1. A Review of Recent Hard X-ray Studies of Classical Novae (CNe)
M. Tsujimoto (ISAS) & D. Takei (Rikkyo U.)
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2. 4th International MAXI Workshop
Scope & Goal
Scope : Recent observational results in hard (1-10 keV) and super-hard ( keV) X-rays.
An emphasis on Suzaku results.
Results in other wavelengths not included.
Goal : To convey three ideas.
Swift changed the game completely.
– Expanded opportunities for hard X-ray obs. from CNe.
Hard X-rays have potential to address important questions.
– Non-thermal processes in CNe, WD mass and evolution.
MAXI has some roles to play in future outlook.
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3. 4th International MAXI Workshop
Talk plan
Historical context.
Recent results.
Future outlook.
Further reading:
“Classical Novae 2nd edition” M. F. Bode and A. Evans (2008), Cambridge Astrophysics Series Vol. 43
“X-ray Observations of Classical Novae” D. Takei (2010), Astronomical Herald (天文月報), 1 2 3 1 2 3 4 5 6 7 1 2
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1-1. CNe and hard X-rays
Page et al. (2010, MNRAS)
Soft ( keV)
Classical Novae (CNe)
Binary of WD and late-type dwarf/giant.
TNR on WD surface.
Mejecta~ Mo
Vejecta= km/s
~10/yr discovered.
Soft (< 1 keV) X-rays
Emission from heated WD atmosphere; a.k.a. SSS.
Hard (>1 keV) X-rays
Early appearance.
Different flux evolution.
Hard ( keV)
V2491 Cyg
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1-2. Discovery: V838 Her
Lloyd et al. (1992)
Hard X-rays discovered by ROSAT ToO observation on day 5 of V838 Her in 1991.
Lloyd et al. (1992, Nature)
Distinctive from SSS emission in early appearance & spectral hardness.
Interpreted as plasma by ejecta shocks.
O’Brien+ (1994, MNRAS), Mukai & Ishida (2001, ApJ), etc.
Hard X-rays in post CN explosions are rare; faint and disappear quickly.
Orio+ (A&A, 2001), Ness+ (ApJ, 2007), etc.
ToO observations risky.
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1-3. Advent of Swift era
V2491 Cyg
Page et al. (2010, MNRAS)
Swift (2004-) changed the game completely.
X-ray snapshots for optically-discovered bright CNe at a high cadence from day >1.
Observations by “observatory-type” satellites (Chandra, XMM-Newton, Suzaku) planned when most needed.
Data by advanced technologies (CCD & grating spectroscopy, high-resolution imaging, super-hard band detectors, ...) accumulated.
Suzaku
XMM-Newton
V2491 Cyg
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2. Recent results
Evidence for shocks for X-ray plasma.
Non-solar elemental abundance in plasma.
Reestablished accretion after nova.
Non-thermal processes.
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2-1. Evidence for shocks
Tsujimoto et al. (2009, PASJ)
V458 Vul
Internal
Companion
Ne X
Mg XI
Si XIII
Accumulating evidence for the shock origin of the hard X-ray plasma.
Emission lines from optically-thin thermal plasma.
Blue-shifted absorption.
Shocks:
Internal shocks: collision among nova winds at different velocities.
External shocks: collision of winds by nova and companion (recurrent novae, symbiotic novae)
S XV WD
External
Ness. (2010, AN)
V2491 Cyg
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2-2. Elemental abundance
Takei et al. (in prep., PASJ)
V2672 Oph
Mukai & Ishida (2001, ApJ)
V382 Vel
Si XIII, Si XIV
Metal abundances (N, O, Ne, Mg, Si, S, Ar, Fe) : [m/H]CN/[m/H]solar (assuming [He/H]CN=[He/H]solar).
Plasma abundance reflects WD core composition and nuclear products. An indicator of MWD.
V458 Vul speculated to be ONe-type by X-ray. Confirmed to be CO-type by optical.
Fe deficiency.
Reason unknown; Non-equilibrium ionization, dust condensation, sinking deep into WD?
M(i)WD<~1.1Mo
M(i)WD>~1.1Mo
Accretion
Mixing
Synthesizing C O Si N S CO Mg
ONe
g=GMWD/RWD
RWD
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2-3. Rekindled accretion
Fe XXV, Fe XXVI
Fe I WD
Accretion process stops after a CN. How early does it resume?
Some CNe occur in magnetized WDs (~10 IPs; BWD~106 gauss, 1 Polar; BWD>107 gauss).
IPs = Strong emitters of Fe lines (Fe I, Fe XXV, & Fe XXVI) powered by accretion.
Reestablished accretion probed w. Fe lines.
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Takei et al. (Submitted, PASJ)
V2491 Cyg 1 2 3 4 5 6 1 2 3 4 5 6 7
Fe I
Fe XXV
Fe XXVI
2-3. Rekindled accretion
V2491 Cyg
Page et al. (2010, MNRAS)
Suzaku
XMM-Newton 1 2 3 4 5 6
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2-4. Non-thermal process
Takei et al. (2009, ApJL)
V2491 Cyg
Particle acceleration in CN explosions (analogy to SNe and SNRs).
Super-hard ( keV) band X-rays.
Upper limit in V382 Vel (SAX; Orio et al. 2001, MNRAS).
Detection in V2491 Cyg (Suzaku; Takei et al. 2010, ApJL)
GeV gamma-rays
Detection in V407 Cyg (Fermi; Abdo et al. 2010, Sci).
Talk by Dr. Hays [O-12].
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Abdo et al. (2010, Sci)
V407 Cyg
2-4. Non-thermal process
Hachisu & Kato (2010, ApJL)
GeV emission from V407 Cyg.
Radiation: IC or p0 decay.
Acceleration: Shock acceleration at ext. shock.
Superhard X-ray emission from V2491 Cyg.
Radiation: Synchrotron, IC, brems, ?
Acceleration: DSA inconsistent w. observed G=0.1. Some exotic mechanims?
Ne X
Mg XI
Si XIII
S XV
Companion WD
External
Suzaku
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3. Future outlook
Unique capabilities of hard X-rays.
Penetrating power through the Galactic plane.
Coverage of both thermal & non-thermal features.
Diagnoses of MWD (still immature).
Problems within reach of hard X-rays.
Abundance pattern to distinguish C-O/O-Ne type WDs.
Mass distribution of Galactic CNe. How many WDs close to Mch? Do they gain or lose mass?
Post-nova evolution of non-thermal emission.
Differences in hard X-rays between magnetic & non- magnetic WDs.
Cause for the Fe deficiency.
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Sokoloski et al. (2006, Nature)
RS Oph
3. Possible MAXI utility
Courtesy: T. Yoshida
MAXI/GSC spectrum
(1 day integration)
Post-nova evolution of non-thermal emission.
Any relation with curious optical behavior?
Super-hard non-thermal emission detected from one source (V2491 Cyg) only once.
RS Oph by RXTE (Sokoloski et al. 2006, Nature).
Unbiased survey of CNe.
Histogram of MWD.
Current survey (only in optical) biased for low MWD.
MAXI sensitivity is insufficient, but attempt exists (Shimanoe et al. [P-35]).
SuperMAXI?
2x1034 kpc ~ 0.1 mCrab.
CNe obs. initiated by X-rays, similarly to BH/NS binaries.
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END
Swift changed the game completely.
Hard X-rays have potential to address important questions.
MAXI has roles to play in future outlook.
2010/11/ /12/2
4th International MAXI Workshop