GRB 160123A

D. Malesani (DARK/NBI), S. D. Barthelmy (GSFC), T. Sakamoto (AGU) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 08:58:20 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160123A (trigger=671447).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 150.286, -33.779 which is 
   RA(J2000) = 10h 01m 09s
   Dec(J2000) = -33d 46' 43"
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 ~1500 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 08:59:38.1 UT, 78.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 150.3125, -33.7754
which is equivalent to:
   RA(J2000)  = 10h 01m 14.99s
   Dec(J2000) = -33d 46' 31.3"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 80 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 (1.31 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 2.9
(+2.66/-2.30) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
295 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 19.2 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 18.0 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.10. 

Burst Advocate for this burst is D. Malesani (malesani AT dark-cosmology.dk). 
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.)

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

Using 1168 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 160123A, 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 = 150.31272, -33.77522 which is equivalent
to:

RA (J2000): 10h 01m 15.05s
Dec (J2000): -33d 46' 30.8"

with an uncertainty of 1.8 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.

Y.-D. Hu (IAA-CSIC), D. Xu (NAOC/CAS), Y. Qing (Geneva Observatory), 
Y.-H. Han (NAOC/CAS, HUST) report:

We observed the field of GRB 160123A (Malesani et al., GCN 18926
Loading...
 
 ) using 
the LCOGT-1m located at the Siding Spring Observatory. We obtained 
20x150s R-band images, starting at 12:04:41 UT on 2016-01-23, i.e., 
3.106 hr after the burst.

No optical source is detected at the enhanced XRT position of this GRB 
(Beardmore et al., GCN 18927
Loading...
 
 ), down to a limiting magnitude of R~21.0 
mag, calibrated with nearby USNO B1 stars.

S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. Malesani (DARK/NBI), 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 downlinks,
we report further analysis of BAT GRB 160123A (trigger #671447)
(Malesani, et al., GCN Circ. 18926
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 150.277, -33.790 deg, which is 
   RA(J2000)  =  10h 01m 06.4s 
   Dec(J2000) = -33d 47' 23.1" 
with an uncertainty of 1.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 68%.
 
The mask-weighted light curve shows one peak starting at ~T-15 sec, 
peaking at ~T+0.5 sec, and ending at ~T+10 sec.
T90 (15-350 keV) is 3.95 +- 0.62 sec (estimated error including systematics).
 
The time-averaged spectrum from T-2.05 to T+3.00 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.51 +- 0.16.  The fluence in the 15-150 keV band is 3.5 +- 0.4 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.01 sec in the 15-150 keV band
is 1.3 +- 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/671447/BA/

L.M. McCauley (PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU),
C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U.
Leicester), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A. Maselli 
(INAF-IASFPA) and D. Malesani report on behalf of the Swift-XRT team:

We have analysed 10.0 ks of XRT data for GRB 160123A (Malesani et al.
GCN Circ. 18926
Loading...
 
 ), from 64 s to 24.2 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. The enhanced
XRT position for this burst was given by Beardmore et al. (GCN Circ.
18927
Loading...
 
 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.72 (+/-0.05).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.09 (+0.28, -0.26). The
best-fitting absorption column is  2.6 (+1.2, -1.0) 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 3.4 x 10^-11 (5.2 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.6 (+1.2, -1.0) x 10^21 cm^-2
Galactic foreground: 1.3 x 10^21 cm^-2
Excess significance: 2.2 sigma
Photon index:	     2.09 (+0.28, -0.26)

If the light curve continues to decay with a power-law decay index of
0.72, the count rate at T+24 hours will be 3.6 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-13 (1.9 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/00671447.

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

M. De Pasquale (UCL-MSSL) and D. Malesani (DARK/NBI)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 160123A
82 s after the BAT trigger (Malesani et al., GCN Circ. 18926
Loading...
 
 ).
No optical afterglow consistent with the XRT position (Beardmore et al.
GCN Circ. 18927
Loading...
 
 ) 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            82          231          147         >20.7
u_FC               296          545          246         >19.9
white               82         1196         1041         >21.8
v                  626        11136         1191         >20.3
b                  551        17792         1337         >21.4
u                  296        17792         1563         >20.4
w1                 675        12760         1152         >19.2
m2                 650        12040         1160         >20.0
w2                 601         6977          471         >21.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.10 in the direction of the burst
(Schlegel et al. 1998).

Daniele Malesani (DARK/NBI), Anlaug Amanda Djupvik (NOT), Tom Reynolds 
(NOT and Tuorla Obs.), and Pall Jakobsson (Univ. Iceland) report on 
behalf of a larger collaboration:

We observed the field of GRB 160123A (Malesani et al., GCN 18926
Loading...
 
 ) with 
the Nordic Optical Telescope (NOT) equipped with the NOTCam 
near-infrared camera. Observations were carried out in the J filter. Sky 
conditions were not optimal, with moonlit clouds and a seeing of 1.7". 
Three sets of nine images by 1 minute each were acquired, starting on 
Jan 24.067 UT (16.6 hr after the GRB).

After stacking the best 18 images, no source is detected within the XRT 
localization area (Beardmore et al., GCN 18927
Loading...
 
 ; see also 
http://www.swift.ac.uk/xrt_positions/00671447/), down to a limiting 
magnitude J > 19.5 (Vega), calibrated against the 2MASS catalog.

J. F. Graham, T. Schweyer, and J. Greiner (all MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 160123A (Swift trigger 671447; Malesani, et al., GCN # 18926) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile).

Observations started at  04:02 UT on 25 Jan 2016, approximately 43 hours after the GRB trigger, and lasted for 2 hours. They were performed at an average seeing of 1.64" and at an average airmass of 1.06.

We do not detect a source within the Swift-XRT error circle reported by Beardmore et al. (GCN # 18927) down to (AB magnitudes)

g' > 24.1 mag,
r' > 24.4 mag,
i' > 24.0 mag,
z' > 23.9 mag,
J > 21.3 mag,
H > 20.9 mag, and
K > 20.1 mag.

The given limits are derived based on calibrating the images against GROND zeropoints and 2MASS field stars and are not corrected for the Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.10 in the direction of the burst (Schlegel et al. 1998).

Klotz A., Turpin D. (IRAP-CNRS-OMP),
Boer M., Gendre B., Bardho O. (UNS-CNRS-OCA),
Gendre B. (Etelman Observatory-UVI),
Atteia J.L. (IRAP-CNRS-OMP) report:

We imaged the field of GRB 160123A detected by SWIFT
(trigger 671447) with the TAROT robotic telescope (D=25cm)
located at the European Southern Observatory,
La Silla observatory, Chile.

The observations started 33.1s after the GRB trigger
(14.2s after the notice). The elevation of the field
decreased from 59 degrees above horizon and weather
conditions were good.

The first image is trailed with a duration of 60.0s
(see the description in Klotz et al., 2006, A&A 451, L39).
We do not detect any OT with a limiting magnitude of:
t0+33.1s to t0+93.1s : R > 17.3

The second image is 30.0s exposure in tracking mode:
t0+108.7s to t0+138.7s : R > 18.1

We co-added a series of exposures:
t0+108.7s to t0+305.4s : R > 18.8

Magnitudes were estimated with the nearby USNO-B1 stars
and are not corrected for galactic dust extinction.