1 ACCRETING X-RAY MILLISECOND PULSARS IN OUTBURST M A U R I Z I O F A L A N G A Service...
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Transcript of 1 ACCRETING X-RAY MILLISECOND PULSARS IN OUTBURST M A U R I Z I O F A L A N G A Service...
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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
Collaborators:
J. Poutanen, L. Kuipers, E. Bonning
W. Hermsen, J. M. Bonnet-Bidaud,
L. Stella
ISSI BernDecembre 3, 2007
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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 lye 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.)
ISSI BernDecembre 3, 2007
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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)
The growing family of the X-ray millisecond pulsars
ISSI BernDecembre 3, 2007
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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
Companion Star
Brown dwarf models at different ages (Chabrier et al. 2000)
Cold low-mass white dwarfs with pure-helium composition
IGR J00291+5934 SAX J1808.4-3658 H-rich donor, brown dwarfXTE J1814-338XTE J0292-314XTE J1751-305 H-poor, highly evolved dwarf XTE J1807-294
ISSI BernDecembre 3, 2007
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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)
ISSI BernDecembre 3, 2007
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INTEGRAL IBIS/ISGRI Observation
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
Rev 261/262/263/264; Exposure 343 ks
December 2004 Outburst
(20-40 keV) significance level ~88σ
derived angular distance: 18´
ISSI BernDecembre 3, 2007
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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
ISSI BernDecembre 3, 2007
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OUTBURST PROFILE
Discovery (Eckert et al. 2004)
From RXTE (Galloway et al. 2005)
(Falanga, Kuiper, Poutanen et al. 2005)
ISGRI 20-100 keV
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
ISSI BernDecembre 3, 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
(Powell, Haswell & Falanga, 2007)
ISSI BernDecembre 3, 2007
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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)
ISSI BernDecembre 3, 2007
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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)
ISSI BernDecembre 3, 2007
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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
ISSI BernDecembre 3, 2007
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Spin-up IGR J00291+5934
We measured for the first time a spin-up for an accreting X-ray millisecond Pulsar
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
ISSI BernDecembre 3, 2007
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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
ISSI BernDecembre 3, 2007
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SAX J1808.4-3658
Rotation period: 2.5 ms Orbital period: 2 hrs
Low mass companionWijnands & van del Klis 1998
Chakrabarty & Morgan 1998 Light curve folded at the spin period
For a millisecond pulsar, e.g. SAX-J1808.4-3658, can take ~ 20% of 2.5 ms pulse period the time of flight delay cannot be neglected
Geometry illustration
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Constraints on the neutron star mass-radius relation obtained by fitting the pulse profile of SAX J1808.4-3658 (filled circles with error bars) toghether with a set of equations of state ans strange star
(Poutantn & Gierlinski 2003)
ISSI BernDecembre 3, 2007
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Intermittent MSP:
SAX J1748.9-2021 (Globular Cluster NGC 6440) , Pspin = 2.26 ms, Porb =8.3 hr.
AQL X-1, Pspin = 1.8 ms, Porb = ?
(Altamirano et al. 2007)
ISSI BernDecembre 3, 2007
(Casella et al. 2007)
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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
ISSI BernDecembre 3, 2007