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March 28, 2008. Cool discs, hot flows, Funäsdalen, Sweden. ACCRETING X-RAY MILLISECOND PULSARS IN OUTBURST. M A U R I Z I O F A L A N G A. Service d‘Astrophysique, CEA –Saclay, France. Collaborators: J. Poutanen, L. Kuipers, J. M. Bonnet-Bidaud. March 28, 2008. - PowerPoint PPT Presentation
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ACCRETING X-RAY MILLISECOND PULSARS IN OUTBURST
M A U R I Z I O F A L A N G A
Service d‘Astrophysique, CEA –Saclay, France
Collaborators:
J. Poutanen, L. Kuipers,
J. M. Bonnet-Bidaud
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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MSPs hosted in LMXBs
SXT:L ~ 1031-1032 erg/s in quiescentL ~ 1036-1038 erg/s in outburst, recurence time 2-5 yr.
Close X-ray binaries: Companion: M << Msun, Accretion disk, Compact object NS: B~108G
Rich time variability, such as twin QPOs at kHz frequencies (400 - 1300 Hz, increasing with Mdot); kHz QPOs are thought to reflect Kepler at the inner accretion
disk. (Van der Klis, 2000, astro-ph/00001167)(The Power spectra obtained for SAX J1808.4-3658 during 2002 outburst.)
8 SXT which show X-ray millisecond coherent modulation.Spin frequencies lie between 180 and 600 Hz. (see review by Wijnands 2004, astro-ph/0403409)
Type-I X-ray bursts, with nearly coherent oscillations in the range 300-600 Hz .Burst oscillations reflect the NS spin frequency (D. Chakrabarty, Nature, 2003)(Burst oscilation from SAX J1808.4-3658 during 2002 outburst.)
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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…now we know 8 LMXBs (transients) which show X-ray millisecond coherent modulation:
SAX J1808.4-3658: Ps = 2.5ms, Porb = 2hr (Wijnands & van der Klis 1998)
XTE J1751-306: Ps = 2.3ms, Porb = 42min (Markwardt et al. 2002)
XTE J0929-314: Ps = 5.4ms, Porb = 43.6min (Galloway et al. 2002)
XTE J1807-294: Ps = 5.3ms, Porb = 40min (Markwardt et al. 2003)
XTE J1814-388: Ps = 3.2ms, Porb = 4.3hr (Markwardt et al. 2003)
IGR J00291+5934: Ps = 1.67ms, Porb = 2.46hr (Eckert et al. 2004)
HETE J1900.1-2455: Ps = 2.65ms, Porb = 1.4hr (Markwardt et al. 2005)
Swift J1756.9-2508: Ps = 5.49ms, Porb = 54.7min (Krimm et al. 2007)
The growing family of the X-ray millisecond pulsars
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
4 Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
A Decade of Accreting millisecond X-ray Pulsars
Amsterdam, 14 - 18 April 2008
SAX J1808.4-3658
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Companion mass Mc/Msun
Com
pani
on r
adiu
s R
c/R
sun
Brown dwarfs0.1 Gyr
5 Gyr
1 Gyr
White dwarfs
XTE J0929-314XTE J1751-305XTE J1807-294
IGR J00291+5934SAX J1808..4-3658XTE J1814-338
Assuming that the companion star should fill its Roche lobe to allow sufficient accretion on the compact star (Bildsten & Chakrabarty, 2001)
Companion Star
Brown dwarf models at different ages (Chabrier et al. 2000, Deloye&Bildsten, 2003)
Cold low-mass white dwarfs with pure-helium composition
IGR J00291+5934 SAX J1808.4-3658 H-rich donor, brown dwarfXTE J1814-338HETE J1900.1-2455XTE J0292-314XTE J1751-305 H-poor, highly evolved dwarf XTE J1807-294Swift J1756.9-2508
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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L R2T4
α = (Fpers/fb)∆t
Helium-rich Thermonuclear Bursts and the Distance to the Accretion-powered MSP
Ledd ~ 3.8 x 1038 erg s-1
The time between bursts was long enough for hot CNO burning to significantly deplete the accreted hydrogen, so that ignition occurred in a pure helium layer underlying a stable hydrogen burning shell.
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Strohmayer et al (1996); Strohmayer, Markwardt (1999)
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
4U 1728-34
(D. Chakrabarty, Nature, 2003)
Milliseconds Bursts oscillations
SAX J1808.4-3658 XTE J1739-285
(Kaaret et al. 2007)
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OUTBURST PROFILE
XTE J1807-294
Discovery (Eckert et al. 2004)
From RXTE (Galloway et al. 2005)
(Falanga et al. 2005)(Falanga et al. 2005)
(Wijnands 2005, astro-ph/0403409)
XTE J1807-294
ISGRI 20-100 keV
Outburst are extended as a consequence of
X-ray irradiation of the disk? (King & Ritter 1998)
Distinct knee
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
9 Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
Outburst are extended as a consequence of X-ray irradiation of the disk (King & Ritter 1998)
(Powell, Haswell & Falanga, 2007)
SAX J1808.4-3658
XTE J1751-3054U 1705-44
Central object prevents the disk to cool down due to Irradiation, on a viscous time-scale,accounting for the exponential decay of the outburst on a timescale τ~20–40 d.
Theory: dwarf novae, SXTHot viscose state
Rh < Rdisc
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OUTBURST PROFILE
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
(Galloway et al. 2007
(Piro & Bildsten, 2005)
NEW: Intermittent Pulsation
HETE J1900.1-2455
After 60 days: Period disappeared(Kaaret, et al. 2007)
(Falanga et al. 2007)
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Intermittent MSP
(Altamirano et al. 2007)
ISSI BernDecembre 3, 2007
(Casella et al. 2007)
SAX J1748.9-2021 (Globular Cluster NGC 6440) , Pspin = 2.26 ms, Porb = 8.3 hr
AQL X-1, Pspin = 1.8 ms, Porb = 19 hr
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The reason for the lack of coherent pulsations in the persistent emission from LMXBs
Different explanations: Gravitational deflection (lensing effect)(Wood et al.1988)
Electron scattering (Brainerd & Lamb, 1987; Titarchuk et al. 2002) ~1/(1+τc) or (τc > 4)Weak surface magnetic fields due to magnetic screening (e.g., Cumming et al. 2001)Rayleigh-Taylor instability: Depending on the accretion rate, a star may be in the stable or unstable regime of accretion. (Kulkarni & Romanova 2008)
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INTEGRAL Observation IGR J00291+5934
IGR J00291+5934
(20 - 40 keV)V709 Cas
Cas Gamma
2S0114+650
Cas A
IGR J00291+5934
(80 - 200 keV)
(40-80 keV) significance level ~51σ
(80-200 keV) significance level ~17σ
December 2004 Outburst
Exposure 343 ks
(20-40 keV) significance level ~88σ
derived angular distance: 18´
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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Geometry of the emission region
XTE J1807-294
Thermal disk emission
The plasma is heated by the accretion shock as the material collimated by the hotspot on to the surface. The seed photons for Comptonization are provided by the hotspot.
Seed photons from the hotspot
Thermal Comptonization in plasma of Temperature ~ 40 keV
B ~ 108 G
Rm
(Falanga, Bonnet-Bidaud, Poutanen et al. 2005)
θ
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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XTE J1751-305
IGR J00291+5934
disc
spot
kTbb =0.66keVkTe = 60 keVtT = 0.9
Spectral energy distributionSpectral energy distribution
HETE J11900.1-2455
Gierlinski & Poutanen 2003Poutanen & Gierlinski 2001
Falanga et al 2005Falanga et al 2007
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Spectral evolution
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
IGR J00291+5934
XTE J1751-305
Gierlinski & Poutanen 2003 Falanga et al. 2005
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(Falanga, Kuiper, Poutanen et al. 2005)
PULSE PROFILE IGR J00291+5934
Rev 261/262/263, ~205
Porbit = 2.457 hr
Ps = 1.67 ms
Pdot = +8.4 x 10-13 Hz/s
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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Pulsed fraction and Time lag : IGR J00291+5934
(Falanga et al. 2005)
If the spectrum has a sharp cutoff, the rms amplitude of the pulse at energies above the cutoff increases dramatically.
F(E) ≈E-(Γ0-1) exp(-[E/Ec]β),Componization photon index Γ(E) = Γ0 + β(E/Ec)β
(Falanga, Kuiper, Poutanen et al. 2005)
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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(Falanga et al. 2005)
Hard X-ray
Soft X-ray
Hot corona Accretion disk
Time lag IGR J00291+5934
Compton scattering model
Time lag are normally hard
The energy spectra often observed in LMXBs suggests that the dominant radiative mechanism in the system is Compton scattering of soft photons in a hot plasma.
(For a review of models for spectral variability and time lags see Poutanen 2001)
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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Time/Phase Lag Model Accretioncolumn
Disk
Disk soft photons
Soft photonsNeutron Star
Hard photons1-Cill
Hard photonsCill
θhot
θref
Compton cloud
(Falanga & Titarchuk 2007)
∆t(Cill,ref,hot,neref,ne
hot) =
upscattering lag + downscattering lag
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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Recycling model for MSPs LMXB phase preceding the MSP stage;
mass transfer stops;the radio MSP switches on
Most binary MSPs have short orbital periods and mass function identifying the companions as low mass evolved dwarfs
X-ray transients can be the missing link between LMXBs and MSPs!
Old Neutron stars spin up by accretion from a companion
Radio Pulsar Millisecond Radio Pulsar
Spin up by
mass ac
cretio
n
Accreting NS in LMXBs are conventionally thought to be the progenitors of millisecond or „recycled“ radio pulsars (Alpar et al. 1982)
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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Spin-up IGR J00291+5934
υ = + 8.4 × 10-13 Hz s-1
υ = + 3.7 × 10-13 (L37/η-1I45) (Rm/Rco)1/2 (M/1.4Msun) (υspin/600)-1/3 Hz s-1
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
(Burderi et al. 2007)
(Falanga et al. 2005)
We measured for the first time a spin-up for an accreting X-ray millisecond Pulsar
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Is the Spin-up real?
An error in the source coordinates can give rise to timing error which may introduce a spurious spin-up or spin-down
1 YearOur observation
υ = + 5.8 × 10-14 Hz s-1
0.2 arcsec0.092 arcsec 0.2 arcsec
0.092 arcsec
0.092 arcsec source position error would introduce a non-existant spin-up rate of
Such an apparent spin-up would require a fairly large ~ 0.7 arcsec source position error during our observation
YES
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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« Une étoile cannibale »
« Star eats companion »
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Pulsar spin-up Animation
NASA, D. Barry
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kTdisc=0.43 keVkTseed = 0.75 keVAseed = 26 km2
kTe = 37 keVT = 1.7
disc
Strohmayer et al. (2003) Kirsch et al. (2003)
XTE J1751-305
XTE J1814-338XTE J1807-294
Gierlinski & Poutanen 2003
Modeling the Pulse Profile
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Strong-field General Relativity is required to describe the lightcurve observed at infinit.
(Gierlinski & Poutanen, 2005)(Morsink et al. 2007)
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The geometry of the model The geometry of the model
(Schwarzschild metric)
• Motion of Matter (Time-like geodesics)
• Curved photon trajectories (Null-like geodesics)
• Doppler shift : (1 + z)
• The solid angle : d(R,d,i,db) (Gravitational lensing effect)
• Travel time delay
• The observed flux : F = Idd
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Modeling the Pulse Profile: oblateness of rapidly rotating NS
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
Morsink et al. 2007
i = 20°, = 41°
i = 70°, = 49°
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slow pulsar (dashes)
fast pulsar, =401 Hz
Fsc,E(fast) ~ 3+ Fsc,E(slow)
Fbb(fast) = Fbb(slow) x 5
Poutanen & Gierliński (2003)
Doppler boosting Iobs4 Iem
Aberration cos obs cos e
Light curves of MSPLight curves of MSP
=1/(1 - cos ) – Doppler factor
=1/
– Lorentz factor
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Constraints on the neutron star mass-radius relation
obtained by fitting the pulse profile of SAX J1808.4-3658 Complications:
Shape of the star
Shape of the spot
Influence of the accretion disk
(Poutantn & Gierlinski 2003)
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Important Questions
Missing link between LXMB and ms radio pulsar ?
Analysis suggests that the spin frequency is limited to 760 Hz (95% confidence; Chakrabarty et al. 2003)
Several have suggested that gravitational radiation from a non-spherical neutron star might limit the maximum fraquency (Bildsten et al. 1998)
Detection by LISA?
Detecting more of these source with more instrument than before
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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Thank You…
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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Pulsar spin-up
R(magnetosphere)
The accreting matter transfers its specific angular momentum (the Keplerian AM at the magnetospheric radius) to the neutron star: L=(GMRm)1/2
M
The process goes on until the pulsar reaches the keplerian velocity at Rm (equilibrium period); Pmin when Rm = Rns
The conservation of AM tells us how much mass is necesssary to reach Pmin starting from a non-rotating NS
Accretion regime
Rm < Rcor
(Illarionov & Sunyaev 1975)
R(corotation)
Propeller regime
Rm > Rcor
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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Pulse profile IGR J00291+5934
ISGRI 9.1σ 20-35 keV
ISGRI 7.3 σ 35-60 keV
ISGRI 5.0 σ 60-100 keV
Rev 261/262/263, ~205
Porbit = 2.457 hr
Ps = 1.67 ms
Pdot = +8.4 x 10-13 Hz/s
ISGRI 2.0 σ 100-150 keV
HEXTE
1.1 σ 100.9-151.1 keV
HEXTE
3.3 σ 60.1-100.9 keV
HEXTE
8.3 σ 35.2-60.1 keV
HEXTE
11.4 σ 20.3-35.2 keV
JEM-X 4.0 σ 5-10 keV
(Falanga et al. 2005)
Cool discs, hot flows, Funäsdalen, SwedenMarch 28, 2008
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INTEGRAL CODED MASK (IBIS, SPI & JEM -X)
Observation
Coded Mask Shadow
Deconvolved Image Corrected Image
End Image