Detection of a 55 Hz high-frequency QPO in MAXI J1820+070 with NICER
ATel #11951; Liang Zhang (Ihep), Li Chen (Beijing Normal University), Qingcu Bu (Ihep), Mingyu Ge (Ihep), Yue Huang (Ihep), Shumei Jia (Ihep), Xiang Ma (Ihep), Lian Tao (Ihep), Jinlu Qu (Ihep), Liming Song (Ihep)
on 14 Aug 2018; 12:19 UT
Credential Certification: Liang Zhang (liang.zhang@mail.bnu.edu.cn)
Subjects: X-ray, Binary, Black Hole, Transient
Referred to by ATel #: 11960
We report the detection of a 55 Hz high-frequency QPO in the new black hole transient MAXI J1820+070 (ATel #11488, #11510, #11576, #11578, #11820). We analysed the NICER observations of MAXI J1820+070 during March 12 to April 16 (ObsId 1200120101-1200120130). For the timing analysis, we produced a 16-s power density spectra (PDS) for each observation with a time resolution of 2 ms, so that the Nyquist frequency is 256 Hz. We find a clear high-frequency QPO in the PDS of ObsID 1200120107. The centroid frequency of the QPO obtained from the fit with a model of multiple Lorentzian functions is 55.12+/-0.06 Hz, the FWHM is 2.00+/-0.20 Hz, the fractional rms is about 1%. A weak second harmonic at the frequency of ~110 Hz was also present in the PDS. The high-frequency QPO was clearly detected until the observation 1200120120. During this period, the centroid frequency of the QPO was stable at ~55 Hz.
The frequency of this high-frequency QPO in MAXI J1820+070 is close to the 67-Hz QPO seen in GRS 1915+105. However, the 67-Hz QPO in GRS 1915+105 normally appears in a relatively soft state, but the 55-Hz QPO we observed in MAXI J1820+070 is present in the hard state. We are making a detailed analysis on this QPO to explore its physical origin.
