The signature of double-peak structure of Ton 599 flare

ATel #16539; V. V. Vlasyuk, O. I. Spiridonova (Special Astrophysical Observatory of the Rus. Ac. Sci.)
on 19 Mar 2024; 12:56 UT
Credential Certification: Alexander Moskvitin (mosk@sao.ru)

Tweet

The flat spectrum radio quasar (FSRQ) Ton 599 (4C 29.45, PKS 1156+295) reached an exceptionally high brightness level in the optical bands on the night of February 26, 2024, as was reported in (ATel #16488). As it was noted therein its brightness has risen strongly since the beginning of February this year.

The regular studies of this object were started in 2023 January just after its previous flare. All our estimates were taken using by 1-meter and 0.5-meter SAO RAS reflectors, equipped by BVRI CCD-photometers with back-illuminated CCDs as detectors.

In addition to this description we have to note that brightness of Ton 599 started its growth since the January. According to our estimates, the total brightness curve in R-band (MR) for Ton 599 in 2024 may be well represented by a combination of 4 linear curves with distinct slopes, as shown below.

This allows us to conclude that current flare in FSRQ Ton 599 has double-peaked exponential nature with time-scales in interval between 3 and 30 days. The second peak of flare is in progress now.

Epochs, MJD	MR range	Slope, mags/day	Comment
60305--60355	16m.7--15m.0	0.04	the slow initial growth from faint state
60355--60366	15m.0--13m.3	0.10	the stage before maximum
60366--60374	13m.3--15m.8	-0.30	the fastest fading after maximum
60374--60388	15m.8--14m.5	0.10	the second flare growth stage

The typical errors of the slopes do not exceed 10% of value presented. Let us to note that transition between processes with different slopes usually needs 1-3 days only.

Typical accuracy of our data was about 0m.01 under good transparency and seeing value (FWHM) below 2". The estimates of brightness from the both (1-m and 0.5-m) telescopes agree well within their instrumental errors.

Data from our both telescope were calibrated using by stars 1--4 from (Raiteri et al., A&AS 130, 495, 1998).

More accurate reduction is necessary. We strongly encourage further multi-wavelength observations.