Massimo Fiorucci

VRI Photometry of Stars in the Fields of 16 Blazars

We present a list of photometric VRI comparison sequences in the fields of 16 blazars. For six of these objects, comparison stars were calibrated for the first time during the present work. For most of the other 10 blazars, we improved the old sequences by either calibrating stars in the R and I bands or adding new comparison stars. Finding charts for 15 of these sequences are also reported.

The 65 Day Period in 3C 66A during Bright State

Historically, 3C 66A has been considered a relative quiescent blazar. For that reason, 3C 66A was selected as a comparison source for OJ 287 in the OJ-94 project. However, after more detailed observation it turns out that the variability of 3C 66A itself is very interesting. We have analyzed the entire project data set of 3C 66A from fall of 1993 to spring of 1998 by using structure function analysis, Deeming periodograms, Scargle periodograms, and the folded light curves. Here we present the first preliminary evidence for the 65 day period in 3C 66A observed during the bright state. Our analysis indicates that this period is slowly slowing down. We will also discuss the possible physical mechanism producing the observed periodicity.

Ten-year optical monitoring of PKS 0735+178: historical comparison, multiband behavior, and variability timescales

Aims. New data and results on the optical behavior of the prominent blazar PKS 0735+178 (also known as OI 158, S3 0735+17, DA 237, IES 0735+178, 3EG J0737+1721) are presented, through the most continuous BVR/data available in the period 1994-2004 (about 500 nights of observations). In addition, the whole historical light curve, and a new photometric calibration of comparison stars in the field of this source are reported. Methods. Several methods for time series analysis of sparse data sets are developed, adapted, and applied to the reconstructed historical light curve and to each observing season of our unpublished optical database on PKS 0735+178. Optical spectral indexes are calculated from the multi-band observations and studied on long-term (years) durations as well. For the first time in this source, variability modes, characteristic timescales, and the signal power spectrum are explored and identified over 3 decades in time with sufficient statistics. The novel investigation of mid-term optical scales (days, weeks), could be also applied and compared to blazar gamma-ray light curves that will be provided, on the same timescales, by the forthcoming GLAST observatory. Results. In the last 10 years the optical emission of PKS 0735+178 exhibited a rather achromatic behavior and a variability mode resembling the shot-noise. The source was at an intermediate or low brightness level, showing a mild flaring activity and a superimposition/succession of rapid and slower flares, without extraordinary and isolated outbursts, but, at any rate, characterized by one major active phase in 2001. Several mid-term scales of variability were found, the more common falling into duration intervals of about 27-28 days, 50-56 days and 76-79 days. Rapid variability in the historical light curve appears to be modulated by a general, slower, and rather oscillating temporal trend, where typical amplitudes of about 4.5, 8.5, and 11-13 years can be identified. This spectral and temporal analysis, accompanying our data publication, suggests the occurrence of distinctive signatures at mid-term durations that can likely be of transitory nature. On the other hand the possible pseudo-cyclical or multi-component modulations at long times could be more stable, recurrent and correlated to the bimodal radio flux behavior and the twisted radio structure observed over several years in this blazar.

The continuum spectral features of blazars in the optical region

Many quasi-simultaneous optical observations of 37 blazars were obtained at the Perugia University Observatory over the last ten years. In this paper we analyze the dereddened spectral flux distribution in the optical frequency range, and we compare our results with the overall spectral energy distribution (SED). The implications for existing models of the objects are briefly discussed. In particular, we show how the LBLs have a spectral slope α � 1.5, as expected from Synchrotron Self- Compton models, while the optical emission of HBLs and FSRQs is probably contaminated by other components. Moreover, we show evidence of how the spectral index vs. flux plot exhibits a characteristic loop-like pattern that is probably due to changes in the injection of accelerated particles.

THE PERUGIA UNIVERSITY AUTOMATIC OBSERVATORY

In this paper we describe the hardware and software architecture of the Automatic Imaging Telescope (AIT), recently developed at the Perugia University Observatory. It is based on an existing 0.4 m telescope which was transformed into an automatic device. During the night, all the observatory functions are controlled by two PCs in an unattended mode. The system is equipped with an autoguider and the software was designed to allow the automatic reduction of the data at the end of the night. Since October 1994 the AIT has been collecting a large amount of BVRcIc data for about 30 blazars.

The activity of the blazar OJ 287 in 2005: XMM-Newton observations and coordinated campaign

Two guest‐observer XMM‐Newton observations of the peculiar blazar OJ 287 in 2005 are briefly presented, along with the multiwavelength data obtained during a coordinated intensive WEBT campaign, and data obtained within longer‐term independent monitor programs, performed also by other facilities. During that year OJ 287 showed an interesting variability trend in the optical band. The X‐ray observations, performed in correspondence with two active optical states (a flare and an outburst), indicate different flux levels, spectral slopes, and emission components, while VLBA radio maps are consistent with a jet precession model. A further XMM‐Newton observation of OJ 287 is granted and foreseen in spring 2008, providing the opportunity of a multifrequency campaign to be performed in conjunction with GLAST.

Variability Characteristics of Blazar OJ 287

Blazar OJ 287 is one of the best observed extragalactic objects. It’s historical light curve goes back to 1890’s. Based on the historical behaviour Sillanpaa et al. (1988) showed that OJ 287 displays large periodic outbursts, with a period of 11.7 years. We have monitored OJ 287 intensively for two years, during the OJ-94 project. This project was created for monitoring OJ 287 during its predicted new outburst in 1994. In the data archive we have over 7000 observations on OJ 287, in the radio, infrared and optical bands. This data archive contains the best ever obtained light curves for any extragalactic object. The optical light curve shows continuous variability down to time scales of tens of minutes. The variability observed in OJ 287 can be broken down to (at least) four different categories: 1. The large outbursts that occur every 11.7 years. The last one of these happened during November 1994, almost at the predicted time. These outbursts can be due to the binary black hole model proposed by Sillanpaa et al. (1988).