A Review of Recent Hard X-ray Studies of Classical Novae (CNe) M. Tsujimoto (ISAS) & D. Takei (Rikkyo U.) 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop 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 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. 2010/11/30-2010/12/2 4th International MAXI Workshop

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), 2010-07. 1 2 3 1 2 3 4 5 6 7 1 2 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop 1 2 3 4 5 6 7 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 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop 1 2 3 4 5 6 7 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. 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop 1 2 3 4 5 6 7 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 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop 1 2 3 4 5 6 7 2. Recent results Evidence for shocks for X-ray plasma. Non-solar elemental abundance in plasma. Reestablished accretion after nova. Non-thermal processes. 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop 1 2 3 4 5 6 7 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 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop 1 2 3 4 5 6 7 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 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop 1 2 3 4 5 6 7 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. 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop 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 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop 1 2 3 4 5 6 7 2-4. Non-thermal process Takei et al. (2009, ApJL) V2491 Cyg 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]. 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop 1 2 3 4 5 6 7 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 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop 1 2 3 4 5 6 7 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. 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop 1 2 3 4 5 6 7 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 erg/s @8.5 kpc ~ 0.1 mCrab. CNe obs. initiated by X-rays, similarly to BH/NS binaries. 2010/11/30-2010/12/2 4th International MAXI Workshop

4th International MAXI Workshop END Swift changed the game completely. Hard X-rays have potential to address important questions. MAXI has roles to play in future outlook. 2010/11/30-2010/12/2 4th International MAXI Workshop