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Swift Observations of Novae. Julian Osborne & the Swift nova-CV group. http://www.swift.ac.uk/nova-cv/. Swift Observations of Novae. Julian Osborne & the Swift nova-CV group. http://www.swift.ac.uk/nova-cv/. Nova: Thermo-nuclear runaway on an accreting white dwarf. - PowerPoint PPT Presentation
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Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
Swift Observations of Novae
Julian Osborne & the Swift nova-CV group
http://www.swift.ac.uk/nova-cv/
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
Swift Observations of Novae
Julian Osborne & the Swift nova-CV group
http://www.swift.ac.uk/nova-cv/
Nova: Thermo-nuclear runaway on an accreting white dwarf
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
Previous best nova in X-rays
Krautter et al 1996
Nova Cyg 1992(V1974 Cyg)
• Rosat PSPC• 18 observations• Super-soft Source lasts ~400 days
• Duration of SSS phase generally unknown – important constraint on WD mass (Tturnoff ~ M-6.3)
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
X-rays from novae
Potential sources of X-ray emission from classical/recurrent novae:
• Thermal emission from hot white dwarf • shock breakout• residual nuclear burning after ejecta dispersal
• High velocity shocks• internal shocks within the ejecta• shock of ejecta with shell from previous nova or planetary nebula• shock of later fast wind with earlier slower wind
• Re-established accretion
• Compton degraded gamma-ray emission (before optical peak)
• not yet seen
Swift
Swift
Swift
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
Nova X-ray light-curves
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
Swift novae stats
• Swift has observed ~40 novae within 4000 days of outburst
• 25 detected in X-rays• 7 novae have >100 ksec each: U Sco, KT Eri,
N LMC 2009, CSS 081007, V2491 Cyg, V458 Vul & RS Oph
• Observations start within 1 day (pre-nova for V2491 Cyg & U Sco)
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
RS Oph: XRT light curve
Osborne et al 11
0.3-10 keV light curve shows:
• Cooling hot gas emerging from red giant wind• Bright interval which lasts ~64 d•Shock breakout from wind since last outburst 21 yrs ago during bright phase
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
RS Oph: XRT light curve
0.3-10 keV light curve shows:
• Cooling hot gas emerging from red giant wind• Bright interval which lasts ~64 d•Shock breakout from wind since last outburst 21 yrs ago during bright phase
Osborne et al 11
32 milliCrab
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
RS Oph BAT detection
• RS Oph was detected by the BAT in the softest band
• Emission was likely thermal rather than compton degraded radioactivity
BAT 14-25 keV
Bode et al 2006
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
RS Oph shock development
Asymmetric shock propagates into RG wind Walder et al 2008
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
RS Oph: XRT light curve
0.3-10 keV light curve shows:
• Cooling hot gas emerging from red giant wind• Noisy onset of super-soft phase, which lasts ~64 day in total • Turnoff time → MWD~1.35 M☼
Osborne et al 11
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
RS Oph X-ray spectra
• 1st appearance of hot WD on day 26
• kTBB=31 eV on day 29, = 56 eV on day 50.5
• Variable neutral oxygen absorption (0.54 keV)
• Late flux decline consistent with temperature drop to kT = 41 eV at day 76.9Osborne et al 11
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
RS Oph X-ray spectra
• NLTE WD model atmosphere (Rauch+ 10) spectral fits (declining wind absorption with O=OSun/3, Ness et al 07)
• Initial low temperature and large radius change to changes to high temperature and smaller radius• Peak Luminosity ~ LEdd
• Late count rate decline due to cooling & shrinkageOsborne et al 11days
wavelength
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
A quasi-periodic modulation
Day 33-45 Day 45-58
Beardmore et al 2009
Period near 35s in soft X-rays between days 33-59
WD spin?
Nuclear burning instability?
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
A quasi-periodic modulation
Day 33-45
Period near 35 sec confirmed by XMM
Ness et al 2007
Orio et al 2007
Period near 33 sec also seen by Chandra LETG on day 40
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
Nova 1999b Aql(V1494 Aql)• Chandra ACIS• ~42 minute period
Drake et al 2003Nova Sgr 2002c(V4743 Sgr)• Chandra grating• 22 minute period• Softening decline in ~2 hrs
Ness et al 2003
Periods in SS novae
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
Quasi-periods in SS novae
• Previously seen modulation has been multiply periodic – therefore not due to WD rotation
• These 20-30 min periods have been ascribed to non-radial g-mode oscillations in the white dwarf (cf hot planetary nebula nuclei) induced by compression-opacity instability [Drake et al 2003]
• RS Oph periods at ~35 sec are very much shorter• Possible origin in the ε mechanism (nuclear burning
instability) for which models predict periods 4 min - 1 sec [Kawaler 1988, Sastri & Simon 1973]– Consistent with modulation (mostly) visible during SS
phase
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
18
100 sec hardness and count rate values compared to expected hardness for kT=52 eV blackbody and ISM plus variable neutral absorption
GK Per
Extreme early variabilityH
R =
(0.
6-2.
0keV
)/(0
.3-0
.6ke
V)
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
Nova 1999b Aql(V1494 Aql)
• Chandra ACIS• X-ray burst lasts ~14 mins
Drake et al 2003
Flux variation unexplained
Brief flux increase
Does not look like variable absorption
Rapid variability in SS novae
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
General trend of hardening at times of low flux is consistent with neutral absorption model
Variable absorption?
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
General trend of hardening at times of low flux is consistent with neutral absorption model
Counter-examples exist, due to ionization of oxygen?- Reduction of variability due to blob expansion/ionization?
Variable absorption?
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
Variable absorption?
Ratio of bright phase spectrum to faint phase shows complexity of the spectral change with intensity
This is not simple absorption
Its probably not absorption at all
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
RS Oph Summary
• Recurrent nova in 455 day binary
• Initially very hard X-ray source due to wind shock
• Super-soft phase lasted ~64 days, short duration suggests high mass WD
• SS phase started with v large variability. X–ray spectral behaviour not simple, UV unaffected
• 35 sec qpo present at some times during SS phase – WD instability?
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
• Early decline of SSS phase strongly suggests a very high mass WD (early fuel exhaustion due to ignition at low accreted mass)
• From SSS: M_burnt ~ 3x10-7 M_sun• To reach ignition: M_acc ~ 4x10-6 M_sun• From shock: M_ej ~ 10-7-10-6 M_sun• Nova cycle mass budget: accreted mass >4x
ejected mass → future SN • but uncertainties large
RS Oph Summary
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
V2491 Cyg
V2491 Cyg was observed – and detected - pre-outburst as part of the BAT survey follow-up. This X-ray source may have been the counterpart of the BAT source.
Page et al 2010
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
V2491 Cyg
Short-term X-ray variability is seen, though there is no strict periodicity.
Similar (unexplained) variability has been seen in other SS novae.
Numbers in the top right corner indicate the day after outburst.
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
V2491 Cyg
The UV (1928 Å) evolution is very different from that seen in X-rays, showing a fading trend beyond at least 20 days after the outburst. Earlier observations were saturated.
The UV curve has inflections at ~40 and ~57 days, at the times of the X-ray peak and the end of the rapid decline.
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
V2491 Cyg
Page et al 2010
Blackbody fit parameters while the super-soft source was visible
Absolute values probably not reliable
A rising temperature and shrinking radius are seen between days 30 - 57
Where is the expected constant luminosity nuclear burning phase?
Grey points show luminosity upper limits from linking X-ray to UV.
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
V2491 Cyg
Page et al 2010
McDonald CO LTE model fits
Show same trends of rising temperature and shrinking radius as BB fits
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
V2491 Cyg
Page et al, subm
McDonald LTE models are worse spectral fits than BB
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
V2491 Cyg
Flickering is visible after day ~57. If this is the recovery of accretion due to viscous expansion of a disk, then disk was removed to 2x1010 cm. With Porb=0.96 days, Rdisk ~ 3x1010 cm. Inner disk only destroyed by nova
Page et al 2010
0.3-10 keV
0.3-10 keV
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
V2491 Cyg
Estimates of the time to reach ignition pressure for V2491 Cyg derived from the observed pre-nova luminosities of Ibarra et al (2009).
Curves are from the Nauenberg (1972) WD M-R relationship (points from Althaus et al 2005), ranges reflect distance and accretion efficiency uncertainties.
Page et al 2010
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
V2491 Cyg
It is highly unusual to see a nova in X-rays pre-outburst. The only others which have been detected pre/inter-outburst have actually been recurrent novae (e.g. RS Oph and V2487 Oph).
A high inter-outburst accretion rate is expected if a nova is to be observably recurrent.
It seems possible that V2491 Cyg will be a recurrent nova.
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
KT Eri
Nova Eri 2009
mV,peak = 5.4
14 Nov 2009
Early SS X-ray behaviour shows large-scale variability like RS Oph
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
KT Eri
Clear spectral variations of a very super-soft spectrum
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
KT Eri
Spectrum varies on both low and high energy sides
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
KT Eri
Ratio of bright over faint spectra shows variation is mostly Oxygen line emission
Ratio:
day 83.5 over day
82.0
Energy (eV)
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
KT Eri
No correlation of X-ray with optical flux
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
KT Eri
Is there a ~35 sec modulation in KT Eri, just like in RS Oph?
Yes, there is!
(ATEL 2423, Beardmore et al)
NB: No such modulation is seen in the AGN Mkn 421, which also had ~150 XRT c/s (ie <0.4%).
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
XRT Chandra XRT
06 Feb 2010 = day 83.6
KT Eri
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
KT Eri
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
KT Eri
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
KT Eri
Summary
• SS phase onset around day 60 shows large scale variability like RS Oph
• Spectrum is very soft (even for a SSS), kT_BB = 16 eV
• Large spectral variability does not look like simple temperature or absorption variations
• X-ray and optical flux unrelated
• Variable strength ~35 sec qpo during SS phase, period & amplitude not a strong function of SSS intensity
• This is the second SS nova to show ~35 sec qpo, favouring a WD instability origin over a rotation-based mechanism
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
Behaviour in 1945
Previous outburst with template from 7 outbursts(Schaefer 2010)
U Sco – the fastest nova
U Sco is the only eclipsing recurrent nova. Porb = 1.2 day
Outbursts regularly every 10.3 yrs, next was predicted at 2009.3±1.0
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
U Sco
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
U Sco
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
U Sco
Osborne et al ATEL 2442
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
Days: 12.1-13.8, 14.3-16.2, 16.3-18.5, 19.2-20.6
U Sco
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
U Sco
Quiescent eclipse (Schaefer arXiv:0912.4426)
1 mag.
Optical eclipses only seen after day 14
Early optical eclipses are broad and shallow
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
U Sco
• BB spectral fits show shrinking photosphere revealing higher temperatures
• Luminosity peak ~ Eddington
• Radius is cold WD value by day ~27
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
U Sco
Summary
• U Sco is the fastest declining nova known, suggesting a very high mass
• It is the only eclipsing RN, offering a unique opportunity to dissect the progress of the outburst
• The SS phase onset between day 8-12 coincides with the optical plateau, although this is not generally true of novae
• Broad and shallow eclipses are seen in the UV & optical from day 14 only.
• Lack of strong X-ray eclipses appears to imply scattering
• Very strong optical emission line wings (‘horns’) will constrain the ejecta geometry
• The UV spectrum is very rich, giving great hope of a radial deconstruction of the properties of the evolving nova ejecta
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
V407 Cyg
Summary
Abdo et al 2010 Science
Fermi detection of Nova V407 Cyg at <100 MeV
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
V407 Cyg
Fermi detection during initial hard phase
Short-lived bright X-ray phase ends at time of UV faster decline
Shore et al 2011
X-ray flux
X-ray HR
UV flux
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
V407 Cyg
Complex X-ray spectrum:
Enhanced abundances & 2 temperatures required for initially highly absorbed cooling optically thin emission (N>250, O~35, Ne<3, Na>20, Mg<2.3)
BB-like soft component seen before day 60
Shore et al 2011
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
V407 Cyg
• First nova of V407 Cyg
• Secondary is Mira-type with strong wind
• RS Oph-like nova evolution of X-rays and optical line profiles
• Enhanced abundances seen in X-rays indicative of nuclear explosion
• High ionization lines eventually became highly asymmetric
• Indicates explosion off-centre in Mira wind
• Mira has longest P~750 d and does not fill Roche lobe
• Measured shock velocity of ~2500 km/s consistent with Fermi detection at ~3 days
• Orbital period likely >30 years
Shore et al 2011
He II
C V
C V
Swift Novae – Julian Osborne – MAXI 1st year meeting – Shibuya, Japan (30 Nov – 2 Dec)
Summary
• The scheduling flexibility and multi-wavelength capability of Swift make it the best rapid-response nova observing facility
• Extensive datasets are revealing novel behaviours
• The short SS phase durations measured suggest high MWD
→SN1a?
•
Nova SSS years
V723 Cas >12
V574Pup 3.5
V5116 Sgr 2.9
V1281 Sco 1.2
V597 Pup 1.4
RS Oph 0.25
V2491 Cyg 0.16
V458 Vul >1.4
CSS 081007 0.41
N LMC 2009 0.63
• Blackbody fits show similar trends to static NLTE model atmosphere fits, but lack of outflow in model limits inference from SSS spectral fits
• Periodic & aperiodic X-ray variability still to be understood. Not shown: Orbital modulation likely in some cases. X-ray & UV/opt are correlated/anti-correlated/unrelated