Jiang-He Yang

The gamma-ray Doppler factor determinations for a Fermi blazar sample ∗

Observations suggest that γ-ray loud blazars are strongly beamed. The Fermi mission has detected many of blazars, which provide us with a good opportunity to investigate the emission mechanism and the beaming effect in the γ-ray region. We compiled the X-ray observations for 138 Fermi blazars (54 flat spectrum radio quasars, 36 low-peaked BL Lacertae objects, and 48 high-peaked BL Lacertae objects) and calculated their Doppler factors, δγ. It is interesting that the calculated Doppler factors, δγ, are strongly correlated with the γ-ray luminosity.

The lower limit of the Doppler factor for a Fermi blazar sample

We selected 457 blazars (193 flat spectrum radio quasars, 61 low-synchrotron peaked blazars, 69 intermediate-synchrotron peaked blazars and 134 high-synchrotron peaked blazars) from the second Fermi -LAT catalog (2FGL) of γ-ray sources, which have X-ray observations. We calculated the lower limits for their Doppler factors, δ γ , and compared the lower limits with the available Doppler factors and the apparent superluminal velocities in the literature.

Rapid variability in S5 0716+714

S5 0716+714 is one of the targets in our long term blazar monitoring program carried out with the 1.56-m telescope at Sheshan Station of Shanghai Astronomical Observatory, China. We report a very rapid variability of ΔI = 0.611 ± 0.102 mag over 3.6 min detected in our monitoring program during the period from December 2000 to March 2007. The rapid variability suggests that the mass for the central black hole is log( M/M ⊙ ) = 7.68 − 8.38.

Brightness temperature for 166 radio sources

Using the database of the University of Michigan Radio Astronomy Observatory (UMRAO) at three radio frequencies (4.8, 8 and 14.5 GHz), we determined the short-term variability timescales for 166 radio sources. The timescales are 0.15 d (2007+777) to 176.17 d (0528–250) with an average timescale of Δ t obs = 17 . 1  16 . 5 d for the whole sample. The timescales are used to calculate the brightness temperatures, T B . The value of log T B is in the range of log T B = 10.47 to 19.06 K. In addition, we also estimated the boosting factor for the sources. The correlation between the polarization and the Doppler factor is also discussed.

Radio Polarization of BL Lacertae Objects

In this paper, using the database of the university of Michigan Radio Astronomy Observatory (UMRAO) at three (4.8 GHz, 8 GHZ, and 14.5 GHz) radio frequencies, we studied the polarization properties for 47 BL Lacertae objects(38 radio selected BL Lacertae objects, 7 X-ray selected BL Lacertae, and two inter-middle objects (Mkn 421 and Mkn 501), and found that (1) The polarizations at higher radio frequency is higher than those at lower frequency, (2) The variability of polarization at higher radio frequency is higher than those at lower frequency, (3) The polarization is correlated with the radio spectral index, and (4) The polarization is correlated with core-dominance parameter for those objects with known core-dominance parameters suggesting that the relativistic beaming could explain the polarization characteristic of BL Lacs.

Optical Photometrical Observations and Variability for Quasar 4C 29.45

We reported the result of the long-term optical variability of the blazar 4C 29.45s (QSO 1156 + 295, Ton 599), carried out by optical photometric observations in the Johnson V, Cousins RI passbands during 1997 April to 2002 March. We used the 1.56-m telescope of the Shanghai Astronomical Observatory at Sheshan, China, and compiled the post-1974 optical photometric data of the blazar by combining our new observations with the published optical data, and found maximum variations in different passbands: Delta U = 4.41 mag, Delta B = 5.55 mag, Delta V = 4.53mag, Delta R = 5.80mag, and Delta I = 5.34mag. The average color indices are: U - B = -0.54 +/- 0.18 mag, B - V = 0.56 +/- 0.21 mag, B - R = 0.93 +/- 0.18mag, B - I = 1.51 +/- 0.24mag, V - R = 0.44 +/- 0.15mag, and V - I = 1.03 +/- 0.23mag. The post-1974 data give us an excellent opportunity to search for the existence of a possible periodicity in the light curve. In searching for periodicity in the R passband light curve, we performed a Jurkevich test and power spectral (Fourier) analysis methods, as well as CLEANest algorithms to remove false signals. We found possible periods of 3.55 and 1.58 years. A possible mechanism for the periodic variability was analyzed.

The estimations of four basic parameters for gamma-ray loud blazars

The method used in our previous papers is adopted to estimate four basic parameters (the central black hole mass ( M ), the boosting factor (or Doppler factor) ( δ ), the propagation angle ( Φ ) and the distance along the axis to the site of the γ -ray production ( d )) for 59 γ -ray loud blazars (20 BL Lacertae objects and 39 fl at spectrum radio quasars). The central black hole masses estimated for this sample are in a range of from 10 7 M ⊙ to 10 9 M ⊙ In the case of black hole mass, there is no clear difference between BL Lacertae objects and fl at spectrum radio quasars, which is consistent with the previous results suggesting that the central black hole masses do not play an important role in the evolutionary sequence of blazars

Intrinsic Correlations for Flaring Blazars Detected by Fermi

Blazars are an extreme subclass of active galactic nuclei. Their rapid variability, luminous brightness, superluminal motion, and high and variable polarization are probably due to a beaming effect. However, this beaming factor (or Doppler factor) is very difficult to measure. Currently, a good way to estimate it is to use the timescale of their radio flares. In this Letter, we use multiwavelength data and Doppler factors reported in the literature for a sample of 86 flaring blazars detected by Fermi to compute their intrinsic multiwavelength data and intrinsic spectral energy distributions and investigate the correlations among observed and intrinsic data. Quite interestingly, intrinsic data show a positive correlation between luminosity and peak frequency, in contrast with the behavior of observed data, and a tighter correlation between γ-ray luminosity and the lower-energy ones. For flaring blazars detected by Fermi, we conclude that (1) observed emissions are strongly beamed; (2) the anti-correlation between luminosity and peak frequency from the observed data is an apparent result, the correlation between intrinsic data being positive; and (3) intrinsic γ-ray luminosity is strongly correlated with other intrinsic luminosities.

Variability and Period Analysis for BL Lac AO 0235+164

Variability is one of the extreme observational properties of BL Lacertae objects. AO 0235+164 is a well studied BL Lac through the whole electro-magnetic wavebands. In the present work, we show its optical R band photometric observations carried out during the period of Nov, 2006 to Dec. 2012 using the Ap6E CCD camera attached to the primary focus of the

THE RELATIONSHIP AMONG XBLs, RBLs AND FSRQs

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