Re-brightening and decaying of MAXI J1348-630 as observed with NICER

ATel #13465; Liang Zhang, Diego Altamirano (University of Southampton), Ron Remillard (MIT), Zaven Arzoumanian, Keith Gendreau, Peter Bult, Tod E. Strohmayer (NASA/GSFC), Jeroen Homan (Eureka Scientific & SRON), Virginia A. Cuneo (IAC-ULL), James F. Steiner (Center for Astrophysics | Harvard & Smithsonian)
on 11 Feb 2020; 15:20 UT
Credential Certification: Liang Zhang (liang.zhang@mail.bnu.edu.cn)

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MAXI J1348-630 is a new black hole candidate discovered by MAXI/GSC on 2019 January 26 (ATel #12425). The source underwent a full outburst extending through the end of April 2019 (ATel #12441, #12447, #12456, #12469, #12470, #12471, #12477, #12491, #12497). After the main outburst, two outburst re-flares were detected, one starting at the end of May and another in the middle of Sep, respectively (ATel #12829, #12838, #13188). Starting from the beginning of Feb 2020, a new re-brightening was detected at optical wavelengths (ATel #13451) by XB-NEWS, and confirmed by MAXI/GSC (ATel #13459).

NICER observed MAXI J1348-630 between 2020 Feb 7 (MJD 58886) and 2020 Feb 10 (MJD 58889). On Feb 7, the source count rate in the NICER 0.5-10 keV band was ~55 count/sec (all 52 detectors). The 0.5-10 keV power spectrum was dominated by a strong broadband noise component with a total fractional rms of 39.6% in the 0.1-64 Hz range. On Feb 8 and 9, the source count rate in the NICER 0.5-10 keV was around 40 count/sec, and further decreased to ~25 count/sec on Feb 10. This indicates that the source was fading during the reflare. The 0.1-64 Hz fractional rms also shows a slow decrease to ~33% on Feb 10.

The 0.6-10 keV X-ray continuum spectrum during Feb 7-10 can be well modeled with an absorbed (N_H = 6.5(1) x10²¹ cm^-2) power-law (Gamma=1.64(2)) model. A disk component is not needed in the spectral fit. The 0.6-10 keV unabsorbed flux in this observation was 1.44E^-10 ergs/cm²/s. Our spectral fits together with the power spectrum characteristics suggest that MAXI J1348-630 is currently in the hard state.

NICER will continue to monitor MAXI J1348-630 at a cadence of about 1 ksec per day until the outburst fades, then a few ksec per week afterwards.

NICER is a 0.2-12 keV X-ray telescope operating on the International Space Station. The NICER mission and portions of the NICER science team activities are funded by NASA.