MAXI/GSC observations of past and current activity in SRGA J144459.2-604207
ATel #16483; H. Negoro (Nihon U.), T. Mihara (RIKEN), M. Serino (AGU), M. Nakajima, K. Kobayashi, M. Tanaka, Y. Soejima, Y. Kudo (Nihon U.), T. Kawamuro, S. Yamada, S. Wang, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, H. Hiramatsu, H. Nishikawa, A. Yoshida (AGU), Y. Tsuboi, S. Urabe, S. Nawa, N. Nemoto, E. Goto (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, S. Ogawa, T. Kurihara (JAXA), Y. Ueda, K. Setoguchi, T. Yoshitake, Y. Nakatani, Y. Okada (Kyoto U.), M. Yamauchi, Y. Hagiwara, Y. Umeki, Y. Otsuki (Miyazaki U.), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU), M. Sugizaki (NAOC), and W. Iwakiri (Chiba U.)
on 25 Feb 2024; 13:46 UT
Credential Certification: Hitoshi Negoro (negoro@phys.cst.nihon-u.ac.jp)
The accreting X-ray pulsar SRGA J144459.2-604207 was discovered by the SRG/ART-XC (ATel #16464), and its nature was revealed by MAXI, Swift, and NICER X-ray observations (ATel #16469, #16471, #16474, #16480). 2MASS 14445957-6042066 is proposed as an optical counterpart (#16470), but not confirmed yet in radio (ATel #16475) and optical (ATel #16476, #16477) bands.
We reexamined past activity of the source using MAXI/GSC data in more than 14 years, and found the following two faint activities in 2022 January and 2023 December (for the first seven years, also see Hori et al. 2018, ApJS 235, a7).
Activity in 2022 January:
The 2-10 keV flux had increased since 2022 January 3 (MJD 59583) and reached a plateau on January 6 and 7. Unfortunately, due to an ISS power problem, MAXI was shutdown from January 8 to 12, and no significant flux was detected after January 12. Using GSC data on January 6 and 7, we obtained the source position at
(R.A., Dec) = (221.149 deg, -60.550 deg) = (14 44 35, -60 32 59) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.50 deg and 0.43 deg, respectively. The roll angle of the long axis from the north direction is 31.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). SRGA J144459.2-604207 is well inside of the error region (0.156 arcdeg apart from the best position).
The 2-4 keV and 4-10 keV count rates averaged over January 6 and 7 are 0.014 +/- 0.04 c/cm2/s (~13 mCrab, 2-4 keV) and 0.030 +/- 0.005 c/cm2/s (~26 mCrab, 4-10 keV), respectively.
Activity in 2023 December:
The 2-10 keV flux had also increased for three or four days since 2023 December 9 (MJD 60287), and tended to decreased on December 14 (59292). From December 15 to 25, the source region was shaded by the SpaceX Dragon, and no enhancement was found after December 25. The data on December 12 and 13 showed the source position at
(R.A., Dec) = (221.071 deg, -60.596 deg) = (14 44 17, -60 35 45) (J2000)
with a statistical 90% C.L. elliptical error region with long and short radii of 0.21 deg and 0.15 deg, respectively. The roll angle of the long axis from the north direction is 62.0 deg counterclockwise. The localization is also well consistent with SRGA J144459.2-604207 (0.134 deg apart). The 2-4 keV and 4-10 keV count rates averaged over December 12 and 13 are 0.023 +/- 0.04 c/cm2/s (~22 mCrab) and 0.046 +/- 0.005 c/cm2/s (~39 mCrab), respectively.
The spectral hardness in the above two epochs is also consistent with that obtained in the current outburst. We also note that both events also triggered the Nova-Alert system, but we could not confirm the outbursts because of the above problems.
Current Activity:
The MAXI/GSC detected an X-ray burst at 11:07 UT on February 22 (also see ATel #16474). The GSC data show an outburst peak around February 22 and a following decline. The 2-4 keV and 4-10 keV count fluxes are 0.174 +/- 0.017 photons/cm2/s (~82 mCrab) and
0.165 +/- 0.011 photons/cm2/s (~130 mCrab), respectively (http://maxi.riken.jp/v7l3h/J1444-607/index.html). The current outburst is likely the brightest in these three.
