A research team from the Xinjiang Astronomical Observatory (XAO), Chinese Academy of Sciences, has recently released long-term radio observational data on gamma-ray-loud active galactic nuclei (AGNs)—among the most extreme and energetic galaxies in the universe.

As some of the most remarkable cosmic objects, these galaxies host supermassive black holes at their centers that drive bright cores and powerful relativistic jets, which extend beyond the galaxy’s size with distances of hundreds to millions of light-years.

This study offers a unique insight into the behavior of these cosmic powerhouses, shedding light on how black holes influence their environments across the cosmos.

The research was led by Professor CUI Lang from the Galaxy and Cosmology Group at XAO, with team members including Krishna Mohana A, WANG Xin, CHANG Ning, TAN Guiping and LIU Xiang. The findings have been published in The Astrophysical Journal Supplement Series.

This research is part of the SMMAN program (quasi-Simultaneous Multiwavelength Monitoring of Gamma-Ray-Loud AGNs with the Nanshan 26 m radio telescope) launched in 2016, which tracks 131 northern (δ > ∼ 0∘) AGNs from the Fermi-LAT third source catalog.

This first data release covered over eight years of observations (2016–2024) at 4.8 GHz and 23.6 GHz. The main goal of the program is to provide multi-frequency radio data obtained at lower frequencies that complements Fermi-LAT gamma-ray observations and other multiband radio/optical-UV/X-ray monitoring programs, enabling a detailed study of the radio/multiband properties of gamma-ray-loud AGNs.

As the core targets of the SMMAN monitoring program, gamma-ray-loud AGNs display distinctive observational characteristics across electromagnetic wavelengths. AGNs exhibit strong flux variability across the electromagnetic spectrum, providing key insights into the complex physics of accretion and plasma jets. A special class, blazars, have jets pointed toward Earth, producing Doppler-boosted emission that varies dramatically over minutes to years. These galaxies blaze across the electromagnetic spectrum—from radio waves to gamma rays—making them ideal cosmic laboratories to study the physics of extreme jets and high-energy processes.

The researchers measured radio signals from active galaxies using a cross-scan method, sweeping the telescope in two orthogonal directions. Observations were made at 4.8 GHz and 23.6 GHz, with multiple passes to capture precise signals. Each pass is analyzed as a Gaussian-shaped signal, and corrections are applied for telescope pointing, atmospheric effects, and instrumental gain. This careful method ensures reliable flux density measurements of SMMAN target sources.

The researchers studied the characteristics of variability, spectral index, luminosity, and gamma-ray loudness across the different AGN classes in the sample. Variability is stronger at 23.6 GHz than at 4.8 GHz, with BL Lacertae (BL Lac) objects more variable than flat-spectrum radio quasars (FSRQs). BL Lacs typically show flatter radio spectra, while FSRQs, blazar candidates of uncertain type (BCUs), and radio galaxies (RDGs) span flat to steep spectra. FSRQs are the most radio-luminous, BCUs intermediate, and RDGs fainter. Gamma-ray loudness is highest for FSRQs and BL Lacs, intermediate for BCUs, and lowest for RDGs.

The first data release from this long-term monitoring program in the lower frequency bands provides unique coverage of the radio part of the spectral energy distribution (SED), complementing other historical and ongoing multi-frequency surveys. Together, the SMMAN dataset offers a unique opportunity to track SED evolution, search for quasiperiodic oscillations, and explore supermassive black hole binary systems, shedding new light on the dynamic behavior of these energetic galaxies.