Orbital and superorbital variability of the new black hole LMXB MAXI J 1820+070 during the 2018 outburst
Abstract
The bright X-ray transient MAXI J1820+070 (=ASSASN-18ey), discovered in March 2018, has been identified as a low-mass X-ray binary, and a new black hole candidate. Multi-wavelength observations of MAXI J1820+070 were undertaken with a number of telescopes from the time of its discovery to the present day. We report here the results from optical monitoring of MAXI J1820+070 by AAVSO, SAAO 1m and SALT telescopes over the period of its outburst from March to October 2018. Our high-speed photometry undertaken with the SHOC instrument on the SAAO 1-m telescope reveals high frequency variability of the source in the frequency range ~0.01- 0.03 Hz, much of it consistent with red noise. The AAVSO CCD optical observations of MAXI J1820+070 have produced an excellent continuously sampled light curve. A Lomb-Scargle and dynamic power spectrum analysis of this light curves confirms the orbital period of MAXI J1820+070 as 0.6855 days (=16.452 h) and the presence of super-hump modulation with a period of 0.7033 days (=16.879 h). It is also confirmed that MAXI J1820 exhibits disc precession with a period of 27.548 days. We also report the comparison study of temporal evolution of NICER and Swift X-ray data with the optical data. No obvious X-ray - optical correlartions are seen. From the power spectral analysis of optical data we find that the superhump modulation begins about 100 days after the outburst began, but within a few weeks it is then dominated by a modulation on the orbital period. The transition between these two modes of behaviour occurs almost precisely at the same time that there is a sudden rise in X-ray brightness in both NICER and Swift observations, coincident with a reported transition from a hard intermediate state to a soft state .
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E1705T