Transient NS X-ray binaries with

Simbol-X

Sergio Campana Osservatorio astronomico

di Breracampana@merate.mi.astro

.itBologna, May 2007

Outline

RXTE/ASM light curve

A brief history: what we discovered and what we know now, focusing of hard X-ray emission

The future: Simbol-X

X-ray binaries: variable

State transitions: SIGMA

Barret & Vedrenne 1994

Limiting luminosity for all LMXRBs (NS+BH) at 4x1036 erg/s

Maccarone 2003

Campana et al. 1998

Hard tails: INTEGRAL

Tarana et al. 2007

4U 1820-30

Paizis et al. 2006

BH XRB

NS XRB

Homan et al. 2007

State transitions: jets

Belloni 2007

Campana et al. 1998 Di Salvo et al. 2000

Farinelli et al. 2007

Occasional detection of very hard tails (BMC)

GX 17+2

Very hard tails: PDS/XTE

From outburst to quiescence

FAST !

e-folding time changing from ~20 d to ~1 d at transition

BeppoSAX data

Campana et al. 1998

NS transients in quiescence

Canonical spectrum: Soft component (NS atmosphere, kT~0.1-0.3 keV; ≥50% of the flux)

Hard component (Power law, photon index ~1-2; ≤50% of the flux)

ExN

(E)

ExN

(E)

Lx=1032-1033 erg/s

NS transients in quiescence: variability

Campana et al. 2003 Rutledge et al. 2001Campana &Stella 2004

Aql X-1

Transient X-ray pulsars

Campana et al. 2007

Wijnands 2005

SAX J1808.4-3658

mcr

ab

SAX J1808.4-3658 in quiescence

NS atmosphere model can account less than 10% of

the total flux and it is not required by the fit

XMM-Newton data

Campana et al. 2002

Heinke et al. 2007

Simbol-X strenghts (for XRBs)

• Broad-band capabilities (0.5-80 keV)

• Large effective area at low and high energies

• Good timing capabilities

• Focusing instrument and thus low background

(e.g. wrt RXTE)

Simbol-X: atoll spectrum

kTC

100 ks

Fx=10-9 erg/s/cm2

Lx=4x1036 erg/s @ 5 kpc

Monitoring of parameters

variations: study the physics

3σ

Simbol-X: very hard tails

kTc=5 keV 40 ks

Tau=3

CONT: Fx=2x10-9 erg/s/cm2

TAIL: Fx=6x10-12 erg/s/cm2

Tail/Cont(0.5-20)= 0.1%

NS transient in quiescence

100 ks

Diagnostic of the

power law tail and of

its variability

SAX J1808.4-3658 in quiescence

100 ks

XMM

Summary

Different mechanisms for explaining the transition to and the quiescent emission of NS XRTs approach the problem from the point of view of physics

Simbol-X is the first observatory able to disclose the high energy part of the spectrum at very high S/N and for persistent and transient sources, making possible a thorough study of the emission mechanisms through monitoring the variability