Astron. Astrophys. Suppl. Ser.
Volume 121, Number 1, January 1997
|Page(s)||119 - 138|
|Published online||15 January 1997|
Optical photometric monitoring of γ-ray loud blazars.*
I. Observations from November 1994 to November 1995
Osservatorio Astronomico di Torino, Strada Osservatorio 20, I-10025 Pino Torinese (TO), Italy
2 Istituto di Fisica Generale dell'Università, Via Pietro Giuria 1, I-10125 Torino, Italy
Corresponding author: Send offprint request to: M. Villata email: email@example.com
Accepted: 21 May 1996
The results of the optical monitoring between November 1994 and November 1995 of twenty γ-ray loud blazars included in the Torino blazar monitoring program are presented. All data were taken with the REOSC astrometric telescope of the Torino Astronomical Observatory, equipped with a pixels charge-coupled device (CCD) camera. Observations have been carried out in the standard B, V (Johnson), and R (Cousins) bands. Source magnitudes are calculated with respect to reference stars in the same frame. For half blazar fields it was possible to perform a photometric calibration through the observation of Landolt's fields during photometric nights. In the other cases either photometric sequences from the literature were adopted or, when lacking, magnitudes were simply normalized to their minimum value. Most of the monitored objects show a more or less pronounced brightness variability on both short and long time scales. In a few cases also noticeable intranight variations were detected. Data simultaneous to pointings of the Compton Gamma Ray Observatory (CGRO) are present in our light curves: when the γ data are available they will provide a useful information in order to understand the possible correlations between the optical and γ-ray emissions. For one source (PKS 2254+074) we performed also photopolarimetry, deducing magnitudes, amount of polarization, and position angle in the UBVRI bands.
Key words: quasars: general / gamma rays: theory
Figures 9, 11, 13, 20, 23, 26, 27, and 33 appear only in the electronic version of A&A on WWW at http://ed-phys.fr. Tables 4–48 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsweb.u-strasbg.fr/Abstract.html
© European Southern Observatory (ESO), 1997