Ray Blazars Research Articles

Rapid Optical Variability of Gamma-Ray–loud Blazars

We present the optical (B, V, and R) photometry for nine GeV and/or TeV gamma -ray blazars, which were observed from 2000 through 2001 with the 1 m telescope at Yunnan Astronomical Observatory. The GeV gamma -ray-loud source PKS 1510-089 was very active during our observation period, showing an apparent variation of 2.0 mag within 41 minutes in the R band. This is the most violently rapid variability in our optical monitoring program since 1982. Some physics parameters are calculated for this source, namely, the emission size, Doppler factor delta, the efficiency (eta) for conversion of accreted matter into energy, and luminosity. An eta = 62.2 was obtained, strongly implying that relativistic beaming is responsible for the rapid variability of the gamma -ray-loud source. The influence of variable seeing conditions on the observations was investigated. There is a weak correlation between the observed variability and the local seeing conditions for the object 1ES 2344+51.4.

Superluminal blazars and the extragalactic gamma ray background

The detection of a few dozen extragalactic gamma ray blazars of extremely high luminosity by the EGRET instrument on board the Compton Gamma Ray Observatory appears to suggest that blazars make the overwhelming contribution to the cosmic gamma ray background in the energy range 100 MeV - 10 GeV. In this paper we point out that the superluminal effect which boosts and beams the gamma ray emission in the jets of blazars will flatten the source count in the low flux part. Consequently, the unresolved blazars would not be expected to make much contribution to the gamma ray background. From our direct modelling of the source count, we conclude that the contribution of the unresolved blazars to the gamma ray background is only 10% of the latest estimate of the EGRET data. The implication for the cosmological evolution of the blazars is discussed.

Constraints on the jet Lorentz factor in superluminal very high energy ?-ray blazars

We show that it can be possible to obtain lower limits on the jet Lorentz factors in superluminal very high energy (VHE) γ-ray blazars (e.g. Mrk, 421) which are more restrict than that ones derived only from the observations of superluminal motion. To do that we need to define some parameters of the blazars (i.e. accretion disk luminosity, disk inner radius, or disk temperature at the inner radius) which can be fixed in some sources based on the optical-UV observations. Moreover the knowledge is required on: (a) the variability time scale of radiation emitted from the shock (blob) region; (b) the maximum energy of emitted γ-rays; (c) and the value of an apparent speed of the shock from measurements of superluminal motion in the source. Based on the available observations of Mrk 421 and QSO 1633+382 we put constraints on the jet Lorentz factor in these sources as a function of their disk inner radius.

Comptonization as Blazar High Energy Emission

We explain the overall continuous Grazar (Gamma Ray Blazar) spectrum from the synchrotron turnover to the EGRET GeV detections by means of Comptonization in the parsec scale jet's substructures.While making use of the constraints on the synchrotron spectrum and other measurable quantities, no exotic particle acceleration is needed to achieve the high energy output.We show, that the “Lighthouse Model” of blobs of relativistic electrons, travelling with the jet plasma at relativistic speeds, produce both, correct timescales and shapes for the lightcurve, and correct ratios and slopes of the synchrotron, X-ray and γ-ray branches.

Implications of Gamma-Ray Transparency Constraints in Blazars: Minimum Distances and Gamma-Ray Collimation

We develop a general expression for the gamma - gamma absorption coefficient, alpha(sub gamma(gamma)) for gamma-rays propagating in an arbitrary direction at an arbitrary point in space above an X-ray-emitting accretion disk. The X-ray intensity is assumed to vary as a power law in energy and radius between the outer disk radius, R(sub 0), and the inner radius, R(sub ms) which is the radius of marginal stability for a Schwarzschild black hole. We use our result for alpha(sub gamma(gamma)) to calculate the gamma - gamma optical depth, tau(sub gamma(gamma)) for gamma - rays created at height z and propagating at angle Phi relative to the disk axis, and we show that for Phi = 0 and z greater than or approx equal to R(sub 0), tau(sub gamma(gamma)) proportional to Epsilon(sup alpha)z(sup -2(alpha) - 3), where alpha is the X-ray spectral index and Epsilon is the gamma - ray energy. As an application, we use our formalism to compute the minimum distance between the central black hole and the site of production of the gamma-rays detected by EGRET during the 1991 June flare of 3C 279. In order to obtain an upper limit, we assume that all of the X-rays observed contemporaneously by Ginga were emitted by the disk. Our results suggest that the observed gamma - rays may have originated within less than or approx equal to 45 GM/sq c from a black hole of mass greater than or approx equal to 10(exp 9) solar mass, perhaps in active plasma located above the central funnel of the accretion disk. This raises the possibility of establishing a direct connection between the production of the observed gamma - rays and the accretion of material onto the black hole. We also consider the variation of the optical depth as a function of the angle of propagation Phi. Our results indicate that the focusing of the gamma - rays along the disk axis due to pair production is strong enough to explain the observed degree of alignment in blazar sources. If the gamma - rays are produced isotropically in gamma - ray blazars, then these objects should appear as bright MeV sources when viewed along off-axis lines of sight.