SMMAN: quasi-Simultaneous Multi-wavelength Monitoring of gamma-ray-loud AGNs with the Nanshan 26-m radio telescope

Abstract

Active Galactic Nuclei (AGNs) are characterized by strong temporal flux density variability across the electromagnetic spectrum, offering insights into the complex physical processes governing accretion and plasma outflows. To systematically investigate AGNs flux density variability in radio bands, a long-term program was initiated in late 2016: quasi-Simultaneous Multiwavelength Monitoring of gamma-ray-loud AGNs with the Nanshan 26-m radio telescope (SMMAN). This work presents the first data release of the SMMAN program, spanning over eight years from 2016 to 2024 with observations at 4.8 and 23.6 GHz. The SMMAN sample includes 131 northern ($δ>\sim0^{\circ}$) sources selected from the Fermi Large Area Telescope third source catalog. The characteristics of variability, spectral index, luminosity, and $γ$-ray loudness factor are examined for different AGN classes within the sample. Target sources exhibit stronger variability at 23.6 GHz compared to 4.8 GHz, with BL Lac objects being more variable than flat-spectrum radio quasars (FSRQs). BL Lacs generally have flatter radio spectra, while FSRQs, blazar candidates of uncertain type (BCUs), and radio galaxies (RDGs) span a wider range from flat to steep. FSRQs are more radio-luminous than BL Lacs and other classes, with BCUs intermediate and RDGs generally fainter. FSRQs and BL Lacs have higher $γ$-ray loudness factors than RDGs, while BCUs have intermediate values. The SMMAN dataset, incorporated with other historical and ongoing monitoring programs, will provide a unique opportunity to investigate the evolution of spectral energy distributions, search for quasi-periodic oscillations, and analyze supermassive black hole binary systems.

Figures (35)

• Figure 1: Top: the Hammer-Aitoff projection of the SMMAN monitored sources in sky distribution (in equatorial coordinates). Bottom: the redshift distribution of the sources in the SMMAN program. The redshift values were obtained from the NASA/IPAC Extragalactic Database (NED) and the SIMBAD astronomical database wenger2000. Redshift measurements are available for 124 of the 131 sources in our monitored sample, of which 121 are spectroscopic and three are photometric.
• Figure 2: Example of a 4+4 cross-scan observation of the calibrator source 3C 286 at 4.8 GHz. The first four subplots display longitude (azimuthal) subscans, followed by the next four showing latitude (elevational) subscans. For each of these eight subplots, the upper panel presents the subscan results, with the red curve representing the Gaussian fit model and the grey line indicating the actual observed data. The lower panel beneath each subscan plot shows the residuals of the model fit. The final subplot summarizes the fitted Gaussian amplitudes from all individual subscans, with a solid red horizontal line indicating the mean amplitude.
• Figure 3: The number of radio measurements for the SMMAN sources (131 objects).
• Figure 4: UpSet plot describing the overlapping of the SMMAN sources with other monitoring programs. Reading chart: the horizontal set size bar chart displays the total number of sources within each distinct monitoring program. Vertical intersection size bar chart, positioned at the top, illustrates the number of sources of each particular intersection or combination of monitoring programs. The solid dots and lines (linked by a vertical line) signify the sources that belong to a particular intersection.
• Figure 5: Multiband light curve of S4 0954+65 using SMMAN, RATAN-600, F-GAMMA, and ROBIN monitoring program data at $\sim4.8$ and $\sim23$ GHz.