GCN Circular 24048

M. Nakajima, H. Negoro (Nihon U.), W. Iwakiri (Chuo U.), 
W. Maruyama, M. Aoki, K. Kobayashi (Nihon U.), 
S. Nakahira, T. Mihara, M. Matsuoka (RIKEN), 
T. Sakamoto, M. Serino, S. Sugita, T. Hashimoto, A. Yoshida (AGU), 
Y. Tsuboi, R. Sasaki, H. Kawai, T. Sato (Chuo U.), N. Kawai, M. Sugizaki, 
Y. Tachibana, K. Morita, M. Oeda, K. Shiraishi (Tokyo Tech), 
S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N.Isobe, R. Shimomukai, 
M. Tominaga (JAXA), Y. Ueda, A. Tanimoto, T. Morita, S. Yamada, 
S. Ogawa (Kyoto U.), H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), 
M. Yamauchi, S. Iwahori, Y. Kurihara (Miyazaki U.), T. Kawamuro (NAOJ), 
K. Yamaoka (Nagoya U.), M. Shidatsu (Ehime 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 12:24:20 UT on 2019 April 4. Assuming that the source 
flux was constant over the transit, we obtain the source position at
(R.A., Dec) = (12.088 deg, 27.486 deg) = (00 48 21, +27 29 09) (J2000) 
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.13 deg and 0.12 deg, respectively.
The roll angle of the long axis from the north direction is 136.0 deg 
counterclockwise. 
  Without assumptions on the source constancy, we obtain a rectangular error box
for the transient source with the following corners: 
(12.621, 28.061) deg = (00 50 29, +28 03 39) (J2000) 
(12.378, 28.204) deg = (00 49 30, +28 12 14) (J2000) 
(11.610, 27.173) deg = (00 46 26, +27 10 22) (J2000) 
(11.851, 27.032) deg = (00 47 24, +27 01 55) (J2000)
There is an additional systematic uncertainty of 0.1 deg (90% containment 
radius).

The X-ray flux averaged over the scan was 399 +- 41 mCrab (4.0-10.0keV, 
1 sigma error). There was no significant excess flux in the previous transit 
at 10:51 UT on 2019 April 4 with an upper limit of 20 mCrab.

Note that we noticed that Fermi had detected a GRB at 07:01 on April 4.
Then, we rename this burst, referred to as GRB 190304A in the MAXI 
new-transient ML, GRB 190404B. We apologize for a series of mistakes.