ChandraX‐Ray Observations of Pictor A: High‐Energy Cosmic Rays in a Radio Galaxy

We report X-ray observations of the nearby, powerful radio galaxy Pictor Awith the Chandra Observatory and optical and near uv observations of itswestern radio hot spot with the Hubble Space Telescope. X-ray emission isdetected from the nucleus, a 1.9 arcmin (110 kpc) long jet to the west of thenucleus, the western radio hot spot some 4.2 arcmin (240 kpc) from the nucleus,and the eastern radio lobe. The morphology of the western hot spot isremarkably similar to that seen at radio and optical wavelengths, where theemission is known to be synchrotron radiation. The X-ray spectrum of the hotspot is well described by an absorbed power law with photon index \Gamma = 2.07(+/- 0.11). The X-ray jet coincides with a weak radio jet and is laterallyextended by \simeq 2.0 arcsec (1.9 kpc). The observed jet is up to \simeq 15times brighter in X-rays than any counter jet, a difference ascribed torelativistic boosting as the western radio lobe is probably the closer. Thejet's spectrum is well modelled by an absorbed power law with \Gamma = 1.94(+0.43/-0.49) and poorly fitted by a Raymond-Smith thermal plasma model. (Abstract truncated).Comment: 42 pages, 9 figures (3 JPEG, 6 Postscript), accepted for publication in the Astrophysical Journal, Vol 546, Jan 10 2001 issue. Section 4.3.2 revised October 1