MAXI/GSC detection of bright X-ray burst-like activity positionally consistent with XTE J1810-197 and XTE J1810-189
ATel #18039; H. Negoro (Nihon U.), M. Serino (AGU), M. Nakajima, K. Saito, T. Yokoyama, M. Wada (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, Y. Kawakubo, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.), M. Shidatsu, C. Kang, M. Uenishi, T. Usuki, S. Yatsuzuka, H. Aoe (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), W. Iwakiri (Chiba U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U), and S. Ogawa (TUS)
on 12 Sep 2026; 16:49 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)
MAXI/GSC detected bright X-ray burst-like activity lasting more than 30 sec at 12:43 UT on September 12, 2026. Assuming that the source flux was constant over the transit, we obtain the source position at
(R.A., Dec) = (272.340 deg, -19.668 deg) = (18 09 22, -19 40 05 (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.22 deg and 0.16 deg, respectively. The roll angle of long axis from the north direction is 48 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:
(R.A., Dec) = (272.719, -18.766) deg = (18 10 52, -18 45 57) (J2000)
(R.A., Dec) = (272.998, -18.916) deg = (18 11 59, -18 54 57) (J2000)
(R.A., Dec) = (271.874, -20.764) deg = (18 07 29, -20 45 50) (J2000)
(R.A., Dec) = (271.593, -20.612) deg = (18 06 22, -20 36 43) (J2000)
The X-ray flux averaged over the scan was approximately 450 mCrab at 4.0-10.0 keV. There was no significant excess flux in the previous transit at 11:10 UT or in the next transit at 14:16 UT with an upper limit of 20 mCrab for each.
The anomalous X-ray pulsar (AXP) XTE J1810-197 lies within both the error regions. The 76-m Lovell Telescope detected intense radio emission from XTE J1810-197 on December 8, 2018 (Lyne et al., ATel #12284). MAXI also detected weak activity from the same region (Mihara et al., ATel #12291). However, no 5.54-s pulsation reported previously (e.g., Woods et al. 2005, ApJ, 629, 985) was found during this activity. The X-ray burster XTE J1810-189 also lies within the rectangular error region. Furthermore, MAXI detected an X-ray burst likely originating from XTE J1810-189 on April 19, 2023 (Kobayashi et al., ATel #16000). Finally, the position of SGR 1806-20 is marginally within the rectangular error region if the additional systematic uncertainty is taken into account. However, SGR 1806-20 is an unlikely candidate because the duration of this burst-like activity is much longer than typical bursts from SGR 1806-20.
Thus, XTE J1810-189 is currently the most likely candidate, even though it is located relatively far (~0.85 deg) from the central error position.
Follow-up observations are encouraged.
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