AR-2019-2020

506 (QHUJ\ NH9 +] +] 7LPH /DJ PV (QHUJ\ NH9 +] +] Figure 16: Fractional rms (left) and time lag (right) as a function of photon energy from the low intensity level data of AstroSat observation conducted during March 3 - 4, 2018. The red filled circle and black open triangle represent the QPO frequency at ∼ 6 . 60 Hz and the sub-harmonic at ∼ 3 . 17 Hz, respectively. The red solid line and black dotted line represent the model fit derived from the fluctuation propagation model for the QPO and the sub-harmonic, respectively. periodic modulation, while its spectrum shows double-peaked hydrogen and helium emission lines (similar to those seen in accretion discs in low-mass X-ray binaries). These properties suggest that 4FGL J0935.3+0901 is a compact X-ray emitting binary belongs to the millisecond pulsar (MSP) class. Detailed optical spectroscopic analysis indicates that this binary could be a transitional MSP system at a sub-luminous disc state, although the other possibility, the binary in a rotation- powered state showing the optical emission lines due to intrabinary interaction processes, can not be excluded. Puzzling blue dips in the black hole candidate Swift J1357.2-0933, from ULTRACAM, SALT, ATCA, Swift, and NuSTAR A few years ago, a low-mass black hole in our galaxy was discovered to show strange dips in its optical light. Not corresponding to any stars or planet orbiting it, and appearing to be fairly regular for such a normally chaotic system, these dips meant that the system itself presented something of an enigma. Called Swift J1357.2-0933 (or J1357), this has led it to being a subject of much study, to try and discover the underlying processes. By observing in optical light (ULTRACAM/NTT, Chile; and SALT, South Africa), X-rays (Swift and NuSTAR, Low Earth Orbit) and radio (ATCA), John A. Paice , Poshak Gandhi, Ranjeev Misra and collaborators found that the dips were not only present once again - four years after their discovery - but J1357 was found to be much bluer during them than outside of them. Additionally, superimposing many of the dips together, it was also confirmed that there is no dip in the X-rays at the same time as that in the optical (see Fig. 17). When also considering behaviour of each band with respect to one another, it was postulated that the black hole could (amongst other features) host a recessed disc, as well as a red-coloured jet base that is sporadically occulted by outer material.