PREDNASAJUCI / LECTURER :

Sergey Shugarov

(1) Astronomical Institute, Slovak Academy of Sciences,
059 60 Tatranská Lomnica

NAZOV / TITLE :

Photometric investigation of two X-ray novae: V3721 Oph and Swift J1727.8-1613.

ABSTRAKT / ABSTRACT :

An analysis of UBVRI observations of these stars obtained in Slovakia, Italy, Poland, Crimea and the Caucasus is 
being carried out. The outbursts of both objects were first detected in X-rays, and were soon found on patrol CCD 
cameras as novae with an outburst amplitude of about 8 mag. The outburst of V3721 Oph occurred in 2018 and lasted  
200 days. The outburst of Swift J1727.8-1613 was in August 2023. Over 2 months of our observations the brightness 
decreased by 2 mag and then the star disappeared in the rays of the Sun. However, X-ray observations still show 
increased radiation flux. Further photometric observations are planned to begin soon.

For V3721 Oph, 16-hour oscillations associated with the orbital period appeared at the SSS (X-ray SuperSoftSource) 
stage; subsequently this period was dissipated again. We have traced the detailed evolution of these oscillations. 
Two-color diagrams showed decrease of color temperature from 17000K to 6000K. After reaching a state of quiescence, 
we found 3 short repeated outbursts. 

The source Swift J1727.8-1613 showed a maximum X-flux a few days after its discovery. Later the hard X-ray also changed 
tt a soft one, the object entered the SSS stage with a monotonous decrease in brightness. The orbital period of the object 
has not yet been discovered. However, analysis of our photometric observations allowed us to assume the existence of an 
orbital period of 0.131 days. New observations and more complete analysis are needed to prove the existence of this period.