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A Multiwavelength Cross-Correlation Variability Study of Fermi-LAT Blazars  [PDF]
V. Pati?o-álvarez,A. Carrami?ana,L. Carrasco,V. Chavushyan
Physics , 2013,
Abstract: We carried out a multiwavelength cross-correlation analysis of a sample of 16 blazars detected by Fermi/LAT. The purpose is to investigate if there exists correlations between the distinct bands we analyze in this work. We searched for cross-correlated delays between emissions in optical, near-infrared and {\gamma}-ray bands for 16 blazars detected by Fermi-LAT, using three methods previously discussed in the literature: the interpolated cross-correlation function, the discrete cross-correlation function and the Z-transformed discrete cross-correlation function. Our results confirm the expectation that in all our sample the four NIR bands vary simultaneously. For three objects of our sample (3C 273, Mrk 501, and PMN J0808-0751), no correlation is found between any of the bands available for this study. For the remaining thirteen, a correlation was found between the V band and the NIR bands, indicating that in most of them the V band and the NIR bands vary simultaneously. For 4 objects (3C 454.3, PKS 0235+164, PKS 1510-089, and PKS 2155-304) a delayed correlation between the {\gamma}-ray emission and the NIR+V bands was found.
Multiwavelength Properties of Blazars  [PDF]
C. Megan Urry
Physics , 1997, DOI: 10.1016/S0273-1177(97)00619-4
Abstract: The multiwavelength spectra of blazars appear to be dominated by nonthermal emission from a relativistic jet oriented close to the line of sight. The recent detection of many blazars at gamma-ray energies strongly supports this scenario. High quality multiwavelength monitoring data for the brightest one or two blazars suggest the optical through X-ray continuum is synchrotron emission from an inhomogeneous jet. The gamma-rays are likely due to Compton scattering of lower energy photons, either from within the jet or from the surrounding gas. The physical properties of the jet and the way in which it is produced are still largely a mystery but are probably related in some way to accretion onto a central supermassive black hole. There is little direct observational evidence for accretion disks in blazars, although there is evidence for winds which might emanate from disks.
Coordinated RXTE and multiwavelength observations of blazars  [PDF]
Rita M. Sambruna
Physics , 1999,
Abstract: Results from recent multiwavelength observations of blazars are reviewed, with particular emphasis on those involving the Rossi X-ray Timing Explorer (RXTE). I discuss blazars' spectral energy distributions, their correlated variability at various energies, and the insights they offer on the physical processes in the jet. New results on Mrk 501, PKS 2155--304, and PKS 2005--489 are highlighted.
Multiwavelength behavior of blazars in the AGILE era  [PDF]
S. Vercellone,for the AGILE Team
Physics , 2009,
Abstract: The AGILE gamma-ray satellite accumulated data over two years on several blazars. Moreover, for all of the sources detected by AGILE, we exploited multiwavelength observations involving both space and ground based telescopes and consortia, obtaining in several cases broad-band spectral energy distributions (SEDs) which span from the radio wavelengths up to the TeV energy band. I will review both published and yet unpublished AGILE results on gamma-ray blazars, discussing their time variability, their gamma-ray flare durations and the theoretical modeling of the SEDs. I will also highlight the GASP-WEBT and Swift fundamental contributions to the simultaneous and long-term studies of gamma-ray blazars.
Multiwavelength Properties of Blazars  [PDF]
C. Megan Urry
Physics , 1999, DOI: 10.1016/S0927-6505(99)00043-2
Abstract: Blazar spectral energy distributions (SEDs) are double peaked and follow a self-similar sequence in luminosity. The so-called "blue" blazars, whose first SED component peaks at X-ray energies, are TeV sources, although with a relatively small fraction of their bolometric luminosities. The "red" blazars, with SED peaks in the infrared-optical range, appear to emit relatively more power in the gamma-ray component but at much lower energies (GeV and below). Correlated variations across the SEDs (of both types) are consistent with the picture that a single electron population gives rise to the high-energy parts of both SED components, via synchrotron at low energies and Compton-scattering at high energies. In this scenario, the trends of SED shape with luminosity can be explained by electron cooling on ambient photons. With simple assumptions, we can make some estimates of the physical conditions in blazar jets of each "type" and can predict which blazars are the most likely TeV sources. Upper limits from a mini-survey of candidate TeV sources indicate that only ~10% of their bolometric luminosity is radiated in gamma-rays, assuming the two SED components peak near 1 keV and 1 TeV. Finally, present blazar samples are too shallow to indicate what kinds of jets nature prefers, i.e., whether the low-luminosity "blue" blazars or the high-luminosity "red" blazars are more common.
Monitoring of Bright Blazars with MAGIC in the 2007/2008 Season  [PDF]
Konstancja Satalecka,Ching-Cheng Hsu,Elisa Bernardini,Giacomo Bonnoli,Nicola Galante,Florian Goebel,Elina Lindfors,Pratik Majumdar,Antonio Stamerra,Robert Wagner
Physics , 2009, DOI: 10.1063/1.3125785
Abstract: Because of the short duty-cycles and observation-time constraints, studies of bright TeV (E>100 GeV) blazars are mostly restricted to flaring episodes or rather short (days to few weeks) multiwavelength campaigns. At the same time, long-term studies of these objects are essential to gain a more complete understanding of the blazar phenomenon and to constrain theoretical models concerning jet physics. Only unbiased long-term studies are adequate for the determination of flaring state probabilities and for estimating the statistical significance of possible correlations between TeV flaring states and other wavebands or observables, such as neutrino events. Regular observations also provide triggers for multiwavelength ToO observations originating from the TeV waveband. These are particularly needed to identify and study orphan TeV flares, i.e. flares without counterparts in other wavebands. In 2007/8 the MAGIC telescope has monitored three TeV blazars on a regular basis: Mrk 501, Mrk 421, and 1ES 1959+650. We present preliminary results of these observations including the measured light curves and a correlation study for VHE gamma-rays and X-rays and VHE gamma-rays and optical R-band for Mrk 421.
General physical properties of bright Fermi blazars  [PDF]
G. Ghisellini,F. Tavecchio,L. Foschini,G. Ghirlanda,L. Maraschi,A. Celotti
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.15898.x
Abstract: We studied all blazars of known redshift detected by the Fermi satellite during its first three months survey. For the majority of them, pointed Swift observations ensures a good multiwavelength coverage, enabling us to to reliably construct their spectral energy distributions (SED). We model the SEDs using a one-zone leptonic model and study the distributions of the derived interesting physical parameters as a function of the observed gamma-ray luminosity. We confirm previous findings concerning the relation of the physical parameters with source luminosity which are at the origin of the blazar sequence. The SEDs allow to estimate the luminosity of the accretion disk for the majority of broad emitting line blazars, while for the line-less BL Lac objects in the sample upper limits can be derived. We find a positive correlation between the jet power and the luminosity of the accretion disk in broad line blazars. In these objects we argue that the jet must be proton-dominated, and that the total jet power is of the same order of (or slightly larger than) the disk luminosity. We discuss two alternative scenarios to explain this result.
Multiwavelength Spectral Studies Of Fermi-LAT Blazars  [PDF]
Manasvita Joshi,Alan Marscher,Svetlana Jorstad,Markus Boettcher,Ivan Agudo,Valeri Larionov,Margo Aller,Mark Gurwell,Anne Lahteenmaki
Physics , 2011,
Abstract: We present multiwavelength spectral analyses of two Fermi-LAT blazars, OJ 287 and 3C 279, that are part of the Boston University multiwaveband polarization program. The data have been compiled from observations with Fermi, RXTE, the VLBA, and various ground-based optical and radio telescopes. We simulate the dynamic spectral energy distributions (SEDs) within the framework of a multi-slice, time-dependent leptonic jet model for blazars, with radiation feedback, in the internal shock scenario. We use the physical jet parameters obtained from the VLBA monitoring to guide our modeling efforts. We discuss the role of intrinsic parameters and the interplay between synchrotron and inverse Compton radiation processes responsible for producing the resultant SEDs.
Recent highlights in the X-ray study of blazars  [PDF]
Elena Pian
Physics , 2002,
Abstract: Blazars exhibit flux and spectral variations of largest amplitude at the highest frequencies. Therefore, monitoring their variability at X- and gamma-rays is the most effective tool to peer into the mighty powerhouse of these sources. High energy observations of the brightest blazars with the latest generation of satellites have allowed a detailed study of their behavior and have critically improved our understanding of the physics of blazar jets. I will review some of the recent results of blazar multiwavelength monitoring with emphasis on the X-ray campaigns accomplished with BeppoSAX and I will describe some of the future programs for blazar investigation from space, particularly with INTEGRAL.
Highlights of Recent Multiwavelength Observations of VHE Blazars with VERITAS  [PDF]
J. Grube,for the VERITAS collaboration
Physics , 2009,
Abstract: We present long-term observations of several VHE (E > 100 GeV) blazars with VERITAS, together with contemporaneous Swift and RXTE X-ray data. The observed targets include Mrk 421, Mrk 501, 1ES 2344+514. Strong flux and spectral variability is seen in Mrk 421 on nightly time-scales between January and June 2008, revealing a highly correlated X-ray to GeV/TeV connection. Modest X-ray variability is evident in Mrk 501. Observations of 1ES 2344+514 in December 2007 show VHE gamma-ray and X-ray flux doubling on nightly time-scales.
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