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Explosion, turn-off and recovery of accretion in novae revealed by X-rays Margarita Hernanz Institut de Ciències de l’Es

Explosion, turn-off and recovery of accretion in novae revealed by X-rays Margarita Hernanz Institut de Ciències de l’Espai (CSIC-IEEC) - Barcelona (Spain) . OUTLINE Classical and recurrent novae explosions: scenarios Origin of X-ray emission

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Explosion, turn-off and recovery of accretion in novae revealed by X-rays Margarita Hernanz Institut de Ciències de l’Es

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  1. Explosion, turn-off and recovery of accretion in novae revealed by X-rays Margarita Hernanz Institut de Ciències de l’Espai (CSIC-IEEC) - Barcelona (Spain)

  2. OUTLINE • Classical and recurrent novae explosions: scenarios • Origin of X-ray emission • Summary of X-ray observations - Theoretical implications • Possibility to accelerate cosmic rays in novae (symbiotic recurrent) : RS Oph and V407 Cyg • Conclusions

  3. White dwarfs • Endpoints of stellar evolution (M< 10M): no Enuc available; compression until electrons become degenerate • Chemical composition: He, CO, ONe; masses: typical 0.6 M, maximum: MChandrasekhar (~1.4M) • When isolated, they cool down to very low L (~10-4.5L): • When in interacting binary systems, they can explode

  4. White dwarfs in close binary systems Symbiotic system: WD + Red Giant accretion from a red giant wind Cataclysmic variable: WD + Main Sequence Roche lobe overflow Classical nova Recurrent nova Hydrogen burning in degenerate conditions on top of the white dwarf Credit: David Hardy Prec~104-105 yr; Porb~hr-day a~few 105 km~ few 1010cm rate ~35/yr in Galaxy Prec<100 yrs; Porb~100’s days a ~1013-1014 cm rate ~10 known in Galaxy

  5. In recurrent novae, initial mass of the WD should be very large (close to Chandrasekhar mass), to drive such frequent outbursts • Feasible scenario of type Ia supernova explosions, provided that less mass is ejected than accreted in each explosion • X-ray observations: way to study if WD mass grows or diminishes after each nova explosion • Solve the controversy between single degenerate and double degenerate scenarios of type Ia supernovae Credit: David Hardy

  6. Scenario for classical novae Mass transfer from the companion star onto the white dwarf (cataclysmic variable) Hydrogen burning in degenerate conditions on top of the white dwarf Thermonuclear runaway Explosive H-burning Decay of short-lived radioactive nuclei in the outer envelope (transported by convection) Envelope expansion, L increase and mass ejection

  7. Novae observations: optical light curve apparent luminosity (mv) time L increases very fast by factors greater than104 -absolute Lmax~104-5L

  8. Novae observations: light curves UV satellites: Lbol(LV+LUV)=ct. V+UV FH Ser 1970 - Gallagher & Code 1974 V TOT V UV Lbol(LV+LUV+ LIR) =ct. IR Nova Cyg 1978 – Stickland et al. 1981 IR emission dust formation

  9. Photosphere recedes as matter expands and becomes transparent Supersoft X-ray emission reveals the hot white dwarf photosphere, close to the burning shell

  10. Origin of X-ray emission (I) • Residual steady H-burning on top of the white dwarf: • photospheric emission from the hot WD: • Teff~ (2-10)x105K (L~1038erg/s) supersoft X-rays • detected by ROSAT/PSPC in only 3 classical novae, out of 39 observed up to 10 years after explosion: • GQ Mus (N Mus1983), N Cyg 1992, N LMC 1995 • (Orio et al. 2001). A few more detections with BeppoSAX, Chandra, XMM-Newton; many more with Swift/XRT • duration related to H-burning turn-off time. “Old” theory: τnuc~100yr; observations: <9 - 12 yr; typically: < 2yr • new models: L-MH,rem-Teff compatible with short durationof soft X-ray phase (Tuchmann & Truran 1998; Sala & Hernanz, 2005)  very small remnant H-mass

  11. Origin of X-ray emission (II) • Internal (external) shocks in the ejecta:thermal plasma emission • detected early after explosion (N Her 1991, N Pup 1991, N Cyg 1992, N Vel 1999): internal shocks; recurrent nova RS Oph: external, V2491 Cyg 2008 ? • Reestablished accretion: emission “as a CV” (idem) • Hard (but also soft) X-rays, depending on the thermal plasma T

  12. Origin of X-ray emission (II, cont’d) • Restablished accretion: • emission “CV-like” How and when? • Interaction between ejecta and new accretion flow? • Magnetic or non magnetic white dwarf?

  13. Origin of X-ray emission (III) • Compton degradation of γ-rays emitted by classical novae CAN NOT be responsible of their early hard X-ray emission: • Cut-off at 20 keV (photoelectric abs.) • Fast disappearence: 2days (w.r.t Tmax,i.e., before visual outburst) Gómez-Gomar,Hernanz,José,Isern, 1998, MNRAS

  14. Observations– Supersoft X-ray emission • EXOSAT and ROSAT discoveries: • GQ Mus (1983):1st detection of X-rays in a nova, EXOSAT (Ögelman et al. 1984). One of the longest supersoft X-ray phases: 9 yrÖgelman et al.1993; Shanley et al. 1995; Orio et al. 2001; Balman & Krautter 2001 • V1974 Cyg (1992): complete light curve with ROSAT- rise, plateau and decline – 1.5 yrKrautter et al. 1996, Balman et al. 1998 • N LMC 1995: ROSAT & XMM-Newton – 8 yrs • ROSAT discovery Orio &Greiner 1999[XMM-Newton obs.Orio et al. 2003]

  15. V1974 Cyg (1992): ROSAT’s soft X-ray light curve rise: until day 147 plateau: 18 months BB fits not good – too large L Krautter et al. 1996, ApJ ONe WD atmospheres MacDonald & Vennes Balman et al. 1998, ApJ

  16. V1974 Cyg (1992): ROSAT’s soft X-ray spectra F=6x10-10erg/cm2/s kTBB=21eV, kTbr=0.32keV F=3.2x10-9erg/cm2/s kTBB=30eV ( kTbr=0.002keV) F=3x10-11erg/cm2/s kTBB=20 eV,kTbr=0.29keV F=3.1x10-9erg/cm2/s kTBB=30eV (kTbr=0.002keV)

  17. Models that best explain the supersoft X-ray emission of V1974 Cyg 1992 and its evolution • WD envelope models with steady H-burning (no accretion) • Mwd=0.9 M, 50% mixing with CO core (but V 1974Cyg 1992 was a neon nova!) • or • Mwd=1.0 M, 25% mixing with ONe core • [in goog agreement with models of the optical and UV light curve (Kato & Hachisu, 2006)] • Menv~2x10-6 M • WD properties from X-ray observation of turn-off Sala & Hernanz, A&A 2005

  18. Observations– Supersoft X-ray emission • BeppoSAX V382 Vel (1999): supersoft X-ray flux not constant; model atmosphere not a good fit; emission lines from highly ionized nebula were required (Orio et al 2002) Chandra grating observations detected emission lines (Burwitz et al., 1992, Ness et al. 2005). Turn-off 7-9 months

  19. Observations– Supersoft X-ray emission • Chandra LETGS: • V382 Vel (1999) • Burwitz et al. 2002 • Ness et al. 2005

  20. Observations – Supersoft X-ray emission • Chandra and XMM-Newton (novae in outburst) • puzzling temporal behaviours • grating observations • V1494 Aql (1999) -burst and pulsationsDrake et al. 2003 • V4743 Sgr (2002) - strong variability and complex spectra Ness et al 2003, Rauch, Orio, González Riestra et al., 2010: fits with NLTE WD atmospheric models •  see Rauch’s talk – C1

  21. Observations – Supersoft X-ray emission V4743 Sgr (2003) Temporal variability: P ~ 22 min. Ness et al. 2003, ApJ

  22. Observations – Supersoft X-ray emission V4743 Sgr (2003) Non LTE model atmospheres Rauch, Orio, González-Riestra et al., 2010, ApJ

  23. Observations – Supersoft X-ray emission • XMM-Newton • Monitoring campaigns of post-outburst novae • Nova LMC 1995 - Orio et al. 2003: H-burning still on in 2000 •  see Orio’s talk C2, about Nova LMC 2009 • Galactic novae V5115 Sgr and V5116 Sgr 2005: Hernanz, Sala et al.

  24. XMM-Newton - AO1 Cycle -Summary • No supersoft X-ray emission related to residual H-burning detected •  all novae had already turned-off • 3 out of 5 were emitting [thermal plasma (+ BB)] spectrum  ejecta/accretion

  25. Supersoft X-ray emission related to residual H-burning found in 2 novae from 2005 (V5115 Sgr & V5116 Sgr) novae had not turned-off yet

  26. Nova Sgr 2005 b – V5116 Sgr – 610 days post-outburst partial eclipse by an asymmetric disk? Sala, Hernanz, Ferri & Greiner, ApJL 2008

  27. Nova Sgr 2005 b – V5116 Sgr – 610 days post-outburst RGS spectra Sala,Hernanz, Ferri, Greiner, AN (2010)

  28. Nova Sgr 2005 b – V5116 Sgr: new obs. March 20091348 days post-outburst U filter L=(3-7)x1032 erg/s (10 kpc) Swift/XRT light light curve SSS turn-off: 2 - 3 years post-outburst compatible with Hachisu & Kato (2007) prediction

  29. SUMMARY of XMM-Newton campaign on Galactic novae • 11 novae have been observed between 3 months and 5 years after outburst (9 years) • Only 2, V5115 Sgr 2005a and V51116 Sgr 2005b, were still bright in supersoft X-rays, revealing remaining H-nuclear burning – one of them with a puzzling temporal behavior • SSS phase absent means that either we missed it or Mejected > Maccreted: Mwd decreases after each nova outburst  WD can’t reach MCHANDRA and explode as SNIa

  30. Observations – Supersoft X-ray emission • Swift/XRT • Ness et al. 2007, Osborne (today’s talk, C1) • The largest sample. Example: two extreme cases • V723 Cas (1995): L and Teff not well determined (BB) Ness et al. 2008 – Still SSS 12 yrs after outburst.New XMM-Newton observations in 2010, still active • V2491 Cyg (2008): duration SS phase10 days • Also observed with XMM-Newton and Suzaku: Ness et al. 2011, Takei et al. 2011

  31. Observations – Supersoft X-ray emission • V723 Cas (1985) • Swift observations in 2007: Ness et al. 2008, MNRAS • not turned-off yet • XMM-Newton obs. in 2010: still on

  32. Observations – Supersoft X-ray emission V2491 Cyg (2010) Page et al., 2010, MNRAS (Other interest of this nova: later)

  33. Observations – Supersoft X-ray emission V2491 Cyg (2010) Ness et al. 2011

  34. SUMMARY of Swift/XRT campaign From Julian Osborne: see talk in C1

  35. 2007-2008 Novae in M31 XMM-Newton & Chandra monitoring: d and line of sight absorption known Henze et al. 2011, A&A 2008-2009  see talks by Henze C1 Pietsch C2 this afternoon

  36. Observationsof novae where H has turned off : Recovery of accretion and/or ejecta emission

  37. 6.7 keV Fe XXV neutral Fe Kα fluorescence line 6.4 keV 6.97 keV FeXXVI Nova Oph 1998 = V2487 Oph - 4.3 yrs post explosion • Identification of three Fe Kαemission lines: ~neutral Fe: 6.4 keV He-like Fe: 6.68 keV H-like Fe: 6.97 keV • If Thigh ~ (10-20) keV, He-like and H-like lines well reproduced & only 6.4 keV fluorescent line added • If complex absorption -partial covering absorber- low (ISM)+ high NH Thigh~(10-20) keV Fluorescent Fe Kα line at 6.4 keVreveals reflection on cold matter (disk and/or WD): accretion

  38. Lunabs[0.2-10 keV]= 8.4 x1034 erg/s +0.2 -0.4 NH=2x1021 cm-2 (frozen) +0.3 -0.1 +20 -30 Tbb=120 eV +0.6 -0.4 Covf=0.6±0.1 +8 -3 Lbb=4±1 x1034 erg/s +10 -8 NHPCA=24 x1022 cm-3 Tlow=0.3 keV EMlow=0.5 x1057 cm-3 Thigh=13 keV EMhigh=6±1 x1057 cm-3 Nova Oph 1998 = V2487 Oph 4.3 yrs post explosion d=10 kpc • LBB ~ 50% LTOT[0.2-10] keV - f(emitting surface/wd surface)~10-4 (hot spots) • Luminosity, spectral shape .. Intermediate polar? need Pspinvs. Porb

  39. N Oph 1998 = V2487 Oph Mar. 24, 2007 8.8yr post outburst • Spectral model: similar to previous observations • No clear periodicities in X-rays, but hint of orbital period ≈ 6.5 hrs • Optical observations seem to confirm the orbital P

  40. V2487 Oph (1998): 1st nova seen in X-rays before its explosion (ROSAT) Positional correlation with a source previously discovered by ROSAT (RASS) in 1990 suggests that the “host” of the nova explosion had been seen in X-rays before the outburst (Hernanz & Sala 2002, Science) new case: V2491 Cyg (2008b): previous ROSAT, XMM and SWIFT detections(Ibarra et al. 2009, A&A)

  41. Nova Oph 1998 = V2487 Oph Hard X-rays • Detection with INTEGRAL/IBIS survey in the 20-100 keV band (Barlow et al. 2006, MNRAS): kT=25 keV ; flux compatible with our XMM-Newton results, but the IBIS spectrum has low S/N. • Hints for large MWDfrom the optical light curve (Hachisu & Kato, 2002, ApJ) • also large MWDfrom large Thighdeduced from X-ray spectra – but Thigh not well constrained • The recent nova – V2491 Cyg (2008b) – has also been detected in hard X-rays with Suzaku (Takei et al. 2009)

  42. Observations wih Suzaku and XMM-Newton: V2491 Cyg (2008) prompt and short duration hard X-rays Takei et al. 2009 and 2011

  43. Nova Oph 1998=V2487 Oph - Recurrent Nova • Previous outburst in 1900 June 20, discovered in the Harvard College Observatory archival photograph collection Pagnotta and Schaefer, IAUC 8951, 200; 2009 AJ) • recurrent nova - P=98 yrs • MWD very close to MCHANDRA  relevance for the SNIa scenario challenge for theory to get recurrent nova explosions with such short time scales X-ray emission CV-like ≠ RN scenario • The recent nova – V2491 Cyg (2008b) – has also been claimed to be recurrent. It was also a very fast nova, expected to be massive, very luminous in X-rays (Ibarra et al. 2009, A&A), and detected in very hard X-rays (Takei et al. 2009)

  44. Models of recurrent novae – TNR on accreting WDs • Search combinations of initial conditions leading to short recurrence periods: • Prec = ΔMacc / (dM/dt) = 98 yrs (21 years for RS Oph) • ΔMacc: required accreted mass on top of the WD to power the outburst through a TNR • Mwdini? Accretion rate? Lwdini? • Accretion rate: related to mass loss from the red giant wind • effective dM/dt onto the WD: 2x10-7 - 10-8 M/yr

  45. . M=10-8 M/yr Accreted masses to reach H-ignition conditions critical accreted mass does not depend only on Mwd Mwd very close to MCHANDRA Lini Hernanz & José 2008

  46. . M=10-8 M/yr Recurrence Periods V2487 Oph 1998: Prec=98 yr Lini * RS Oph: Prec=21 yr . * M=2 10-7 M/yr & L=10-2L * Hernanz & José 2008

  47. CONCLUSIONS (recovery of accretion) • X-rays are crucial to study the recovery of accretion in post-outburst novae: type of CV, mass of the WD • Magnetic WD: challenge for accretion –traditionally assumed to occur through a normal accretion disk in a non magnetic WD. But some cases of novae in magnetic CVs are known: V1500 Cyg (1975), V4633 Sgr (1998) – asynchronous polar as a consequence of the nova outburst (Lipkin & Leibowitz, 2008), V2487 Oph (1998), V2491 Cyg (2008) •  see Pietsch’s talk C2: M31N 2007-12b, an IP? • Massive WD: if Thigh(plasma) is large and/or the nova is recurrent. Novae as scenarios for type Ia supernovae • but very “ad-hoc” conditions are required to obtain a recurrent nova (Precurrence < 100 years) • but XMM spectra (V2487 Oph) looks CV-like ≠ RN scenario

  48. An interesting case: the recurrent nova RS Oph, which erupted in 2006 Previous eruption in 1985 – Prec ~21 yrs Short recurrence period  large MWD close to MChandra(deduced from models) possible SNIa scenario (but should be CO WD!) Porb=456d; RG companion – symbiotic recurrent nova Detected as a very variable SSS by Swift/XRT (Bode et al. 2006), XMM-Newton (Nelson, Orio et al. 2008, Ness et al. 2009)

  49. Supersoft X-ray light curve of the recurrent nova RS Oph (Swift observations, Bode et al. 2006) Mwd=1.35 M Menv= 4x10-6 M Kato & Hachisu, 2007

  50. RS Oph in quiescence observed with XMM-Newton Nelson, Mukai, Orio, et al., 2011: observations in quiescence, 537 and 744 after outburst  accretion rate ≈ theoretical In previous eruptions: very faint X-ray source in quiescence, hard to reconcile with large accretion rates needed to explain frequent (every 20 yrs) outbursts

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