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ACCRETING X-RAY MILLISECOND PULSARS IN OUTBURST

Decembre 3, 2007. ISSI Bern. 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.

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ACCRETING X-RAY MILLISECOND PULSARS IN OUTBURST

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  1. Decembre 3, 2007 ISSI Bern 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

  2. Decembre 3, 2007 ISSI Bern MSPs hosted in LMXBs Close X-ray binaries: Companion: M << Msun, Accretion disk, Compact object NS: B~108G • 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) • 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.) • 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.) • SXT: L ~ 1031-1032 erg/s in quiescent • L ~ 1036-1038 erg/s in outburst, recurence time 2-5 yr.

  3. Decembre 3, 2007 ISSI Bern The growing family of the X-ray millisecond pulsars …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)

  4. IGR J00291+5934 SAX J1808..4-3658 XTE J1814-338 Brown dwarfs Companion radius Rc/Rsun 0.1 Gyr 1 Gyr XTE J0929-314 XTE J1751-305 XTE J1807-294 5 Gyr White dwarfs Companion mass Mc/Msun Decembre 3, 2007 ISSI Bern Companion Star Assuming that the companion star should fill its Roche lobe to allow sufficient accretion on the compact 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 dwarf • XTE J1814-338 • XTE J0292-314 • XTE J1751-305 H-poor, highly evolved dwarf • XTE J1807-294

  5. Decembre 3, 2007 ISSI Bern Recycling model for MSPs • LMXB phase preceding the MSP stage; • mass transfer stops; • the radio MSP switches on Old Neutron stars spin up by accretion from a companion Spin up by mass accretion • Most binary MSPs have short orbital • periods and mass function identifying the • companions as low mass evolved dwarfs Radio Pulsar Millisecond Radio Pulsar Accreting NS in LMXBs are conventionally thought to be the progenitors of millisecond or „recycled“ radio pulsars(Alpar et al. 1982) X-ray transients can be the missing link between LMXBs and MSPs!

  6. IGR J00291+5934 Decembre 3, 2007 ISSI Bern (80 - 200 keV) INTEGRAL IBIS/ISGRI Observation Rev 261/262/263/264; Exposure 343 ks December 2004 Outburst IGR J00291+5934 2S0114+650 Cas Gamma Cas A V709 Cas (20 - 40 keV) (20-40 keV) significance level ~88σ derived angular distance: 18´ (40-80 keV) significance level ~51σ (80-200 keV) significance level ~17σ

  7. Decembre 3, 2007 ISSI Bern Geometry of the emission region 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. θ B ~ 108 G Seed photons from the hotspot Thermal Comptonization in plasma of Temperature ~ 40 keV XTE J1807-294 Rm Thermal disk emission (Falanga, Bonnet-Bidaud, poutanen et al. 2005)

  8. Decembre 3, 2007 ISSI Bern HETE J1900.1-2455 Type I X-ray burst

  9. Decembre 3, 2007 ISSI Bern PULSE PROFILE OUTBURST PROFILE IGR J00291+5934 Discovery(Eckert et al. 2004) From RXTE (Galloway et al. 2005) ISGRI 20-100 keV Rev 261/262/263, ~205 Porbit = 2.457 hr Ps = 1.67 ms Pdot = +8.4 x 10-13 Hz/s (Falanga, Kuiper, Poutanen et al. 2005)

  10. Distinct knee Outburst are extended as a consequence of X-ray irradiation of the disk?(King & Ritter 1998) Decembre 3, 2007 ISSI Bern OUTBURST PROFILE Discovery(Eckert et al. 2004) XTE J1807-294 XTE J1807-294 From RXTE (Galloway et al. 2005) ISGRI 20-100 keV (Falanga et al. 2005) (Falanga et al. 2005) (Wijnands 2005, astro-ph/0403409) (Powell, Haswell & Falanga, 2007)

  11. Decembre 3, 2007 ISSI Bern Pulsed fraction and Time lag : IGR J00291+5934 (Falanga, Kuiper, Poutanen et al. 2005) (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 indexΓ(E) = Γ0 + β(E/Ec)β

  12. Hard X-ray Soft X-ray Hot corona Accretion disk Decembre 3, 2007 ISSI Bern (Falanga et al. 2005) Time lag IGR J00291+5934 Time lag are normally hard Compton scattering model 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 seePoutanen 2001)

  13. Accretion column θhot Hard photons 1-Cill Hard photons θref Disk soft photons Cill Neutron Star Soft photons Disk Compton cloud Decembre 3, 2007 ISSI Bern (Falanga & Titarchuk 2007) Time/Phase Lag Model ∆t(Cill,ref,hot,neref,nehot) = upscattering lag + downscattering lag

  14. Decembre 3, 2007 ISSI Bern 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

  15. Decembre 3, 2007 ISSI Bern YES 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 0.2 arcsec 0.092 arcsec 0.2 arcsec 0.092 arcsec 1 Year Our observation 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 υ= + 5.8 ×10-14 Hz s-1

  16. « Star eats companion » «Une étoile cannibale »

  17. Pulsar spin-up Animation NASA, D. Barry

  18. SAX J1808.4-3658 Wijnands & van del Klis 1998 Rotation period: 2.5 ms Low mass companion Orbital period: 2 hrs Light curve folded at the spin period Chakrabarty & Morgan 1998 Geometry illustration 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

  19. Decembre 3, 2007 ISSI Bern 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)

  20. Decembre 3, 2007 ISSI Bern 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) (Casella et al. 2007)

  21. Decembre 3, 2007 ISSI Bern 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

  22. Decembre 3, 2007 ISSI Bern Thank You…

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