GRB 221008A

Y. Soejima, H. Negoro, M. Nakajima (Nihon U.), M. Serino (AGU), 
W. Iwakiri (Chuo. U.), K. Kobayashi, M. Tanaka (Nihon U.), 
T. Mihara, T. Kawamuro, S. Yamada, T. Tamagawa, M. Matsuoka (RIKEN), 
T. Sakamoto, S. Sugita, H. Hiramatsu, A. Yoshida (AGU), 
Y. Tsuboi, J. Kohara (Chuo U.),  M. Shidatsu, M. Iwasaki (Ehime U.),
N. Kawai, M. Niwano, R. Hosokawa, Y. Imai, N. Ito, Y. Takamatsu (Tokyo Tech), 
S. Nakahira,  S. Ueno, H. Tomida, M. Ishikawa,  T. Kurihara (JAXA), 
Y. Ueda, S. Ogawa, K. Setoguchi, T. Yoshitake, K. Inaba (Kyoto U.), 
M. Yamauchi, T. Sato, R. Hatsuda, R. Fukuoka, Y. Hagiwara, Y. Umeki (Miyazaki U.), 
K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC) 
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 2022-10-08T00:53:50 UT.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (29.687 deg, -18.876 deg) = (01 58 44, -18 52 33) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.12 deg and 0.09 deg, respectively.
The roll angle of long axis from the north direction is 25.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(29.400, -18.665) deg = (01 57 35, -18 39 53) (J2000)
(29.338, -18.887) deg = (01 57 21, -18 53 13) (J2000)
(30.076, -19.070) deg = (02 00 18, -19 04 12) (J2000)
(30.137, -18.847) deg = (02 00 32, -18 50 49) (J2000)
The X-ray flux averaged over the scan was 803 +- 56 mCrab
(4.0-10.0keV, 1 sigma error).
There was no significant excess flux in the previous transit at 10/07 23:21 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 221008A. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00109

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.

S. Dichiara (PSU), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), J.P.
Osborne (U. Leicester), K.L. Page (U. Leicester), A. D'Ai
(INAF-IASFPA), A. Melandri (INAF-OAB), T. Sbarrato (INAF-OAB) 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 221008A (Soejima et al. GCN Circ. 32630
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 ) in a series of
observations tiled on the sky. The total exposure time is 1.2 ks,
distributed over 4 tiles; the maximum exposure at a single sky location
was 466 s. The data were collected between T0+50.0 ks and T0+51.4 ks,
and are entirely in Photon Counting (PC) mode. 

No uncatalogued X-ray sources have been detected. The 3-sigma upper
limit in the field (not including the regions where the tiles overlap)
ranges from ~0.03 to ~0.06 ct s^-1, corresponding to a 0.3-10 keV
observed flux of 1.1e-12 to 2.4e-12 erg cm^-2 s^-1 (assuming a typical
GRB spectrum).

A previously-catalogued X-ray source has been detected, however because
it is a catalogued object it is unlikely to be the afterglow.

The results of the XRT-team automatic analysis of the tiled XRT
observations, including a position-specific upper limit calculator, are
available at https://www.swift.ac.uk/xrt_products/TILED_GRB00109.

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