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Title:
Cassiopeia A: On the origin of the hard X-ray continuum and the implication of the observed O Viii Ly-alpha /Ly-beta distribution
Authors:
Bleeker, J. A. M.; Willingale, R.; van der Heyden, K.; Dennerl, K.; Kaastra, J. S.; Aschenbach, B.; Vink, J.
Affiliation:
AA(SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands), AB(Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK), AC(SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands), AD(Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85740 Garching, Germany), AE(SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands), AF(Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85740 Garching, Germany), AG(Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany; Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027, USA; Chandra Fellow)
Publication:
Astronomy and Astrophysics, v.365, p.L225-L230 (2001) (A&A Homepage)
Publication Date:
01/2001
Origin:
EDP Sciences
A&A Keywords:
ISM: SUPERNOVA REMNANTS, ISM: INDIVIDUAL OBJECTS: CAS A, X-RAYS: ISM
DOI:
10.1051/0004-6361:20000048
Bibliographic Code:
2001A&A...365L.225B

Abstract

We present the first results on the hard X-ray continuum image (up to 15 keV) of the supernova remnant Cas A measured with the EPIC cameras onboard XMM-Newton. The data indicate that the hard X-ray tail, observed previously, that extends to energies above 100 keV does not originate in localised regions, like the bright X-ray knots and filaments or the primary blast wave, but is spread over the whole remnant with a rather flat hardness ratio of the 8-10 and 10-15 keV energy bands. This result does not support an interpretation of the hard X-radiation as synchrotron emission produced in the primary shock, in which case a limb brightened shell of hard X-ray emission close to the primary shock front is expected. In fact a weak rim of emission near the primary shock front is discernable in the hardest X-ray image but it contains only a few percent of the hard X-ray emissivity. The equivalent width of the Fe-K line blend varies by more than an order of magnitude over the remnant, it is hard to explain this as Fe-emission from the reverse shock heated ejecta given the ejecta temperature and the age of the remnant. The uniquely high wavelength-dispersive RGS-spectrometer has allowed, for the first time, to extract monochromatic images in several highly ionised element species with high spectral resolution. We present here a preliminary result on the measurement of the O Viii Ly-alpha and Ly-beta brightness distribution and brightness ratios. The large observed decrease of the Ly-alpha /Ly-beta ratio going from the N to the SE can be explained by small-scale (10arcsec ) variations in the N_H column over the remnant and the potential presence of resonance scattering of the O Viii Ly-alpha photons in the limb brightened shell.
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