GRB 141029A

S. Nakahira (JAXA), H. Negoro (Nihon U.),
S. Ueno, H. Tomida, M. Kimura, M. Ishikawa, Y. E. Nakagawa (JAXA),
T. Mihara, M. Sugizaki, M. Morii, M. Serino, J. Sugimoto, T. Takagi, A. Yoshikawa, M. Matsuoka (RIKEN),
N. Kawai, T. Yoshii, Y. Tachibana (Tokyo Tech),
A. Yoshida, T. Sakamoto, Y. Kawakubo, H. Ohtsuki (AGU),
H. Tsunemi, D. Uchida (Osaka U.),
M. Nakajima, K. Fukushima, T. Onodera, K. Suzuki, T. Namba, M. Fujita, F. Honda (Nihon U.),
Y. Ueda, M. Shidatsu, T. Kawamuro, T. Hori (Kyoto U.),
Y. Tsuboi, A. Kawagoe (Chuo U.),
M. Yamauchi, Y. Morooka, D. Itoh (Miyazaki U.),
K. Yamaoka (Nagoya U.)
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 04:32:09 UT .
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (69.413 deg, -16.481 deg) = (04 37 39, -16 28 51) (J2000) 
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.28 deg and 0.23 deg respectively. 
The roll angle of long axis from the north direction is 170.0 deg counterclockwise. 
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 137 +- 24 mCrab
(4-10keV, 1 sigma error).
There was no significant excess flux in the previous transit at 02:59 UT.
with an upper limit of 20 mCrab.

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 141029A. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00031

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; and 2009, MNRAS, 397, 1177).

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

D. Xu (DARK/NBI), G.-J. Feng, X. Zhang, A. Esamdin, L. Ma (XAO) report:

We observed the field of the three X-ray afterglow candidates (see
http://www.swift.ac.uk/xrt_products/TILED_GRB00031/) of GRB 141029A
detected by MAXI/GSC (Nakahira et al., GCN16981
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 ), using the 1m
telescope located at Nanshan, Xinjiang, China. We obtained 2x300s and
1x600s R-band images, starting at 19:37 UT on 2014-10-29 (i.e., 15.09
hr after the trigger).

As reported, the X-ray source 1 (S1) and source 2 (S2) have catalogued
optical counterparts already, and the X-ray source 3 (S3) located at
R.A. = 04:37:20.17, Dec. = -16:08:09.3  (with Error Radius=8.8������)
doesn't have a catalogued optical counterpart. However, no optical
source is detected at the S3 position in the Nanshan images, down to a
limiting magnitude of R=20.5 mag.

S. Nakahira (JAXA), N. Kawai (Tokyo Tech), T. Sakamoto (AGU), K. Yamaoka (Nagoya U),$B!!(B
H. Negoro (Nihon U.), M. Serino (RIKEN), P. A. Evans (U. Leicester), K. L. Page (U Leicester)
on behalf of the MAXI team and the Swift-MAXI collaboration

The Swift ToO observation of GRB141029A (Nakahira et al., GCN16981
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 )
was performed starting from 2014-10-29T09:00:37
with 4-point tiling to cover the MAXI error circle.

We found three X-ray sources in the MAXI error circle
as shown in the Swift observation summary page
http://www.swift.ac.uk/xrt_products/TILED_GRB00031/.
One of the sources ("source 1") showed suggestive fading between the
two tilings centered at 15500 s and 20700 s after the MAXI detection
with count rates of 2.7 +- 0.3 c/s and 1.7 +- 0.2 c/s respectively.
Assuming a power-law spectrum with photon index of 2.4 the X-ray flux
at the first Swift pointing is estimated as 6.8 x 10^-11 erg/cm2/s,
two order of magnitude fainter than 5.6 x 10^-9 erg/cm2/s at the MAXI detection.

The fading behavior was confirmed by additional Swift TOO observation
conducted from 2014-10-30T10:14:59 with a detected count rate of 0.27+-0.02 c/s.

This fading source matches a catalogued X-ray source 1RXS J043657.1-161258,
whose position in the ROSAT All-Sky Survey Bright Source Catalog is
9.1" away from the Swift position with a 3-sigma positional error of 40.1".
The source flux in the catalog corresponds to 9.3 x 10^-12 erg/s/cm2,
indicating that the fluxes in the present Swift observations were
in much elevated states.
The source was also reported to be variable (Fuhrmeister and Schmitt 2003).

Thus, we conclude that 1RXS J043657.1-161258 is the most likely source of the MAXI transient.

This optical counterpart of 1RXS J043657.1-161258 has been studied,
and found to be variable with with possible rotational period of P=0.3787d or P =2.74d
(Kiraga et al. 2012).

These characteristics of the source suggest that the X-ray transient
observed by MAXI was a strong flare from an active star system
such as RS CVn star, dMe star, or a cataclysmic variable.

Non-detection of an optical counterpart of source 3 reported by Xu et al. ( GCN16994
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 )
further supports that this transient was not a gamma-ray burst.

We thank the Swift team for performing the observation.