burst is A. Cholden-Brown (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.)

O.J. Roberts (USRA/NASA) and C. Meegan (UAH) report on 
behalf of the Fermi GBM Team:

"At 18:11:16.40 UT on the 8th of February 2017, the Fermi
Gamma-Ray Burst Monitor triggered and located GRB 170208A
(trigger 508270281 / 170208758), which was also detected by 
Swift (A. Cholden-Brown et al. 2017, GCN 20631
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 ). The GBM 
on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger
time using the Swift-XRT position is 117 degrees.

This burst was also independently detected by INTEGRAL SPI-ACS.

The GBM light curve consists of a long GRB with several
episodes of bright emission over a duration (T90) of about
7 s (50-300 keV). The time-averaged spectrum from T0+0 s
to T0+7.2 s is best fit by a power law function with an 
exponential high-energy cutoff.  The power law index is 
-0.92 +/- 0.09 and the cutoff energy, parameterized as Epeak 
is 246.9 +/- 30.5 keV

The event fluence (10-1000 keV) in this time interval is 
(3.10 +/- 0.19)E-06 erg/cm^2. The 1-sec peak photon flux
measured starting from T0-0.13 s in the 10-1000 keV band
is 8.1 +/- 0.4 ph/s/cm^2.

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

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

Using 1316 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 170208A, 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 = 166.56468, -46.76827 which is equivalent
to:

RA (J2000): 11h 06m 15.52s
Dec (J2000): -46d 46' 05.8"

with an uncertainty of 1.7 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.

D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, P. Oleynik,
M. Ulanov, A. Tsvetkova, A. Lysenko, A.Kozlova, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration GRB 170208A
(Swift-BAT detection: Cholden-Brown et al., GCN Circ. 20631
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 ;
Fermi-GBM detection: Roberts and Meegan, GCN Circ. 20633
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 )
triggered Konus-Wind at T0=65479.756 s UT (18:11:19.756).

The burst light curve shows a multipeaked structure
started at ~T0-0.4 s with a total duration of ~8 s.
The emission is seen up to ~1 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB170208_T65479/

As observed by Konus-Wind, the burst
had a fluence of 2.62(-0.31,+0.37)x10^-6 erg/cm2,
and a 64-ms peak flux, measured from T0-0.012 s,
of 1.94(-0.65,+0.67)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 2 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.52(-0.46,+0.56)
and Ep = 153(-24,+36) keV (chi2 = 67/60 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.7
(chi2 = 67/59 dof)

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.

M. H. Siegel (PSU) and A. Cholden-Brown (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170208A
125 s after the BAT trigger (Cholden-Brown et al., GCN Circ. 20631
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 ).
No optical afterglow consistent with the enhanced XRT position
(Evans et al. GCN Circ. 20634
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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           125          275          148         >21.4
u_FC               337          587          246         >20.7
white              125         1365          373         >21.9
v                  667         1415           97         >19.3
b                  593         1503           87         >19.4
u                  337         1489          324         >20.2
w1                 717         1464           78         >19.4
w2                 642         1390           97         >19.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.13 in the direction of the burst
(Schlegel et al. 1998).

B. Sbarufatti (INAF-OAB/PSU), K.L. Page (U. Leicester), B. Mingo (U.
Leicester), A.P. Beardmore (U. Leicester), P. D'Avanzo (INAF-OAB), V.
D'Elia (ASDC), A. D'Ai (INAF-IASFPA), D.N. Burrows (PSU) and A.
Cholden-Brown report on behalf of the Swift-XRT team:

We have analysed 5.5 ks of XRT data for GRB 170208A (Cholden-Brown et
al. GCN Circ. 20631
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 ), from 105 s to 13.0 ks after the  BAT trigger. The
data comprise 56 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. 20634
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.075 (+0.030, -0.029).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.97 (+/-0.17). The
best-fitting absorption column is  4.5 (+1.0, -0.9) x 10^21 cm^-2, in
excess of the Galactic value of 1.3 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 4.1 x 10^-11 (6.4 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.5 (+1.0, -0.9) x 10^21 cm^-2
Galactic foreground: 1.3 x 10^21 cm^-2
Excess significance: 6.2 sigma
Photon index:	     1.97 (+/-0.17)

If the light curve continues to decay with a power-law decay index of
1.075, the count rate at T+24 hours will be 6.5 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.7 x
10^-13 (4.2 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/00737438.

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

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC),
A. Cholden-Brown (PSU), J. R. Cummings (CPI),
N. Gehrels (GSFC), H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), 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-240 to T+962 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 170208A (trigger #737438)
(Cholden-Brown, et al., GCN Circ. 20631
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 ). The BAT ground-calculated
position is
RA, Dec = 166.544, -46.786 deg which is
   RA(J2000)  =  11h 06m 10.5s
   Dec(J2000) = -46d 47' 08.8"
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 17%.

The mask-weighted light curve shows a pulse from ~T0 to ~T+1.5 s,
followed by some weaker emissions that last till ~T+8 s. T90 (15-350 keV)
is 7.45 +- 0.54 sec (estimated error including systematics).

The time-averaged spectrum from T-0.04 to T+8.06 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.04 +- 0.13.  The fluence in the 15-150 keV band is 1.5 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.04 sec in the 15-150 keV band
is 5.4 +- 0.6 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/737438/BA/

V. Sharma and D. Bhattacharya (IUCAA), V. Bhalerao (IITB), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data showed clear detection of GRB 170208A (Swift detection: A. Cholden-Brown et al., GCN Circ. 20631
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 ) in the 40-200 keV energy range. The light curve shows multiple peaks structure with maximum counts at 18:11:16.0 UT peak, which coincides with Swift trigger. The measured peak count rate is 316.9 counts/sec above the background in combined data of four quadrants, with a total of 1106.2 counts. The local mean background count rate was 425.1 counts/sec. Using cumulative rates, we measure a T90 of 10.7 secs.

CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.

K. L. Murata (Nagoya U), L. Townsend (UCT), I. Monageng (SAAO), Y. Moritani
(Kavli IPMU), M. Jian (U of Tokyo), S. Chimasu (Tokai U), A. Kawachi (Tokai
U), A. Okazaki (Hokkai-Gakuen U) and T. Nagayama (Kagoshima U)

We observed the field of GRB 170208A (Cholden-Brown et al., GCN Circular
#20631
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 ) with the near-infrared (J, H, Ks) simultaneous imaging camera
SIRIUS attached to 1.4 m telescope IRSF (InfraRed Survey Facility) in
Sutherland observatory, South Africa.

The observations started on 2017-02-08 18:56:55 UT (~ 43 min. after the
burst). We could not detect the afterglow within the enhanced XRT error
circle (Evans et al., GCN Circular #20634
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 ) in the three bands. We have
obtained the following preliminary upper limits (Vega magnitude system):

 J > 16.50
 H > 16.25
 Ks > 15.92

Given magnitudes were calibrated against 2MASS point sources in this field.
The upper limits were determined as the magnitudes of the faintest star
within 1 arcmin from the enhanced XRT position.

This observation was carried out by IRSF and OISTER collaboration.