The Optical Polarization Properties of X-ray Selected BL Lacertae Objects

Abstract

We discuss the optical polarization properties of X-ray selected BL Lacertae objects (XSBLs) as determined from three years of monitoring 37 BL Lac objects and candidates. The observed objects include a complete X-ray flux limited sample drawn from the EMS Survey. The majority of the XSBLs classi- fied solely on the appearance of their spectra are members of the class of BL~Lacs since they possess intrinsically polarized and variable continua. The duty cycle of polarized emission from XSBLs is 40\%. The majority of XSBLs ($\approx 85$\%) have preferred polarization position angles on time scales as long as three years. This reflects stability in the geometry of the region emitting the polarized optical emission. We discuss the observed spectral dependence of the degree of polarization and some of the possible mechanisms for producing the observed characteristics. While dilution of the polarized emission by the host galaxy starlight is present in some objects, we demon- strate that the average polarization properties derived from our observations are not drastically affected by this effect. The objects in our monitored sample did not display the larger than one magnitude variations generally used to characterize the optical variability of blazars in general.

LaTex file, 21 pages, with tables appended as a poscript file. Contact [email protected] for postscript figure files. Institute for Advanced Study number AST 93/45

Cited by in corpus (30)

• The Deep X-ray Radio Blazar Survey (DXRBS). I. Methods and First Results
• ASCA Observations of Blazars and Multiband Analysis
• The Properties of the Radio-Selected 1Jy Sample of BL Lacertae Objects
• The Properties of the X-Ray-Selected EMSS Sample of BL Lac Objects
• The Chandra Multiwavelength Project: Optical Followup of Serendipitous Chandra Sources
• Optical Flux and Spectral Variability of Blazars
• Polarization microvariability of BL Lac objects
• The Radio Structure of High-Energy Peaked BL Lacertae Objects
• Intra-night optical variability of core dominated radio quasars: the role of optical polarization
• A Search for Low-Luminosity BL Lacertae Objects
• Optical quasi-periodic oscillation and color behavior of blazar PKS 2155-304
• PKS 0116+082: An Optically Variable Compact Steep-Spectrum Source in an NLRG
• Long-term optical variability of PKS 2155-304
• Upper limits from five years of blazar observations with the VERITAS Cherenkov telescopes
• Highly Polarized Optically-Selected BL Lacertae Objects
• Rapid optical variability of TeV blazars
• Multiwavelength Monitoring of the BL Lacertae Object PKS 2155-304 in May 1994. I. The Ground-Based Campaign
• Very High Energy outburst of Markarian 501 in May 2009
• Polarimetry of optically selected BL Lac candidates from the SDSS
• Multiband optical polarimetry of the BL Lac object PKS 2155--304. Intranight and long term variability
• Discovery of an Ultra-Steep Spectrum, Highly Polarized Red Quasar at z = 1.462
• Imaging of the Host Galaxies of Three X-Ray Selected BL Lacertae Objects
• A Lyman-alpha-only AGN from the Sloan Digital Sky Survey
• Variations in the broadband spectra of BL Lac objects: millimetre observations of an X-ray-selected sample
• Comparative intra-night optical variability of X-ray and $\gamma$-ray detected narrow-line Seyfert 1 galaxies
• Can Turbulence Dominate Depolarization of Optical Blazars?
• Radio spectra of a sample of X-ray selected BL Lacs
• Optical monitoring in southern blazars. Analysis of variability and spectral colour behaviours
• Dual-Beam Optical Linear Polarimetry from Southern Skies. Characterisation of CasPol for high precision polarimetry
• A long-term multiwavelength study of the flat spectrum radio quasar OP 313