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A Review of Recent Hard X-ray Studies of Classical Novae (CNe)

A Review of Recent Hard X-ray Studies of Classical Novae (CNe). M. Tsujimoto (ISAS) & D. Takei (Rikkyo U.). Scope & Goal. Scope : Recent observational results in hard (1-10 keV) and super-hard (10-100 keV) X-rays. An emphasis on Suzaku results. Results in other wavelengths not included.

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A Review of Recent Hard X-ray Studies of Classical Novae (CNe)

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  1. A Review ofRecent Hard X-ray Studies of Classical Novae (CNe) M. Tsujimoto (ISAS) & D. Takei (Rikkyo U.) 4th International MAXI Workshop

  2. Scope & Goal Scope : Recent observational results in hard (1-10 keV) and super-hard (10-100 keV) X-rays. • An emphasis on Suzaku results. • Results in other wavelengths not included. Goal : To conveythree 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. 4th International MAXI Workshop

  3. 1 2 3 3 4 5 6 7 1 2 1 2 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), 2010-07. 4th International MAXI Workshop

  4. 3 4 5 6 7 1 2 1 2 3 1 2 1-1. CNe and hard X-rays Page et al. (2010, MNRAS) Soft (0.3-1.5 keV) • Classical Novae (CNe) • Binary of WD and late-type dwarf/giant. • TNR on WD surface. • Mejecta~10-5-10-6 Mo • Vejecta=103-104 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 (1.5-10 keV) V2491 Cyg 4th International MAXI Workshop

  5. 3 4 5 6 7 1 2 1 2 3 1 2 Lloyd et al. (1992) 1-2. Discovery: V838 Her • 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. 4th International MAXI Workshop

  6. 3 4 5 6 7 1 2 1 2 3 1 2 Page et al. (2010, MNRAS) V2491 Cyg 1-3. Advent of Swift era • 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 4th International MAXI Workshop

  7. 3 4 5 6 7 1 2 1 2 3 1 2 2. Recent results • Evidence for shocks for X-ray plasma. • Non-solar elemental abundance in plasma. • Reestablished accretion after nova. • Non-thermal processes. 4th International MAXI Workshop

  8. 3 4 5 6 7 1 2 1 2 3 1 2 Ne X Mg XI Si XIII S XV V458 Vul Tsujimoto et al. (2009, PASJ) Ness. (2010, AN) V2491 Cyg 2-1. Evidence for shocks Internal Companion 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) WD External 4th International MAXI Workshop

  9. 3 4 5 6 7 1 2 1 2 3 1 2 V382 Vel Mukai & Ishida (2001, ApJ) Takei et al. (in prep., PASJ) V2672 Oph RWD 2-2. Elemental abundance 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 S N CO Mg ONe g=GMWD/RWD 4th International MAXI Workshop

  10. 3 4 5 6 7 1 2 1 2 3 1 2 Fe XXV, Fe XXVI Fe I 2-3. Rekindled accretion 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. 4th International MAXI Workshop

  11. V2491 Cyg 3 4 5 6 7 1 2 1 2 3 1 2 1 2 Takei et al. (Submitted, PASJ) Page et al. (2010, MNRAS) 3 2 3 4 5 4 V2491 Cyg Suzaku XMM-Newton 5 6 Fe I Fe XXV Fe XXVI 2-3. Rekindled accretion 1 6 4th International MAXI Workshop

  12. 3 4 5 6 7 1 2 1 2 3 1 2 Takei et al. (2009, ApJL) V2491 Cyg 2-4. Non-thermal process • Particle acceleration in CN explosions (analogy to SNe and SNRs). • Super-hard (10-100 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]. 4th International MAXI Workshop

  13. 3 4 5 6 7 1 2 1 2 3 1 2 Abdo et al. (2010, Sci) Ne X Mg XI Si XIII S XV Companion WD External V407 Cyg Hachisu & Kato (2010, ApJL) 2-4. Non-thermal process • 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? Suzaku 4th International MAXI Workshop

  14. 3 4 5 6 7 1 2 1 2 3 1 2 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. 4th International MAXI Workshop

  15. 3 4 5 6 7 1 2 1 2 3 1 2 Sokoloski et al. (2006, Nature) Courtesy: T. Yoshida MAXI/GSC spectrum (1 day integration) RS Oph 3. Possible MAXI utility • 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 erg/s @8.5 kpc ~ 0.1 mCrab. • CNe obs.initiated by X-rays, similarly to BH/NS binaries. 4th International MAXI Workshop

  16. END • Swift changed the game completely. • Hard X-rays have potential to address important questions. • MAXI has roles to play in future outlook. 4th International MAXI Workshop

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