Abstract C​​hanging-look blazars (CLBs) are whose optical spectral lines at different epochs show significant changes and present a clear transition between standard FSRQ BL Lacertae (BL Lac). Changing-look phenomena in highly for enhancing our understanding of certain physical problems active galactic nuclei (AGNs), such as the potential mechanism state accretion process supermassive black holes central engine AGNs, possible intrinsic variation jet, connection disk jet. Currently, CLBs...

Abstract Changing-look active galactic nuclei (AGNs) are a special class of AGNs that change their spectral type from 1 to 2 or vice versa. In recent years, number changing-look blazars (CLBs) were also reported, which transition between flat-spectrum radio quasars and BL Lacs. The physical properties CLBs still unclear. Using the mclust R package for Gaussian mixture modeling, we performed clustering analysis sample 105 selected literature. Three kinds found lie in parameter distributions...

Abstract A sample of 312 low-frequency-peaked BL Lacertae objects (LBLs) and 694 flat-spectrum radio quasars (FSRQs) with the parameters both redshift gamma-ray photon spectral index (Γ γ ) is compiled from Fourth Catalog Active Galactic Nuclei Data Release 2 Fermi Large Area Telescope (LAT). The multiwavelength data sources are downloaded Space Science Center, then matched to corresponding Fermi-LAT Source 2. synchrotron radiation peak frequency Compton dominance (CD) obtained by using a...

There are still some significant and unanswered questions about the incredible very-high-energy $\ensuremath{\gamma}$-ray signatures. To help understand mechanism, focusing on linear quadratic perturbation mode for subluminal regime, we revisit expected signature Lorentz invariance violation (LIV) effects $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ absorption in TeV spectra of gamma-ray bursts (GRBs). We note that there is a critical energy pair production process, which...

Context. Unusually, there are still certain characteristics of the changing-look (CL) active galactic nuclei (AGNs) that remain undetected. Consequently, trigger mechanism behind CL phenomenon observed in partial AGNs remains unknown. Aims. We explore light curve and spectral energy distribution (SED) blazar OQ 334 as obtained by Fermi -LAT. Methods. By examining variability equivalent width (EW), we categorise -LAT curves during epoch MJD 54628−58677 into seven distinct epochs, including...

We develop a model for possible origin of hard very high energy spectra from distant blazar. In the model, both primary photons produced in source and secondary outside contribute to observed $\gamma$-rays emission. That is, are through synchrotron self-Compton (SSC) process, protons interaction with background along line sight. apply characteristic case was (VHE) $\gamma$-ray emissions blazar 1ES 1101-232. Assuming suitable electron proton spectra, we obtain excellent fits This indicated...

Context. Very high-energy (VHE) γ-ray measurements of distant TeV blazars can be nicely explained by spectra induced ultra cosmic rays.

Abstract Based on the long-term data in literature, we present evidence for optical spectral index variability behaviour BL Lacertae object OJ 287. First find that period of 287 is agreement with flux about 11.96 yr. It considered different processes induce variability, and each process should have a definite signature index, thus leading to periodicity index. We also time lag between density half period. This result tends support argument when brightness variations increases, spectra become...

Abstract In this paper, we present a long-term multiwavelength investigation focusing on 12 distinct samples of Fermi-4LAC bright flat-spectrum radio quasars (FSRQs). Detailed variability and spectral analyses γ -ray, X-ray, ultraviolet/optical data obtained by the Fermi Large Area Telescope, Swift X-ray Ultraviolet Optical Telescope were performed over period about 14 yr, spanning from 2008 October to 2022 October. These provide insights into characterizing variations within different...

We investigate rapid TeV flaring in markarian 501 the frame of a time-dependent one-zone synchrotron self-Compton (SSC) model. Inthis model, electrons are accelerated to extra-relativistic energy through stochastic particle acceleration and evolve with time, nonthermal photons produced by both inverse Comtpon scattering off photons. Moreover, during pre-flare relativistic steady state those flare whose injection rate is changed at some time interval. apply model Markarian on July 9, 2005...

Abstract In this paper, we have selected a sample of 64 teraelectronvolt blazars, with redshift, from those classified in the fourth Fermi Large Area Telescope source catalog. 3 https://fermi.gsfc.nasa.gov/ssc/data/access/lat/8yr_catalog/ We obtained values relevant physical parameters by performing log-parabolic fitting average-state multiwavelength spectral energy distributions. estimate range radiation zone parameters, such as Doppler factor ( D ), magnetic field strength B radiative...

We present the results of optical photometric (BVRI) monitoring three gamma-ray–loud BL Lac objects (3C 66A, PKS 0735+178, and Lacertae) in 1999–2002. During our observations, these showed significant rapid variations: 3C 66A 0735+178 exhibit short-timescale (∼1 hr) variability B band, exhibits intraday V. find that there is a strong correlation between brightness color for Lac. have analyzed relationship gamma-ray discuss theoretical models emission. found shorter time compared with...

Many quasi-simultaneous optical observations of 17 blazars are obtained from previous papers published over the last 19 years in order to investigate spectral slope variability and understand radiation mechanism blazars. The long-period dereddened slopes calculated. We analyse average distribution, which suggests that spectra flat spectrum radio quasars (FSRQs) high energy peaked BL Lac objects (HBLs) probably deformed by other emission components. low objects(LBLs), scatter around 1.5, show...

We present the optical photometries (B, V, R, and I) of BL Lac object S5 0716+714 (z > 0.3), which were observed with 1 m telescope at Yunnan Astronomical Observatory 1.56 Shanghai from 2001 February to 2006 April. Our results show a significant rapid variation exhibit short time variability ΔI = 0.60 mag in 28 minutes, ΔR 1.58 23 ΔV 1.06 10 ΔB 1.36 33 minutes. find strong correlation between V − R color index magnitude 292 CCD photometry showed they are good similitude Raiteri et al., Qian...

There are still some important unanswered questions about the detailed particle acceleration and escape occurring during quiescent epoches. As a result, distribution that is adopted in blazar spectral model have numerous unconstrained shapes. To help remedy this problem, we introduce analytical transport to reproduce broadband energy of blazar. In model, exact electron solved from generalized equation contains terms describing first-order secondary-order \emph{Fermi} acceleration, due both...

ABSTRACT An equivalent–width-based classification may cause the erroneous judgement to flat spectrum radio quasars (FSRQs) and BL Lacerate objects (BL Lac) due diluting line features by dramatic variations in jet continuum flux. To help address issue, this work explores possible intrinsic on basis of a random forest supervised machine learning algorithm. In order do so, we compile sample 1680 Fermi blazars that have both gamma-rays radio-frequencies data available from 4LAC-DR2 catalogue,...

The present work considers a plane shock front propagating along cylindrical jet. Electrons experience diffusive acceleration around the front, and subsequently drift away into downstream flow, in which they emit most of their energy. Assuming proper boundary condition at interface between zone zone, we solve transport equation for electrons flow where combined effects escape, synchrotron inverse Compton cooling Thomson regime are taken account. Using electron spectrum obtained this manner...

We present optical photometry (B, V, R, and I) of the BL Lac object H0323+022 (z = 0.147) for years 2000-2003. These were observed in high-luminosity state with 1 m telescope at Yunnan Astronomical Observatory 1.56 ShangHai Observatory. Our results show significant rapid variation exhibit a short time variability 19 minutes I band. find strong correlation between B − V color index magnitude CCD good agreement Bai et al., who R magnitudes about ΔI 0.80 mag ΔR 0.63 mag.

ABSTRACT The jets of blazars are renowned for their multiwavelength flares and rapid extreme variability; however, there still some important unanswered questions about the physical processes responsible these spectral temporal changes in emission properties. In this article, we develop a time-dependent particle evolution model time-varying spectrum blazars. model, introduce electric magnetic fields, which consistently include variability relevant quantities transport equation. electron...

We describe the theory of Fermi-type acceleration, including first-order Fermi acceleration at a parallel shock front and second-order in test particle limit. Including turbulent derivation general Fokker–Planck equation, we take into account basic particle-transport equation with spatially homogeneous isotropic distribution. In cases some special physical processes, construct equations, compile analytical or semi-analytical solutions 11 different cases. Even though, traditionally, one...

We present optical photometry (V, R, and I) of the BL Lac object OJ 287 (0851+203, z = 0.306), which was observed in a low, fainter state with 1 m telescope at Yunnan Astronomical Observatory. Our results show significant short-term variability R band over 31 minutes. find strong correlation between V - color index magnitude band. CCD is good agreement prediction Sillanpää coworkers an period about 11.6 yr.

ABSTRACT The classifications of Fermi-LAT unassociated sources are studied using multiple machine learning (ML) methods. update data from 4FGL-DR3 divided into high Galactic latitude (HGL, |b| > 10°) and low (LGL, ≤ regions. In the HGL region, a voting ensemble four binary ML classifiers achieves 91 per cent balanced accuracy. LGL an additional Bayesian–Gaussian (BG) model with three parameters is introduced to eliminate abnormal soft spectrum active galactic nuclei (AGNs) training...