GRB 240514E

H. Negoro (Nihon. U). S. Ogawa (JAXA), W. Iwakiri (Chiba U.), M. Nakajima, Y. Kudo, H. Shibui, 
K. Takagi, H. Takahashi, K. Tatano, H. Nishio (Nihon U.), T. Mihara, T. Kawamuro, S. Yamada, 
S. Wang, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN),T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, 
H. Hiramatsu, H. Nishikawa, Y. Kondo, A. Yoshida (AGU), Y. Tsuboi, H. Sugai, N. Nagashima (Chuo U.), 
M. Shidatsu, Y. Niida (Ehime U.),I. Takahashi, M. Niwano, S. Sato, N. Higuchi, Y. Yatsu (Tokyo Tech), 
S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, M. Kurihara (JAXA), Y. Ueda, Y. Okada (Kyoto U.), 
M. Yamauchi, Y. Otsuki, T. Hasegawa, M. Nishio (Miyazaki U.), K. Yamaoka (Nagoya U.), and 
M. Sugizaki (NAOC)

The MAXI/GSC detected an uncatalogued X-ray transient source at 19:04 UT 
on May 14, 2024. Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (76.718 deg, -21.544 deg) = (05 06 52, -21 32 38) (J2000) 
with a statistical 90% C.L. elliptical error region 
with long and short radii of 0.61 deg and 0.42 deg, respectively. 
The roll angle of long axis from the north direction is 131.0 deg counterclockwise. 
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 100 +- 23 mCrab
(4.0-10.0keV, 1 sigma error).
There was no significant excess flux in the previous transit at 17:32 UT 
with an upper limit of 20 mCrab. No observation for the region was made 
for more than 19 hours after the detection.

The source did not show significant rapid variations during the scan.
Given a relatively high galactic longitude, (l, b) = (222.1, -32.2), 
and the spectral softness, the source is most likely a GRB afterglow.

T. Mihara (RIKEN), Y. Tsuboi (Chuo U.), W. Iwakiri (Chiba U.), H. Negoro, M. Nakajima, Y. Kudo, H. Shibui, K. Takagi, H. Takahashi, K. Tatano, H. Nishio (Nihon U.), T. Kawamuro, S. Yamada, S. Wang, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, M. Serino, S. Sugita, Y. Kawakubo, H. Hiramatsu, H. Nishikawa, Y. Kondo, A. Yoshida (AGU), H. Sugai, N. Nagashima (Chuo U.), M. Shidatsu, Y. Niida (Ehime U.), I. Takahashi, M. Niwano, N. Higuchi, Y. Yatsu (Tokyo Tech), S. Nakahira, S. Ueno, H. Tomida, M. Ishikawa, S. Ogawa, M. Kurihara (JAXA), Y. Ueda, Y. Okada (Kyoto U.), M. Yamauchi, Y. Otsuki, T. Hasegawa, M. Nishio (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (NAOC) report on behalf of the MAXI team:

This is a cross post of ATel #16622.

MAXI team reported a possible GRB afterglow, GRB 240514E (GCN 36485
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 ).
It is not confirmed yet, as Swift cannot follow-up this region for a week. 
We report here that there is a flare star system BD-21 1074 in the MAXI error box.
It is also an X-ray source 1RXS J050649.5-213505 in the ROSAT catalog 
(0.8e-11 erg/s/cm2 in 0.1-2.4 keV) in Hunsch et al. 1999 (A&AS 135, 319).
Because the nearby stars above this ROSAT flux level are about 90 stars scattering
all over the sky, 
the chance coincidence of a GRB and a flare star is rare.
There is no counterpart in the 3MAXI 7-year catalog with the sensitivity of 0.6e-11 erg/s/cm2 in 4-10 keV.
If it was a flare from BD-21 1074, it would be the first detection with MAXI,
and also the first detection of X-ray flare from BD-21 1074.
<br>
BD-21 1074ABC are dMe stars triplet at the distance of 19.8 pc (Gaia DR3).
Optical flares were reported in Messina et al. 2014 (A&A 570, 19). 
The observational results with MAXI are consistent with a stellar flare, i.e. 
soft X-ray spectrum, no variability during the scan,
no detection in the previous scan at 92 min before,
and no detection in the next scan at 19 h later.
The measured X-ray luminosity was 1.0e32 erg/s,
which is the highest class of flares as a dMe star. 
<br>
Since BD-21 1074 might be in an active phase,
optical spectroscopic observations are recommended.