GRB 170127A

C. B. Markwardt (NASA/GSFC), S. D. Barthelmy (GSFC),
S. B. Cenko (GSFC), A. Cholden-Brown (PSU), A. D'Ai (INAF-IASFPA),
V. D'Elia (ASDC), J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Swift Team:

At 14:21:15 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170127A (trigger=735326).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 174.336, -45.852, which is 
   RA(J2000)  =  11h 37m 21s
   Dec(J2000) = -45d 51' 05"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a couple weak peaks
with a duration of about 35 sec.  The peak count rate
was ~900 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began observing the field at 14:22:51.5 UT, 95.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 174.35974, -45.83603 which
is equivalent to:
   RA(J2000)  = 11h 37m 26.34s
   Dec(J2000) = -45d 50' 09.7"
with an uncertainty of 4.1 arcseconds (radius, 90% containment). This
location is 82 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 7.10e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
101 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
0.07. 

Burst Advocate for this burst is C. B. Markwardt (Craig.Markwardt 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  promptly downlinked XRT event data for GRB 170127A, we find an
enhanced XRT position of the afterglow: RA, Dec: 174.3600, -45.8358
which is equivalent to:
   RA (J2000)  = 11 37 26.41
   Dec (J2000) = -45 50 08.7
with an uncertainty of 2.2 arcseconds (radius, 90% confidence).
Analysis of the promptly available data is online at
http://www.swift.ac.uk/sper/735326.

Position enhancement is 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.

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

Using 1366 s of XRT Photon Counting mode data and 2 UVOT
images for GRB 170127A, 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 = 174.35970, -45.83565 which is equivalent
to:

RA (J2000): 11h 37m 26.33s
Dec (J2000): -45d 50' 08.3"

with an uncertainty of 2.4 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.

F. E. Marshall (NASA/GSFC) and C. B. Markwardt (NASA/GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170127A
102 s after the BAT trigger (Markwardt et al., GCN Circ. 20538
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 ).
No optical afterglow consistent with the enhanced XRT position
(Evans et al. GCN Circ. 20548
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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

u_FC               102          351          246         >20.5
v                  409         1533          136         >18.7
b                  359         1632          175         >20.4
u                  102         1607          529         >20.7
w1                 458         1583          136         >19.4
m2                 434         1558          136         >20.0
w2                 385         1658          175         >20.2

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.07 in the direction of the burst
(Schlegel et al. 1998).

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

We have analysed 6.2 ks of XRT data for GRB 170127A, from 86 s to 58.8
ks after the  BAT trigger. The data comprise 168 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 light curve can be modelled with an initial power-law decay with an
index of alpha=1.28 (+/-0.15), followed by a break at T+329 s to an
alpha of 8.0 (+0.0, -1.1).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.49 (+/-0.10). The
best-fitting absorption column is  1.3 (+/-0.4) x 10^21 cm^-2, in
excess of the Galactic value of 8.5 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.5 x 10^-11 (5.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     1.3 (+/-0.4) x 10^21 cm^-2
Galactic foreground: 8.5 x 10^20 cm^-2
Excess significance: 2.0 sigma
Photon index:	     1.49 (+/-0.10)

If the light curve continues to decay with a power-law decay index of
5.19, the count rate at T+24 hours will be 2.0 x 10^-13 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.9 x
10^-24 (10.0 x 10^-24) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00735326.

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

P. Schady, P. Wiseman and J. Greiner (all at MPE Garching) report on behalf of the GROND team:

We observed the field of GRB 170127A (Swift trigger 735326; Markwardt et al., GCN #20538
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 ) 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 05:23 UT on 2017-01-27, 15 hrs after the GRB trigger. They were performed at high seeing that varied between 1.5� and 2" and at an average airmass of 1.4.

In combined images with 36 min of total exposures in g�r'i'z' and 30 min in JHK at a mid-time of 05:40 UT on 2017-01-28, we do not detect a source within the Swift-XRT error circle reported by Evans et al. (GCN #20548
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 ) down to the following 3 sigma upper limits (all in AB system)

g' > 24.0 mag
r' > 23.7 mag
i' > 23.1 mag
z' > 23.0 mag
J > 20.7 mag
H > 20.3 mag
K > 17.7 mag

Given magnitudes are calibrated against GROND zeropoints and 2MASS field stars and are not corrected for the Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.06 in the direction of the burst (Schlafly & Finkbeiner 2011).

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

Using the data set from T-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 170127A (trigger #735326)
(Markwardt et al., GCN Circ. 20538
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 ).  The BAT ground-calculated position is
RA, Dec = 174.382, -45.827 deg which is
   RA(J2000)  =  11h 37m 31.6s
   Dec(J2000) = -45d 49' 38.6"
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 97%.

The mask-weighted light curve shows some weak overlapping pulses that
starts at ~T-5 s and ends at ~T+65 s. T90 (15-350 keV) is
62.26 +- 10.39 sec (estimated error including systematics).

The time-averaged spectrum from T-4.65 to T+64.51 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.10 +- 0.30.  The fluence in the 15-150 keV band is 5.2 +- 1.0 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+7.31 sec in the 15-150 keV band
is 0.3 +- 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/735326/BA/