GRB 170113A

D. Xu (NAOC/CAS), K. E. Heintz (Univ. Iceland and DARK/NBI), D. 
Malesani, J. P. U. Fynbo (DARK/NBI) report on behalf of a larger 
collaboration:

We observed the optical afterglow of GRB 170113A (Evans et al. GCN 
20446
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 ; Veres et al., GCN 20452
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 ; Guidorzi et al., GCN 20448
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 ) with the ESO 
Very Large Telescope UT 2 (Kueyen) equipped with the X-shooter 
spectrograph, covering the wavelength range 3500-20000 AA. Spectroscopy 
started at 01:17:53 UT on 2017-01-14 (i.e., 15.23 hr after the GRB) and 
consisted of 4 exposures of 1200 s each.

 From the acquisition image prior to the spectroscopy, the afterglow has 
m(r)~21.7 mag, calibrated with nearby USNO B1 stars.

The spectrum exhibits several absorption features such as Si II, Fe II, 
Mg II, as well as emission features such as [O II] doublet, Hbeta, 
[OIII] doublet, all at a common redshift of z=1.968. We conclude this is 
the redshift of the GRB.

We acknowledge the excellent support from the ESO staff, particularly 
Luca Sbordone, Laura Magrini, Cedric Ledoux, and Elizabeth (Liz) 
Bartlett, in obtaining these observations.

T. Kruehler (MPE Garching) reports:

I observed the field of GRB 170113A (Swift trigger 732526; Evans
et al. GCN #20446
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 ) simultaneously in g'r'i'z'JHK with GROND
(Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG
telescope at the ESO La Silla Observatory (Chile).

Observations started at 01:34 UT on 2017-01-14, 15.5 hr after the GRB
trigger. Based on combined images with 22 min of total exposure time
in g'r'i'z' and 18 min in JHK at a mid-time of 01:50 UT on 2017-01-14,
I derive the following preliminary magnitudes and upper limits
(all in the AB system) for the optical/NIR afterglow (Evans et al.,
GCN 20446
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 , Guidorzi et al., GCN 20448
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 , Siegel et al., GCN 20455
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 ):

g' = 22.3 +- 0.1 mag
r' = 22.0 +- 0.1 mag
i' = 21.8 +- 0.1 mag
z' = 21.6 +- 0.1 mag
J = 20.9 +- 0.2 mag
H = 20.8 +- 0.3 mag
K > 19.0 mag

Given magnitudes are calibrated against GROND zeropoints and 2MASS
field stars and are not corrected for the expected Galactic
foreground extinction corresponding to a reddening of
E_(B-V)=0.099 mag in the direction of the burst (Schlafly &
Finkbeiner 2011).

I acknowledge excellent help in obtaining these data from the
supporting astronomer on La Silla, Regis Lachaume.

C. B. Markwardt (GSFC), S. D. Barthelmy (GSFC),
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 170113A (trigger #732526)
(Evans et al., GCN Circ. 20446
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 ).  The BAT ground-calculated position is
RA, Dec = 61.735, -71.933 deg which is
   RA(J2000)  =  04h 06m 56.5s
   Dec(J2000) = -71d 55' 58.0"
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 86%.

The mask-weighted light curve shows a multi-peaked structure that starts
at ~T0 and ends at ~T+25 s. The main peak occurs at ~T+2 s. T90 (15-350 keV)
is 20.66 +- 4.44 sec (estimated error including systematics).

The time-averaged spectrum from T-0.61 to T+23.84 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.75 +- 0.59,
and Epeak of 73.3 +- 33.6 keV (chi squared 72.24 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 6.7 +- 0.7 x 10^-7 erg/cm2
and the 1-sec peak flux measured from T+1.63 sec in the 15-150 keV band is
1.1 +- 0.1 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.57 +- 0.13 (chi squared 79.06 for 57 d.o.f.).  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/732526/BA/

M. H. Siegel (PSU) and P. A. Evans (U. Leicester)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170113A
68 s after the BAT trigger (Evans et al., GCN Circ. 20446
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 ).
A fading source consistent with the XRT position
(Goad et al. GCN Circ. 20450
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 )
is detected in the initial UVOT exposures.

The preliminary UVOT position is:
   RA  (J2000) =  04:06:55.86 =  61.73276 (deg.)
   Dec (J2000) = -71:56:34.9  = -71.94302 (deg.)
with an estimated uncertainty of 0.44 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)          68          217          147         18.27+-0.06
white              560         1009          186         19.56+-0.11
white             1163         1875           97         19.65+-0.17
white             6392         6592          196         20.64+-0.26
v                  609         1751          136         19.09+-0.36
v                 5367         7002          393         >19.49
b                  535         1850          136         19.33+-0.19
b                 6188         6388          196         >20.39
u (fc)             280          530          245         18.76+-0.13
u                  683         1825          116         19.33+-0.27
u                 5983         7615          390         >20.44
uvw1               659         1801          136         >19.38
uvm2               634         1776          136         >19.12
uvw2               585         1727          136         >19.42

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.11 in the direction of the burst
(Schlegel et al. 1998).

A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), A. Cholden-Brown (PSU),
S. J. LaPorte (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester),
K.L. Page (U. Leicester), B. Mingo (U. Leicester), V. D'Elia (ASDC) and
 report on behalf of the Swift-XRT team: report on behalf of the
Swift-XRT team:

We have analysed 8.0 ks of XRT data for GRB 170113A, from 50 s to 19.1
ks after the  BAT trigger. The data comprise 243 s in Windowed Timing
(WT) mode (the first 7 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. 

The late-time light curve (from T0+5.2 ks) can be modelled with a
power-law decay with a decay index of alpha=1.14 (+/-0.10).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.88 (+/-0.07). The
best-fitting absorption column is  1.82 (+0.26, -0.24) x 10^21 cm^-2,
in excess of the Galactic value of 1.1 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.77 (+/-0.08) and a
best-fitting absorption column of 1.43 (+0.26, -0.25) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.9 x 10^-11 (4.7 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.43 (+0.26, -0.25) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^21 cm^-2
Excess significance: 2.3 sigma
Photon index:	     1.77 (+/-0.08)

If the light curve continues to decay with a power-law decay index of
1.14, the count rate at T+24 hours will be 0.030 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-12 (1.4 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/00732526.

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

P. Veres (UAH), C. Meegan (UAH) and A. von Kienlin (MPE)
report on behalf of the Fermi GBM Team:

"At 10:04:10.11 UT on 13 January 2017, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 170113A (trigger 505994655 / 170113420).
which was also detected by the Swift/BAT (Evans et al., GCN 20446
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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 is 145 degrees.

The GBM light curve shows a single pulse
with a duration (T90) of about 49 s (50-300 keV).
The time-averaged spectrum from T0-10 s to T0+47 s is
adequately fit by a simple power law function with
index -2.05 +/- 0.08.

The event fluence (10-1000 keV) in this time interval is
(3.8 +/- 0.4)E-6 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+4.5 s in the 10-1000 keV band
is 2.9 +/- 0.4 ph/s/cm^2.

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

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

Using 1363 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 170113A, 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 = 61.73332, -71.94279 which is equivalent
to:

RA (J2000): 04h 06m 56.00s
Dec (J2000): -71d 56' 34.0"

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.

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 170113A (Evans et al. GCN 20446
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 ) on January 13, 
from 10:53:32 UT (50 minutes since the GRB) with 1-m LCO telescope units 
in Sutherland with SDSS r and i filters. We clearly detect the 
Swift-UVOT optical counterpart with the following values:

Mid Time      Exposure       Filter       Magnitude (AB)
(hours)           (s)
-------------------------------------------------------
0.89             5x60         SDSS-R      19.06 +- 0.11
0.89             5x60         SDSS-I      18.84 +- 0.08
-------------------------------------------------------

as calibrated against nearby USNO-UCAC4 sources.

P.A. Evans (U Leicester), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), H. A. Krimm (CRESST/NSF/USRA),
B. Mingo (U Leicester), P. T. O'Brien (U Leicester),
B. Sbarufatti (INAF-OAB/PSU), R. L. C. Starling (U Leicester) and
E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift Team:

At 10:04:05 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170113A (trigger=732526).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 61.648, -71.925, which is 
   RA(J2000)  =  04h 06m 36s
   Dec(J2000) = -71d 55' 28"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multiple peaks
with a duration of about 30 sec.  The peak count rate
was ~2100 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 10:05:04.2 UT, 58.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 61.73063, -71.94326 which
is equivalent to:
   RA(J2000)  = 04h 06m 55.35s
   Dec(J2000) = -71d 56' 35.7"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This
location is 113 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.  We cannot determine whether the source is
fading at the present time. No spectrum from the promptly downlinked
event data is yet available to determine the column density. 

The initial flux in the 2.5 s image was 1.01e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 67 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	04:06:55.85 =  61.73272
  DEC(J2000) = -71:56:34.5  = -71.94293
with a 90%-confidence error radius of about 0.62 arc sec. This position is 3.7
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.39 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.11. 

Burst Advocate for this burst is P.A. Evans (pae9 AT star.le.ac.uk). 
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.)