X-ray Observations of the Radio Galaxy Pictor A

Abstract

Strong X-ray emission is detected from the active nucleus of an emission- line radio galaxy Pictor A, during observations with the EXOSAT observatory. The nuclear X-ray emission is observed to be steady on time- scales of a few minutes to a few hours. The X-ray spectrum is adequately explained by a simple power law with the photon index {GAMMA}=1.8±0.3 (90 per cent confidence), similar to that observed from various Seyfert galaxies. There is no evidence for any significant absorption local to the source, nor is there any evidence for a separate soft X-ray component. There is evidence for the presence of a line feature centred between 6 and 8 ke V in the X-ray spectrum. The observations support the presence of a large amount of matter in non-spherical geometry around the nuclear source in Pictor A. The line-of-sight to the X-ray source is probably encountering an edge-on matter distribution around the source. No soft X-rays are detected from the highly polarized optical counterpart of the western radio hotspot. Two very weak soft X-ray sources are detected serendipitously within 30 arcmin of the radio galaxy. The analysis of archival X-ray data obtained with the Einstein observatory gives spectral index and flux consistent with the results obtained from the EXOSAT observatory. The far-IR fluxes from Pictor A have also been obtained from the IRAS observations and the broad-band multiwavelength spectrum of Pictor A is shown.