The radio state of the blazar Ton 599 in the first quarter of 2024

ATel #16557; Mikhailov A. G. (SAO RAS), Muhakharov T. V. (SAO RAS), Sotnikova Yu. V. (SAO RAS), Kovalev Yu. A. (ASC Lebedev), Kharinov M. A. (IAA RAS), Rahimov I. A. (IAA RAS), Semenova T. A. (SAO RAS), Andreeva T. S. (IAA RAS), Cherepkova Yu. V. (SAO RAS)
on 26 Mar 2024; 15:36 UT
Credential Certification: Alexander Mikhailov (mag10629@yandex.ru)

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The blazar Ton 599 showed the strongest radio flares in its history almost a year ago, in February 2023 (ATel#15872,#15873,#15894). Recently, this source demonstrated flaring activity at the optical band in February-March 2024 (ATel#16488,#16539), but remained relatively calm at high radio frequencies of 19-44 GHz as on February 4th 2024 (ATel#16488). Here we report the rising of the flux density of this blazar in March 2024. The observations were carried out with the radio telescope RATAN-600 at the frequencies 1.2, 2.3, 4.7, 8.2, 11.2, 14.4, and 22.3 GHz quasi-simultaneously. The average flux densities over the past three months (in Jy) are listed in the Table, their uncertainties are given in parenthesis.

epoch	22.3 GHz	14.4 GHz	11.2 GHz	8.2 GHz	4.7 GHz	2.3 GHz	1.2 GHz
January	1.85 (0.16)	2.03 (0.11)	1.95 (0.07)	1.97 (0.03)	2.09 (0.06)	2.03 (0.06)	1.59 (0.15)
February	2.38 (0.18)	2.72 (0.14)	2.65 (0.10)	2.51 (0.03)	2.23 (0.06)	2.00 (0.07)	-
March	2.99 (0.39)	2.78 (0.15)	2.50 (0.13)	2.96 (0.10)	2.43 (0.11)	1.96 (0.13)	1.21 (0.38)

The radio spectrum switches from the flat, with the spectral index being close to zero at 2-22 GHz, to the rising shape, with the spectral index reaching a value of +0.68 (0.07) at 11-22 GHz. The flux density at 22 GHz correlates with high-frequency spectral index (see the link below). We are continuing systematic monitoring of Ton 599 and encourage multi-wavelength observations of this blazar.

The light curve of Ton599 in 2023-2024.2 at 22.3 GHz and the spectral index variation at 11-22 GHz