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

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

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

CN Vital Statistics Central System: WD (CO or ONe) + late-type MS star, P ~ 1.5-8(+) hrs M acc ~ few x M ¤ yr -1 L qu ~ L ¤ At Outburst (TNR on WD): L ~ few x 10 4 L ¤  ( ~ L Edd ) M ej ~ – M ¤  (obs and models disagree) v ej ~ few several 1000 km/s Inter-outburst period: ~10 3 –10 5 yrs (~ 1000 o/b’s?).

The CN Population Historically ~ 3 yr -1 observed in Milky Way, cf. ~ 12 yr -1 expected (Liller & Meyer, 1987) Galactic nova rate = 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 = yr -1 (Darnley et al., 2006) Bimodal wrt speed class (Arp, 1956; Capaccioli et al., 1989) - if so, related to CO vs ONe WDs?

Beyond V: Shrinkage of pseudo- photosphere at L bol ~ const as mass loss rate decreases Modified Bath and Harkness (1989, CN I) relation: T eff = T 0 x 10  V / 2.5 K where  V is decline in V mag from peak and T 0 = 8000K e.g. T eff = 5x10 5 K,  V = 4.5 mag

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

Nova GK Persei: Vital Statistics Very fast “neon” nova (Feb 22 nd 1901) d = 470 pc (expansion parallax) L max ~ 5x10 38 erg/s; L qu = erg/s M ej ~ M ¤, v ej = 1200 km/s Central System: P = d; WD (intermediate polar) + K2IV Primary Mass ~ 1 M ¤ ; Secondary Mass ~ 0.3 M ¤ Dwarf nova outbursts (outer edge of accretion disk?)

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: keV (red); keV (blue – see Balman 2005) “Supernova Remnant in Miniature”

The Light Echoes 1901 Sep 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) 1902 Jan

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. ( HIRAS data) T d = 23 ± 1K, M d = 0.04 M ¤ (M HI ~ M ¤ ) IRAS/HI “ cloud ” ejecta from previous phase of binary evolution? If v = 20 km s -1 :   yrs; last major ejection ~ 3x10 4 yrs ago - Suggest ejection from “ born again ” AGB star - Current secondary mass and spectral type + luminosity class consistent with ~ 1 M ¤  lost

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

A Non-Artist’s Impression Initial Expulsion of PN Envelope 1901 CN Outburst   yrs SW Measured proper motion of central binary from 1917 – 1993…

p.m. = ± arcsec/yr p.a. = 191 o ± 5 o (thru E from N) v s = 45 ± 4 km/s [OIII] image plus IRAS 100  m contours H  image plus contours of the light echoes from 1902 What is this “cat o’ nine tails”?

Recent Addition 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) V458 Vul (2007)

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

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, N H = 2.4  0.6 x 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 (v 0 ~ 4000 km 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)

2006 Outburst Discovered Feb 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) V t = 1.37d

Swift XRT Observations: First 26 days day (see also Sokoloski et al for RXTE observations + Nelson et al. 2008, Drake et al. 2009, Ness et al for XMM/Chandra) + Detected with BAT at outburst

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

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

Short Period Oscillations M WD ~ 1.4 M  (~M Ch )  from duration of SSS “plateau” and L (P also suggests high mass) + M acc >M ejec SN Ia?? (see also Hachisu et al. 2007; Orio et al., 2008; Osborne et al. 2009) Period not stable Duration of modulation and short period consistent with  (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)

First VLBA image – 5GHz, Day 13.8 Res’n ~ 3 mas Peak T b ~5x10 7 K Significant contribution from non-thermal synchrotron emission i.e. particles accelerated in shock wave. Radius consistent with X-ray results

First VLBA image – 5GHz, Day 13.8 Res’n ~ 3 mas Peak T b ~5x10 7 K Significant contribution from non-thermal synchrotron emission i.e. particles accelerated in shock wave. Radius consistent with X-ray results (O’Brien et al. 2006, Nature; Rupen et al. 2008, ApJ)

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

[OIII] 0.4 arcsec HST Optical Observations of the Nebular Remnant HST DDT, t = 155d and 449d t = 155d, 2 orbits, [OIII]5007, H , [NeV]3426 Extended structure detected in [OIII] and [NeV] (+possibly H  ) 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 [NeV] [OIII] N W (Bode et al. 2007) N

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 = 39 o (v 0 = 5100 km/s)  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) [OIII] (Ribeiro et al. 2009, ApJ sub.) Model + Filter Ground-based spectrum HST

Some Open Questions Evolutionary track of a binary to the CN or RN phase? (Politano)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)?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)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)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)Mass ejected - resolution of discrepancy between observations and theory? (Hernanz; Pietsch) Jet formation? (Sokoloski)Jet formation? (Sokoloski) Link between RNe and SNe Ia? (Podsiadlowski; Hernanz; Di Stefano; Nelson; Sokoloski)Link between RNe and SNe Ia? (Podsiadlowski; Hernanz; Di Stefano; Nelson; Sokoloski) Refinement of MMRD possible?Refinement of MMRD possible? Relationship of nova rates and sub-types to stellar populations? (Henze; Orio; Pietsch)Relationship of nova rates and sub-types to stellar populations? (Henze; Orio; Pietsch)