GRB 170205A

S.W.K. Emery (UCL-MSSL), E. Troja (NASA/GSFC/UMCP) and A.A. Breeveld (UCL-MSSL)  
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170205A
314 s after the BAT trigger (Troja et al., GCN Circ. 20603
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 ).
A source consistent with the XRT position
(Beardmore et al. GCN Circ. 20610
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 ) and also detected by
Guidorzi et al. GCN 20605
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 , Butler et al. GCN 20609
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  and Kruehler et al. GCN 20612
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is detected in the initial UVOT exposures.

The preliminary UVOT position is:
    RA  (J2000) =  17:28:40.69 = 262.16955 (deg.)
    Dec (J2000) = -00:03:47.3  =  -0.06313 (deg.)
with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:

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

white(FC)       314             464           147        17.52 +/- 0.04
u(FC)                520             540             19        17.30 +/- 0.22
white             4361           4561          197         20.84 +/- 0.33
v                         619        17292        1101        >20.3
b                         545             565             19         17.79 +/- 0.24
u                      3951        12169          785         20.65 +/- 0.33
w1                     496        10592          924        >20.6
m2                  6287        17909          741        >20.6
w2                  4567        16378        1082        >21.1

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.35 in the direction of the burst
(Schlegel et al. 1998).

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 170205A
(Swift-BAT detection: Troja et al., GCN Circ. 20603
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 ),
triggered Konus-Wind at T0=45549.824 s UT (12:39:09.824).

The burst light curve shows a double-peaked structure which
started at ~T0-32 s and had a total duration of ~56 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/GRB170205_T45549/

As observed by Konus-Wind, the burst
had a fluence of 1.22(-0.20,+0.24)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0-0.220 s,
of 3.29(-1.62,+1.99)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+24.832 s)
is best fit in the 20 keV - 10 MeV range
by a power law with spectral index = -2.19(-0.12,+0.13)
(chi2 = 58/69 dof).
Fitting this spectrum by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields
alpha = -1.75 (-0.24,+0.62) and
an upper limit on Ep of 75 keV (chi2 = 56/68 dof).
For the CPL model, the burst fluence is
6.2(-0.8,+1.4)x10^-6 erg/cm2,
and the 64-ms peak flux is 1.8(-0.8,+2.8)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

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

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

Using the data set from T-10 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 170205A (trigger #736843)
(Troja, et al., GCN Circ. 20603
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 ).  The BAT ground-calculated position is
RA, Dec = 262.157, -0.058 deg which is
  RA(J2000)  =  17h 28m 37.8s
  Dec(J2000) = -00d 03' 30.4"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 91%.

The mask-weighted light curve shows that the burst consisted of two peaks of
roughly equal peak counts, the first from T-2 sec to T+12 sec and the second
from T+12 sec to T+30 sec.  T90 (15-350 keV) is 26.1 +- 3.2 sec (estimated
error including systematics). It is possible that the burst is longer than this since
there was no data before T-10 seconds, following the re-enabling of data collection
after an SAA passage.

The time-averaged spectrum from T-1.42 to T+46.40 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.85 +- 0.06.  The fluence in the 15-150 keV band is 3.8 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.30 sec in the 15-150 keV band
is 4.3 +- 0.3 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/736843/BA/

T. Kruehler (MPE Garching), D. Xu (NAOC,CAS), K. E. Heintz (Univ.
Iceland & DARK/NBI) and G. Fedorets (NOT) report on behalf of the
Nordic GRB collaboration:

We observed the field of GRB 170205A (Troja et al. GCN 20603
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 )
with the NOT equipped with ALFOSC. Photometry in the r and i-band
started at 05:49 UTC on 2017-02-06, 17.2 hr after the GRB trigger,
and was obtained under adverse atmospheric conditions (seeing
around 2.5").

Calibrating our images against magnitudes of field stars from the
SDSS catalog, we measure preliminary brightnesses of the optical
afterglow (Troja et al. GCN 20603
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 , Guidorzi et al. GCN 20605
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 , Butler
et al. GCN 20609
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 ) of

r = 22.2 +- 0.2 mag and
i = 22.0 +- 0.2 mag.

These magnitudes are not corrected for the expected foreground
extinction corresponding to a reddening of E_B-V = 0.30 mag
(Schlafly & Finkbeiner 2011).

V. D'Elia (ASDC), A. Cholden-Brown (PSU), S. J. LaPorte (PSU), J.A.
Kennea (PSU), P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester),
J.P. Osborne (U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri
(INAF-OAB) and E. Troja report on behalf of the Swift-XRT team:

We have analysed 10 ks of XRT data for GRB 170205A (Troja et al. GCN
Circ. 20603
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 ), from 271 s to 34.9 ks after the  BAT trigger. The data
are entirely in Photon Counting (PC) mode. The enhanced XRT position
for this burst was given by Beardmore et al. (GCN Circ. 20610
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.89 (+0.03, -0.04).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.87 (+0.14, -0.13). The
best-fitting absorption column is  3.4 (+0.7, -0.6) x 10^21 cm^-2, in
excess of the Galactic value of 2.0 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 (5.7 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.4 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 2.0 x 10^21 cm^-2
Excess significance: 3.8 sigma
Photon index:	     1.87 (+0.14, -0.13)

If the light curve continues to decay with a power-law decay index of
0.89, the count rate at T+24 hours will be 0.021 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.5 x
10^-13 (1.2 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/00736843.

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

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

Using 2830 s of XRT Photon Counting mode data and 4 UVOT
images for GRB 170205A, 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 = 262.16934, -0.06320 which is equivalent
to:

RA (J2000): 17h 28m 40.64s
Dec (J2000): -00d 03' 47.5"

with an uncertainty of 1.4 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.

Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William
H. Lee (UNAM), Michael G. Richer (UNAM), Ori Fox (STScI), J. Xavier
Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (UVI), Eleonora
Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), Jes��s
Gonz��lez (UNAM), Carlos Rom��n-Z����iga (UNAM), Neil Gehrels (GSFC), Harvey
Moseley (GSFC), John Capone (UMD), V. Zach Golkhou (ASU), and Vicki Toy
(UMD) report:

We observed the field of GRB 170205A (Troja, et al., GCN 20603
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 ) with the
Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the
1.5m Harold Johnson Telescope at the Observatorio Astron��mico Nacional on
Sierra San Pedro M��rtir from 2017/02 5.53 to 2017/02 5.58 UTC (2.3 minutes
to 1.25 hours after the BAT trigger), obtaining a total of 0.61 hours
exposure in the r and i bands and 0.29 hours exposure in the Z and Y bands.

In comparison with the USNO-B1 and 2MASS catalogs, we obtain the following
detections for the optical afterglow (see, also, Guidorzi, et al., GCN
20605
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 ):

r = 18.31 +/- 0.01
i = 17.90 +/- 0.01
Z = 18.06 +/- 0.01
Y = 19.26 +/- 0.07

These magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the GRB.  The source fades (from i~16 mag)
as t^(-1.6) until ~15 minutes after the GRB, after which the fade flattens
to t^(-1.1).

We thank the staff of the Observatorio Astron��mico Nacional in San Pedro
M��rtir.

C. Guidorzi (U. Ferrara), S. Kobayashi, I.A. Steele (LJMU), A. Gomboc 
(U. Nova Gorica), C.G. Mundell (U. Bath) on behalf of a large 
collaboration report:

We observed Swift GRB 170205A (Troja et al. GCN 20603
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 ) on February 05, 
from 14:40 UT (2.0 hours since the GRB) with the 2-m LCO FTN in Hawaii 
with SDSS r and i filters. We detect the optical afterglow at the 
Swift-UVOT position with the following values:

Mid Time      Exposure       Filter       Magnitude (AB)
(hours)           (s)
-------------------------------------------------------
2.0             2x120         SDSS-R        20.3 +- 0.1
2.1             2x120         SDSS-I        20.0 +- 0.1
-------------------------------------------------------

as calibrated against nearby SDSS sources.

E. Troja (NASA/GSFC/UMCP), D. N. Burrows (PSU),
A. Cholden-Brown (PSU), H. A. Krimm (CRESST/NSF/USRA),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC) and
K. L. Page (U Leicester) report on behalf of the Swift Team:

At 12:39:09 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170205A (trigger=736843).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 262.151, -0.053 which is 
   RA(J2000) = 17h 28m 36s
   Dec(J2000) = -00d 03' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 25 sec.  The peak count rate
was ~5000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 12:40:10.9 UT, 61.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
262.1696, -0.0626 which is equivalent to:
   RA(J2000)  = 17h 28m 40.70s
   Dec(J2000) = -00d 03' 45.3"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 75 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 (1.97 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 6.4
(+5.93/-4.46) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 7.05e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 314 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	17:28:40.69 = 262.16953
  DEC(J2000) = -00:03:47.3  =  -0.06313
with a 90%-confidence error radius of about 0.62 arc sec. This position is 1.9
arc sec. from the center of the XRT error circle. The estimated magnitude is
17.62 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.35. 

Burst Advocate for this burst is E. Troja (eleonora.troja 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.)