GRB 151212A

S. Nakahira(JAXA), H. Negoro (Nihon U.),
S. Ueno, H. Tomida, M. Ishikawa, Y. E. Nakagawa (JAXA),
T. Mihara, M. Sugizaki, M. Serino, M. Shidatsu, J. Sugimoto, T. Takagi, M. Matsuoka (RIKEN),
N. Kawai, M. Arimoto, T. Yoshii, Y. Tachibana, Y. Ono, T. Fujiwara (Tokyo Tech),
A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU),
H. Tsunemi, R. Imatani (Osaka U.),
M. Nakajima, K. Tanaka, T. Masumitsu (Nihon U.),
Y. Ueda, T. Kawamuro, T. Hori, A. Tanimoto (Kyoto U.),
Y. Tsuboi, S. Kanetou, Y. Nakamura, R. Sasaki (Chuo U.),
M. Yamauchi, D. Itoh (Miyazaki U.),
K. Yamaoka (Nagoya U.),
M. Morii (ISM)
report on behalf of the MAXI team:


The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient
source at UT 2015-12-12T14:00:27.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (68.109 deg, -3.775 deg) = (04 32 26, -03 46 30) (J2000)
with statistical uncertainties of ~0.5 degree.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).

The source showed a relatively soft energy spectrum, and a simple power-law fit gives a photon
index of 2.25 and the X-ray flux over the scan was 60 +- 12 mCrab (2-10keV, 1 sigma error).

There was no significant excess flux in the previous transit at UT 12:27
and in the next transit at 15:34 with an upper limit of 20 mCrab for each.

Detection Information:
http://maxi.riken.jp/alert/novae/7368487901/7368487901.htm

P. A. Evans (U. Leicester) reports on behalf of the Swift team:

Swift has initiated a series of observations, tiled on the sky, of the
MAXI GRB 151212A. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00050

Any uncatalogued X-ray sources detected in this analysis will be
reported on this website and via GCN COUNTERPART notices. The probability of finding
serendipitous sources, unrelated to the MAXI event is high: any X-ray source
considered to be a probable afterglow candidate will be reported via a GCN Circular
after manual consideration.

Details of the XRT automated analysis methods are detailed in Evans et
al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).

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

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

Swift-XRT has performed follow-up observations of the MAXI-detected
burst GRB 151212A (Nakahira et al. GCN Circ. 18685
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 ) in a series of
observations tiled on the sky. The total exposure time is 1.3 ks,
distributed over 7 tiles; the maximum exposure at a single sky location
was 437 s. The data were collected between T0+8.4 ks and T0+8.6 ks, and
are entirely in Photon Counting (PC) mode. 

An uncatalogued X-ray source is detected and is above the RASS limit,
and is therefore likely the GRB afterglow.  The position of this source
is RA, Dec=68.1521, -3.9615 which is equivalent to:

RA (J2000): 04:32:36.50
Dec(J2000): -03:57:41.3

with an uncertainty of 5.2 arcsec (radius, 90% confidence).  This
position is 11.5 arcmin from the MAXI position.  We cannot determine at
the present time whether the source is fading.

The results of the XRT-team automatic analysis of the likely afterglow
are at http://www.swift.ac.uk/xrt_products/TILED_GRB00050/index_1.php.
The results of the full analysis of the tiled XRT observations are
available at http://www.swift.ac.uk/xrt_products/TILED_GRB00050.

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

P. Wiseman (MPE Garching), S. Schmidl (TLS Tautenburg) and J. Greiner (MPE
Garching) report on behalf of the GROND team:

We observed the field of GRB 151212A (MAXI trigger; Nakahira et al., GCN
#18685
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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 03:27 UT on December 13, 2015, 13.5 hrs after the
GRB trigger. They were performed at an average seeing of 1.7" and at an
average airmass of 1.1, and through a significant layer of clouds.

We detect a single source at the border of the enhanced Swift-XRT error
circle (http://www.swift.ac.uk/xrt_positions/00020570/), which we propose
is the afterglow, at RA, Dec 68.150, -3.9626, which is equivalent to:

RA (J2000.0) = 04:32:36.1
Dec (J2000.0) = -03:57:45.3

with an uncertainty of 0.5" in each coordinate.

Based on the 72 min of total exposures in g'r'i'z'J and H, at a mid-time of
14.1 hrs after the burst, we measure the following preliminary magnitudes
and upper limits (AB magnitude system):

g' = 24.3 +/- 0.2 mag,
r' = 23.6 +/- 0.2 mag,
i' = 23.1 +/- 0.2 mag,
z' = 23.3 +/- 0.3 mag,
J > 21.2 mag, and
H > 20.7 mag.

We cannot say anything about fading at this time, but the power-law-like
magnitudes lead us to suspect this is the afterglow.

Given magnitudes and upper limits are calibrated against SDSS as well as
2MASS field stars and are not corrected for the expected Galactic
foreground extinction corresponding to a reddening of E_(B-V)=0.03 mag in
the direction of the burst (Schlegel et al. 1998).

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

The Swift/UVOT began observing the field of MAXI-detected GRB 151212A
(Nahakira et al., GCN Circ. 18685
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 ) 42183 s after the trigger.
No optical afterglow consistent with the XRT source given by Evans
et al. (GCN Circ 18687
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 ) is detected in the UVOT exposures.

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

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

u              42183       48392          2939 >21.4

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.04 in the direction of the burst
(Schlegel et al. 1998).

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

We observed the field of GRB 151212A detected by MAXI (Nakahira et al., GCN Circ. 18685
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 ) 
with the iTelescope.Net (http://www.itelescope.net) T18 (Plane Wave CDK) telescope located 
at the AstroCamp Observatory (Nerpio, Spain).  20 images of 60 sec exposures were taken 
in the Red filter starting from December 12 22:43:00 (UT) about 8.7 hours after the trigger 
and stopped on December 12 23:17:03 (UT).  We do not detect the optical afterglow both in the 
individual images and the stacked image at the X-ray afterglow position 
(Roegiers et al., GCN Circ. 18687
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 ).  The estimated five sigma upper limit of the combined 
image (total exposure of 1200 sec) is ~17.0 using the USNO-B1 catalog.