J. H. Fan

OPTICAL INTRA-DAY VARIABILITY IN BLAZARS

We selected a sample of a dozen blazars which are the prime candidates for simultaneous multi-wavelength observing campaigns in their outburst phase. We searched for optical outbursts, intra-day variability (IDV) and short-term variability in these blazars. We carried out optical photometric monitoring of nine of these blazars in 13 observing nights during our observing run of 2006 October 27-2007 March 20 using the 1.02 m optical telescope equipped with CCD detector and BVRI Johnson broadband filters at Yunnan Astronomical Observatory, Kunming, China. From our observations, our data favor the hypothesis that three blazars, AO 0235+164, S5 0716+714, and 3C 279, were in the outburst state; one blazar, 3C 454.3, was in the post-outburst state; three blazars, S2 0109+224, PKS 0735+178, and OJ 287, were in the pre/post-outburst state; one blazar, ON 231, was in the low state; and the state of one blazar, 1ES 2344+514, was not known because there are not many optical data available for the blazar to compare with our observations. We observed densely sampled 1534 image frames of these nine blazars. Out of three nights of observations of AO 0235+164, IDV was detected in two nights. Out of five nights of observations of S5 0716+714, IDV was detected in two nights. In one night of observations of PKS0735+178, IDV was detected. Out of six nights of observations of 3C 454.3, IDV was detected in three nights. No IDV was detected in S2 0109+224, OJ 287, ON 231, 3C 279, and 1ES 2344+514 in their one, four, one, two, and one nights of observations, respectively. AO 0235+164, S5 0716+714, OJ 287, 3C 279, and 3C 454.3 were observed in more than one night and short-term variations in all these blazars were also noticed. From our observations and the available data, we found that the predicted optical outbursts with time intervals of similar to 8 years in AO 0235+164 and similar to 3 years in S5 0716+714 have possibly occurred.

CCD photometry of 14 BL Lacertae objects and theoretical model

We present the results of monitoring, over a period of 1 year, a sample of 14 BL Lac objects in BVRI bands. Seven sources exhibit short time-scale variability, and five sources exhibit medium time-scale variability with large amplitude. The evidence of relativistic beaming and accretion disks for 10 BL Lac objects is discussed.

Radio variability properties for radio sources

In this paper, we used the database of the university of Michigan Radio Astronomy Observatory (UMRAO) at three (4.8 GHz, 8.0 GHZ, and 14.5 GHz) radio frequency to analyze the radio light curves by the power spectral analysis method in search of possible periodicity. The analysis results showed that the radio sources display astrophysically meaningful periodicity ranging from 2.2 to 20.8 years in their light curves at the three frequencies. We also calculated the variability parameters and investigated the correlations between the variability parameter and the flux density. For the variability parameters, we found that the parameters at higher frequency are higher than those in the lower frequency. In addition, the variability parameters of BL Lacertae objects are larger than those of flat-spectrum radio quasars. suggesting that they are more variable than flat spectrum radio quasars.

The Relation between Gamma-Ray and Near-Infrared Radiation in Gamma-Ray-loud Blazars

We collect 16 gamma-ray-loud blazars (seven BL Lac objects and nine flat-spectrum radio quasars) with both observed near-infrared and gamma-ray flux densities and find that the near-IR luminosity correlates better with gamma-ray luminosity than with X-ray. Possible constraints on the gamma-ray emission mechanism are discussed. We suggest that the gamma-ray radiation is probably created by inverse Compton scattering of the radiation from hot circumnuclear dust by beamed, ultrarelativistic electrons.

THE SPECTRAL INDEX PROPERTIES OF FERMI BLAZARS

In this paper, a sample of 451 blazars (193 flat spectrum radio quasars (FSRQs), 258 BL Lacertae objects) with corresponding X-ray and Fermi ?-ray data is compiled to investigate the correlation both between the X-ray spectral index and the ?-ray spectral index and between the spectral index and the luminosity, and to compare the spectral indexes ?X, ??, ?X?, and ??X? for different subclasses. We also investigated the correlation between the X-ray and the ?-ray luminosity. The following results have been obtained. (1) Our analysis indicates that an anti-correlation exists between the X-ray and the ?-ray spectral indexes for the whole sample. However, when we considered the subclasses of blazars (FSRQs, the low-peaked BL Lacertae objects (LBLs) and the high-peaked BL Lacertae objects (HBLs)) separately, there is not a clear relationship for each subclass. For the average values, , we have ; and (2) For the correlations between the X-ray and the ?-ray luminosities, we have log ?L ? = (1.033 ? 0.002)log ?L X + (0.213 ? 0.094) for the whole sample, log ?L ? = (0.741 ? 0.004)log ?L X + (12.378 ? 0.162) for HBLs, and log ?L ? = (1.032 ? 0.003)log ?L X + (0.643 ? 0.138) for the LBLs and FSRQs; the correlation slope for HBLs is different from that for FSRQs and LBLs. For the average values, , we have , , and for the X-ray luminosity; and , , and for the ?-ray luminosity. (3) There is an anti-correlation between the effective spectral index, ?X?, and log ?L ? for the whole sample, and the subclasses (FSRQs, LBLs, and HBLs). The effective spectral index shows that (4) For the spectral index difference, ??X?(=?X? ? ??) of the effective spectral index, ?X?, and the ?-ray spectral index, ??, we obtain (5) Based on the Fermi-detected sources, we can say that the HBLs are different from FSRQs, while the LBLs are similar to FSRQs.

Optical Observations of 3C 273 From 2000 to 2008

The quasar 3C 273 is one of the widely studied quasars that is also a selected target in our monitoring program. In this paper, we present the optical V, R, and I photometric observations done with the 1.56 m telescope at the Shanghai Astronomical Observatory from 2000 to 2008. Our monitoring results show 1118 sets of observations (258 sets for the V band, 414 sets for the R band, and 446 sets for the I band). The observations indicate that (1) the variations in the three bands are Delta V = 1.363 +/- 0.088 mag from V = 12.204 +/- 0.062 to V = 13.567 +/- 0.062, Delta R = 1.299 +/- 0.023 mag from R = 12.014 +/- 0.014 to R = 13.313 +/- 0.013, and Delta I = 1.041 +/- 0.088 mag from I = 11.628 +/- 0.046 to I = 12.669 +/- 0.075. Compared with the result by Toone, who presented the yearly averaged light curve during the period of 1980-2004 and found that the source shows a slow brightening with = 12.95 in 1996-1997 to = 12.5 in 2003-2004, our observations show that it is variable and both a state brighter than the yearly averaged brightness of = 12.5 and a state fainter than the yearly averaged brightness of = 12.95 were detected in our observing period. Intra-day variation timescales are from 13 minutes to 245 minutes. (2) The color indices are variable with V-R from -0.27 to 0.68, V-I from 0.11 to 1.14, and R-I from 0.14 to 0.86. The average values are = 0.18 +/- 0.10, = 0.64 +/- 0.14, and = 0.46 +/- 0.11.

PHOTOMETRIC MONITORING OF OJ 287 FROM 2002 TO 2007

OJ 287 is one of the best studied blazars. It is also a prime target in our long-term blazar monitoring program carried out with the 1.56 m telescope at the Sheshan Station of the Shanghai Astronomical Observatory, China. Here, we present optical photometry results of V, R, and I passbands of the BL Lacertae object OJ 287 (0851+202) carried out from 2002 January to 2007 February. The largest variations of ΔV = 1.96 mag (14.01-15.97 mag), ΔR = 2.36 mag (13.39-15.75 mag), and ΔI = 1.95 mag (12.79-14.74 mag) were detected in our observations. Intraday variation timescales of ~10 minutes to 2 hr were detected in optical passbands.

Multiband optical variability of the blazar S5 0716+714 in outburst state during 2014–2015

We analyzed the multi-band optical behaviour of the BL Lacertae object, S5 0716+714, during its outburst state from 2014 November - 2015 March. We took data on 23 nights at three observatories, one in India and two in Bulgaria, making quasi-simultaneous observations in B, V, R, and I bands. We measured multi-band optical fluxes, colour and spectral variations for this blazar on intraday and short timescales. The source was in a flaring state during the period analyzed and displayed intense variability in all wavelengths. R band magnitude of 11.6 was attained by the target on 18 Jan 2015, which is the brightest value ever recorded for S5 0716+714. The discrete correlation function method yielded good correlation between the bands with no measurable time lags, implying that radiation in these bands originate from the same region and by the same mechanism. We also used the structure function technique to look for characteristic timescales in the light curves. During the times of rapid variability, no evidence for the source to display spectral changes with magnitude was found on either of the timescales. The amplitude of variations tends to increase with increasing frequency with a maximum of

The Binary Black Hole Scenario for the BL Lacertae Object AO 0235+16

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Multiband optical variability of the blazar OJ 287 during its outbursts in 2015 – 2016

22% seen during flaring states in B band. A mild trend of larger variability amplitude as the source brightens was also found. We found the duty cycle of our source during the analyzed period to be