Sharp Polarimetric Eyes: More Trees than Forest?

Abstract

Abstract:The Fermi Gamma-ray Space Telescope (Fermi) has focused the intensive multi-wavelength and international observational effort on blazars since it was launched in 2008. Part of this effort involves systematic monitoring of the highly variable polarization of the continuum emission from these objects. These observations are valuable in that they provide direct information on the degree of ordering and orientation on the sky of the magnetic field within the non-thermal emission region(s). Unfortunately, it is not yet possible to measure the polarization of the inverse-Compton continuum, only that of the lower-energy synchrotron emission. The inability to directly compare the polarization of the two dominant continuum sources in blazars is a drawback and leads to more ambiguities in determining their relative locations. There are many compelling examples of strong connections between γ-ray, X-ray, UV/optical/IR, and radio behavior in blazars that suggest the same region produces much of the observed emission at all wavelengths at least some of the time. However, the wealth of polarization behavior seen relative to flux changes invariably results in a complex situation that is difficult to interpret and model. The long-term blazar monitoring program undertaken at Steward Observatory is designed to primarily obtain accurate optical polarimetry of γ-ray-bright blazars during the Fermi mission with the goal of gaining important insights into the jet structure and physics of these objects. Data from this program are available to all researchers as soon as reductions are completed. I briefly detail the current status and progress of the program and the data products available. Although the wide variety of polarization behavior in blazars adds another layer of complexity to an already difficult problem, I summarize several important conclusions that can be drawn from the polarization information gathered during the Fermi era.

Mid-IR Variability and Dust Reverberation Mapping of Low-z Quasars. I. Data, Methods, and Basic Results

“…Since PG 1226+023 (also known as 3C 273) is saturated in CRTS and PTF, we have looked for alternative datasets to build its optical light curve. In fact, this object had been systematically monitored from late 2008 to the middle of 2018 as part of the Steward Observatory (SO) spectropolarmetric monitoring project (Smith 2016). 1 These observations were carried out with the SPOL CCD spectropolarimeter (Schmidt et al 1992) at either the SO 2.3 m Bok Telescope on Kitt Peak or the SO 1.54 m Kuiper Telescope on Mt.…”

Multiwavelength Variability of BL Lacertae Measured with High Time Resolution

“…They are thought to be powered by relativistic jets of high-energy plasma flowing away from the central engine at nearly the speed of light (e.g., Lister et al 2016;Jorstad et al 2017), with trajectories closely aligned to the line of sight. The observed phenomena include ultraluminous emission (apparent luminosity as high as ∼ 10 50 erg s −1 , e.g., Abdo et al 2010aAbdo et al , 2011aGiommi et al 2012;Şentürk et al 2013), high amplitudes of variability on timescales as short as several minutes at various wavebands (e.g., H. E. S. S. Collaboration et al 2010;Jorstad et al 2013;Weaver et al 2019), and high degrees of optical linear polarization (which can exceed 40%; e.g., Smith 2016). Both theoretical work (e.g., Königl 1981;Marscher 1987) and observations (e.g., Hartman et al 1999;Jorstad et al 2001;Lister et al 2011) have found a tight connection between the high-energy and radio emission from the jets.…”

Multi-wavelength Behavior of Blazars: Combined Order and Disorder

“…This causes a rapid X-ray synchrotron and VHE γ-ray flare, as well as a flattening of the polarized flux density spectrum, since much of the emission at that time should come from a single cell or a few cells. Data by the author's group and from the Steward Observatory polarization spectral monitoring [18] indeed provide evidence for the predicted wavelength dependence [11]. The author's group plans to expand its monitoring of the multi-color optical polarization of blazars to confirm and study this trend.…”