Departement of Physics
Faculty of Material Sciences and Technology
Slovak University of technology in Bratislava
Slovakia
ESAC
Spain

The nova observations
- September 2002 – discovery
(Haseda et al. 2002)
- March 2003 – Chandra large amplitude fast X-ray variability of ~22 min with overtones
(Ness et al. 2003)
- April 2003 – XMM-Newton fast X-ray variability with multiple frequency detection
(Leibowitz et al. 2006)
- 2003 and 2005 – unfiltered CCD photometry detection of orbital period of 6.7 h and fast variability of ~24 min
(Kang et al. 2006)

The first interpretations (Ness et al. 2003) day 180
- supersoft X-ray source phase (SSS) – final stage of nova activity
- continuous spectrum
- deep absorptions lines
- kT ≈ 30 – 50 eV
- L bol
≈ 10 36 – 10 38 ergs s -1

The first interpretations (Ness et al. 2003) day 180
- supersoft X-ray source phase (SSS) – final stage of nova activity
- continuous spectrum
- deep absorptions lines
- kT ≈ 30 – 50 eV
- L bol
≈ 10 36 – 10 38 ergs s -1
- after 13 ks a strong decline
- count rate from ~ 40 to almost 0
- hardness ratio decreased
- soft spectrum to hard spectrum
- detected fast variability with overtones:
P
1
= 1324 s (22 min)
P
2
= 668 s ≈ P1/2
P
3
= 448 s ≈ P1/3

The first interpretations (Ness et al. 2003) day 180
- supersoft X-ray source phase (SSS) – final stage of nova activity
- continuous spectrum
- deep absorptions lines
- kT ≈ 30 – 50 eV
- L bol
≈ 10 36 – 10 38 ergs s -1
- after 13 ks a strong decline
- count rate from ~ 40 to almost 0
- hardness ratio decreased
- soft spectrum to hard spectrum
- detected fast variability with overtones:
P
1
= 1324 s (22 min)
P
2
= 668 s ≈ P1/2
P
3
= 448 s ≈ P1/3
- decline unexplained, eclipse unlikely
- the spectrum should harden
- min. too long (6 ks, P orb
- fast variability
≈ 24 ks)
- white dwarf rotation (overtones!!!)
- pulsations of the white dwarf

The first interpretations (Leibowitz et al. 2006) day 196
- detection of 12 significant signals
- detection of 6 significant signals in reanalysed day 180
- 0.75 mHz has double structure;
0.729 and 0.763 mHz ... day 196
0.721 and 0.777 mHz ... day 180
- overtones
- double frequency; 1.459,1.504 mHz
- relations 2 x f, f
1
+ f
2

The first interpretations (Leibowitz et al. 2006) day 196
- detection of 12 significant signals
- detection of 6 significant signals in reanalysed day 180
- 0.75 mHz has double structure;
0.729 and 0.763 mHz ... day 196
0.721 and 0.777 mHz ... day 180
- overtones
- double frequency; 1.459,1.504 mHz
- relations 2 x f, f
1
+ f
2
- 0.75 mHz - white dwarf rotation
- other signals – WD pulsations

The first interpretations (Kang et al. 2006) days 258-265 and 1003-1011
- combination of 3 frequencies f f
1
= 0.041 mHz
= 0.705 mHz
2 f
3
= 0.755 mHz
P
P
P
3
1
2
= 402 min = 6.7 h (Kang et al. 2006)
= 24 min
= 22 min
(Kang et al. 2006)
(X-ray from Ness et al. 2003) f
3
- f
1
= 0.714 mHz ≈ 0.71 mHz ≈ f
2 f f f
1
– orbital frequency
2
3
– beat frequency between f
1
and f
3
– spin period of the white dwarf
=> an intermediate polar candidate

New observations
- 8 data sets (days 50 – 1286)
- Chandra/LETGS
- XMM-Newton/MOS,RGS
- detrending with a 5 th order polynome

Method used for period analysis
- Lomb-Scargle method (Scargle 1982)
- formal errors HWHM
- Sine fitting
- fitting of the model with n signals, 5 th order polynome and mean background
- goodness criterion a likelihood
- error determination from confidence
contours from likelihood difference

Method used for period analysis – tests
- synthetic data sampled as day 180
- added Poisson/Gaussian noise
- single frequency case f = 0.72 mHz
- two frequency case f f
2
1
= 0.72 mHz
= 0.76 mHz

Method used for period analysis – tests
- synthetic data sampled as day 180
- added Poisson/Gaussian noise
- single frequency case f = 0.72 mHz
- two frequency case f f
2
1
= 0.72 mHz
= 0.76 mHz

Method used for period analysis – tests
- synthetic data sampled as day 180
- added Poisson/Gaussian noise
- single frequency case f = 0.72 mHz
- two frequency case f f
2
1
= 0.72 mHz
= 0.76 mHz
- L-S and sine fitting with n = 1 found a single frequency at 0.744 mHz
- sine fitting with n = 2 found both signals

Method used for period analysis – tests
- synthetic data sampled as day 180
- added Poisson/Gaussian noise
- single frequency case f = 0.72 mHz
- two frequency case f f
2
1
= 0.72 mHz
= 0.76 mHz
- L-S and sine fitting with n = 1 found a single frequency at 0.744 mHz
- sine fitting with n = 2 found both signals

Analysis – Lomb-Scargle
- broad peaks
- blending?

Analysis – Lomb-Scargle
- broad peaks – blending?

Analysis – sine fitting
- detection criterion 3-σ
- error measured from 3-σ contours
- analysed interval 0.6 – 0.9 mHz
- 3-σ closed contour => 2 signals
- 3-σ open lines => 1 signal

Analysis – sine fitting
- detection criterion 3-σ
- error measured from 3-σ contours
- analysed interval 0.6 – 0.9 mHz
- 3-σ closed contour => 2 signals
- 3-σ open lines => 1 signal
- day 180 case: n = 2 fit better than n = 1
ΔL = 1978.48
Leibowitz day 196 day 180

Analysis – sine fitting
- detection criterion 3-σ
- error measured from 3-σ contours
- analysed interval 0.6 – 0.9 mHz
- 3-σ closed contour => 2 signals
- 3-σ open lines => 1 signal
- day 180 case: n = 2 fit better than n = 1
ΔL = 1978.48
- other observations – single frequency
Leibowitz day 196 day 180 day 1286

Analysis – sine fitting
- detection criterion 3-σ
- error measured from 3-σ contours
- analysed interval 0.6 – 0.9 mHz
- 3-σ closed contour => 2 signals
- 3-σ open lines => 1 signal
- day 180 case: n = 2 fit better than n = 1
ΔL = 1978.48
- other observations – single frequency
- overtones:
180 ------2 x f
2
196 2 x f
1
1286 2 x f
1
2 x f
2 f
1
+ f
-------
-------------
2
Leibowitz day 196 day 180 day 1286

Analysis – frequency detection
Test – day 302, synthetic data modulated with 0.72 and 0.76 mHz
Detections - L-S: 0.731 mHz
- 2-D, 3-σ open lines: 0.736 mHz
- 2-D, global minimum: 0.678 and 0.745 mHz f = 0.72 mHz f
1
= 0.72 mHz, f
2
= 0.76 mHz

Analysis – frequency detection
- two close frequencies f
1
and f
2
forms a beating with a frequency of f
1
– f
2
- if data longer than 1/(f
1
– f
2
) => long enough
- 2 signals in synthetic test data shorter than beating
- day 180 detection
- day 302 nondetection
=> amplitudes and noise!

Results – frequency evolution
- days 50 – 526, changes
- days 180 – 196, approaching
- days 302 – 526, merging?
- days 742 – 1286, constant?

Results – amplitudes, amplitude evolution
- after day 180 – decline, connection to fast decline during day 180?
- after day 526 – increase

Summary of the observational results
- double frequency nature of the 0.75 mHz peak at days 180 and 196
- single signal after day 526 (196 – 526, not sure, short data sets)
- frequency changing up to day 526
- signal constant after day 526
- relative amplitudes decline after day 180
- relative amplitudes increase after day 526
=> different behaviour of signals before and after day 526 – decline from SSS phase -> nova was turning off!

Interpretation – white dwarf rotation
- signals must be stable
- if two close signals – spin and beat period (between orbital and spin)
- does not agree up to day 526
- agree after day 526
P orb
= 6.72 ± 0.01 h (Kang et al. 2006)

Interpretation – before day 526 – QPOs?
- QPOs – vertical thickening in acc disc – eclipsing or reflecting the light
- only 4 detections of QPOs in X-ray:
- VW Hyi, 63 – 68 s (van der Woerd et al. 1987)
- SS Cyg, 83 s
- U Gem, 585 s
(Mauche 1997)
(Cordova and Mason 1984)
- OY Car, 2240 s (Ramsay et al. 2001)
- our periods: 1292 – 1391 s

Interpretation – before day 526 – QPOs?
- QPOs – vertical thickening in acc disc – eclipsing or reflecting the light
- only 4 detections of QPOs in X-ray:
- VW Hyi, 63 – 68 s (van der Woerd et al. 1987)
- SS Cyg, 83 s
- U Gem, 585 s
(Mauche 1997)
(Cordova and Mason 1984)
- OY Car, 2240 s (Ramsay et al. 2001)
- our periods: 1292 – 1391 s
- time scale of rotating vertical thickening in acc.disc, a Keplerian frequency
=> SS Cyg, VW Hyi
=> U Gem
~ 10
~ 10
9
10
cm
cm – too far, region not emitting X-rays
=> V4743 Sgr
=> OY Car
~ 10
~ 10
10
10
cm – too far, region not emitting X-rays
cm – too far, region not emitting X-rays

Interpretation – before day 526 – QPOs?
- beating between white dwarf rotation in X-ray with vertical thickening rotating in the inner disc radiating as QPOs in X-ray f beat
= f
QPOs
– f spin
=> f
QPOs
= f beat
+ f spin
≈ 680 s ( f spin
= 0.75 mHz)
=> distance of the QPOs source to ~ 10 10 cm – too far, not X-ray

Interpretation – before day 526 – QPOs?
- eclipse of the central X-ray source (WD) by vertical thickening in the acc.disc...OY Car case
- OY Car
- eclipsing system, periodic dip detected in X-ray
- inclination high enough, i = 83.3°

Interpretation – before day 526 – QPOs?
- eclipse of the central X-ray source (WD) by vertical thickening in the acc.disc...OY Car case
- OY Car
- eclipsing system, periodic dip detected in X-ray
- inclination high enough, i = 83.3°
- V4743 Sgr
- eclipse unprobable, periodic dips undetected in X-ray (P orb
= 24.1 ks)
- very narrow and shallow eclipse like feature in optical data
- partial eclise of the acc.disc edge by the secondary
=> inclination not enough to eclipse the WD by the secondary
=> inclination not enough for a vertical thickening to eclipse the WD

Interpretation – before day 526 – QPOs?
- eclipse of the central X-ray source (WD) by vertical thickening in the acc.disc...OY Car case
- OY Car
- eclipsing system, periodic dip detected in X-ray
- inclination high enough, i = 83.3°
- V4743 Sgr
- eclipse unprobable, periodic dips undetected in X-ray (P orb
= 24.1 ks)
- very narrow and shallow eclipse like feature in optical data
- partial eclise of the acc.disc edge by the secondary
=> inclination not enough to eclipse the WD by the secondary
=> inclination not enough for a vertical thickening to eclipse the WD
=> QPOs unlikely!

Interpretation – before day 526 – WD pulsations?
- the central accretor after nova explosion resembles PN nuclei
- PN nuclei
- pulsations 1000 – 5000 s (Ciardullo and Bond 1996)
- frequencies changing, ex. NGC 246, 0.01 mHz/1 month
- frequency change in V4743 Sgr, 0.01 mHz/2 weeks

Interpretation – before day 526 – WD pulsations?
- the central accretor after nova explosion resembles PN nuclei
- PN nuclei
- pulsations 1000 – 5000 s (Ciardullo and Bond 1996)
- frequencies changing, ex. NGC 246, 0.01 mHz/1 month
- frequency change in V4743 Sgr, 0.01 mHz/2 weeks
1 - instabilities in hydrogen burning shells (Sastri and Simon 1973)
- typical periods much shorter than our case, ~10 s
- RS Oph case with 35s X-ray oscillations (Beardmore et al. 2009)
=> unlikely

Interpretation – before day 526 – WD pulsations?
- the central accretor after nova explosion resembles PN nuclei
- PN nuclei
- pulsations 1000 – 5000 s (Ciardullo and Bond 1996)
- frequencies changing, ex. NGC 246, 0.01 mHz/1 month
- frequency change in V4743 Sgr, 0.01 mHz/2 weeks
1 - instabilities in hydrogen burning shells (Sastri and Simon 1973)
- typical periods much shorter than our case, ~10 s
- RS Oph case with 35s X-ray oscillations (Beardmore et al. 2009)
=> unlikely
2 - instabilities in partial ionisation zone of C and O (Starrfield et al. 1984)
- GW Vir isolated hot WD case
- deep absorption lines of C and O in V4743 Sgr (Ness et al. 2009)
- C-O WD with enough C and O?
=> possible

Interpretation – before day 526 – WD pulsations?
- pulsation frequency correlation with temperature (Kjeldsen and Bedding 1995)
- for hydrostatic equilibrium and for stellar atmospheres
- ratio of frequencies
(f
1
/ f
2
) 2 = T
2
/ T
1

Interpretation – before day 526 – WD pulsations?
- pulsation frequency correlation with temperature (Kjeldsen and Bedding 1995)
- for hydrostatic equilibrium and for stellar atmospheres
- ratio of frequencies
(f
1
/ f
2
) 2 = T
2
/ T
1
- agreement for days
180, 302, 371
- disagreement for days
196, 526, 742, 1286
T bb
in 10 3 K

Conclusion
- WD pulsations
- present before day 526
- during SSS phase f-T relation valid, except for:
- after strong decline in 180 (day 196)
- decline from SSS (day 526)
- none after SSS phase (after day 526)

Conclusion
- WD pulsations
- present before day 526
- during SSS phase f-T relation valid, except for:
- after strong decline in 180 (day 196)
- decline from SSS (day 526)
- none after SSS phase (after day 526)
- WD rotation
- during SSS phase– modulation buried in the overall brightness
- after SSS phase –visible and dominant
=> an intermediate polar candidate

Questions
- what is the strong decline during day 180? (observed also in RS Oph, ...)

Questions
- what is the strong decline during day 180?
- why is the f-T relation valid during the SSS phase?
- the same origine as stellar atmospheres in hydrostatic equilibrium?
- “quasihydrostatic” equilibrium?
- after strong decline in 180 (day 196) or decline from SSS (day 526)
- f-T relation not valid
- out of “quasihydrostatic” equilibrium?
- approaching frequencies during days 180 and 196 merged into one?
- why are the frequencies of pulsations and of the WD rotation so similar?

End thank you for...
...attention
...collaboration
...opportunity
...funding
...lunch
...