suzaku observation of a white dwarf as a new candidate of cosmic-ray origin

The X-ray Universe 2008The X-ray Universe 2008 27— 30 May 2008, @Granada, Spain27— 30 May 2008, @Granada, Spain

11/11/11

SuzakuSuzaku observation of a White observation of a White Dwarf Dwarf

as a new Candidate of as a new Candidate of Cosmic-ray OriginCosmic-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. Based on Terada Y. et. alet. al, 2008 PASJ 60, 387-397, 2008 PASJ 60, 387-397

22/11/11


What is the Cosmic-ray origin ?What is the Cosmic-ray origin ?Hillas diagramHillas 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 density3 order of mag. larger

EEmaxmax = = e v B Le v B L ~6x1016(P/1s)-1(B/1012G)(L/106cm)2 eV

for neutron stars case

If MWDs can accelerate particles (even if weak), If MWDs can accelerate particles (even if weak), they become important CR source having large space density.they become important CR source having large space density.If MWDs can accelerate particles (even if weak), If MWDs can accelerate particles (even if weak), they become important CR source having large space density.they become important CR source having large space density.

Magnetized White Dwarfs Magnetized White Dwarfs are one of candidates !!are one of candidates !!

33/11/11


Rotating compact objects, NS vs WDsRotating compact objects, NS vs WDs

Some white dwarfs have induced potential of 10Some white dwarfs have induced potential of 101515 ～～ 10101616 Volts Volts !!!! Enough to accelerate CRs.Enough to accelerate CRs.

Some white dwarfs have induced potential of 10Some white dwarfs have induced potential of 101515 ～～ 10101616 Volts Volts !!!! Enough to accelerate CRs.Enough to accelerate CRs.

Manchester etal 2001Edwards etal 2001

Makishima etal 1999

Terada PhD and references thereinWichramasinghe and Ferrario 2000

Neutron starNeutron star

radiation

Spin axis

Magnetic field

Dynamo of bicyclesDynamo of bicycles

Induced potentialInduced potential 10101616 ～～ 10101818 Volts Volts

Induced potentialInduced potential a few Voltsa few Volts

10101212 ～～ 10101313 Gauss, msec Gauss, msec ～～ sec, 10 kmsec, 10 km

101022 ～～ 101033 Gauss, 100 ms Gauss, 100 ms ～～ sec, 10 cmsec, 10 cm

44/11/11


Previous searchs for non-thermal Previous searchs for non-thermal electrons in white dwarfselectrons in white dwarfs

Radio observations of WD binariesAM Her, AE Aqr, DQ Her, ST LMi, BG Cmi, AR UMa

→ 1 ～ 20 mJy Synchrotron emission? (max. optical flares)AM Hercules ((BB ~30MG, ~30MG, P P ~0.129days)~0.129days)

Flare: (>2 TeV) (5.6±2.1)×10-11 photons/s/cm2 Quiescence: (>0.5TeV) < 6×10-12 photons/s/cm2

Accretion Energy ~ 1033 erg/s, Thermal X-ray ~ 1032 erg/s Non thermal emission ~ 1031 erg/s

Pavelin etal 1994, Bond 2002, Mason&Gray 2007

Non-thermal electrons should exist in WD!Non-thermal electrons should exist in WD!Non-thermal electrons should exist in WD!Non-thermal electrons should exist in WD!

Schlegel etal 1995Bhat etal 1991

Reynolds etal 1991ASCA

Non thermal?

Cyclotron

Black body

e- thermal bremsstrahlung

Thermal

WDWDMSMS

Energy (keV)

Old reports on TeV γ bandMeintjes etal 1992, 1994, Bhat etal 1991

Needs confirmation with recent observatory!

Optical

55/11/11


SuzakuSuzaku observation of a White dwarf observation of a White dwarf ：： AE AquariiAE Aquarii

Magnetic Cataclysmic variables: AE AquriiMagnetic Cataclysmic variables: AE Aqurii

Suzaku observationSuzaku observation

Late starWhite Dwarf

Accretion

X-ray CCD (XIS): separate X-ray CCD (XIS): separate thermal emissionthermal emissionHard X-ray Detector(HXD): Deep Hard X-ray Detector(HXD): Deep non thermalnon thermal search 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 5x1033 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

66/11/11


Discovery of Hard X-ray Pulses!Discovery of Hard X-ray Pulses!

Periodogram around Spin period

PPXISXIS=33.0769s, P=33.0769s, PPINPIN=33.0764+-0.005s=33.0764+-0.005s

Pulse profile in 2005

Well-known thermal modulation Well-known thermal modulation + Sharp pulse in over 4 keV+ Sharp pulse in over 4 keVWell-known thermal modulation Well-known thermal modulation + Sharp pulse in over 4 keV+ Sharp pulse in over 4 keV

10—30 keV10—30 keV

0.5—10 keV0.5—10 keV

New!New!New!New!

77/11/11


The Pulses enhances at flaresThe Pulses enhances at flaresLight curves

Pulse profiles at flares and quiescence

Flares

Norm

Similar to the nature of non-thermal radio/TeV emissionsSimilar to the nature of non-thermal radio/TeV emissionsSimilar to the nature of non-thermal radio/TeV emissionsSimilar to the nature of non-thermal radio/TeV emissions

Crab like???Crab like???

88/11/11


Having Non-thermal spectral property?Having Non-thermal spectral property?

Phase averaged spectra Phase resolved spectra

2.9keV+0.53keV MEKAL (XIS)2.9keV+0.53keV MEKAL (XIS) + + PLPL Index 1.1 Index 1.1 +-+- 0.6 (PIN) 0.6 (PIN)

No Thermal lines in the Pulse spectrumNo Thermal lines in the Pulse spectrumin over 2 keV band.in over 2 keV band.

Photon Index of 2.0 +- 0.3Photon Index of 2.0 +- 0.3or 50 keV MEKAL (PIN)or 50 keV MEKAL (PIN)

Peak

Although it is statistically insufficient, Although it is statistically insufficient, non thermal origin is more feasible.non thermal origin is more feasible.Although it is statistically insufficient, Although it is statistically insufficient, non thermal origin is more feasible.non thermal origin is more feasible.

99/11/11

The X-ray Universe 2008The X-ray Universe 2008 27— 30 May 2008, @Granada, Spain27— 30 May 2008, @Granada, SpainFirst discovery of First discovery of White dwarf equivalent of Pulsars?White dwarf equivalent of Pulsars?

Hard X-ray Power Law component vs NS spectraHard X-ray Power Law component vs NS spectra

Becker and Trumper 1999Possenti et al 2002

Luminosity

AE Aqr

Index

AE Aqr

Dense accretion materials (Difference from NS cases)Dense accretion materials (Difference from NS cases) n = 1011cm-3 (Itoh+ ‘06)

>> Goldreigh&Julian(’69)density 104 cm-3 (Ikhasanov&Bierman’06)

Electric Potential: short-circuited by materials.

Propeller EffectPropeller Effect: Low density at near the WD (<10: Low density at near the WD (<101010cm)cm)→ one possible site ?

WD

Hard X-ray Pulse

Companion staraccretion

Spin down energy (erg/s)

X-r

ay F

lux

(erg

/s)

Where is the acceleration site in the system? Where is the acceleration site in the system?

1010/11/11


What is the emission mechanism?What is the emission mechanism?

① ① Non-thermal bremsstrahlungNon-thermal bremsstrahlung ② ② Inverse Compton scatteringInverse Compton scattering ③ ③ Curvature radiationCurvature radiation

④ ④ Synchrotron radiationSynchrotron radiation

Too small efficiencyToo small efficiency..

Lorents factor of γLorents factor of γ ～～ 101044 (B/10 (B/1055))-1 -1 to generate 30 keV X-ray.to generate 30 keV X-ray. High efficiency with Life time of 8 μsec (B/10High efficiency with Life time of 8 μsec (B/1055))-2-2(γ/10(γ/1044))-1-1

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 1.4Photon index 1.1 is similar to the NS case of 1.4

⑤ ⑤ OthersOthers

Most feasibleMost feasible among themamong them..

Any ideas ?Any ideas ?

1111/11/11


SummarySummary• Suzaku observed a White dwarf binary, AE Aquarii, toSuzaku 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 Suzaku discovered the Hard X-ray pulsationthe Hard X-ray pulsation in over 4 keV in over 4 keV band (both with the XIS and the HXD). The pulse intensityband (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 luminosityof the Pulse. The photon index is 1.1 and the luminosity comes at 0.09% of the Spin down energy (6x10comes at 0.09% of the Spin down energy (6x103333erg/s).erg/s).

• One possibility of the origin of the pulse is SynchrotronOne 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 AE Aquarii should be a white dwarf equivalent of a pulsarwhite dwarf equivalent of a pulsar..

• White dwarfs should play an important contribution to CosmicWhite dwarfs should play an important contribution to Cosmic ray origin as ray origin as silent but numerous particle-acceleration sitesilent but numerous particle-acceleration site..

Please check Terada Y. Please check Terada Y. et. alet. al, 2008 PASJ 60, 387-397, 2008 PASJ 60, 387-397(Free access of PASJ WWW site. http://pasj.asj.or.jp/v60/v60n2.html)(Free access of PASJ WWW site. http://pasj.asj.or.jp/v60/v60n2.html)

suzaku observation of a white dwarf as a new candidate of cosmic-ray origin

Documents