scholarly journals Evidence of Relativistic Beaming in BL Lac-Type Objects

1984 ◽  
Vol 110 ◽  
pp. 187-188
Author(s):  
Diana M. Worrall
Keyword(s):  
Radio Emission ◽  
Time Scale ◽  
Source Region ◽  
Model Fitting ◽  
X Ray ◽  
Extragalactic Object ◽  
Relativistic Beaming ◽  
International Ultraviolet Explorer ◽  
Bl Lac ◽  
Separate Source

Multifrequency observations of a variable extragalactic object, when all acquired within the inferred variability time scale of the source, can provide clues to the source's energy mechanisms. A guest observer program with the International Ultraviolet Explorer satellite has provided the focus for such measurements of a few BL Lac-type and related objects at frequencies in the radio, mm, IR, visual and UV. Earlier-epoch X-ray measurements are included in subsequent model fitting. This paper summarizes some of the observations in this program. Synchrotron self-Compton (SSC) models are then applied to the data, leading to the conclusions that the objects are relativistically beamed and that radio emission, at least below a frequency of ~20 GHz, is from a separate source region.

scholarly journals On the Location of Radio and X-Ray Emission in the Algol System

1980 ◽  
Vol 88 ◽  
pp. 229-232
Author(s):  
D. R. Florkowski
Keyword(s):  
Radio Emission ◽  
Mass Loss ◽  
Flux Density ◽  
Spectral Index ◽  
Time Scale ◽  
Synchrotron Source ◽  
X Ray ◽  
Algol System

The radio behaviour of Algol at centimeter wavelengths has been reviewed by Hjellming (1976, 1977), and by Gibson (1976). The observed radio emission can be roughly divided into two types: a quiescent type and a flare-like or outburst type. The quiescent emission is characterized by a low flux density, usually between 20 − 50 mJy, and a nearly flat spectral index. The latter means that the value of the flux density is nearly independent of wavelength. The variations in flux density, when present, are gradual and have a time scale on the order of days. The flare-like behaviour shows rapid and large changes in flux density. The amplitude of an outburst is wavelength dependent, the shorter wavelengths having larger amplitudes. Woodsworth and Hughes (1976, hereafter WH) attributed the two types of behaviour to two physically distinct sources. The quiescent type of emission is produced by a very large, thermally emitting cloud which surrounds the eclipsing system. The flare-like variations are due to a synchrotron source that is associated with mass loss. Their model is inconsistent with optical and X-ray information concerning the Algol system. However, a model with two radio components can be modified to agree with other types of data.

scholarly journals X-Ray Observations of Active Galactic Nuclei

1983 ◽  
Vol 104 ◽  
pp. 347-347
Author(s):  
C. Megan Urry ◽  
Richard F. Mushotzky ◽  
Allyn F. Tennant ◽  
Elihu A. Boldt ◽  
Stephen S. Holt
Keyword(s):  
Luminosity Function ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Source Population ◽  
Bl Lac Objects ◽  
X Ray ◽  
Relativistic Beaming ◽  
Bl Lac ◽  
Ultraviolet Observations ◽  
Bl Lacs

HEAO 1 A2 and Einstein SSS spectral observations of Seyfert galaxies and BL Lac objects suggest that in both cases, the X-ray emission is due to relativistic particles. The five BL Lac objects have very soft spectra and at higher energies (above 10 keV) may have hard tails. Combining our X-ray data with radio, infrared, optical, and ultraviolet observations, we can fit the BL Lac spectra with the familiar synchrotron self-Compton model if we allow for relativistic beaming (Urry and Mushotzky 1982, Urry et al. 1982). We show that Doppler beaming of an underlying (Seyfert-like) source population flattens the observed luminosity function, and we emphasize that the relative numbers of BL Lacs and quasars in given spectral intervals are strong functions of selection effects, the degree of Doppler beaming, and the form of the intrinsic luminosity function.

scholarly journals Hour time-scale QPOs in the X-ray and radio emission of LS I +61°303

2018 ◽  
Vol 476 (2) ◽  
pp. 2516-2521 ◽  
Author(s):  
S Nösel ◽  
R Sharma ◽  
M Massi ◽  
G Cimò ◽  
M Chernyakova
Keyword(s):  
Radio Emission ◽  
Time Scale ◽  
X Ray

scholarly journals Energy Distribution and Variability of BL LAC Objects. The Cases of PKS 2155–304 and 3C 66A.

1983 ◽  
Vol 104 ◽  
pp. 39-40
Author(s):  
L. Maraschi ◽  
D. Maccagni ◽  
E. G. Tanzi ◽  
M. Tarenghi ◽  
A. Treves
Keyword(s):  
Energy Distribution ◽  
Power Law ◽  
Maximum Amplitude ◽  
X Rays ◽  
Bl Lac Objects ◽  
X Ray ◽  
International Ultraviolet Explorer ◽  
Bl Lac ◽  
One Year ◽  
Ultraviolet Observations

PKS 2155–304 was repeatedly observed in 1979 and 1980 with the International Ultraviolet Explorer. Variations up to a factor of 2 in one year and by 20% in a day are found. The maximum amplitude of variation in X-rays is similar but the timescales are much shorter (a factor of 2 in one day; Urry and Mushotzky, 1982). In all cases the 1200–3100 A continuum is well fitted by a power law with frequency spectral index αUV between −0.7±0.03 and −0.9±0.03. Optical and ultraviolet observations taken within one day show different spectral slopes (Fig. 1). Separate power law fits in the two bands yield αopt = −0.46±0.01 and αUV = −0.80±0.02. The observations by Urry and Mushotzky indicate that the energy distribution steepens further in the soft X-ray region.

scholarly journals X-Ray Properties of Compact Extragalactic Radio Sources

1988 ◽  
Vol 129 ◽  
pp. 109-110 ◽  
Author(s):  
D. M. Worrall
Keyword(s):  
Radio Emission ◽  
Gaussian Distribution ◽  
Radio Sources ◽  
Radio Luminosity ◽  
Bl Lac Objects ◽  
X Ray ◽  
Logarithmic Plot ◽  
Bl Lac ◽  
5 Ghz ◽  
Bl Lacs

A good correlation is known to exist between the X-ray and radio luminosity of flat-spectrum, core-dominated radio sources (e.g., Owen, Helfand and Spangler 1981). Worrall (1987) presents a logarithmic plot of spectral luminosity in the source frame at 2 keV versus that at 5 GHz for a variety of QSOs, Highly Polarized QSOs (HPQs), and BL Lac Objects. Friedmann cosmology with Ho = 100h km s−1 Mpc−1, qo = 0 is assumed. Exclusion of objects which are optically or X-ray selected, or in which the radio emission is not dominated by a flat-spectrum compact core, gives a sub-sample consisting of 50 QSOs, 20 HPQs, and 10 BL Lacs, of which 5,4,3, respectively, are known superluminals. The dispersion of these data about the log-log correlation (assuming a Gaussian distribution), is σobs = 0.44 ± 0.06 (90% confidence errors for one interesting parameter).

Coronal Magnetic Structure near the Source Region of a Type II Radio Burst

1977 ◽  
Vol 3 (2) ◽  
pp. 157-159 ◽  
Author(s):  
R. T. Stewart
Keyword(s):  
Magnetic Structure ◽  
Source Region ◽  
Magnetic Flux Density ◽  
Type Ii ◽  
X Ray ◽  
Magnetic Structures ◽  
Source Regions ◽  
Coronal Streamer ◽  
Separate Source ◽  
Field Lines

The magnetic structure in the source region of a type II burst and along the path of the type II disturbance has remained an enigma despite over 20 years of radio observations of the Sun (see e.g. reviews by Wild and Smerd (1972) and McLean (1974)). This paper describes the first radioheliograph observations of a type II burst near coronal magnetic structures depicted by soft X-ray pictures. It will be shown that three separate lanes in a type II burst are associated with three separate source regions each located almost radially above a soft X-ray loop. To explain these observations a model is derived in which a wide-fronted m.h.d. disturbance travels from the flare explosion along magnetic field lines and then intersects successively with three coronal streamer structures each located above a soft X-ray loop. An estimate of the magnetic flux density along the soft X-ray loops is obtained from the velocity of the m.h.d. disturbance.

scholarly journals Mark III VLBI Observations of the Nucleus of M81 at 2.3 and 8.3 GHz

1982 ◽  
Vol 97 ◽  
pp. 387-388
Author(s):  
N. Bartel ◽  
B. E. Corey ◽  
I. I. Shapiro ◽  
A. E. E. Rogers ◽  
A. R. Whitney ◽  
...  
Keyword(s):  
Spiral Galaxy ◽  
Time Scale ◽  
X Ray ◽  
Extragalactic Object ◽  
Vlbi Observations ◽  
Radio Range ◽  
Normal Spiral

The normal spiral galaxy M81, which has some characteristics of a Seyfert (Peimbert, Torres-Peimbert, 1981), has a flat spectrum in the radio range (de Bruyn et al., 1976), variable on the time scale of days (Crane et al., 1976), and detectable radiation at infrared (Rieke, Lebofsky, 1978) and X-ray wavelengths (Elvis, van Speybroeck, 1981). At a distance of ∼3.3 Mpc, M81 is the nearest extragalactic object with a nucleus detectable with VLBI (Kellermann et al., 1976). We report here on simultaneous VLBI observations made with the Mark III system at 2.3 and 8.3 GHz. Observations on 14 and 16 March 1981 utilized the 100 m diameter telescope in Effelsberg, W. Germany (MPIR); the 43 m telescope at Green Bank, WV (NRAO); and the 40 m telescope near Big Pine, CA (OVRO).

scholarly journals X-ray intensity variations in BL Lac sources H2155-304 and PKS 0548-322

1986 ◽  
Vol 119 ◽  
pp. 273-274
Author(s):  
P.C. Agrawal ◽  
K.P. Singh ◽  
G.R. Riegler
Keyword(s):  
Time Scale ◽  
Compact Objects ◽  
Bl Lac Objects ◽  
X Ray ◽  
Bl Lac ◽  
Bl Lacs ◽  
Einstein Observatory

The X-ray Observations of two BL Lac Objects H2155-304 and PKS 0548-322 made with HRI and MPC on the Einstein Observatory show intensity variations on time scale of hours in both the sources. X-ray spectra of the two BL Lacs are derived. Limits on the mass of the accreting compact objects are obtained from time scale and magnitude of variations. Implications of the results are briefly discussed.

scholarly journals The Unification of Radio-Loud AGN

1996 ◽  
Vol 175 ◽  
pp. 379-380
Author(s):  
C. M. Urry ◽  
Paolo Padovani
Keyword(s):  
Uv Light ◽  
Radio Galaxies ◽  
Current Status ◽  
High Luminosity ◽  
Relativistic Jets ◽  
Bl Lac Objects ◽  
X Ray ◽  
Relativistic Beaming ◽  
Bl Lac ◽  
Bl Lacs

In a recent review paper we summarized the current status of unification of radio-loud AGN (Urry & Padovani 1995 PASP 107, 803), connecting high-luminosity (FR II) radio galaxies with quasars, and low-luminosity (FR I) radio galaxies with BL Lac objects. Unified schemes are motivated by the knowledge that AGN appearance depends strongly on orientation (Fig. 1): optical/UV light from the centers of many AGN is obscured by circumnuclear matter, and in radio-loud AGN, bipolar relativistic jets beam light along the jet axes. Understanding these radiation anisotropics allows us to unify apparently distinct classes of AGN that differ primarily because of orientation.Our review described the classification and general properties of AGN and summarized the evidence for anisotropic emission caused by circumnuclear obscuration and relativistic beaming. We outlined the evidence, both observed isotropic properties and statistical arguments, for connecting FR IIs with quasars and FR Is with BL Lacs. The population statistics (with beaming) are in accordance with available data and suggest γ ≃ 5 for low-luminosity AGN and γ ≃ 10 for high-luminosity AGN. The distinctions between X-ray-selected and radio-selected BL Lac objects, and between BL Lacs and flat-spectrum variable quasars, still not understood, provide clues to the underlying physics of blazars. Our review discussed several possible problems and complications, and concluded with a list of the ten questions we believe are the most pressing in this field.

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