INTEGRAL and RXTE Observations of Centaurus A

INTEGRAL and RXTE performed three simultaneous observations of the nearby radio galaxy Centaurus A in 2003 March, 2004 January, and 2004 February with the goals of investigating the geometry and emission processes via the spectral/temporal variability of the X-ray/low energy gamma ray flux, and intercalibration of the INTEGRAL instruments with respect to those on RXTE. Cen A was detected by both sets of instruments from 3-240 keV. When combined with earlier archival RXTE results, we find the power law continuum flux and the line-of-sight column depth varied independently by 60% between 2000 January and 2003 March. Including the three archival RXTE observations, the iron line flux was essentially unchanging, and from this we conclude that the iron line emitting material is distant from the site of the continuum emission, and that the origin of the iron line flux is still an open question. Taking X-ray spectral measurements from satellite missions since 1970 into account, we discover a variability in the column depth between 1.0 x 10{sup 23} cm{sup -2} and 1.5 x 10{sup 23} cm{sup -2} separated by approximately 20 years, and suggest that variations in the edge of a warped accretion disk viewed nearly edge-on might be the cause. The INTEGRAL OSA 4.2 calibration of JEM-X, ISGRI, and SPI yields power law indices consistent with the RXTE PCA and HEXTE values, but the indices derived from ISGRI alone are about 0.2 greater. Significant systematics are the limiting factor for INTEGRAL spectral parameter determination

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INTEGRAL and RXTE performed three simultaneous observations of the nearby radio galaxy Centaurus A in 2003 March, 2004 January, and 2004 February with the goals of investigating the geometry and emission processes via the spectral/temporal variability of the X-ray/low-energy gamma-ray flux, and intercalibration of the INTEGRAL instruments with respect to those on RXTE. Cen A was detected by both sets of instruments from 3 to 240 keV. When combined with earlier archival RXTE results, we find the power-law continuum flux and the line-of-sight column depth varied independently by 60% between 2000 January and 2003 March. Including the three archival RXTE observations, the iron-line flux was essentially unchanging, and from this we conclude that the iron-line-emitting material is distant from the site of the continuum emission, and that the origin of the iron-line flux is still an open question. Taking X-ray spectral measurements from satellite missions since 1970 into account, we discover a variability in the column depth between 1.0 x 10(23) and 1.5 x 10(23) cm(-2) separated by approximately 20 yr, and suggest that variations in the edge of a warped accretion disk viewed nearly edge-on might be the cause. The INTEGRAL OSA 4.2 calibration of JEM-X, ISGRI, and SPI yields power-law indices consistent with the RXTE PCA and HEXTE values, but the indices derived from ISGRI alone are about 0.2 greater. Significant systematics are the limiting factor for INTEGRAL spectral parameter determination

A High-velocity Scatterer Revealed in the Thinning Ejecta of a Type II Supernova

International audienceWe present deep, nebular-phase spectropolarimetry of the Type II-P/L SN 2013ej, obtained 167 days after explosion with the European Southern Observatory's Very Large Telescope. The polarized flux spectrum appears as a nearly perfect (92% correlation), redshifted (by ∼4000 km s −1) replica of the total flux spectrum. Such a striking correspondence has never been observed before in nebular-phase supernova spectropolarimetry, although data capable of revealing it have heretofore been only rarely obtained. Through comparison with 2D polarized radiative transfer simulations of stellar explosions, we demonstrate that localized ionization produced by the decay of a high-velocity, spatially confined clump of radioactive 56 Ni-synthesized by and launched as part of the explosion with final radial velocity exceeding 4500 km s −1-can reproduce the observations through enhanced electron scattering. Additional data taken earlier in the nebular phase (day 134) yield a similarly strong correlation (84%) and redshift, whereas photospheric-phase epochs that sample days 8 through 97 do not. This suggests that the primary polarization signatures of the high-velocity scattering source only come to dominate once the thick, initially opaque hydrogen envelope has turned sufficiently transparent. This detection in an otherwise fairly typical core-collapse supernova adds to the growing body of evidence supporting strong asymmetries across nature's most common types of stellar explosions, and establishes the power of polarized flux-and the specific information encoded by it in line photons at nebular epochs-as a vital tool in such investigations going forward