Recent changes in a flickering variability of the black hole X-ray transient V616 Mon = A0620-00

TL;DR

This study presents a long-term optical photometry analysis of the black hole X-ray transient V616 Mon, revealing changes in flickering variability and refining its orbital period through extensive observations over more than a decade.

Contribution

It provides new insights into the flickering behavior and orbital period of V616 Mon based on 13 years of multi-band optical photometry.

Findings

Detected variability changes during active and passive states.

Refined the orbital period to 0.32301407 days.

Identified flickering sources in the accretion disk and bright spot.

Abstract

V616 Mon = A0620-00 is a prototype of black hole transient X-ray binaries. Our 2003-16 optical photometry of the object during X-ray quiescence, obtained by 50-250 cm telescopes in Crimea, Caucasus Mountains and Slovakia, consists of ~ 7660 CCD frames in Johnson-Cousins $V,R,R_C,I$ bands and the integral light. During 2003, 2008-9 and 2015-16 passive states, the phase light curve of the binary exhibited mainly variations caused by an ellipsoidal shape of the red dwarf component. During 2004-6 and 2009-14 active states a significant aperiodic broad-band variability (flickering) was present, arising in a black hole accretion disk and a bright spot, where the mass transfer stream hits the outer edge of the disk. Long term photometry of our minima times, together with available positions of superior conjunctions of the red dwarf found from spectroscopy, allowed us to refine the orbital period of V616 Mon to 0.32301407(5) days.