IR Monitoring and Polarimetry of Blazars and Radio Galaxies
We observe at near-IR wavelengths (J, H, and K) at the 1.8-meter Perkins telescope at Lowell observatory using the MIMIR camera (see below). This is in support of our monitoring program with the VLBA at 43 GHz of a sample of gamma-ray blazars. We combine our optical and IR observations with those of other observers around the world to generate multi-wavelengths light curves such as those shown in Willamson et al. 2014. We perform H-band polarization observations of the brightest (in R band) gamma-ray blazars from our sample of blazars that we monitor with the VLBA and at optical wavebands in photometric and polarimetric modes. The VLBA monitoring provides images at 43 GHz in total and polarized intensity. The goal is to use polarization to pinpoint on the VLBA images the location(s) of the IR and optical emission. We analyze variations in the polarization to perform multiwaveband mapping. Even if the variations are not simultaneous, the time delays indicate whether the higher-frequency emission occurs upstream or downstream of the bright core that we see on the VLBA images. The method was successfully used, e.g., in D'Arcangelo et al. (2009). The H-band polarimetry is performed with the MIMIR near-IR wide-field imager, spectrometer, and polarimeter, constructed by Professor Dan Clemens of Boston University.
We observed 4 blazzrs with the NASA Spitzer Space telescope using all three instruments available prior to 2012 in order to measure the IR spectral energy distribution. The results provided clear evidence of hot (1200 K) dust around the gamma-ray quasar 4C+21.35 and indications of similar dust in the quasar CTA102 (Malmrose et al. 2011). The spectra contained no signature of similar dust in the BL Lac object W Comae (1219+285) or the quasar PKS 1510-089.
We observed with the NASA Infrared Telescope Facility (IRTF) using the MIRSI camera to obtain unique measurements of the quasar 3C 454.3 at 4.9, 10.6, and 20.7 microns during the dramatic gamma-ray outburst in 2010 (Jorstad et al. 2013; Fig. 24). We continued to use IRTF with a combination of SpeX and MORIS to obtain simultaneous optical and near-IR measurements for construction of spectral energy distributions of gamma-ray blazars in our sample through 2014.
In collaboration with Dr. Ann Wehrle we observed with the Herschel Space Telescope two gamma-ray blazars, 3C 454.3 (the results are presented in Wehrle et al. 2012 and Jorstad et al. 2013) and BL Lac (paper in preparation), using the Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging REceiver (SPIRE). These observations were important components of extensive multi-wavelength studies of these objects.