General
Description
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.
Members
Principal investigator
José Antonio
Acosta Pulido
Project staff
María Jesús
Arevalo Morales
Josefa
Becerra González
Carlos
Lázaro Hernando
Jorge
Otero Santos
Collaborators
Jorge Andrés
Pérez Prieto
Dr.
M.I. Carnerero Martín
Dr.
C.M. Raiteri
Dr.
A. Capetti
Dr.
F. D'Ammando
Dr.
N. Castro Segura
Results
- 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.
Scientific activity
Related publications
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A wiggling filamentary jet at the origin of the blazar multi-wavelength behaviourContext. Blazars are beamed active galactic nuclei (AGNs) known for their strong multi-wavelength variability on timescales ranging from years down to minutes. Many different models have been proposed to explain this variability. Aims. We aim to investigate the suitability of the twisting jet model presented in previous works to explain the multiRaiteri, C. M. et al.
Advertised on:
122024 -
Distance estimation of gamma-ray-emitting BL Lac objects from imaging observationsAims. The direct redshift determination of BL Lac objects is highly challenging as the emission in the optical and near-infrared bands is largely dominated by the non-thermal emission from the relativistic jet, which points very close to our line of sight. Therefore, the optical spectra of BL Lac objects often show no spectral lines from the hostNilsson, K. et al.
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112024 -
Optical variability of the blazar 3C 371: From minute to year timescalesContext. The BL Lac object 3C 371 was observed by the Transiting Exoplanet Survey Satellite (TESS) for approximately a year, between July 2019 and July 2020, with an unmatched two-minute imaging cadence. In parallel, the Whole Earth Blazar Telescope (WEBT) Collaboration organized an extensive observing campaign, providing three years of continuousOtero-Santos, J. et al.
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62024 -
Multiwavelength variability analysis of Fermi-LAT blazarsBlazars present highly variable gamma-ray emission. This variability, which can range from a few minutes to several years, is also observed at other wavelengths across the entire electromagnetic spectrum. We make use of the first 12 yr of data from the Fermi Large Area Telescope, complemented with multiwavelength (MWL) archival data from differentPeñil, P. et al.
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42024 -
Multi-year characterisation of the broad-band emission from the intermittent extreme BL Lac 1ES 2344+514Aims: The BL Lac 1ES 2344+514 is known for temporary extreme properties characterised by a shift of the synchrotron spectral energy distribution (SED) peak energy ν synch, p above 1 keV. While those extreme states have only been observed during high flux levels thus far, additional multi-year observing campaigns are required to achieve a coherentMAGIC Collaboration et al.
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22024 -
Extreme photometric and polarimetric variability of blazar S4 0954+65 at its maximum optical and γ-ray brightness levelsIn 2022 the BL Lac object S4 0954+65 underwent a major variability phase, reaching its historical maximum brightness in the optical and γ-ray bands. We present optical photometric and polarimetric data acquired by the Whole Earth Blazar Telescope (WEBT) Collaboration from 2022 April 6 to July 6. Many episodes of unprecedented fast variability wereRaiteri, C. M. et al.
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122023 -
A Reemerging Bright Soft X-Ray State of the Changing-look Active Galactic Nucleus 1ES 1927+654: A Multiwavelength View1ES1927+654 is a nearby active galactic nucleus (AGN) that has shown an enigmatic outburst in optical/UV followed by X-rays, exhibiting strange variability patterns at timescales of months to years. Here we report the unusual X-ray, UV, and radio variability of the source in its postflare state (2022 January-2023 May). First, we detect an increaseGhosh, Ritesh et al.
Advertised on:
92023 -
Variability and evolution of the optical polarization of a sample of gamma-ray blazarsWe present a polarization variability analysis of a sample of 26 γ-ray blazars monitored by the Steward Observatory between 2008 and 2018 in the optical band. We investigate the properties and long-term variability of their optical polarization, searching for differences between blazar types. We observe that BL Lac objects are typically lessOtero-Santos, J. et al.
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82023 -
Multimessenger Characterization of Markarian 501 during Historically Low X-Ray and γ-Ray ActivityWe study the broadband emission of Mrk 501 using multiwavelength observations from 2017 to 2020 performed with a multitude of instruments, involving, among others, MAGIC, Fermi's Large Area Telescope (LAT), NuSTAR, Swift, GASP-WEBT, and the Owens Valley Radio Observatory. Mrk 501 showed an extremely low broadband activity, which may help to unravelAbe, H. et al.
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62023 -
Multiwavelength observations of the extraordinary accretion event AT2021lwxWe present observations from X-ray to mid-infrared wavelengths of the most energetic non-quasar transient ever observed, AT2021lwx. Our data show a single optical brightening by a factor >100 to a luminosity of 7 × 10 45 erg s -1 and a total radiated energy of 1.5 × 10 53 erg, both greater than any known optical transient. The decline is smooth andWiseman, P. et al.
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72023 -
The optical behaviour of BL Lacertae at its maximum brightness levels: a blend of geometry and energeticsIn 2021 BL Lacertae underwent an extraordinary activity phase, which was intensively followed by the Whole Earth Blazar Telescope (WEBT) Collaboration. We present the WEBT optical data in the BVRI bands acquired at 36 observatories around the world. In mid-2021 the source showed its historical maximum, with R = 11.14. The light curves display manyRaiteri, C. M. et al.
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62023 -
Follow-up Survey for the Binary Black Hole Merger GW200224_222234 Using Subaru/HSC and GTC/OSIRISThe LIGO/Virgo detected a gravitational wave (GW) event, named GW200224_222234 (also known as S200224ca) and classified as a binary-black hole coalescence, on 2020 February 24. Given its relatively small localization skymap (71 deg 2 for a 90% credible region; revised to 50 deg 2 in GWTC-3), we performed target-of-opportunity observations using theOhgami, Takayuki et al.
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42023 -
Disentangling the nature of the prototype radio weak BL Lac. Contemporaneous multifrequency observations of WISE J141046.00+740511.2Context. The γ-ray emitting source WISE J141046.00+740511.2 has been associated with a Fermi-LAT detection by crossmatching with Swift/XRT data. It has shown all the canonical observational characteristics of a BL Lac source, including a power-law, featureless optical spectrum. However, it was only recently detected at radio frequencies and itsMarchesini, E. J. et al.
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22023 -
Long-term multi-wavelength study of 1ES 0647+250Context. The BL Lac object 1ES 0647+250 is one of the few distant γ-ray emitting blazars detected at very high energies (VHEs; ≳100 GeV) during a non-flaring state. It was detected with the MAGIC telescopes during a period of low activity in the years 2009−2011 as well as during three flaring activities in the years 2014, 2019, and 2020, with theMAGIC Collaboration et al.
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22023 -
Multiwavelength periodicity search in a sample of γ-ray bright blazarsWe present the results of a long-term periodicity search in a sample of γ-ray blazars within a multiwavelength context. These blazars have been selected from the Steward Observatory sample as part of its optical monitoring program between 2008 and 2018. We study 15 sources with a temporal coverage in their optical total and polarized emissionOtero-Santos, J. et al.
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22023 -
Rapid quasi-periodic oscillations in the relativistic jet of BL LacertaeBlazars are active galactic nuclei (AGN) with relativistic jets whose non-thermal radiation is extremely variable on various timescales 1-3. 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.
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92022 -
ASTRI Mini-Array core science at the Observatorio del TeideThe 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.
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82022 -
A Radio, Optical, UV, and X-Ray View of the Enigmatic Changing-look Active Galactic Nucleus 1ES 1927+654 from Its Pre- to Postflare StatesThe 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.
Advertised on:
52022 -
A statistical study of the optical spectral variability in gamma-ray blazarsBlazars 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.
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42022 -
Investigation of the correlation patterns and the Compton dominance variability of Mrk 421 in 2017Aims: 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.
Advertised on:
112021
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