The X-ray Universe 2008 27 30 May 2008

The X-ray Universe 2008 27— 30 May 2008, @Granada, Spain Suzaku observation of a White Dwarf as a new Candidate of Cosmic-ray Origin Yukikatsu Terada (Saitama Univ), T. Hayashi (Tokyo Metro. Univ), M. Ishida (ISAS/JAXA), K. Makishima (U. Tokyo; RIKEN), K. Mukai(NASA/GSFC), T. Dotani, S. Okada, A. Bamba, R. Nakamura (ISAS/JAXA), S. Naik(Physics Research lab, India), and K Morigami (Saitama Univ) /11 Based on Terada Y. al, 2008 PASJ 60, 387 -397 et.

27— 30 May 2008, @Granada, Spain The X-ray Universe 2008 What is the Cosmic-ray origin ? Hillas diagram Emax = e v B L ~6 x 10 16 (P/1 s)-1 (B/1012 G)(L/106 cm)2 e. V for neutron stars case Neutron Stars and White Dwarfs Magnetic field B : 3 -4 order of mag. smaller Rotation velocity v ∝ P -1 : 4 order of mag. Smaller System Length. L : 3 order of mag. larger Space density 3 order of mag. larger If MWDs can accelerate particles (even if weak), they become important CR source having large space density. 2/11

The X-ray Universe 2008 27— 30 May 2008, @Granada, Spain Rotating compact objects, NS vs WDs Terada Ph. D and references therein Wichramasinghe and Ferrario 2000 Manchester etal 2001 Edwards etal 2001 Makishima etal 1999 Dynamo of bicycles 102～ 103 Gauss, 100 ms～sec, 10 cm ms～ Induced potential a few Volts Spin axis Magnetic field radiation Neutron star 1012～ 1013 Gauss, msec～sec, 10 km msec～ Induced potential 1016～ 1018 Volts Some white dwarfs have induced potential of 1015 ～ 1016 Volts !! Enough to accelerate CRs. 3/11

27— 30 May 2008, @Granada, Spain The X-ray Universe 2008 Previous searchs for non-thermal electrons in white dwarfs Radio observations of WD binaries Pavelin etal 1994, Bond 2002, Mason&Gray 2007 AM Her, AE Aqr, DQ Her, ST LMi, BG Cmi, AR UMa → 1 ～ 20 m. Jy Synchrotron emission? (max. optical flares) AM Hercules (B ~30 MG, P ~0. 129 days) ASCA Reynolds etal 1991 Bhat etal 1991 Schlegel etal 1995 Cyclotron Black body 2 (5. 6± 2. 1)× 10 -11 photons/s/cm Non thermal? Thermal Optical Meintjes etal 1992, 1994, Bhat etal 1991 Flare: (>2 Te. V) e- thermal bremsstrahlung MS Old reports on Te. V γ band WD Quiescence: (>0. 5 Te. V) 2 < 6× 10 -12 photons/s/cm Needs confirmation with recent observatory! Accretion Energy ~ 1033 erg/s, 　Thermal X-ray ~ 10 32 erg/s 31 　Non thermal emission ~ 10 erg/s Energy (ke. V) Non-thermal electrons should exist in WD! 4/11

27— 30 May 2008, @Granada, Spain The X-ray Universe 2008 Suzaku observation of a White dwarf： AE Aquarii Magnetic Cataclysmic variables: AE Aqurii Accretion White Dwarf • Fastest rotator among MCVs with ~33 sec period (close to break-up condition; Casares etal 1996) • Stable spin down for 20 years (de Jager 1991, Mauche 2006), spin down energy 5 x 1033 erg/s • Radio synchrotron flares (Bastian etal 1988, A. Simon etal 1990) • Pulsed Te. V gamma-rays (Brink etal 1990, Meintjes etal 1992, 1994) Late star • Low plasma temperature; inhibited accretion (ASCA) Magnetic propeller effect (XMM; Itoh etal 2006) Suzaku observation Main purpose search for non thermal tail in hard X-ray band. Observation Energy (ke. V) X-ray CCD (XIS): separate thermal emission Hard X-ray Detector(HXD): Deep non thermal search 2005/10/30 21: 39 – 11/02 1: 02 70 ksec (XIS) / 53 ksec (HXD) 2006/10/25 05: 34 – 10/26 9: 11 47 ksec (XIS) / 41 ksec (HXD) 5/11

27— 30 May 2008, @Granada, Spain The X-ray Universe 2008 Discovery of Hard X-ray Pulses! Periodogram around Spin period Pulse profile in 2005 0. 5— 10 ke. V 10— 30 ke. V New ! PXIS=33. 0769 s, PPIN=33. 0764+-0. 005 s Well-known thermal modulation 6/11 + Sharp pulse in over 4 ke. V

27— 30 May 2008, @Granada, Spain The X-ray Universe 2008 The Pulses enhances at flares Light curves Flares Norm Pulse profiles at flares and quiescence Crab like? ? ? Similar to the nature of non-thermal radio/Te. V emissions 7/11

27— 30 May 2008, @Granada, Spain The X-ray Universe 2008 Having Non-thermal spectral property? Peak Phase averaged spectra 2. 9 ke. V+0. 53 ke. V MEKAL (XIS) + PL Index 1. 1 +- 0. 6 (PIN) or 50 ke. V MEKAL (PIN) Phase resolved spectra No Thermal lines in the Pulse spectrum in over 2 ke. V band. Photon Index of 2. 0 +- 0. 3 Although it is statistically insufficient, non thermal origin is more feasible. 8/11

27— 30 May 2008, @Granada, Spain First discovery of Hard X-ray Power Law component vs NS spectra White dwarf equivalent of Pulsars? The X-ray Universe 2008 Index AE Aqr X-ray Flux (erg/s) Luminosity Becker and Trumper 1999 Possenti et al 2002 AE Aqr Where is the acceleration site in the system? accretion Hard X-ray Pulse WD Spin down energy (erg/s) Companion star Dense accretion materials (Difference from NS cases) n = 1011 cm-3 (Itoh+ ‘ 06) >> Goldreigh&Julian(’ 69)density 104 cm-3 (Ikhasanov&Bierman’ Electric Potential: short-circuited by materials. Propeller Effect: Low density at near the WD (<1010 cm) 9/11 → one possible site ?

The X-ray Universe 2008 27— 30 May 2008, @Granada, Spain What is the emission mechanism? ① Non-thermal bremsstrahlung ② Inverse Compton scattering ③ Curvature radiation Too small efficiency. ④ Synchrotron radiation Most feasible among them. ü Lorents factor of γ～ 104 (B/105)-1 to generate 30 ke. V X-ray. ü High efficiency with Life time of 8 μsec (B/105)-2(γ/104)-1 ü Can generate anisotropic emission to generate sharp signal ü Photon index 1. 1 is similar to the NS case of 1. 4 ⑤ Others Any ideas ? 10/11

The X-ray Universe 2008 Summary 27— 30 May 2008, @Granada, Spain • Suzaku observed a White dwarf binary, AE Aquarii, to search for possible non-thermal emission from the system. • Suzaku discovered the Hard X-ray pulsation in over 4 ke. V band (both with the XIS and the HXD). The pulse intensity enhances at the soft-X flares. • There are no thermal lines in the phase resolved spectra of the Pulse. The photon index is 1. 1 and the luminosity comes at 0. 09% of the Spin down energy (6 x 1033 erg/s). • One possibility of the origin of the pulse is Synchrotron emission from low density region near the white dwarf. AE Aquarii should be a white dwarf equivalent of a pulsar. • White dwarfs should play an important contribution to Cosmic ray origin as silent but numerous particle-acceleration site. 11/11 Please check Terada Y. al, 2008 PASJ 60, 387 -397 et.