Hu-Bing Xiao

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.

Optical monitoring of BL Lac object S5 0716+714 and FSRQ 3C 273 from 2000 to 2014

Context. Using the 1.56 m telescope at the Shanghai Observatory (ShAO), China, we monitored two sources, BL Lac object S5 0716+714 and flat spectrum radio quasar (FSRQ) 3C 273. For S5 0716+714, we report 4969 sets of CCD (Charge-coupled Device) photometrical optical observations (1369 for V band, 1861 for R band and 1739 for I band) in the monitoring time from Dec. 4, 2000 to Apr. 5, 2014. For 3C 273, we report 460 observations (138 for V band, 146 for R band and 176 for I band) in the monitoring time from Mar. 28, 2006 to Apr. 9, 2014. Aims. The observations provide us with a large amount of data to analyze the short-term and long-term optical variabilities. Based on the variable timescales, we can estimate the central black hole mass and the Doppler factor. An abundance of multi-band observations can help us to analyze the relations between the brightness and spectrum. Methods. We use Gaussian fitting to analyze the intra-day light curves and obtain the intra-day variability (IDV) timescales. We use the discrete correlation function (DCF) method and Jurkevich method to analyze the quasi-periodic variability. Based on the VRI observations, we use the linear fitting to analyze the relations between brightness and spectrum. Results. The two sources both show IDV properties for S5 0716+714. The timescales are in the range from 17.3 min to 4.82 h; for 3C 273, the timescale is Δ T = 35.6 min. Based on the periodic analysis methods, we find the periods P V = 24.24 ± 1.09 days, P R = 24.12 ± 0.76 days, P I = 24.82 ± 0.73 days for S5 0716+714, and P = 12.99 ± 0.72, 21.76 ± 1.45 yr for 3C 273. The two sources displayed the “bluer-when-brighter” spectral evolution properties. Conclusions. S5 0716+714 and 3C 273 are frequently studied objects. The violent optical variability and IDV may come from the jet. Gaussian fitting can be used to analyze IDVs. The relations between brightness (flux density) and spectrum are strongly influenced by the frequency.

The intrinsic γ-ray emissions of Fermi blazars

The beaming effect is important for understanding the observational properties of blazars. In this work, we collect 91 Fermi blazars with available radio Doppler factors. γ-ray Doppler factors are estimated and compared with radio Doppler factors for some sources. The intrinsic (de-beamed) γ-ray flux density (\(f_γ^{\rm in}\)), intrinsic γ-ray luminosity (\(L^{\rm in}_γ\)) and intrinsic synchrotron peak frequency (\(ν_{\rm p}^{\rm in}\)) are calculated. Then we study the correlations between \(f_γ^{\rm in}\) and redshift and find that they follow the theoretical relation: log f = −2.0 log z + const. When the subclasses are considered, we find that stationary jets are perhaps dominant in low synchrotron peaked blazars. Sixty-three Fermi blazars with both available short variability time scales (∆ T ) and Doppler factors are also collected. We find that the intrinsic relationship between \(L^{\rm in}_γ\) and \(\Delta T ^{\rm in}\) obeys the Elliot & Shapiro and Abramowicz & Nobili relations. Strong positive correlation between \(f_γ^{\rm in}\) and \(ν_{\rm p}^{\rm in}\) is found, suggesting that synchrotron emissions are highly correlated with γ-ray emissions.

The variability and periods in the 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, it is violently variable in the optical bands. 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 70 cm meniscus telescope at Abastumani Observatory, Georgia. It shows a large variation of Δ R = 4.88 mag (14.20 - 19.08 mag) during our monitoring period. When periodicity analysis methods are adopted to its R observations from our Abastumani monitoring programme and those in the literature, the signs of some periods, P 1 = 8.26 yr, P 2 = 0.55 yr, P 3 = 0.85 yr, P 4 = 1.99 yr are found.

Optical variability of PHL 1811 and 3C 273

In this work, we reported the optical photometry monitoring results for two brightest nearby quasars, PHL 1811 and 3C 273 using the ST-6 camera at Abastumani Observatory, Georgia. For PHL 1811, we found 3 microvariability events with time scale of Δ T = 6.0 min. For 3C273, we found that the largest variations are Δ V = 0.369 ± 0.028 mag, Δ R = 0.495 ± 0.076 mag, and Δ I = 0.355 ± 0.009 mag. When periodicity analysis methods are adopted to the available data, a period of p = 5.80 ± 1.12 years is obtained for PHL 1811, and p = 21.10 ± 0.14, 10.00 ± 0.14, 7.30 ± 0.09, 13.20 ± 0.09, 2.10 ± 0.06, and 0.68 ± 0.05 years are obtained for 3C 273.