GRB 190306A

M. Shidatsu (Ehime U.), H. Negoro (Nihon U.), M. Serino (AGU),
M. Nakajima, A. Sakamaki, W. Maruyama, M. Aoki, K. Kobayashi (Nihon U.),
T. Mihara, S. Nakahira, F. Yatabe, Y. Takao, M. Matsuoka (RIKEN),
T. Sakamoto, S. Sugita, T. Hashimoto, A. Yoshida (AGU), N. Kawai, 
M. Sugizaki, Y. Tachibana, K. Morita (Tokyo Tech), S. Ueno, H. Tomida, 
M. Ishikawa, Y. Sugawara, N. Isobe, R. Shimomukai, T. Midooka (JAXA),
Y. Ueda, A. Tanimoto, T. Morita, S. Yamada, S. Ogawa (Kyoto U.),
Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.),
H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), M. Yamauchi, 
K. Hidaka, S. Iwahori (Miyazaki U.), T. Kawamuro (NAOJ), 
K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU)
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered on a bright uncatalogued X-ray
transient source at 2019 March 06 UT 20:51:59.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (222.563 deg, 30.944 deg) = (14 50 15, +30 56 38) (J2000)
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.34 deg and 0.33 deg, respectively.
The roll angle of long axis from the north direction is 142.0 deg
counterclockwise. There is an additional systematic uncertainty of 
0.1 deg (90% containment radius). The X-ray flux averaged over the scan 
was 81 +- 16 mCrab (4.0-10.0keV, 1 sigma error).
There was no significant excess flux in the previous transit at UT 19:19
and in the next transit at UT 22:24 with an upper limit of 20 mCrab for each.

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 190306A. Automated analysis of the XRT data will
be presented online at http://www.swift.ac.uk/xrt_products/TILED_GRB00078

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.

D.N. Burrows (PSU), A. Tohuvavohu (PSU), S. J. LaPorte (PSU), J.P.
Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'Ai
(INAF-IASFPA) 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 190306A (Shidatsu et al. GCN Circ. 23937
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 ) in a series of
observations tiled on the sky. The total exposure time is 1.2 ks,
distributed over 7 tiles; the maximum exposure at a single sky location
was 379 s. The data were collected between T0+24.2 ks and T0+25.6 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 ~0.05 to ~0.15 ct s^-1, corresponding to a 0.3-10 keV
observed flux of 1.8e-12 to 6.1e-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 http://www.swift.ac.uk/xrt_products/TILED_GRB00078.

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