Jun-Hui Fan

The Optical Microvariability and Spectral Changes of the BL Lacertae Object S5 0716+714

We monitored the BL Lac object S5 0716+714 in the optical band during October 2008, December 2008 and February 2009 with a best temporal resolution of about 5 minutes in the BVRI bands. Four fast flares were observed with amplitudes ranging from 0.3 to 0.75 mag. The source remained active during the whole monitoring campaign, showing microvariability in all days except for one. The overall variability amplitudes are delta B ~ 0.89 mag, delta V ~ 0.80 mag, delta R ~ 0.73 mag and delta I ~0.51 mag. Typical timescales of microvariability range from 2 to 8 hours. The overall V - R color index ranges from 0.37 to 0.59. Strong bluer- when-brighter chromatism was found on internight timescales. However, different spectral behavior was found on intranight timescales. A possible time lag of ~ 11 mins between B and I bands was found on one night. The shock-in-jet model and geometric effects can be applied to explain the sources intranight behavior.

Radio-to-UV monitoring of AO 0235+164 by the WEBT and Swift during the 2006-2007 outburst

Context. The blazar AO 0235+164 was claimed to show a quasi-periodic behaviour in the radio and optical bands in the past, with the main outbursts repeating every 5–6 years. However, the predicted 2004 outburst did not occur, and further analysis suggested a longer time scale, according to which the next event would have occurred in the 2006–2007 observing season. Moreover, an extra emission component contributing to the UV and soft X-ray flux was detected, whose nature is not yet clear. An optical outburst was observed in late 2006–early 2007, which triggered a Whole Earth Blazar Telescope (WEBT) campaign as well as target of opportunity (ToO) observations by the Swift satellite. Aims. In this paper, we present the radio-to-optical data taken by the WEBT together with the UV data acquired by the UltraViolet and Optical Telescope (UVOT) instrument onboard Swift to investigate both the outburst behaviour at different wavelengths and the nature of the extra emission component. Methods. Multifrequency light curves have been assembled with data from 27 observatories; optical and UV fluxes have been cleaned from the contamination of the southern active galactic nucleus (AGN). We have analysed spectral energy distributions at different epochs, corresponding to different brightness states; extra absorption by the foreground galaxy has been taken into account. Results. We found the optical outburst to be as strong as the big outbursts of the past: starting from late September 2006, a brightness increase of ~5 mag led to the outburst peak in February 19–21, 2007. We also observed an outburst at mm and then at cm wavelengths, with an increasing time delay going toward lower frequencies during the rising phase. Cross-correlation analysis indicates that the 1 mm and 37 GHz flux variations lagged behind the R -band ones by about 3 weeks and 2 months, respectively. These short time delays suggest that the corresponding jet emitting regions are only slightly separated and/or misaligned. In contrast, during the outburst decreasing phase the flux faded contemporaneously at all cm wavelengths. This abrupt change in the emission behaviour may suggest the presence of some “shutdown” mechanism of intrinsic or geometric nature. The behaviour of the UV flux closely follows the optical and near-IR one. By separating the synchrotron and extra component contributions to the UV flux, we found that they correlate, which suggests that the two emissions have a common origin.

Optical monitoring of S5 0716+714 from 1994 to 2000

We present multicolor optical (Johnson BV and Cousins RI) monitoring results of 5.3 yr for S5 0716+714. The four-band light curves showed a high duty cycle of variability. We studied its intranight variability and the quasi-periodic oscillations and found that the variability can be explained by a relativistic jet model.

The core dominance parameter of extragalactic radio sources

In this paper, based on a paper by Liu and Zhang (2002), we have chosen a sample of 542 extragalactic sources (27 BL Lac objects, 300 galaxies (radio galaxies and Seyfert galaxies), and 215 quasars), for which we have calculated the core-dominance parameters and investigated the relation between core-dominance parameter and the core and extended lu- minosities. The core-dominance parameter of galaxies is smaller than that in quasars, which is smaller than that in BL Lac objects. log R= 1:40 0:74 for galaxies, log R= 0:53 0:92 for quasars, and log R= 0:01 0:65 for BL Lac objects on average respectively. For quasars, there is clear correlation between the core-luminosity and core-dominance parameter and an anti-correlation between the extended luminosity and the core-dominance parameter, which is explained by the beaming eect.

Long-term variation time scales in OJ 287

The light curve data from 1894 to 2008 are compiled for the BL Lacertae object OJ 287 from the available literature. Periodicity analysis methods (the Discrete Correlation Function-DCF, the Jurkevich method, the power spectral (Fourier) analysis, and the CLEANest method) are performed to search for possible periodicites in the light curve of OJ 287. Significance levels are given for the possible periods. The analysis results confirm the existence of the 12.2 ± 0.6 yr time scale and show a hint of a ~53 yr time scale. The 12.2±0.6 yr period is used as the orbital period to investigate the supermassive binary black hole system parameters.

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.

Beaming Effect in Fermi Blazars

� -ray loud blazars (flat spectrum radio quasars—FSRQs and BL Lacertae objects—BLs) are very bright in the � -ray bands, which is perhaps associated with a beaming effect. Therefore, one can expect that the � -ray luminosity is correlated with the beaming factor. In this paper, we consider the relation between the radio Doppler factors and ;

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.