Cannot find file /Users/meyer/Downloads/HST_2024_Pictor_A-2.pdf 0 Assigned ID: 5710 ----- Attempting Submission 1 (Tue Mar 26 21:55:49 GMT 2024) ----- 0 ----- Attempting Submission 1 (Mon Aug 12 15:55:39 GMT 2024) ----- HST Polarimetry and Proper Motions of the Pictor A Hotspot The X-ray emission mechanism and particle acceleration mechanism in kpc-scale AGN jets is still poorly understood. Nearby radio galaxy Pictor A hosts one of the nearest and brightest X-ray emitting jets, and is a highly valuable target for long-term monitoring and study. The jet has been deeply observed in the X-rays with Chandra, with a total exposure of nearly 0.5 Ms over 14 years. These observations revealed that the X-ray jet and hotspot unexpectedly vary on timescales as short as a few months to years in both the soft and hard X-rays, which places extreme constraints on the particle acceleration mechanism. The western hotspot of Pictor A, as the brightest in the sky with sufficient spatial separation from the core, has been recently detected in the hard X-rays with NuSTAR and was also approved for a large 2 Ms observation with IXPE in the first GO cycle, to measure its X-ray polarization. We propose HST optical/UV and polarization imaging of the jet and western hotspot of Pictor A. The proposed observations are highly complimentary and will extend the longest time baselines of optical imaging to nearly 30 years, enabling a range of investigations into variability, proper motions, and spectral evolution of the source. This program is focused primarily on the Western hotspot of Pictor A, which is 4' from the central nucleus. The entire size of the source is 7.6 arcminutes between terminal hotspots. The first observing mode is ACS/WFC Polarization, where the hotspot will be positioned near the center of the active dector region for the polarization filters. The observation will combine the linear polarization filters (POL0V, POL60V, POL120V), two orbits each, 3 exposures/orbit, with wide-V F606W. The F606W filter is by far the most efficient in terms of throughput in combination with the polarizers. The second visit will be non-polarization imaging with ACS/WFC in the same filter as used for the polarization (F606W) to aid in the image alignment and also to provide a baseline for a long-term optical proper motions program. We use ORIENT constraints to ensure the hotspot is on the detector with the jet falling on the diagonal so that the jet and core (host galaxy) are both captured in all images. We used a WFCCENTER pointing which is midway between the core and the hotspot -- the finding charts do not show the hotspot because of the size of the source. All pointing/orient constraints have been checked using actual HST images to ensure good target placement. The third visit/mode will be two orbits of WFC3/UVIS imaging in the F225W UV filter. The pointing will be somewhat similar to that used for the V-band imaging, in that we choose a point along the line of the jet to the hotspot and ORIENT constraints, in order to maximize the extent of the jet on the detector. Because of the smaller FOV of the UVIS detectors, it will not be possible to include the inner jet and nucleus of Pictor A in the observations, and the finding charts do not show the hotspot. For all observations we use appropriate dithering to sample the PSF and cover the chip gap, if applicable. The team includes several leading experts in the study of resolved optical jets with HST (E. Meyer, W. Sparks, K. Reddy Solipuram, E. perlman) and the team has collectively lead dozens of previous HST programs on jets and other targets. The team includes experts in polarimetry, including the use of HST polarizers (W. Sparks, E. Perlman, E. Meyer) who have published several dozen refereed papers on large-scale relativistic jets. The team includes experts on HST astrometry and proper motions (J. Anderson, R. van der Marel, E. Meyer) as well as an expert in imaging deconvolution with Chandra (K. Reddy) and experts in radio-wavelength studies of jets (E. Meyer, E. perlman, O. Shuvo, K. Reddy). Supermassive Black Holes and Active Galaxies 6 false false false false false false false false SUPPORTED GALAXY HOTSPOT JET J2000 J2000 GALAXY HOTSPOT JET J2000 J2000 GALAXY HOTSPOT JET J2000 J2000 ACS/WFC Imaging No Yes F606W ACS/WFC Imaging No No F606W WFC3/UVIS Imaging No No F225W /Users/meyer/Dropbox/Research/proposals/2024_proposals/HST_PictorA/phase2/OP-cache/picA_17783_phase2-v01.xml The scheduling data was generated by CASM 32.1.1. CASM was run in Phase II mode. 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