X-ray and near-infrared observation of rebrightening of MAXI J1348-630

ATel #13539; M. Oeda, K. L. Murata, R. Adachi, N. Kawai, K. Miyakawa (Tokyo Tech), K. Morihana (Nagoya U), T. Nagayama (Kagoshima U), M. Shidatsu (Ehime U.), H. Negoro (Nihon U.), T. Mihara (RIKEN), K. Shiraishi, K. Iida, M. Niwano, F. Ogawa, S. Toma, R. Hosokawa, N. Nakamura, Y. Yatsu (Tokyo Tech)
on 3 Mar 2020; 04:27 UT
Credential Certification: Katsuhiro Murata (murata@hp.phys.titech.ac.jp)

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Since 2019 Nov. 25, the MAXI/GSC light curve had shown a rebrightening (MAXI x-ray-star ML: 734). Following this, we requested ToO observations to NICER in X-rays and 1.4 m telescope IRSF (InfraRed Survey Facility) in near-infrared wavelength. Here we report preliminary results.

The black hole candidate X-ray binary MAXI J1348-630 was discovered with MAXI/GSC on 2019 Jan. 26 (ATel #12425, #12430, #12434, #12439, #12441, #12447, #12448, #12456, #12457, #12470, #12477, #12480, #12491, #12497, #12505, #12520, #12829, #13188). The optical counterpart has been identified (ATel #12430) soon after the discovery. After the main outburst ended around 2019 May, the source showed an X-ray and optical rebrightening in 2019 June (Atel #12838, #13188).

The NICER ToO for the 2019 Nov. rebrightening was performed for 250 sec from Nov. 26 02:31:04 and for 870 sec from Nov. 27 01:43:13. The NICER X-ray light curves (linked below Figure) with the new data and its public data so far confirm the 2019 Nov. rebrightening found by the MAXI/GSC. We excluded the data points below 10 counts/s at 2-4 keV from the light curves because it was near the detection limit. The X-ray hardness ratios of the NICER data on Nov. 26 and 27 indicate that the source was in the hard state; the hardness ratios are similar to those during the main outburst and the 2019 June rebrightening phase.

The near-infrared (J, H, Ks) observation of the optical counterpart was performed with the IRSF/SIRIUS (Simultaneous infrared imager for un-biased survey; Nagashima et al. 1999; Nagayama et al. 2003) from Nov. 26 02:38:03 to 02:53:17 and from Nov. 27 01:59:56 to 02:16:16. The near-infrared magnitudes are J~15.9, H~15.6 and Ks~15.6 on Nov. 26, and J~15.9, H~15.7 and Ks~15.6 on Nov. 27. Given magnitudes are calibrated against 2MASS point sources in the field and are expressed in the AB system. The near-infrared J-H color on Nov. 26 and 27 is similar to that in the hard-to-soft intermediate state and redder than the soft state during the main outburst.

Generally, a jet tend to be present in the hard state and it causes redder near-infrared color than the soft state. Therefore, there is a possibility that the infrared radiation on Nov. 26 and 27 originates from jets.

We thank the NICER team and IRSF community for arranging these observations, and Y. Tachibana for useful discussion.

Light curve and hardness ratio of the NICER