Multi-wavelength observations of the Blazar 4C +28.07

The active galactic nucleus 4C +28.07 is a flat spectrum radio quasar, one of the brightest at γ-ray energies. We study its multi-wavelength emission by analysing ∼12.3 years of Fermi-LAT data in the γ-ray band and Swift-XRT/UVOT available data in X-ray and Optical-to-Ultraviolet bands. In the γ-ray band, five flaring periods have been detected, and quasi-simultaneously with these flaring times, the X-ray and UVOT data detected by Swift-XRT/UVOT have also been analysed. In one of the brightest flare periods (Flare 5; observed on Oct 12, 2018) the γ-ray flux reached (6.7 ± 0.81) × 10−6 photon cm−2 s−1 (∼31 × higher than the mean flux over 12.3 years) with detection significance of σ = 6.1. The estimated variability time(∼2 hours) constrains the γ-ray emitting region size to ≤9 × 1014 cm, which is close to the black hole radius. The spectral energy distributions (SEDs) in the γ-ray band for the ∼12.3 years of data show an early cut-off at ∼14 GeV; beyond ∼60 GeV, however, the spectrum hardens and is detected up to ∼316 GeV. Similar spectral behaviour is also noticeable for the SEDs of flares, which can be linked to the photon absorption by the emitting region’s internal and external narrow-band radiation fields. In the quiescent period, the γ-ray emission was described by the Synchrotron-Self-Compton scenario, while the external photons contributions from the Disk and the broad-line region were required to explain the short-term flaring γ-ray emission. Considering the significance of the obtained results from 4C +28.07, we compared the parameters with 3C 279 and M87, to motivate further studies.

Optical Variability of a Newly Discovered Blazar Sample from the BZCAT Catalog

In an optical monitoring program to characterize the variability properties of blazars, we observed 10 sources from the Roma-BZCAT catalog for 26 nights in V and R bands during 2014 October to 2015 June with two telescopes located in India. The sample includes mainly newly discovered BL Lacertae objects (BL Lacs) for which the redshift of some sources is not yet known. We present the results of flux and color variations of the sample on intraday and short timescales obtained by using the power-enhanced F-test and the nested-ANOVA tests, along with their spectral behavior. We find significant intraday variability in the single flat-spectrum radio quasar in our sample, having an amplitude of variation ∼12%. Although a few of the BL Lacs showed probable variation in some nights, none of them passed the variability tests at 99.9% significance level. We find that 78% of the sample showed significant negative color–magnitude correlations, i.e., a redder-when-brighter spectral evolution. Those that do not show strong or clear chromatism predominantly exhibit a redder-when-brighter trend. Unlike on hourly timescales, the high-synchrotron-peaked blazars in the sample (BZGJ0656+4237, BZGJ0152+0147, and BZBJ1728+5013) show strong flux variation on timescales of days to months, where again we detect a decreasing trend of the spectral slope with brightness. We observe a global steepening of the optical spectrum with increasing flux on the intranight timescale for the entire blazar sample. The nonvariability in the BL Lacs in our sample might be caused by the distinct contribution from the disk as well as from other components in the studied energy range.

A New Sample of Gamma-Ray Emitting Jetted Active Galactic Nuclei—Preliminary Results

We are compiling a new list of gamma-ray jetted active galactic nuclei (AGN), starting from the fourth catalog of point sources of the Fermi Large Area Telescope (LAT). Our aim is to prepare a list of jetted AGN with known redshifts and classifications to be used to calibrate jet power. We searched in the available literature for all the published optical spectra and multiwavelength studies useful to characterize the sources. We found new, missed, or even forgotten information leading to a substantial change in the redshift values and classification of many sources. We present here the preliminary results of this analysis and some statistics based on the gamma-ray sources with right ascension within the interval 0h--12h (J2000). Although flat-spectrum radio quasars and BL Lac objects are still the dominant populations, there is a significant increase in the number of other objects, such as misaligned AGN, narrow-line Seyfert 1 galaxies, and Seyfert galaxies. We also introduced two new classes of objects: changing-look AGN and ambiguous sources. About one third of the sources remain unclassified.