Constraints on progenitors of Classical Novae in M31 Ákos Bogdán & Marat Gilfanov MPA, Garching 17 th European White Dwarf Workshop 18/08/2010

Thermonuclear runaway on the surface of white dwarfs WD accretes material in close binary system If critical mass (ΔM~10 -5 M sun ) accreted Nova Increase in brightness: 6-19 mag Classical Novae in a nutshell Ákos Bogdán 17 th European White Dwarf Workshop

Goal: constrain the nature of CN progenitors Method: - accretion of hydrogen-rich material releases energy - if radiated at X-ray wavelengths contributes to total X- ray emission - confront predicted X-ray luminosity with observations Where: bulge of M31 - well observed in X-rays (Chandra) - CNe are well studied: ν=25 yr -1 (Shafter & Irby 2001) Idea Ákos Bogdán 17 th European White Dwarf Workshop

Energy release from one system Energy release from CN progenitors Ákos Bogdán 17 th European White Dwarf Workshop M WD =1M sun R WD =5000 km ΔM=5∙10 -5 M sun (Yaron et al. 2005) ΔE accr ~3∙10 46 erg Mdot=10 -9 M sun /yr Δt =5∙10 4 yr L bol ~2∙10 34 erg/s Consider a white dwarf

Energy release from all progenitors Ákos Bogdán N WD =(ΔM/Mdot)∙ν CN ~ th European White Dwarf Workshop Total number of progenitors: Total bolometric luminosity of progenitors: Comparable to total X- ray luminosity of the bulge of M31! Energy release from CN progenitors

Spectrum of electromagnetic radiation depends on the type of the progenitor Ákos Bogdán 17 th European White Dwarf Workshop Hard X-rays are released from: Magnetic systems: - polars, intermediate polars - aim: constrain their contribution to the CN rate Dwarf novae in quiescence: - aim: constrain the fraction of mass accreted in quiescence Energy release from CN progenitors

The bulge of M31 in X-rays Resolved sources Low mass X-ray binaries SN remnants, supersoft X-ray sources L= erg/s Unresolved emission Multitude of faint discrete sources - Coronally active binaries - Cataclysmic variables L CV,2-10keV =5.7∙10 37 erg/s Truly diffuse emission from hot gas Ákos Bogdán X-ray Optical Infrared 17 th European White Dwarf Workshop

Ákos Bogdán 17 th European White Dwarf Workshop Magnetic Cataclysmic Variables What fraction of CNe is prduced in mCVs? Optically thin bremsstrahlung emission kT ~ 23 keV  absorption correction insignificant (Landi et al. 2009, Brunschweiger et al. 2009) Study the 2-10 keV energy range Bolometric correction ~3.5

Ákos Bogdán 17 th European White Dwarf Workshop No more than ~10% of CNe are produced in mCV Upper limit depends on M WD and Mdot ≈ 85% of WDs are less massive than 0.85 M sun Typical Mdot ≈ 2∙10 -9 M sun /yr (Suleimanov et al. 2005) Realistic upper limit: ~2% Bogdán & Gilfanov 2010 Upper limit on contribution of mCVs Magnetic Cataclysmic Variables

But: in apparent contradiction with our results: 1. Aracujo-Betancor et al. (2005): Fraction of magnetic WDs in the Solar neighborhood is ≈1/5 Ritter & Kolb catalogue (2009): ≈1/3 of CNe arise from mCVs Ákos Bogdán 17 th European White Dwarf Workshop Resolution: accretion rate in mCVs is much lower! In magnetic CVs: Mdot ~ 1.8∙10 -9 M sun /yr (Suleimanov et al. 2005) In non-magnetic CVs: Mdot ~ 1.3∙10 -8 M sun /yr (Puebla et al. 2007) Magnetic Cataclysmic Variables

Ákos Bogdán 1.Aracujo-Betancor (2005): Fraction of magnetic WDs in the Solar neighborhood is ≈1/5 Accretion of the same ΔM takes ~7 times longer in mCVs Lower Mdot in mCVs + If Mdot is smaller, ΔM is larger by factor of ~1.5-2 mCVs undergo CN outburst times less frequently 17 th European White Dwarf Workshop Magnetic Cataclysmic Variables

Ákos Bogdán 2. Ritter & Kolb catalogue (2009): ≈1/3 of CNe arise from mCVs Brighter CNe (Yaron 2005) CNe from mCVs can be observed from larger distance Lower Mdot in mCVs Magnetic Cataclysmic Variables d CV ≈2.2 kpc d mCV ≈6.6 kpc 17 th European White Dwarf Workshop Distance distribution of CNe in Milky Way

DNe show frequent outbursts due to thermal viscous disk instability Bimodal spectral behaviour: In quiescence: Low Mdot (< M sun /yr) Hard X-ray emission from optically-thin boundary layer In outburst: High Mdot (> M sun /yr) UV and soft X-ray emission from optically-thick boundary layer Ákos Bogdán Dwarf Novae 17 th European White Dwarf Workshop In quiescence we observe hard X-rays In outburst soft emission is hidden

Ákos Bogdán Dwarf Novae 17 th European White Dwarf Workshop What fraction of material is accreted in quiescence? Assumptions: ½ of CNe are produced in DNe (Ritter & Kolb 2009) In quiescence: cooling flow model with kT=23 keV (Pandel et al. 2005) Study the 2-10 keV energy range

Ákos Bogdán No more than 10% accreted in quiescence Upper limit depends on M WD and Mdot Typical M WD =0.9 M sun Typical Mdot ≈ M sun /yr Realistic upper limit: ~3% Bogdán & Gilfanov 2010 Upper limit on mass fraction accreted in quiescence 17 th European White Dwarf Workshop Dwarf Novae

No more than ~10% of CNe are produced in magnetic CVs (realistic upper limit ~2%) No more than ~10% of the material is accreted in quiescence in DNe (realistic upper limit ~3%) Results hold for other early-type galaxies Bogdán & Gilfanov, 2010, MNRAS For details: Bogdán & Gilfanov, 2010, MNRAS Ákos Bogdán Summary 17 th European White Dwarf Workshop