Suzaku Discovery of Hard X-ray Pulsations from the Rotating Magnetized White Dwarf, AE Aquarii
Abstract
Since the discovery of cosmic-rays by Hess 1912, the origin and the mechanisms have remained a long-standing mystery in the astrophysics. We noticed that white dwarfs with very strong magnetic field ( 106 G) and rapid spin periods at the same time can have a capability to accelerate particles into 100 TeV energy range, which is comparable to the energies in shock regions of supernova remnants. Thus, we can expect possible non-thermal radiation in the hard X-ray band from magnetized white dwarfs. As an one of the most promising object, the fast rotating magnetized white dwarf, AE Aquarii, was observed with the X-ray satellite Suzaku in 2005 and 2006. As a result, on a sinusoidal spin modulation in the 0.5--10 keV band at the barycentric period of 33.0769±0.0001 s, additional sharp spikes separated by about 0.2 phases are found in the spin-folded hard X-ray light curve. In addition, the phase averaged X-ray spectra can be reproduced by well-known two thermal models with temperatures of 0.53 and 2.90 keV, but the 12-25 keV data requires additional component, which can be explained by either a power-law model with photon index of 1.12-0.62+0.63 or a third thermal component with a temperature of 54-47+26 keV. In this talk, possible emission mechanisms of the hard pulsations are discussed, including in particular non-thermal ones. If the newly discovered hard X-ray pulses are non-thermal origin, and if white dwarfs commonly generate high energy particles, they should be a new candidate of the origin of cosmic rays, as a quiet but numerous acceleration site in the universe.
- Publication:
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AAS/High Energy Astrophysics Division #10
- Pub Date:
- March 2008
- Bibcode:
- 2008HEAD...10.1003T