Super-Hard X-Ray Emission from η Carinae Observed with Suzaku

摘要

We present the Suzaku results of ηCarinae inthe 5-50 keV range conducted twice around the apastron in 2005August for 50 ks and in 2006 February for 20 ks. The X-ray Imaging Spectrometer (XIS) produced hard (5-12 keV)band spectra, resolving K she 11 lines from highly ionized Fe and Ni. The Hard X-ray Detector yielded a significantdetection in the super-hard (1-50 keV) band, which was uncontaminated by near-by sources. We constrained thetemperature of the optically thin thermal plasma emission dominant in the hard band to be 3-4 keV using the K-shellline features with the XIS. We found significant excess emission above the thermal emission in the super-hardband with the PIN, confirming the previous INTEGRAL ISGRI report.The entire 5-50 keV spectra were fitted bya combination of a thermal plasma model plus a flat power-law, or a very hot thermal bremsstrahlung model for theexcess emission. No significant change of the excess emission was found at different epochs within the systematicand statistical uncertainties, and no flare-like flux amplification was seen in the hard band, indicating that the excessemission is a steady phenomenon. We argue that the super-hard emission is attributable to the inverse Compton ofstellar UV photons by non-thermal electrons or to the thermal bremsstrahlung of very hot plasma, and not to thebremsstrahlung by non-thermal electrons colliding with cold ambient matter.