Blazar S4 0954+65: new absolute brightness maximum with quasi-periodical oscillations

ATel #15376; V. V. Vlasyuk, O. I. Spiridonova, A. S. Moskvitin, E. V. Emelianov, T. A. Fatkhullin (Special Astrophysical Observatory of the Rus. Ac. Sci.)
on 12 May 2022; 15:53 UT
Credential Certification: Alexander Moskvitin (mosk@sao.ru)

Tweet

Blazar S4 0954+65 is observing by SAO RAS team on a regular basis in search of possible intra-day variations and correlation between its optical and radio activity events. Since January 2021 we have started optical observations with 1-m reflector Zeiss-1000 and 0.5-m RC500 reflector (JSC ASTROSIB, Russia). We have observed S4 0954+65 with RC500 telescope in BVR passbands practically every night with appropriate atmospheric conditions. The observations with photometers of Zeiss-1000 were less extensive and realized according to telescope's schedule. Typical accuracy of our data was about 0.01 mag. while object was brighter than 15 mag. in active phase under good transparency and seeing value (FWHM) about between 2" and 3".

As our previous data showed, the current activity phase of S4 0954+658 is continued to April, then the most prominent brightness flash for S4 0954+658 was detected by us (R=13.20 mag.) twice at MJD = 59690.74 (with Zeiss-1000) and at MJD = 59690.89 (with RC-500) (ATel #15344).

Few days ago we have changed imaging focus of RC500 from primary (+ lens corrector) to Cassegrain one. The resulting scale on CCD is equal to 0".46 per pixel and total field size decreased from 90 to 30 arcminutes. Accuracy of our data after recombining should me better due to longer focus distance.

One of the first nights in new telescope configuration gave us some intriguing results. First of all, May 11/12 measurements started from new our brightness record (R = 13.19 mag. at MJD = 59710.9070). After brightness fading to R ~ 13.8 mag. at one-hour interval the blazar begun new growth up to new limits R = 13.14 mag. at MJD = 59710.9893 and, at least up to R = 12.93 mag. at MJD = 59710.9949. After last maximum the object became fainter by ~0.25 mag. within 15 minutes. Due to one-minute exposures we can reveal the presence of quasi-periodical flux variations, which modulated total brightness curve within all night period. Their mean period was between 6 and 9 minutes and amplitude was changed from ~0.05 mag. at local minimum to ~0.15 mag. at maxima which were noted above.

All data were taken using by R pass-band and have typical accuracy about or less than 0.01 mag. More accurate reduction is necessary. We strongly encourage further multi-wavelength coverage.