Observations and physics of accreting neutron star ISSI, Bern, Switzerland December 3-7, 2007

Participants Juri Poutanen (University of Oulu, Finland; Team Leader) Andrei Beloborodov (Columbia University, USA) Chris Done (University of Durham, UK) Maurizio Falanga (CEA-Saclay, Service d' Astrophysique, France) Marat Gilfanov (Max Planck Institute f\"ur Astrophysik, Garching, Germany) Tatiana Larchenkova (Astro Space Center, Moscow, Russia) Alexander Lutovinov (Space Research Institute, Moscow, Russia) Sergei Molkov (Space Research Institute, Moscow, Russia) Mike Revnivtsev (MPA, Garching, Germany) Valery Suleimanov (University of Tubingen, Germany) Andrzej Zdziarski (N. Copernicus Astronomical Center, Warsaw, Poland) Young scientists Marja Annala (University of Oulu, Finland) Kris Beckwith (Univ. of Virginia, USA) Askar Ibragimov (University of Oulu, Finland) Sergey Tsygankov (Space Research Institute, Moscow, Russia)

Program for the meeting Juri Poutanen: Introduction Alexander Lutovinov: About a possibility to observe the effect Shapiro for pulsars in globular clusters Sergey Tsygankov: Observational features of X-ray pulsars emission revealed with INTEGRAL and RXTE observatories Marja Annala: X-ray pulsars Maurizio Falanga: X-ray accreting millisecond pulsars in outbursts Valery Suleimanov: Importance of Compton scattering on radiation spectra of accretion columns in millisecond pulsars and intermediate polars Askar Ibragimov: SAX J1808 in 2002

Topics to be covered X-ray bursts & nuclear-powered millisecond pulsars (NMSPs) Accreting millisecond pulsars (AMSPs) X-ray pulsars Theory of accretion columns on a weakly magnetized neutron stars Theory of boundary layers on neutron stars © Michael Kramer

Nuclear-powered millisecond pulsars

SourceOrbital period [h] spin [Hz] 4U ?363 4U ?581 KS ?524 at Gal. center?589 Aql X U ?330 MXB U U ?619 SAX J ?601 A IGR J ?294 SAX J XTE J XTE J ?1122 ? EXO Nuclear-powered millisecond pulsars

Time (s) 4U Strohmayer et al (1996) ; Strohmayer, Markwardt (1999) Time (s) Millisecond oscillations during X-ray bursts

Time (s) simulations by A. Spitkovsky Millisecond oscillations during X-ray bursts

Piro & Bildsten 2006 Observed A(E) is consistent with the black body Pulse fraction in X-ray bursts

RMS in X-ray bursts from AMSP XTE J

Theory of the accretion column for X-ray bursters

Accretion-powered millisecond pulsars Romanova et al. (2004)

Power density spectrum. From Wijnands & van der Klis (1998). April 1998 outburst. From Gilfanov et al. (1998). SAX J : the first accreting millisecond pulsar

SAX J XTE J XTE J Outbursts profiles

1. Wijnands & van der Klis 1998, Chakrabarty & Morgan 1998; 2. Markwardt et al Remillard et al. 2002; Galloway et al. 2002; 4. Markwardt et al Markwardt et al. 2003; 6. Markwardt, Swank, Strohmayer, Dec 3, Morgan, Kaaret, Vanderspek, June 17, 2005; Kaaret et al. 2005; 8. Markwardt et al. June 14, 2007 Source P orb min n spin Hz f X / M Sun M c,min / M Sun 1. SAX J x XTE J x XTE J x XTE J x XTE J x IGR J x HETE J x SWIFT J x Accretion-powered millisecond pulsars

XTE J IGR J XTE J disc spot kT bb =0.66keV kT e = 60 keV t T = 0.9 Spectral energy distribution

kT disc =0.43 keV kT seed = 0.75 keV A seed = 26 km 2 kT e = 37 keV t T = 1.7 disc Solid – persistent emission; histogram - X-ray bursts. Strohmayer et al. (2003). Kirsch et al. (2003) XTE J XTE J XTE J Gierlinski & Poutanen 2003 Pulse profiles

Pulsar geometry

In ms pulsars, rotational velocities are high (b =v/c ~0.1), the Doppler effect plays an important role Doppler effect

Phase slow pulsar (dashes) fast pulsar, =401 Hz F sc,E (fast) ~ d 3+ G F sc,E (slow) F bb (fast) = F bb (slow) x d 5 Poutanen & Gierliński (2003) Doppler boosting I obs =d 4 I em Aberration cos a obs =  d cos a e Light curves of MSP d =1/ g (1 - b cos q ) – Doppler factor g =1/  1-b 2 – Lorentz factor

Mass/ M  Poutanen & Gierlinski (2003) Radius, km Constraints on the equation of state Complications: Shape of the star Shape of the spot Influence of the accretion disk

Count rate Phase Pulses from SAX J1808

Bildsten et al. (1997) X-ray pulsars Obtaining neutron star parameters from the X-ray pulse profiles A

Boundary layers and quasi- periodic oscillations Sco X-1

4U

From Gilfanov, Revnivtsev and Molkov (2003). Frequency-resolved spectra of QPOs and the boundary layer

Matter has a significant latitude velocity component, spreading above the neutron star surface and decelerating due to friction with the neutron star surface (as the wind above the sea). From Inogamov and Sunyaev (1999) BL as a spreading layer

SL model Atoll & Z sources GX Spectra of neutron star BL

Constraints on EOS of NS From Suleimanov and Poutanen (2006) How QPOs are produced ?

Analysis and theoretical modeling of the data on X-ray pulsars (Lutovinov, Tsygankov, Annala, Ibragimov) Modeling the accretion column (Suleimanov, Poutanen) Theoretical modeling the light curves from millisecond pulsars (Poutanen, Larchenkova, Falanga) Impact of the accretion disk on the light curves (Ibragimov, Annala, Poutanen) 2D and optically thin boundary layer models (Poutanen, Suleimanov) Proposed projects