GRB 151127A

A. D'Ai (INAF-IASFPA), P. A. Evans (U Leicester),
A. Maselli (INAF-IASFPA), K. L. Page (U Leicester),
D. M. Palmer (LANL) and T. Sakamoto (AGU) report on behalf of the
Swift Team:

At 09:08:49 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 151127A (trigger=665268).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 19.778, -82.774 which is 
   RA(J2000) = 01h 19m 07s
   Dec(J2000) = -82d 46' 25"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak
structure with a duration of about 0.5 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0.15 sec after the trigger. 

The XRT began observing the field at 09:10:09.0 UT, 79.2 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 19.4797, -82.7707 which
is equivalent to:
   RA(J2000)  = 01h 17m 55.13s
   Dec(J2000) = -82d 46' 14.5"
with an uncertainty of 2.6 arcseconds (radius, 90% containment). This
location is 135 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.02
x 10^21 cm^-2 (Willingale et al. 2013). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 77 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 XRT 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 0.12. 

Burst Advocate for this burst is A. D'Ai (antonino.dai AT ifc.inaf.it). 
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.)

D. Xu (NAOC/CAS), D. Malesani (DARK/NBI), Y. Qin (Geneva Observatory), 
Y.-H. Han (NAOC/CAS, HUST), and Y.-D. Hu (IAA-CSIC) report:

We observed the field of the short GRB 151127A (D'Ai et al., GCN 18643
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 ) 
with the 1-m LCOGT telescope at the Siding Spring Observatory. 
Observations started 27.42 UT on 2015-11-27 (i.e., 1.04 hr after the 
GRB), and we obtained 5x180s R-band and 8x180s I-band images.

No new source is detected inside or close to the XRT position (D'Ai et 
al., GCN 18643
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 ), down to 3-sigma upper limits of R > 20 mag and I > 19 
mag (calibrated against nearby USNO stars), at mean times of 1.17 and 
1.52 hr after the GRB, respectively.

T. Schweyer and J. Greiner (both MPE Garching) report on behalf of
the GROND team:

We observed the field of GRB 151127A (Swift trigger 665268; D'Ai et
al., GCN #18643
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 ) simultaneously in JHK with GROND (Greiner et al.
2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at the ESO La
Silla Observatory (Chile).

Observations started at 09:12:30 UT on 2015-11-27, about 4 min after the 
GRB trigger. They were performed at an average seeing of 2" and at an 
average airmass of 2.3 during morning twilight, with the Sun at -6 deg. 
Due to the sky brightness, only the first two 1-min exposure K-band
images are useful.

We do not detect a source within the 2.6 arcsecond XRT error circle
(D'Ai et al., GCN #18643
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 ), down to a limiting magnitude of 
K(AB) > 16.5 mag.

XMM-Newton will observe GRB GRB151127A at location
(RA=01h 17m 55.13s, DEC=-82d 46' 14.5", J2000),
starting at 13:35:45 UT, on November 28, 2015,
for an exposure of 17500 seconds.




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

Using 466 s of XRT Photon Counting mode data and 1 UVOT
images for GRB 151127A, 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 = 19.47835, -82.77070 which is equivalent
to:

RA (J2000): 01h 17m 54.80s
Dec (J2000): -82d 46' 14.5"

with an uncertainty of 2.1 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.

T. Sakamoto (AGU), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
A. D'Ai (INAF-IASFPA), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), 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-60 to T+243 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 151127A (trigger #665268)
(D'Ai, et al., GCN Circ. 18643
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 ).  The BAT ground-calculated position is
RA, Dec = 19.664, -82.762 deg, which is 
   RA(J2000)  =  01h 18m 39.4s 
   Dec(J2000) = -82d 45' 42.1" 
with an uncertainty of 2.8 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 96%.
 
The mask-weighted light curve shows a single spike starting at T_zero and
ending at ~T+0.25 sec.  T90 (15-350 keV) is 0.19 +- 0.04 sec
(estimated error including systematics).
 
The time-averaged spectrum from T+0.016 to T+0.220 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.26 +- 0.33.  The fluence in the 15-150 keV band is 2.3 +- 0.6 x 10^-8 erg/cm2.
The 1-sec peak photon flux measured from T-0.38 sec in the 15-150 keV band
is 0.4 +- 0.1 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/665268/BA/

P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'ai (INAF-IASFPA), T.G.R.
Roegiers (PSU), L.M. McCauley (PSU), J.A. Kennea (PSU), S.L. Gibson (U.
Leicester), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and
A. D'Ai report on behalf of the Swift-XRT team:

We have analysed 8.2 ks of XRT data for GRB 151127A (D'Ai et al. GCN
Circ. 18643
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 ), from 80 s to 18.4 ks after the  BAT trigger. The data are
entirely in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Goad et al. (GCN Circ. 18647
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.15 (+0.17, -0.15).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.3 (+0.7, -0.5). The
best-fitting absorption column is  1.6 (+1.6, -0.6) x 10^21 cm^-2,
consistent with the Galactic value of 1.0 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 2.9 x 10^-11 (4.4 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.6 (+1.6, -0.6) x 10^21 cm^-2
Galactic foreground: 1.0 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.3 (+0.7, -0.5)

If the light curve continues to decay with a power-law decay index of
1.15, the count rate at T+24 hours will be 1.4 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.2 x
10^-15 (6.4 x 10^-15) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00665268.

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

S.W.K Emery (UCL-MSSL) and A. D'Ai (INAF-IASFPA)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 151127A
77 s after the BAT trigger (D'Ai et al., GCN Circ. 18643
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 ).
No optical afterglow consistent with the XRT position
(Goad et al. GCN Circ. 18647
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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            77          227          147         >20.8
white               77         1017          295         >21.2
w1                 668         6559          452         >20.3
m2                 816         6354          432         >20.0
w2                 594        18458         1696         >21.3

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.12 in the direction of the burst
(Schlegel et al. 1998).

Y. Kitaoka, T. Sakamoto, A. Yoshida (AGU) 

We observed the field of GRB 151127A detected by Swift (trigger #665268; 
D'Ai et al., GCN Circ. 18643
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 ) with the iTelescope.Net (http://www.itelescope.net) 
T30 (20" Plane Wave) telescope located at the Siding Spring Observatory (New South 
Wales, Australia).  20 images of 60 sec exposures were taken in the R filter 
starting from November 27 09:47:56 (UT) about 39.1 minutes after the trigger 
and stopped on November 27 10:23:18 (UT).  We do not detect the optical afterglow 
both in the individual images and the stacked image at the enhanced X-ray afterglow 
position (Goad et al., GCN Circ. 18647
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 ).  The estimated five sigma upper limit of 
the combined image (total exposure of 1200 sec) is ~18.2 using the USNO-B1 catalog.