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

2019 ◽  
Vol 490 (4) ◽  
pp. 5300-5316 ◽  
Author(s):  
F D’Ammando ◽  
C M Raiteri ◽  
M Villata ◽  
J A Acosta-Pulido ◽  
I Agudo ◽  
...  
Keyword(s):  
Near Infrared ◽  
Time Lag ◽  
Geometrical Model ◽  
Optical Data ◽  
X Rays ◽  
Owens Valley ◽  
Spectrum Radio ◽  
Γ Ray ◽  
The Difference ◽  
Radio Quasar

ABSTRACT 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 (γ-rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented γ-ray flaring activity was observed during 2016 November–2017 February, with four major outbursts. A peak flux of (2158 ± 63) × 10−8 ph cm−2 s−1, corresponding to a luminosity of (2.2 ± 0.1) × 1050 erg s−1, was reached on 2016 December 28. These four γ-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 γ-ray activity is found. The γ-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 γ-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.

scholarly journals The large gamma-ray flare of the flat-spectrum radio quasar PKS 0346−27

2019 ◽  
Vol 627 ◽  
pp. A140
Author(s):  
R. Angioni ◽  
R. Nesci ◽  
J. D. Finke ◽  
S. Buson ◽  
S. Ciprini
Keyword(s):  
Spectral Properties ◽  
Emission Region ◽  
Short Time Scale ◽  
Quiescent State ◽  
Emission Model ◽  
X Rays ◽  
High State ◽  
Spectrum Radio ◽  
Multi Wavelength ◽  
Radio Quasar

Aims. In this paper, we characterize the first γ-ray flaring episode of the flat-spectrum radio quasar PKS 0346−27 (z = 0.991), as revealed by Fermi-LAT monitoring data, and the concurrent multi-wavelength variability observed from radio through X-rays. Methods. We studied the long- and short-term flux and spectral variability from PKS 0346−27 by producing γ-ray light curves with different time binning. We complement the Fermi-LAT data with multi-wavelength observations from the Atacama Large Millimeter Array (radio mm-band), the Rapid Eye Mount telescope (near-infrared) and Swift (optical-UV and X-rays). This quasi-simultaneous multi-wavelength coverage allowed us to construct time-resolved spectral energy distributions (SEDs) of PKS 0346−27 and compare the broadband spectral properties of the source between different activity states using a one-zone leptonic emission model. Results. PKS 0346−27 entered an elevated γ-ray activity state starting from the beginning of 2018. The high-state continued throughout the year, displaying the highest fluxes in May 2018. We find evidence of short-time scale variability down to approximately 1.5 h, which constrains the γ-ray emission region to be compact. The extended flaring period was characterized by a persistently harder spectrum with respect to the quiescent state, indicating changes in the broadband spectral properties of the source. This was confirmed by the multi-wavelength observations, which show a shift in the position of the two SED peaks by approximately two orders of magnitude in energy and peak flux value. As a result, the non-thermal jet emission completely outshines the thermal contribution from the dust torus and accretion disk during the high state. The broadband SED of PKS 0346−27 transitions from a typical Low-Synchrotron-Peaked (LSP) to the Intermediate-Synchrotron-Peaked (ISP) class, a behavior previously observed in other flaring γ-ray sources. Our one-zone leptonic emission model of the high-state SEDs constrains the γ-ray emission region to have a lower magnetic field, larger radius, and higher maximum electron Lorentz factors with respect to the quiescent SED. Finally, we note that the bright and hard γ-ray spectrum observed during the peak of flaring activity in May 2018 implies that PKS 0346−27 could be a promising target for future ground-based Cherenkov observatories such as the Cherenkov Telescope Array (CTA). The CTA could detect such a flare in the low-energy tail of its energy range during a high state such as the one observed in May 2018.

scholarly journals Multiepoch, multiwavelength study of accretion onto T Tauri

2018 ◽  
Vol 618 ◽  
pp. A55 ◽  
Author(s):  
P. C. Schneider ◽  
H. M. Günther ◽  
J. Robrade ◽  
J. H. M. M. Schmitt ◽  
M. Güdel
Keyword(s):  
Near Infrared ◽  
Accretion Rate ◽  
Strong Shock ◽  
Field Configuration ◽  
Optical Data ◽  
X Rays ◽  
Coronal Emission ◽  
X Ray ◽  
T Tauri ◽  
The Impact

Classical T Tauri stars (CTTSs) accrete matter from the inner edge of their surrounding circumstellar disks. The impact of the accretion material on the stellar atmosphere results in a strong shock, which causes emission from the X-ray to the near-infrared (NIR) domain. Shock velocities of several 100 km s−1 imply that the immediate post shock plasma emits mainly in X-rays. Indeed, two X-ray diagnostics, the so-called soft excess and the high densities observed in He-like triplets, differentiate CTTSs from their non-accreting siblings. However, accretion shock properties derived from X-ray diagnostics often contradict established ultraviolet (UV)–NIR accretion tracers and a physical model simultaneously explaining both, X-ray and UV–NIR accretion tracers, is not yet available. We present new XMM-Newton and Chandra grating observations of the CTTS T Tauri combined with UV and optical data. During all epochs, the soft excess is large and the densities derived from the O VII and Ne IX He-like triplets are compatible with coronal densities. This confirms that the soft X-ray emission cannot originate in accretion funnels that carry the bulk of the accretion rate despite T Tauri’s large soft excess. Instead, we propose a model of radially density stratified accretion columns to explain the density diagnostics and the soft excess. In addition, accretion rate and X-ray luminosity are inversely correlated in T Tauri over several epochs. Such an anti-correlation has been observed in samples of stars. Hence the process causing it must be intrinsic to the accretion process, and we speculate that the stellar magnetic field configuration on the visible hemisphere affects both the accretion rate and the coronal emission, eventually causing the observed anti-correlation.

scholarly journals The absolute energies of the groups in magnetic β-ray spectra

1924 ◽  
Vol 105 (729) ◽  
pp. 60-69 ◽  
Keyword(s):  
Magnetic Field ◽  
Wave Length ◽  
X Rays ◽  
Homogeneous Groups ◽  
Absorption Energy ◽  
Length Measurements ◽  
Γ Rays ◽  
Γ Ray ◽  
The Absolute ◽  
The Difference

Most β-ray bodies emit several homogeneous groups of β-rays, and the energies of the electrons forming these groups may be found from the deflection they suffer in a magnetic field. Various experiments have shown that these groups are due to the conversion, according to the quantum relation, of γ-rays in the different electronic levels of the atom. In fact, the energy of any group is of the form E 1 = hv — (absorption energy of level). Two β-ray groups due to the conversion of a γ-ray of definite frequency in the K and L levels of the atom will differ in energy by the difference in energy between the K and L absorption energies. Both in testing this equation, and in using it to deduce frequencies of the γ-rays, it is necessary to compare energies of β-rays determined in terms of a magnetic field, with absorption energies deduced from wave-length measurements of X-rays. It is thus important to obtain values of the absolute β-ray energies as accurate as possible. The most accurate previous values were those of Rutherford and Robinson.

scholarly journals Quasi-periodic behaviour in the optical and γ-ray light curves of blazars 3C 66A and B2 1633+38

2020 ◽  
Vol 492 (4) ◽  
pp. 5524-5539 ◽  
Author(s):  
J Otero-Santos ◽  
J A Acosta-Pulido ◽  
J Becerra González ◽  
C M Raiteri ◽  
V M Larionov ◽  
...  
Keyword(s):  
Light Curve ◽  
Confidence Level ◽  
Light Curves ◽  
Data Set ◽  
Spectrum Radio ◽  
Periodic Behaviour ◽  
Optical Light Curve ◽  
Emission Models ◽  
Γ Ray ◽  
Radio Quasar

ABSTRACT 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 University, Crimean Astrophysical Observatory, WEBT–GASP, Catalina Real-Time Transient Survey, Steward Observatory, STELLA Robotic Observatory, and Katzman Automatic Imaging Telescope. In addition, an analysis of the γ-ray light curves from Fermi–LAT is included. Three methods are used to search for any periodic behaviour in the data: the Z-transform Discrete Correlation Function, the Lomb–Scargle periodogram and the Weighted Wavelet Z-transform. We find pieces of evidence of possible quasi-periodic variability in the optical photometric data of both sources with periods of ∼3 yr for 3C 66A and ∼1.9 yr for B2 1633+38, with significances between 3σ and 5σ. Only B2 1633+38 shows evidence of this behaviour in the optical polarized data set at a confidence level of 2σ–4σ. This is the first reported evidence of quasi-periodic behaviour in the optical light curve of B2 1633+38. Also, a hint of quasi-periodic behaviour is found in the γ-ray light curve of B2 1633+38 with a confidence level ≥2σ, while no periodicity is observed for 3C 66A in this energy range. We propose different jet emission models that could explain the quasi-periodic variability and the differences found between these two sources.

scholarly journals The flat-spectrum radio quasar 3C 345 from the high to the low emission state

2018 ◽  
Vol 614 ◽  
pp. A148 ◽  
Author(s):  
M. Berton ◽  
N. H. Liao ◽  
G. La Mura ◽  
E. Järvelä ◽  
E. Congiu ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Emission Lines ◽  
Spectral Energy ◽  
X Rays ◽  
Energy Bands ◽  
Line Region ◽  
Spectrum Radio ◽  
Inverse Compton ◽  
Public Archives ◽  
Radio Quasar

We report simultaneous observations at different energy bands in radio, optical, UV, X-rays and γ rays of the flat-spectrum radio-quasar 3C 345. We built the light curve of the source at different frequencies from 2008, the beginning of the Fermi all-sky survey, to 2016, using new data and public archives. In particular we obtained several optical spectra, to study the behavior of emission lines and the continuum in different activity states and to derive the black hole mass. 3C 345 showed two flaring episodes in 2009, which occurred simultaneously in γ ray, optical/UV and X-rays, and were later followed in radio. The source shows an inverse Compton dominated spectral energy distribution, which moved from higher to lower frequencies from the high to the low state. The reverberation of emission lines during one outburst event allowed us to constrain the location of production of γ rays very close to the broad-line region, and possibly in the jet-base. We report the observation of an increased accretion after the outburst, possibly induced by the decrease of magnetic field intensity with respect to the low state.

scholarly journals The X-ray Spectral Properties for Gamma-ray Loud Blazars

2003 ◽  
Vol 214 ◽  
pp. 299-302
Author(s):  
Ben-Zhong Dai
Keyword(s):  
Correlation Analysis ◽  
Gamma Ray ◽  
X Rays ◽  
Spectral Indices ◽  
Bl Lac Objects ◽  
X Ray ◽  
Weighted Analysis ◽  
Spectrum Radio ◽  
Γ Ray ◽  
Weighted Correlation

We selected a sample of bright γ-ray (E>100 MeV) blazars whose X-rays in 0.1–10.0 keV band are observed by ROSAT and other X-ray satellites, and make a detailed spectral analysis between the soft (0.1–2.0 keV) and hard band (2.0–10.0keV) as well as between X-ray and γ-ray properties using both un-weighted and weighted analysis methods. Our results indicate: (i) there are significant anti-correlations of the spectral indices between soft X-rays and γ-rays, and between hard X-ray and γ-ray of flat-spectrum radio quasars (FSRQs) and BL Lac objects; (ii) in the X-ray band, the correlation is confusing, there is positive correlation of the spectral indices between soft and hard X-ray band using weighted correlation analysis, but this correlation is negative using un-weighted correlation analysis.

scholarly journals Radio VLBA polarization and multiband monitoring of the high-redshift quasar S5 0836 + 710 during a high-activity period

2019 ◽  
Vol 491 (1) ◽  
pp. 858-873 ◽  
Author(s):  
M Orienti ◽  
F D’Ammando ◽  
M Giroletti ◽  
D Dallacasa ◽  
G Giovannini ◽  
...  
Keyword(s):  
High Activity ◽  
Gamma Ray ◽  
High Redshift ◽  
Activity Period ◽  
X Rays ◽  
Large Area ◽  
The Core ◽  
Rotation Measure ◽  
Spectrum Radio ◽  
Γ Ray

ABSTRACT We report on results of a multiband monitoring campaign from radio to γ-rays of the high-redshift flat spectrum radio quasar S5 0836 + 710 during a high-activity period detected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. Two major flares were detected, in 2015 August and November. In both episodes, the apparent isotropic γ-ray luminosity exceeds 1050 erg s−1, with a doubling time-scale of about 3 h. The high γ-ray activity may be related to a superluminal knot that emerged from the core in 2015 April at the peak of the radio activity and is moving downstream along the jet. The low variability observed in X-rays may indicate that X-ray emission is produced by the low-energy tail of the same electron population that produces the γ-ray emission. The analysis of full-polarization pc-scale radio observations suggests the presence of a limb-brightened polarization structure at about 1 mas from the core in which a rotation measure gradient with a sign change is observed transverse to the jet direction. These characteristics are consistent with a scenario in which Faraday rotation is produced by a sheath of thermal electrons with a toroidal magnetic field surrounding the emitting jet.

scholarly journals The VHE γ-Ray View of the FSRQ PKS 1510-089

Galaxies ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 41 ◽  
Author(s):  
Michael Zacharias ◽  
Dijana Dominis Prester ◽  
Felix Jankowsky ◽  
Elina Lindfors ◽  
Manuel Meyer ◽  
...  
Keyword(s):  
High Energy ◽  
High Variability ◽  
Energy Bands ◽  
Current State ◽  
Spectrum Radio ◽  
Very High Energy ◽  
Monitoring Effort ◽  
Γ Ray ◽  
Radio Quasar ◽  
Very High

The flat spectrum radio quasar PKS 1510-089 is a monitored target in many wavelength bands due to its high variability. It was detected as a very-high-energy (VHE) γ-ray emitter with H.E.S.S. in 2009, and has since been a regular target of VHE observations by the imaging Cherenkov observatories H.E.S.S. and MAGIC. In this paper, we summarize the current state of results focusing on the monitoring effort with H.E.S.S. and the discovery of a particularly strong VHE flare in 2016 with H.E.S.S. and MAGIC. While the source has now been established as a weak, but regular emitter at VHE, no correlation with other energy bands has been established. This is underlined by the 2016 VHE flare, where the detected optical and high-energy γ-ray counterparts evolve differently than the VHE flux.

scholarly journals The picture of relativistic jet from Fermi-LAT and multi-band observations of blazar 3C 279

2010 ◽  
Vol 6 (S275) ◽  
pp. 155-159
Author(s):  
Masaaki Hayashida ◽  
Greg Madejski
Keyword(s):  
Gamma Ray ◽  
First Year ◽  
Energy Bands ◽  
X Ray ◽  
Relativistic Jet ◽  
Spectrum Radio ◽  
Successful Launch ◽  
Γ Ray ◽  
Radio Quasar ◽  
Multi Band

AbstractStrong and variable radiation detected over all accessible energy bands in blazar arises from a relativistic, Doppler-boosted jet pointing close to our line of sight. Flat Spectrum Radio Quasar 3C 279 was one of the brightest γ-ray blazars in the sky at the time of the discovery with EGRET. Since the successful launch of the Fermi Gamma-ray Space telescope in 2008, we have organized extensive multi-band observational campaign of 3C 279 from radio to γ-ray bands, also including optical polarimetric observations. The uninterrupted monitoring in the γ-ray band by Fermi-LAT together with the multi-band data provide us with new insights of the relativistic jet of blazar. Here, we present the results of the first-year multi-band campaign of 3C 279 including the discovery of a γ-ray flare event associated with a dramatic change of the optical polarization - as well as a discovery of an “orphan” X-ray flare, unassociated with prominent outbursts in other bands.

scholarly journals Explaining the flat-spectrum radio core Sgr A* with GRMHD simulations of jets

2014 ◽  
Vol 10 (S313) ◽  
pp. 374-379
Author(s):  
Monika A. Mościbrodzka
Keyword(s):  
Electron Temperature ◽  
Near Infrared ◽  
Galactic Nuclei ◽  
Radio Spectrum ◽  
Temperature Plasma ◽  
Accretion Flows ◽  
Current State ◽  
Spectrum Radio ◽  
The Difference ◽  
Sgr A

AbstractThe supermassive black hole in the center of the Milky Way, Sgr A*, displays a nearly flat radio spectrum which is typical for jets in Active Galactic Nuclei. Indeed, time dependent, magnetized models of radiatively inefficient accretion flows, which are commonly used to explain the millimeter, near-infrared, and X-ray emission of Sgr A* also often produce jet-like outflows. However, the emission from these models so far has failed to reproduce the flat radio spectrum. We show that current GRMHD simulations can naturally reproduce the flat spectrum, when using a two-temperature plasma in the disk and a constant electron temperature plasma in the jet. This assumption is consistent with current state-of-the art simulations, in which the electron temperature evolution is not explicitly modeled. Stronger magnetization and stronger shearing seen in the jet sheath could possibly explain the difference in electron heating between jet and disk. The model images and spectra are consistent with the radio sizes and spectrum of Sgr A*.

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