Low Mass X-ray Binaries and Accreting Millisecond Pulsars

1. Low Mass X-ray Binariesand Accreting Millisecond Pulsars A. Patruno R. Wijnands M. van der Klis P. Casella D. Altamirano N. Danegaar ASTRONOMICAL INSTITUTE A. PANNEKOEK UNIVERSITY OF AMSTERDAM

2. Low Mass X-ray Binaries & Accreting Millisecond Pulsars

3. Projects in Amsterdam • Accreting Millisecond Pulsars (AMPs) Periodic Timing Intermittent pulsars • Cooling of LMXBs (cooling curves, EOS) • Magnetars • QPOs • Radio Pulsars (timing, glitches) • Neutron Star oscillations • Thermonuclear bursts

4. Periodic Timing 1: the pulse profiles • Fold pulse profiles • (extreme variability) • 2. Track the phase of each folded profile, i.e., determine the Time Of Arrivals of the pulsations (TOAs) • 3. Fit a model to the TOAs: for example a binary circular orbit + a spin frequency • 4. Look at the residuals ! Fig. from Hartman et al. 2008

5. Periodic Timing 2: the Timing Noise XTE J1807-294 SAX J1808.4-3685 XTE J1814-338 Hartman, Patruno et al. 2008 Patruno Hartman et al. in prep.

6. Periodic Timing 3: the enigmatic FAR relations XTE J1814-338 XTE J1807-294 The fractional amplitude of the pulsations is anticorrelated with the time of arrival of the pulsations (i.e. when the fractional amplitude is larger the pulses arrive earlier than predicted by the model) Patruno et al. in prep.

7. Periodic Timing 4: physical interpretation 1. No glitches: is the hot spot moving ? (it has to preserve the 2nd harmonic’s phase) 2. Why we see timing noise and FAR relations only in some AMPs ? SAX J1808-3658: 50 deg. in 2002 and 2005 outbursts (Hartman et al. 2008) XTE J1807-294: up to ~100 deg. (Patruno et al. in prep) SAX J1748.4-2021: ~140 deg. (Patruno et al. 2008) XTE J1814-338: ~50 deg. Gradually (Papitto et al. 2007) Long et al. 2008

8. 3 months 25 minutes 150 seconds pulsations at ν = 550.27 Hz detected in 0.01% of the exposure Intermittent Pulsar 1: the discovery of pulsations in Aql X-1 Casella et al. 2007 12 years

9. 7 years few hours pulsations at ν = 442.36 Hz in a few % of the exposure few minutes Intermittent pulsar 2: SAX J1748.9-2021 Altamirano et al. 2007 Gavriil et al. 2007 Patruno et al. 2008

10. Intermittent pulsar 3: current situation 7 AMPs with pulsations throughout the outburst HETE J1900.1-2455 only first 2 months SAX J1748.8-2021 intermittent, hundreds of seconds Aql X-1 only for 150 seconds Is magnetic screening ruled out ?

11. Cooling of accreting Neutron Stars Quasi persistent sources: very long outbursts (KS 1731-260: 12.5 years, MXB 1659-29: 2.5 years) compared to “normal” X-Ray Binaries

12. Cooling of accreting Neutron Stars KS 1731-260 y(t)=a exp[-(t-t0)/b] + c MXB 1659-29 a = normalization constant b = e-folding time c = constant offset (core temperature) Flux and Temperature well fitted by an exponential decay plus a constant offset (core temperature)

13. Cooling of accreting Neutron Stars: physical interpretation Rutledge et al. 2002 calculated detailed cooling curves for KS 1731-260 using the mass accretion history of the source. High crust thermal conductivity Enhanced cooling Rutledge et al 2002, Wijnands 2005, Cackett et al. 2006

14. Open issues • What is the origin of the timing noise in AMPs ? • Why pulse shape changes ? (motion of the hot spot, magnetic field instabilities) • Why we see intermittent pulsations ? (magnetic field burial, smearing of pulsation, crustal cracks) • Cooling: are the cooling curves suggesting an enhanced neutrino emission and high crustal thermal conductivity ?

15. THANK YOU !