37 research outputs found

    Detection of a quasi-periodic oscillation in the optical light curve of the remarkable blazar AO 0235+164

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    We present a long term optical RR band light curve analysis of the gravitationally lensed blazar AO 0235+164 in the time span 1982 - 2019. Several methods of analysis lead to the result that there is a periodicity of ~8.13 years present in these data. In addition, each of these five major flares are apparently double-peaked, with the secondary peak following the primary one by ~2 years. Along with the well known system, OJ 287, our finding constitutes one of the most secure cases of long term quasi-periodic optical behaviour in a blazar ever found. A binary supermassive black hole system appears to provide a good explanation for these results.Comment: 7 pages, 3 figures, 1 table, Accepted for publication in MNRA

    Blazar Variability with the Vera C. Rubin Legacy Survey of Space and Time

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    With their emission mainly coming from a relativistic jet pointing toward us, blazars are fundamental sources for studying extragalactic jets and their central engines, consisting of supermassive black holes fed by accretion disks. They are also candidate sources of high-energy neutrinos and cosmic rays. Because of the jet orientation, the nonthermal blazar emission is Doppler beamed; its variability is unpredictable, and it occurs on timescales from less than 1 hr to years. Comprehension of the diverse mechanisms producing the flux and spectral changes requires well-sampled multiband light curves over long time periods. In particular, outbursts are the best test bench for shedding light on the underlying physics, especially when studied in a multiwavelength context. The Vera C. Rubin Legacy Survey of Space and Time (Rubin-LSST) will monitor the southern sky for 10 yr in six photometric bands, offering a formidable tool for studying blazar variability features in a statistical way. The alert system will allow us to trigger follow-up observations of outstanding events, especially at high (keV-to-GeV) and very high (TeV) energies. We here examine the simulated Rubin-LSST survey strategies with the aim of understanding which cadences are more suitable for blazar variability science. Our metrics include light curve and color sampling. We also investigate the problem of saturation, which will affect the brightest and many flaring sources, and will have a detrimental impact on follow-up observations

    Polarimetric Properties of Blazars Caught by the WEBT

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    Active galactic nuclei come in many varieties. A minority of them are radio-loud, and exhibit two opposite prominent plasma jets extending from the proximity of the supermassive black hole up to megaparsec distances. When one of the relativistic jets is oriented closely to the line of sight, its emission is Doppler beamed and these objects show extreme variability properties at all wavelengths. These are called "blazars". The unpredictable blazar variability, occurring on a continuous range of time-scales, from minutes to years, is most effectively investigated in a multi-wavelength context. Ground-based and space observations together contribute to give us a comprehensive picture of the blazar emission properties from the radio to the gamma-ray band. Moreover, in recent years, a lot of effort has been devoted to the observation and analysis of the blazar polarimetric radio and optical behaviour, showing strong variability of both the polarisation degree and angle. The Whole Earth Blazar Telescope (WEBT) Collaboration, involving many tens of astronomers all around the globe, has been monitoring several blazars since 1997. The results of the corresponding data analysis have contributed to the understanding of the blazar phenomenon, particularly stressing the viability of a geometrical interpretation of the blazar variability. We review here the most significant polarimetric results achieved in the WEBT studies.Comment: Review published in "Galaxies" as part of the Special Issue "Polarimetry as a Probe of Magnetic Fields in AGN Jets", Academic Editors: Margo Aller, Jose L. G\'omez and Eric Perlma

    Multi-Frequency Monitoring of Three Gamma-Ray Quasars

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    Abstract. We have performed two campaigns of intensive monitoring of the blazars 3C 273, 3C 279, and PKS 1510−089 in the X-ray, optical, near-IR, and radio regions in March and April 2002. The quasar 3C 279 reveals significant interday variability at all wavelengths. The quasar 3C 273 shows smooth variations in the X-ray and near-IR regions on time scales of 2-3 days. For both quasars the results indicate close connection between X-ray and near-IR emission with a delay of X-rays from 0 to 3 days. The quasar PKS 1510-089 was in a low emission state at all frequencies during the campaigns

    Investigating the multiwavelength behaviour of the flat spectrum radio quasar CTA 102 during 2013–2017

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    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 well as data from the Swift (optical-UV and X-rays) and Fermi (gamma-rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented gamma-ray flaring activity was observed during 2016 November-2017 February, with four major outbursts. A peak flux of (2158 +/- 63) x 10(-8) ph cm(-2) s(-1), corresponding to a luminosity of (2.2 +/- 0.1) x10(50) erg s(-1), was reached on 2016 December 28. These four gamma-ray outbursts have corresponding events in the near-infrared, optical, and UV bands, with the peaks observed at the same time. A general agreement between X-ray and gamma-ray activity is found. The gamma-ray flux variations show a general, strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This gamma-ray/optical relationship is in agreement with the geometrical model that has successfully explained the low-energy flux and spectral behaviour, suggesting that the long-term flux variations are mainly due to changes in the Doppler factor produced by variations of the viewing angle of the emitting regions. The difference in behaviour between radio and higher energy emission would be ascribed to different viewing angles of the jet regions producing their emission.Bulgarian National Science Fund of the Ministry of Education and Science [DN 08-1/2016, DN 18-13/2017, KP-06-H28/3 (2018)]; Foundation for Research and Technology -Hellas; Max-Planck-Institut fur Extraterrestrische Physik; Shota Rustaveli National Science Foundation [FR/217554/16]; Russian Science FoundationRussian Science Foundation (RSF) [17-12-01029]; Institute of Astronomy and Rozhen National Astronomical Observatory [176011, 176004, 176021]; Ministry of Education, Science and Technological Development of the Republic of Serbia; DGAPA (Universidad Nacional Autonoma de M'exico)Universidad Nacional Autonoma de Mexico; PAPIIT projectPrograma de Apoyo a Proyectos de Investigacion e Innovacion Tecnologica (PAPIIT) [IN114917]; Smithsonian InstitutionSmithsonian Institution; Academia SinicaAcademia Sinica - Taiwan; NASA/Fermi Guest Investigator [NNX12AO93G, NNX15AU81G]; Bulgarian National Science Programme 'Young Scientists and Postdoctoral Students 2019', Bulgarian National Science Fund [DN18-10/2017]; National RI Roadmap Projects [DO1-157/28.08.2018, DO1-153/28.08.2018]; Ministry of Education and Science of the Republic of Bulgaria; Regional Government of the Aosta Valley - 'Research and Education' grants from Fondazione CRT; CONICYT project Basal [AFB-170002]; Russian Government Program of Competitive Growth of Kazan Federal University; National Aeronautics and Space AdministrationNational Aeronautics & Space Administration (NASA); Department of Energy in the United StatesUnited States Department of Energy (DOE); Commissariat a l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucleaire et de Physique des Particules in FranceCentre National de la Recherche Scientifique (CNRS); Agenzia Spaziale ItalianaItalian Space Agency; Istituto Nazionale di Fisica Nucleare in ItalyIstituto Nazionale di Fisica Nucleare; Ministry of Education, Culture, Sports, Science and Technology (MEXT)Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT); K. A. Wallenberg FoundationKnut & Alice Wallenberg Foundation; Swedish Research CouncilSwedish Research Council; Swedish National Space Board in Sweden; Istituto Nazionale di Astrofisica in ItalyIstituto Nazionale Astrofisica; Centre National d'Etudes Spatiales in FranceCentre National D'etudes Spatiales; United States Department of Energy (DOE) [DE-AC02-76SF00515]; National Aeronautics & Space Administration (NASA) [NNX08AW31G, NNX11A043G, NNX14AQ89G]; National Science Foundation (NSF) [AST-0808050, AST-1109911]; NASA's Goddard Space Flight CenterThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

    Peculiar emission from the new VHE gamma-ray source H1722+119

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    The BL Lac object H1722+119 was observed in the very high energy band (VHE, E > 100 GeV) by the MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescopes (Aleksić et al. 2016a, b)) between 2013 May 17 and 22, following a state of high activity in the optical band measured by the KVA (Kungliga Vetenskapsakademien) telescope. Optical high states are often used to trigger MAGIC observations, which result in the VHE γ-ray signal detection (see e.g. Aleksić et al. 2015, Ahnen et al. 2016 and references therein)

    The dark arrow of time: a scientific novel

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    This riveting scientific novel combines adventure, love, suspense, magic, pathos, and mystery in a carefully woven plot that is full of unexpected twists and turns. The author is an astrophysicist who has developed an alternative theory, which holds that traveling in time is possible. Time is, in fact, the real protagonist of the novel and of the intrigue surrounding the attempt to seize the secret of Time’s other arrow, the dark arrow normally hidden from us, which points back at our past. The underlying premise is that antimatter is nothing more than common matter moving backwards in time. The justification for this interpretation has been with us for some time, “hiding in plain sight” within Maxwell’s equations, the Lorentz transformations, the CPT theorem of relativistic quantum mechanics, and Feynman diagrams. While the science underlying the narrative is explained whenever necessary, sometimes with the aid of simple mathematical formulas, these scientific asides account for only a small part of the book, which will appeal to a wide audience, including readers who are far from being science buffs

    Swift multi-wavelength observations of the high-redshift Blazar S5 0836+710 (4C 71.07)

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    We present the preliminary results of a year-long Swift monitoring campaign of the high-redshift (z=2.172) flat-spectrum radio quasar (FSRQ) S5 0836+710 (4C 71.07). The campaign, based on one observation per month, 5 ks each observation, for 12 months, allowed us to investigate the synchrotron and nuclear emission contributions to the optical-UV frequency range of its spectral energy distribution and the X-ray spectral variations along a baseline of a year. We obtained a high-accuracy determination of UVOT magnitudes, an X-ray photon index with an uncertainty of the order of 5%, and well-sampled light curves both in the optical-UV and X-ray energy bands to study their possible modulations and correlations. Our study allowed us to exploit the unique Swift capabilities in terms of both simultaneous energy coverage and schedule flexibility. The Swift monitoring campaign was supported by observations by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT) Collaboration, which provided radio, near-infrared, and optical photometric data as well as optical polarimetry. Moreover, a spectroscopic monitoring was obtained at the William Herschel Telescope (WHT) and the Nordic Optical Telescope (NOT). All these observations will allow us to obtain a comprehensive picture of the jet as well as of the nuclear source emission. <P /

    VizieR Online Data Catalog: Mrk 421 multi-wavelength variability, 2007-2009 (Ahnen+, 2016)

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    Data of Mrk 421 are presented for the following instruments and bands from radio to very high energy gamma-rays: Metsahovi (37GHz), OVRO (15GHz), GASP (R band), RXTE/ASM (2-10keV), Swift/BAT(15-50keV), MAGIC (>400 GeV). The observation period is from 10th February 2007 (MJD 54141) to 23rd July 2009 (MJD 55035). Figure 2 includes the light curves of the above mentioned instruments. Figure 3 and 4 show the fractional variability F_var for these light curves of the above mentioned light curves for the whole time span (Fig. 3) and for the separate time spans P1, P2, P3 (Fig. 4). (3 data files). <P /