The Outbursts of Classical and Recurrent Novae

1. The Outbursts of Classical and Recurrent Novae Michael Bode Astrophysics Research Institute Liverpool John Moores University, UK

2. Outline • Classical Novae: Background • GK Persei: A Case Study • Recurrent Novae: Background • RS Ophiuchi 2006: A Case Study • Concluding Remarks/Open Questions

3. Classical Novae Also well defined sequence of spectra through the outburst (pre-max; principal; diffuse-enhanced; Orion; nebular) Visual Light Curve “Speed Class”: Correlations with ejection velocities, peak absolute magnitude (“MMRD” relations - e.g. Della Valle & Livio, 1995)

4. CN Vital Statistics Central System: • WD (CO or ONe) + late-type MS star, P ~ 1.5-8(+) hrs • Macc ~ few x 10-9 M¤yr-1 • Lqu ~ L¤ At Outburst (TNR on WD): • L ~ few x 104 L¤( ~ LEdd) • Mej ~ 10-5 – 10-4 M¤ (obs and models disagree) • vej~ few 100 - several 1000 km/s . • Inter-outburst period: ~103–105 yrs (~ 1000 o/b’s?)

5. The CN Population • Historically ~ 3 yr-1 observed in Milky Way, cf. ~ 12 yr-1 expected • (Liller & Meyer, 1987) • Galactic nova rate = 34+15-12 yr-1 (Darnley et al., 2006) • Fast novae confined to z < 100pc of plane, slow novae up to • z = 1000pc (Galactic Bulge) (Della Valle et al., 1992) • Williams (1990, 1992) defined two classes based on spectra: • “Fe II” novae (~60% of total), lower ejecta velocities, standard • or neon novae • “He/N” novae, high ejecta velocities, neon or coronal novae • ~800 CN catalogued in M31 (Pietsch • et al., 2007), rate = 65+16-15 yr-1 (Darnley • et al., 2006) • Bimodal wrt speed class (Arp, 1956; • Capaccioli et al., 1989) - if so, related • to CO vs ONe WDs?

6. Beyond V: Shrinkage of pseudo- photosphere at Lbol~ const as mass loss rate decreases Modified Bath and Harkness (1989, CN I) relation: Teff = T0 x 10V / 2.5 K where V is decline in V mag from peak and T0 = 8000K e.g. Teff = 5x105 K, V = 4.5 mag

7. Blueshifted Ha rest frame Redshifted Optical Imagery of CN Nebular Remnants RR Pic (1925, S) HR Del (1967, VS - Ha (left), [OIII] (right)) DQ Her (1934, MF) >40 optical; ~10 radio (O’Brien & Bode 2008) GK Per (1901, VF)

8. Nova GK Persei: Vital Statistics • Very fast “neon” nova (Feb 22nd 1901) • d = 470 pc (expansion parallax) • Lmax ~ 5x1038erg/s; Lqu = 1034erg/s • Mej ~ 10-4 M¤, vej = 1200 km/s Central System: • P = 1.904 d; WD (intermediate polar) + K2IV • Primary Mass ~ 1 M¤; Secondary Mass ~ 0.3 M¤ • Dwarf nova outbursts (outer edge of accretion disk?)

9. Multi-frequency imaging of the Central Remnant Optical images from (a) 1917 (Ritchey 1918) and (b) 1993 (Slavin et al. 1995) (All images 4x4 arcmin approx) (c) VLA 5GHz image (synchrotron emission – courtesy E.R. Seaquist) (d) Chandra images: 0.4-0.6 keV (red); 0.8-1 keV (blue – see Balman 2005) “Supernova Remnant in Miniature”

10. The Light Echoes 1901 Sep 1902 Jan • J.C. Kapteyn (1902, AN, 157, 201) concluded v > c • Heroic (34 hr) spectrum of nebulosity by Perrine in 1902 showed it to be very similar to that of the nova a few days after outburst • Apparent expansion velocity ~ 4c (feature marked in 1901 is 5´ from the nova. Also note persistent “bar” to SW in 1902 image)

11. Form of the Ambient Medium? • IRAS 100m and HI (21cm) emission • (Bode et al. 1987, Seaquist et al 1989) • Re-analysed by Dougherty et al. (1996 • HIRAS data) • Td= 23 ± 1K, Md = 0.04 M¤ (MHI ~ M¤) IRAS/HI “cloud” ejecta from previous phase of binary evolution? If v = 20 km s-1: t ~ 105 yrs; last major ejection ~ 3x104 yrs ago • Suggest ejection from “born again” AGB star • Current secondary mass and spectral type + luminosity class consistent with ~ 1 M¤lost

12. Large-scale bipolar IRAS nebulosity coincident with optical • nebula discovered by Tweedy (1995) • INT WFC images (Bode, O’Brien & Summers, 2004): [OIII]5007 (blue), Ha (red) But – what is the cause of the asymmetries?

13. A Non-Artist’s Impression t ~ 105 yrs SW Initial Expulsion of PN Envelope 1901 CN Outburst Measured proper motion of central binary from 1917 – 1993…

14. p.m. = 0.015 ± 0.002 arcsec/yrp.a. = 191o ± 5o (thru E from N)vs = 45 ± 4 km/s What is this “cat o’ nine tails”? [OIII] image plus IRAS 100mm contours Ha image plus contours of the light echoes from 1902

15. Recent Addition V458 Vul (2007) • Nebulosity in IPHAS H survey pre-outburst • Spectral characteristics of PN, ~14,000 yr • Nova flash now illuminating the nebula • d = 13 kpc consistent with light echo and MMRD etc. • High mass WD(?) • (Wesson et al. 2008, ApJL)

16. Recurrent Novae • Inter-outburst period: ~10–100 yrs • TNR on WD • 3 possible sub-types (Anupama 2008; Galactic e.g.s): T CrB, RS Oph, V3890 Sgr, V745 Sco Red giant secondary, P ~ few 100d MWD ~ MCh Very fast optical decline, vej>~4000 km/s Mej ~ 10-7 – 10-6 M¤ U Sco, V394 CrA Evolved/sub-giant secondary, P ~ day MWD ~ MCh Very fast optical decline, vej~10,000 km/s Mej ~ 10-7 M¤ T Pyx, IM Nor, CI Aql MS/sub-giant secondary, P ~ hrs - day MWD < MCh Slower optical decline, vej~800-2500 km/s Mej ~ 10-5 M¤, spectral development as CN

17. RS Oph Vital Statistics • Recurrent Nova – outbursts 1898, (1907), 1933, (1945), 1958, 1967, 1985, 2006 • Central system – high mass WD + Red Giant (M2III); P = 455 days • d = 1.6 ± 0.3 kpc, NH = 2.4 ± 0.6 x 1021 cm-2 • Prior to 1985, spectroscopic evidence for red giant wind, systematic reduction in velocities post-outburst, and emergence of coronal lines, led to suggestion of ejecta (v0 ~ 4000km s-1) interaction with RG wind (u = 20 km s-1) • 1985 outburst first to be observed beyond the visible, but radio imaging and X-ray observations sparse (and no HST of course!) • Shock models by Bode & Kahn (1985), O’Brien, Bode & Kahn (1992)

18. 2006 Outburst • Discovered Feb 12.83 UT (t = 0) • Very similar optical behaviour to previous outbursts • Within 2 days, ToO’s granted on Swift, XMM, Chandra, RXTE, MERLIN, VLA, VLBA, EVN, LT, UKIRT, plus GMRT, Ryle, Spitzer a few days later, and HST at 155d Buil (2006) t = 1.37d V

19. Swift XRT Observations: First 26 days day 3.17 5.03 8.18 10.99 13.60 15.61 + Detected with BAT at outburst 18.17 25.99 (see also Sokoloski et al. 2006 for RXTE observations + Nelson et al. 2008, Drake et al. 2009, Ness et al. 2009 for XMM/Chandra)

20. Comparison with Models XRT spectra fitted with single temperature mekal model. vsfrom kT; interstellar NHfixed and overlying wind NH a free parameter (expect [NH]W µ rs-1here - Bode et al. 2006, ApJ) t -1.5 t -0.6 t -1.5 t -0.6 t -0.5 t -0.5 Appears to settle into stable pattern after ~6 days (cf. end Phase I) but rapidly evolves to what looks more like Phase III behaviour.

21. SSS phase – The Motion Picture • Starts at t ~ 26 days • Initially highly variable • “Plateau” phase(?), to t ~ 58 days: Mburn = (1.7–3.8) x 10-7 M¤ • Secular decline to t ~ 90 days when SSS phase ends: Menv ~ 3 x 10-7 M¤ • Very much compressed version of e.g. V1974 Cyg SSS evolution (where tremµMWD-6.3) (Nelson et al. 2008; Ness et al. 2009 - XMM/Chandra)

22. Short Period Oscillations • Period not stable • Duration of modulation and short period consistent with e (nuclear burning) instability on WD? • P ~35s modulation apparent in SSS phase. Not detectable after t = 59 days: start of secular decline (so far, unique to RS Oph) • MWD ~ 1.4 M¤(~MCh)from duration of SSS “plateau” and L (P also suggests high mass) + Macc>Mejec SN Ia?? • (see also Hachisu et al. 2007; Orio et al., 2008; Osborne et al. 2009)

23. First VLBA image – 5GHz, Day 13.8 Res’n ~ 3 mas Peak Tb~5x107K Significantcontribution fromnon-thermalsynchrotron emission i.e.particles accelerated inshock wave. Radius consistent with X-ray results

24. First VLBA image – 5GHz, Day 13.8 Res’n ~ 3 mas Peak Tb~5x107K Significantcontribution fromnon-thermalsynchrotron emission i.e.particles accelerated inshock wave. Radius consistent with X-ray results (O’Brien et al. 2006, Nature; Rupen et al. 2008, ApJ)

25. 1985, day 77? Evidence of Radio Jet (NB: similar binary phase) (day ~50) 1.7 GHz VLBA (contours - largely synchrotron) vs 43 GHz VLA (colour image - thermal dominates) (Sokoloski et al. 2008, ApJL)

26. [OIII] 0.4 arcsec HST Optical Observations of the Nebular Remnant N • HST DDT, t = 155d and 449d • t = 155d, 2 orbits, [OIII]5007, Ha, [NeV]3426 • Extended structure detected in [OIII] and [NeV] (+possibly Ha) • Elongated structure ~360 mas, E-W (t = 155d). Constant velocity of expansion of outer lobes between epochs • v = 3200 km/s (in plane of sky) • [NeV] may be in “caps” (??) • Deeper image shows more extended structure to E [OIII] N W [NeV] (Bode et al. 2007)

27. Model of Remnant Structure • O’Brien et al. (2006) suggested VLBI evolution modelled by bipolar structure • Here, used Shape to model HST images + ground-based spectra • Outer dumbbell and inner hourglass: latter containing lower velocity, denser material • West lobe is approaching observer • i = 39o +1-10(v0 = 5100 km/s) à binary orbital plane in “waist” • Consistent with early-time optical interferometry, VLBI, X-ray, plus survival of circumstellar dust (Spitzer data - Evans et al. 2007, ApJ) Model Model + Filter HST [OIII] (Ribeiro et al. 2009, ApJ sub.) Ground-based spectrum

28. Some Open Questions • Evolutionary track of a binary to the CN or RN phase? (Politano) • Continuum of inter-outburst timescales (fundamental properties) from CNe through RNe (sub-type)? • Detailed evolution of the TNR - e.g. Super-Eddington and SSS “plateau” phases? (Hernanz; Kato) • Cause of initial rapid variability of the SSS and origin of oscillations (in RS Oph)? (Osborne) • Mass ejected - resolution of discrepancy between observations and theory? (Hernanz; Pietsch) • Jet formation? (Sokoloski) • Link between RNe and SNe Ia? (Podsiadlowski; Hernanz; Di Stefano; Nelson; Sokoloski) • Refinement of MMRD possible? • Relationship of nova rates and sub-types to stellar populations? (Henze; Orio; Pietsch)