0.35-3.5 micron photometry of blazars

Abstract

Thirty-one blazars were observed photometrically in the near-infrared, with additional observations in the optical for many of them. A few of them exhibit spectral behavior indicative of multiple emission components or emission processes. Six objects were also analyzed for any possible correlation between spectral steepness and luminosity. In one object, 0735 + 178, the spectral index a is correlated with the flux level with 99.9% confidence. Two other objects, 0846+513 and 0851+202, showed similar correlations at the 98% and 90% confidence levels, respectively. In all three cases the spectrum became flatter at higher flux levels. The data are consistent with expectations of models of inhomogeneous synchrotron models. In some cases, the self-Compton component may contribute significantly to the optical flux.Key words: quasars-photometry IntroductionThe blazars (BL Lacertae objects and optically violent variable (OVV) quasars) are active galactic nuclei whose emission is characterized by a nonthermal, variable, polarized flux, generally attributed to synchrotron radiation. The photon spectral shape is determined by the energy spectrum of the radiating particles. In its simplest form, the spectrum is nearly a power law with index a (with a defined as L v y 01 ) over a narrow frequency range, as expected for a parent population of particles (generally assumed to be electrons) whose energy spectrum is also a power law. In simple realistic models the spectra will turn down at low and high frequencies due to self-absorption, energy losses, and energy cutoffs in the particle population.While spectra have often been fit with such simple models, it has become increasingly clear that real sources Visiting Astronomer at the Mount Lemmon Observing Facility, operated by the University of Minnesota and the University of California at San Diego.Visiting Astronomer at Steward Observatory, operated by the University of Arizona.Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.Visiting Astronomer at the Infrared Telescope Facility, operated by the University of Hawaii under contract to the National Aeronautics and Space Administration.have photon spectra which are significantly curved, steepening toward higher frequencies (see, for example, Landau et al. 1986). Such curvature can be explained if the sources are inhomogeneous; the rate of steepening is related to the shape of the emitting region, generally thought to be the cone or funnel of a relativistic jet and the variations in particle energies and magnetic field strength along it.Königl 1981 and Ghisellini, Maraschi & Treves 1985 present results of inhomogeneous synchrotron selfCompton models in regions with jetlike geometries. In some combinations of jet geometry and particle-flow accelerations, the low-frequency and high-frequency (integrated) synchrotron fluxes come primarily from...

Automatic optical monitoring of 10 blazars

“…Other recent observations in the optical bands are reported by Moles et al (1985); Adam (1985); Smith et al (1987); Mead et al (1990); Sitko & Sitko (1991);Takalo (1991); Sillanpää et al (1991); Takalo et al (1992);and Xie et al (1994, and references therein). A rapid optical flare (0.56 mag/80 min) was observed in the B-band by Xie et al (1991) but this is to be considered a rare phenomenon (Xie et al 1994).…”

Infrared variability properties of the blazar 3C 279

“…Thus there are 27 years of continuous observations in the K band; the available K data have been compiled from the following 20 publications and are shown in Fig. 1: Rieke et al (1977), O'Dell et al (1978, Neugebauer et al (1979), Sitko et al (1982), Holmes et al (1984), Impey et al (1984), Gear et al (1985Gear et al ( , 1986a, Lepine et al (1985), Roelling et al (1986), Robson et al (1988), Brown et al (1989a), Garcia-Lario, Kidger & de Diego (1989), Kidger & Casares (1989), Mead et al (1990), Sitko & Sitko (1991), Kidger, Garcia-Lario & de Diego (1992a), Takalo et al (1992), Litchfield, Robson & Stevens (1994) and Maraschi et al (1994). Fig.…”

The infrared and optical variability of OJ 287

“…The infrared (JHK) are from Epstein et al (1972), Rieke et al (1977), O'Dell et al (1977O'Dell et al ( , 1978a, Pushell & Stein (1980), Allen et al (1982), Wolstencroft et al (1982), Impey et al (1982Impey et al ( , 1984, Sitko et al (1983), Holmes et al (1984a,b), Brindle et al (1986), Gear et al (1986a,b), Landau et al (1986), Roelling et al (1986), Smith et al (1987), Impey & Neugebauer (1988), Brown et al (1988), Sitko & Sitko (1991), Gear (1993), Kidger et al (1994), Litchfield et al (1994). Some early data are derived from the figure of Soifer & Neugebauer (1980).…”