High radio state of the high-redshift blazar PKS 2126-15
ATel #16834; Yu V. Sotnikova, T. V. Mufakharov, A. G. Mikhailov, T. A. Semenova, A. K. Erkenov (SAO RAS), Yu. A. Kovalev (ASC Lebedev), M. A. Kharinov (IAA RAS), A. E. Volvach (CrAO)
on 30 Sep 2024; 12:01 UT
Credential Certification: Timur Mufakharov (timur.mufakharov@gmail.com)
Subjects: Radio, AGN, Blazar, Quasar
The flat-spectrum radio quasar PKS 2126-15, located at z=3.26, has been identified as one of the first high frequency peaker (HFP) objects with a maximum in its radio spectrum around 8 GHz. It is represented in the BLcat catalogue of blazars monitored with the RATAN-600 radio telescope at 1.2-22.3 GHz since the 2000s. During its almost 25 year monitoring, it retains its convex spectrum shape with a moderate variability level (fractional variability of 15-20%) at 4.7-11.2 GHz and a higher variability at 2.3 GHz (28%) and 22.3 GHz (23%). Since 2020, PKS 2126-15 has shown a constant trend towards increasing its flux density in its optically thick radio spectrum at ν < 11 GHz.
We report its recent, obtained on 2024 September 12th, flux density values during the ongoing brightening of the blazar. Specifically, the simultaneously measured spectral flux density values at 2.3, 4.7, 8.2, 11.2, and 22.3 GHz are 0.61 (0.04), 1.96 (0.1), 2.36 (0.2), 1.93 (0.2), and 1.06 (0.1) Jy, respectively. Accompanying RATAN-600 estimates the RT-22 of CrAO reported 0.48 (0.08) Jy at 36.8 GHz on September 18th. This persistent high radio state together with the long-term radio variability may suggest a complex flaring process occurring in PKS 2126-15. The spectral indices, reflecting the state of the source, are calculate as α 2-8GHz = +0.63 for the optically thick part and α 8-37GHz = -0.90 for the optically thin part of the radio spectrum, both steeper than the values before 2020 when they were around ± 0.5.
The light curves of PKS 2126-15 in the link below. We will continue monitoring the source with RATAN-600 and RT-22. Multiwavelength observations are encouraged.
The light curves of PKS 2126-15 measured with RATAN-600 at 5-22 GHz
