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Swift Observations of RS Swift Observations of RS OphOph

Soft & hard XSoft & hard X--rays rays (energy band: 0.3 (energy band: 0.3 -- 10 10 keVkeV))Epochs: 3 Epochs: 3 –– 185 days185 daysOrders of magnitude more extensive and Orders of magnitude more extensive and dense coverage compared to any previous dense coverage compared to any previous nova Xnova X--ray observationsray observationsUnexpected phenomena seenUnexpected phenomena seen

Swift observations of the superSwift observations of the super--soft phase of RS soft phase of RS OphiuchiOphiuchi

Julian OsborneJulian OsborneUniversity of LeicesterUniversity of Leicester

K.L. Page, A.P. Beardmore, M. R. Goad (Leicester)M.F. Bode (Liverpool JMU), T.J. O’Brien (Manchester)S. Starrfield, J-U. Ness (ASU), J. Krautter (Heidelberg)

G. Schwarz (West Chester), D. Burrows (PSU)N. Gehrels (GSFC), J. Drake (CFA)

A. Evans (Keele), S.P.S. Eyres (Central Lancashire)

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What did Swift do?What did Swift do?

First observation within 3 daysFirst observation within 3 days

Observation rate peaked at 1 per 90 Observation rate peaked at 1 per 90 minsmins

Observations delineate entire XObservations delineate entire X--ray ray outburst to beyond day 220outburst to beyond day 220

UVOT UVOT grismgrism and BAT detectionsand BAT detections

I will talk mostly about XRT data I will talk mostly about XRT data –– ~350 ~350 ksecksec exposureexposure

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Previous best observed nova in X-rays

Krautter et al 1996

Nova Cyg 1992(V1974 Cyg)

• Rosat PSPC• 18 observations• SSS lasts ~400 days

• Duration of SSS phase generally unknown –important constraint on WD mass

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Swift Swift Observations: First 26 days Observations: First 26 days

day3.17

5.038.18

10.99

13.60

15.61

18.17

25.99Bode et al 2006

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Animation by Andrew Beardmore, Leicester

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Swift XSwift X--ray light curveray light curve0.3-10 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☼

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Some Swift SS XSome Swift SS X--ray spectraray 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 76.9

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MultiMulti--epoch blackbody fitsepoch blackbody fits

Page et al Poster

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Nova 1999b Aql(V1494 Aql)

• Chandra ACIS• Burst lasts ~14 mins

Drake et al 2003

Rapid variability in SS novaeRapid variability in SS novae

Flux variation unexplained

Brief flux increase

Does not look like variable absorption

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Variable absorption?Variable absorption?

100 sec hardness and count rate values compared to expected hardness for kT=52 eVblackbody and ISM plus variable neutral absorption

GK Per

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Variable absorption?Variable absorption?General trend of hardening at times of low flux is consistent with neutral absorption model

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Variable absorption?Variable absorption?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?

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Swift UV Swift UV GrismGrism spectraspectra

~1600 Å ~2800 Å

• UV grism data are not calibrated (λ or flux)

• Short λcontinuum hardly varies over 100 days

• Short λ lines fade strongly

NIII] 1750Å

SiIII] 1897Å

CIII] 1909Å

Mike Goad

MgII (piled up)

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Swift UV Swift UV GrismGrism line declineline decline

• Line (inc continuum) flux• Note different scales• Noise probably not real (preliminary extraction)

• Lines are bright at start of SSS and decline with SSS• Lines do not show the massive variability seen in SSS

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Origin of UV emissionOrigin of UV emission

1.1. UV line flux has similar secular decline to UV line flux has similar secular decline to that in soft Xthat in soft X--raysrays

2.2. UV line flux does not show the same UV line flux does not show the same early massive variabilityearly massive variability

UV line flux photoUV line flux photo--excited by SSS ?excited by SSS ?

Emission site = illuminated Red Giant or Emission site = illuminated Red Giant or ejectaejecta blob surfaces ?blob surfaces ?

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A quasiA quasi--periodic Xperiodic X--ray modulationray modulation

Period near 35s

Day 33-45 Day 45-58

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A quasiA quasi--periodic modulationperiodic modulation

Modulation mostly present when SSS is bright, but not always (see bins 70-100)

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Nova 1999b Aql(V1494 Aql)• Chandra ACIS• ~42 minute period

Drake et al 2003

Nova Sgr 2002c(V4743 Sgr)• Chandra grating• 22 minute period• Softening decline in ~2 hrs

Ness et al 2003

Periods in SS novaePeriods in SS novae

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QuasiQuasi--periods in SS novaeperiods in SS novae

Previously seen modulation has been multiply periodic Previously seen modulation has been multiply periodic ––therefore not due to WD rotationtherefore not due to WD rotation

These 20These 20--30 min periods have been ascribed to non30 min periods have been ascribed to non--radial gradial g--mode oscillations in the white dwarf (mode oscillations in the white dwarf (cfcf hot hot planetary nebula nuclei) induced by compressionplanetary nebula nuclei) induced by compression--opacity opacity instability [Drake et al 2003]instability [Drake et al 2003]

RS RS OphOph periods at ~35 sec are very much shorterperiods at ~35 sec are very much shorter

Possible origin in the Possible origin in the εε mechanism (nuclear burning mechanism (nuclear burning instability) for which models predict periods 4 min instability) for which models predict periods 4 min -- 1 sec 1 sec [[KawalerKawaler 1988, 1988, SastriSastri & Simon 1973]& Simon 1973]–– Consistent with modulation (mostly) visible during SS phaseConsistent with modulation (mostly) visible during SS phase

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Conclusions 1Conclusions 1

Swift XSwift X--ray observations have revealed ray observations have revealed the shocked red giant wind and the the shocked red giant wind and the emergence and decline of the hot white emergence and decline of the hot white dwarf surface dwarf surface Massive variability in early superMassive variability in early super--soft soft phase due to due to blobby absorption?phase due to due to blobby absorption?Modulations with periods ~35 sec from the Modulations with periods ~35 sec from the white dwarf are much faster than seen in white dwarf are much faster than seen in other novae other novae –– nuclear burning instability?nuclear burning instability?Short Short λλ early UV flux not highly variable early UV flux not highly variable ––suggests UV flux from suggests UV flux from unobscuredunobscured sitesite

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Conclusions 2Conclusions 2

Early decline of SSS phase strongly Early decline of SSS phase strongly suggests a very high mass WD (early fuel suggests a very high mass WD (early fuel exhaustion due to ignition at low accreted exhaustion due to ignition at low accreted mass)mass)From SSS: From SSS: MburntMburnt ~ 3x10~ 3x10--77 MsunMsunTo reach ignition: To reach ignition: MaccMacc ~ 4x10~ 4x10--66 MsunMsunFrom shock: From shock: MejMej ~ 10~ 10--77--1010--66 MsunMsunNova cycle mass budget: accreted mass Nova cycle mass budget: accreted mass >4x ejected mass >4x ejected mass →→ SN SN

but uncertainties largebut uncertainties large