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The X-ray Universe 2008 The X-ray Universe 2008 27— 30 May Spain Suzaku observation of a White Dwarf as a new Candidate of Cosmic-ray Origin.

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Presentation on theme: "The X-ray Universe 2008 The X-ray Universe 2008 27— 30 May Spain Suzaku observation of a White Dwarf as a new Candidate of Cosmic-ray Origin."— Presentation transcript:

1 The X-ray Universe 2008 The X-ray Universe — 30 May 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) Based on Terada Y. et. al, 2008 PASJ 60,

2 The X-ray Universe 2008 The X-ray Universe — 30 May Spain 2/11 What is the Cosmic-ray origin ? Hillas diagram 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 E max = e v B L ~6x10 16 (P/1s) -1 (B/10 12 G)(L/10 6 cm) 2 eV for neutron stars case If MWDs can accelerate particles (even if weak), they become important CR source having large space density. If MWDs can accelerate particles (even if weak), they become important CR source having large space density. Magnetized White Dwarfs are one of candidates !! are one of candidates !!

3 The X-ray Universe 2008 The X-ray Universe — 30 May Spain 3/11 Rotating compact objects, NS vs WDs Some white dwarfs have induced potential of ~ Volts !!  Enough to accelerate CRs. Some white dwarfs have induced potential of ~ Volts !!  Enough to accelerate CRs. Manchester etal 2001 Edwards etal 2001 Makishima etal 1999 Terada PhD and references therein Wichramasinghe and Ferrario 2000 Neutron star radiation Spin axis Magnetic field Dynamo of bicycles Induced potential ~10 18 Volts Induced potential a few Volts ~10 13 Gauss, msec~sec, 10 km 10 2 ~10 3 Gauss, 100 ms~sec, 10 cm

4 The X-ray Universe 2008 The X-ray Universe — 30 May Spain 4/11 Previous searchs for non-thermal electrons in white dwarfs Radio observations of WD binaries AM Her, AE Aqr, DQ Her, ST LMi, BG Cmi, AR UMa → 1 ~ 20 mJy Synchrotron emission? (max. optical flares) ( B ~30MG, P ~0.129days) AM Hercules ( B ~30MG, P ~0.129days) Flare: (>2 TeV) (5.6±2.1)× photons/s/cm 2 Quiescence: (>0.5TeV) < 6× photons/s/cm 2 Accretion Energy ~ erg/s, Thermal X-ray ~ erg/s Non thermal emission ~ erg/s Pavelin etal 1994, Bond 2002, Mason&Gray 2007 Non-thermal electrons should exist in WD! Schlegel etal 1995 Bhat etal 1991 Reynolds etal 1991 ASCA Non thermal? Cyclotron Black body e- thermal bremsstrahlung Thermal WD MS Energy (keV) Old reports on TeV γ band Meintjes etal 1992, 1994, Bhat etal 1991 Needs confirmation with recent observatory! Optical

5 The X-ray Universe 2008 The X-ray Universe — 30 May Spain 5/11 Suzaku observation of a White dwarf : AE Aquarii Magnetic Cataclysmic variables: AE Aqurii Suzaku observation Late starWhite Dwarf Accretion X-ray CCD (XIS): separate thermal emission Hard X-ray Detector(HXD): Deep non thermal search Energy (keV) Main purpose search for non thermal tail in hard X-ray band. 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) 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 5x10 33 erg/s Radio synchrotron flares (Bastian etal 1988, A.Simon etal 1990) Pulsed TeV gamma-rays (Brink etal 1990, Meintjes etal 1992,1994) Low plasma temperature; inhibited accretion (ASCA)  Magnetic propeller effect (XMM; Itoh etal 2006 ) Observation

6 The X-ray Universe 2008 The X-ray Universe — 30 May Spain 6/11 Discovery of Hard X-ray Pulses! Periodogram around Spin period P XIS = s, P PIN = s Pulse profile in 2005 Well-known thermal modulation + Sharp pulse in over 4 keV + Sharp pulse in over 4 keV Well-known thermal modulation + Sharp pulse in over 4 keV + Sharp pulse in over 4 keV 10—30 keV 0.5—10 keV New!New!

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

8 The X-ray Universe 2008 The X-ray Universe — 30 May Spain 8/11 Having Non-thermal spectral property? Having Non-thermal spectral property? Phase averaged spectra Phase resolved spectra 2.9keV+0.53keV MEKAL (XIS) + PL Index (PIN) + PL Index (PIN) No Thermal lines in the Pulse spectrum in over 2 keV band.  Photon Index of or 50 keV MEKAL (PIN) Peak Although it is statistically insufficient, non thermal origin is more feasible. Although it is statistically insufficient, non thermal origin is more feasible.

9 The X-ray Universe 2008 The X-ray Universe — 30 May Spain 9/11 First discovery of White dwarf equivalent of Pulsars? Hard X-ray Power Law component vs NS spectra Becker and Trumper 1999 Possenti et al 2002 Luminosity AE Aqr Index AE Aqr Dense accretion materials (Difference from NS cases) n = cm -3 (Itoh+ ‘ 06) >> Goldreigh&Julian( ’ 69)density 10 4 cm -3 (Ikhasanov&Bierman ’ 06)  Electric Potential: short-circuited by materials. Propeller Effect: Low density at near the WD (<10 10 cm) → one possible site ? WD Hard X-ray Pulse Companion star accretion Spin down energy (erg/s) X-ray Flux (erg/s) Where is the acceleration site in the system?

10 The X-ray Universe 2008 The X-ray Universe — 30 May Spain 10/11 What is the emission mechanism? ① Non-thermal bremsstrahlung ② Inverse Compton scattering ③ Curvature radiation ④ Synchrotron radiation  Too small efficiency. Lorents factor of γ ~ 10 4 (B/10 5 ) -1 to generate 30 keV X-ray. Lorents factor of γ ~ 10 4 (B/10 5 ) -1 to generate 30 keV X-ray. High efficiency with Life time of 8 μsec (B/10 5 ) -2 (γ/10 4 ) -1 High efficiency with Life time of 8 μsec (B/10 5 ) -2 (γ/10 4 ) -1 Can generate anisotropic emission to generate sharp signal Can generate anisotropic emission to generate sharp signal Photon index 1.1 is similar to the NS case of 1.4 Photon index 1.1 is similar to the NS case of 1.4 ⑤ Others  Most feasible among them. Any ideas ?

11 The X-ray Universe 2008 The X-ray Universe — 30 May Spain 11/11 Summary Suzaku observed a White dwarf binary, AE Aquarii, to Suzaku observed a White dwarf binary, AE Aquarii, to search for possible non-thermal emission from the system. search for possible non-thermal emission from the system. Suzaku discovered the Hard X-ray pulsation in over 4 keV Suzaku discovered the Hard X-ray pulsation in over 4 keV band (both with the XIS and the HXD). The pulse intensity band (both with the XIS and the HXD). The pulse intensity enhances at the soft-X flares. enhances at the soft-X flares. There are no thermal lines in the phase resolved spectra There are no thermal lines in the phase resolved spectra of the Pulse. The photon index is 1.1 and the luminosity of the Pulse. The photon index is 1.1 and the luminosity comes at 0.09% of the Spin down energy (6x10 33 erg/s). comes at 0.09% of the Spin down energy (6x10 33 erg/s). One possibility of the origin of the pulse is Synchrotron One possibility of the origin of the pulse is Synchrotron emission from low density region near the white dwarf. emission from low density region near the white dwarf. AE Aquarii should be a white dwarf equivalent of a pulsar. AE Aquarii should be a white dwarf equivalent of a pulsar. White dwarfs should play an important contribution to Cosmic White dwarfs should play an important contribution to Cosmic ray origin as silent but numerous particle-acceleration site. ray origin as silent but numerous particle-acceleration site. Please check Terada Y. et. al, 2008 PASJ 60, (Free access of PASJ WWW site.


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