Active Galactic Nuclei (AGN) are characterized by a strong emission coming from a very compact region (only few pcs) at the galaxy center. Blazars form a class of AGN, characterized by high luminosity in a broad frequency range, from radiofrequencies to high energies (X-rays and γ-rays), as well as extreme variability and high polarization at optical and near-infrared and radio wavelengths. The broad-band spectral energy distribution shows two bumps: the low-frequency one, from radio to optical/Xrays; and the high-frequency one, from X-rays to γ-rays. The most accepted scenario to explain the observed properties suggests that the emission is coming from a jet of accelerated relativistic particles, closely aligned with the line of sight and originating at the proximity of a supermassive black hole. In this way, the jet emission is strongly amplified and it exceeds any other kind of radiation coming from the galaxy. Synchrotron emission explains the low-frequency bump, whereas leptonic and hadronic models are competing to describe the high-energy bump.
Nowadays, a respectable number of blazers is being monitored daily by the high-energy space observatories, Fermi and AGILE. Blazers also dominate the Universe in the very high energy gamma-ray band (E>100 GeV), which observations are carried out from the ground using Cherenkov telescopes. Hence follow-up programs to simultaneously cover a broad frequency range are mandatory in order to learn more about the unpredictable flux variability observed in ths type of active nuclei and furthermore to try understanding in more detail the physical processes taking place.
In this project two aspects will be covered: on one side, follow-up observations in the optical and near-infrared ranges will be provided, using the telescopes available at the Teide and Roque de Los Muchachos observatories. These observations are carried out within the framework of a more extense collaboration, the GASP-WEBT, which comprises about 30 other observatories. Remarkably, this is the only way to catch and monitor in detail all phases (rising, peak and falling) of correlated flares, which are the test-bed for the theoretical models for high-energy emission; On the other side, long term series of data (several years) taken at different energy ranges will be analized to search for correlations between bands and also any kind of periodicities which may indicate jet-precession, binary black-holes or any other mechanism. Additional insight can be gained by analyzing a number of flares in different targets but, due to the unpredictable nature of such events, this has to be interpreted in statistical terms.
- The host galaxy morphology of the active nucleus Pks 1502+036 is found to correspond to an elliptical (D'Ammando et al 2018). This active nucleus is a powerful gamma ray emitter which implies the presence of a very massive black hole, contrary to the expected from its spectroscopic classification.
- First redshift determination of the very high energy gamma-ray extreme blazar PGC 2402248 from optical spectroscopy obtained using OSIRIS at GTC (Becerra et al, 2018, ATel 11621). This blazar has been previously detected by MAGIC at very high energy (E > 100GeV).
- The analysis of the light curves in the optical range of two blazars reveals a periodic behaviour with cadence of few years.
Rapid quasi-periodic oscillations in the relativistic jet of BL Lacertae
Blazars are active galactic nuclei (AGN) with relativistic jets whose non-thermal radiation is extremely variable on various timescales1-3. This variability seems mostly random, although some quasi-periodic oscillations (QPOs), implying systematic processes, have been reported in blazars and other AGN. QPOs with timescales of days or hours areJorstad, S. G. et al.
ASTRI Mini-Array core science at the Observatorio del Teide
The ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) Project led by the Italian National Institute for Astrophysics (INAF) is developing and will deploy at the Observatorio del Teide a mini-array (ASTRI Mini-Array) composed of nine telescopes similar to the small-size dual-mirror Schwarzschild-Couder telescope (ASTRI-Horn) currentlyVercellone, S. et al.
A Radio, Optical, UV, and X-Ray View of the Enigmatic Changing-look Active Galactic Nucleus 1ES 1927+654 from Its Pre- to Postflare States
The nearby Type II active galactic nucleus (AGN) 1ES 1927+654 went through a violent changing-look (CL) event beginning 2017 December during which the optical and UV fluxes increased by four magnitudes over a few months, and broad emission lines newly appeared in the optical/UV. By 2018 July, the X-ray coronal emission had completely vanished, onlyLaha, Sibasish et al.
A statistical study of the optical spectral variability in gamma-ray blazars
Blazars optical emission is generally dominated by relativistic jets, although the host galaxy, accretion disc, and broad-line region (BLR) may also contribute significantly. Disentangling their contributions has been challenging for years due to the dominance of the jet. To quantify the contributions to the spectral variability, we use theOtero-Santos, J. et al.
Investigation of the correlation patterns and the Compton dominance variability of Mrk 421 in 2017
Aims: We present a detailed characterisation and theoretical interpretation of the broadband emission of the paradigmatic TeV blazar Mrk 421, with a special focus on the multi-band flux correlations. Methods: The dataset has been collected through an extensive multi-wavelength campaign organised between 2016 December and 2017 June. The instrumentsMAGIC Collaboration et al.
Optical spectral characterization of the gamma-ray blazars S4 0954+65, TXS 1515-273, and RX J0812.0+0237
The study of gamma-ray blazars is usually hindered due to the lack of information on their redshifts and on their low-energy photon fields. This information is key to understand the effect on the gamma-ray absorption due to either extragalactic background light and/or intrinsic absorption and emission processes. All this information has also anBecerra González, J. et al.
The complex variability of blazars: time-scales and periodicity analysis in S4 0954+65
Among active galactic nuclei, blazars show extreme variability properties. We here investigate the case of the BL Lac object S4 0954+65 with data acquired in 2019-2020 by the Transiting Exoplanet Survey Satellite (TESS) and by the Whole Earth Blazar Telescope (WEBT) Collaboration. The 2-min cadence optical light curves provided by TESS during threeRaiteri, C. M. et al.
The dual nature of blazar fast variability: Space and ground observations of S5 0716+714
Blazar S5 0716+714 is well-known for its short-term variability, down to intraday time-scales. We here present the 2-min cadence optical light curve obtained by the TESS space telescope in 2019 December-2020 January and analyse the object fast variability with unprecedented sampling. Supporting observations by the Whole Earth Blazar TelescopeRaiteri, C. M. et al.
Multiwavelength Variability of BL Lacertae Measured with High Time Resolution
In an effort to locate the sites of emission at different frequencies and physical processes causing variability in blazar jets, we have obtained high time-resolution observations of BL Lacertae over a wide wavelength range: with the Transiting Exoplanet Survey Satellite (TESS) at 6000-10000 Å with 2 minute cadence; with the Neil Gehrels SwiftWeaver, Z. R. et al.
An intermittent extreme BL Lac: MWL study of 1ES 2344+514 in an enhanced state
Extreme high-frequency BL Lacs (EHBL) feature their synchrotron peak of the broad-band spectral energy distribution (SED) at νs ≥ 1017 Hz. The BL Lac object 1ES 2344+514 was included in the EHBL family because of its impressive shift of the synchrotron peak in 1996. During the following years, the source appeared to be in a low state withoutMAGIC Collaboration et al.
Systematic Search for γ-Ray Periodicity in Active Galactic Nuclei Detected by the Fermi Large Area Telescope
We use nine years of γ-ray data provided by the Fermi Large Area Telescope (LAT) to systematically study the light curves (LCs) of more than 2000 active galactic nuclei (AGN) included in recent Fermi-LAT catalogs. Ten different techniques are used, which are organized in an automatic periodicity-search pipeline, in order to search for evidence ofPeñil, P. et al.
Optical spectral characterization of the TeV extreme blazar 2WHSP J073326.7+515354
The emission from the relativistic jets in blazars usually outshines their host galaxies, challenging the determination of their distances and the characterization of the stellar population. The situation becomes more favourable in the case of the extreme blazars (EHBLs), for which the bulk of the emission of the relativistic jets is emitted atBecerra González, J. et al.
Unveiling the monster heart: unbeamed properties of blazar 4C 71.07
4C 71.07 is a high-redshift blazar whose optical radiation is dominated by quasar-like nuclear emission. We here present the results of a spectroscopic monitoring of the source to study its unbeamed properties. We obtained 24 optical spectra at the Nordic Optical Telescope and William Herschel Telescope and 3 near-infrared spectra at the TelescopioRaiteri, C. M. et al.
Quasi-periodic behaviour in the optical and γ-ray light curves of blazars 3C 66A and B2 1633+38
We report on quasi-periodic variability found in two blazars included in the Steward Observatory Blazar Monitoring data sample: the BL Lac object 3C 66A and the Flat Spectrum Radio Quasar B2 1633+38. We collect optical photometric and polarimetric data in V and R bands of these sources from different observatories: St. Petersburg UniversityOtero-Santos, J. et al.
Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio
We report the results of decade-long (2008-2018) γ-ray to 1 GHz radio monitoring of the blazar 3C 279, including GASP/WEBT, Fermi and Swift data, as well as polarimetric and spectroscopic data. The X-ray and γ-ray light curves correlate well, with no delay ≳ 3 h, implying general cospatiality of the emission regions. The γ-ray-optical flux-fluxLarionov, V. M. et al.
Investigating the multiwavelength behaviour of the flat spectrum radio quasar CTA 102 during 2013-2017
We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as wellD'Ammando, F. et al.
The beamed jet and quasar core of the distant blazar 4C 71.07
The object 4C 71.07 is a high-redshift blazar whose spectral energy distribution shows a prominent big blue bump and a strong Compton dominance. We present the results of a 2-yr multiwavelength campaign led by the Whole Earth Blazar Telescope (WEBT) to study both the quasar core and the beamed jet of this source. The WEBT data are complemented byRaiteri, C. M. et al.
The afterglow and kilonova of the short GRB 160821B
GRB 160821B is a short duration gamma-ray burst (GRB) detected and localized by the Neil Gehrels Swift Observatory in the outskirts of a spiral galaxy at z = 0.1613, at a projected physical offset of 16 kpc from the galaxy's center. We present X-ray, optical/nIR, and radio observations of its counterpart and model them with two distinct componentsTroja, E. et al.
A compact jet at the infrared heart of the prototypical low-luminosity AGN in NGC 1052
The feeble radiative efficiency characteristic of Low-Luminosity Active Galactic Nuclei (LLAGNs) is ascribed to a sub-Eddington accretion rate, typically at log (Lbol/Ledd) ≲ -3. At the finest angular resolutions that are attainable nowadays using mid-infrared (mid-IR) interferometry, the prototypical LLAGN in NGC 1052 remains unresolved down toFernández-Ontiveros, J. A. et al.
The Weakening Outburst of the Young Eruptive Star V582 Aur
V582 Aur is a pre-main-sequence FU Orionis type eruptive star, which entered a brightness minimum in 2016 March due to changes in the line-of-sight extinction. Here, we present and analyze new optical B, V, R C , and I C band multiepoch observations and new near-infrared J, H, and K S band photometric measurements from 2018 January–2019 FebruaryZsidi, G. et al.
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