Transient outburst mechanisms in supergiant fast X-ray transients

Sidoli

reporter: zhangzhen 09.11.23

Confirmed sources: (eight)

• IGR J08408-4503• IGR J11215-5952• IGR J16479-4514• XTE J1739-302 (Smith et al. 1998 arxiv:9805178v1)• IGR J17544-2619• SAX J1818.6-1703• IGR J18410-0535• IGR J18483-0311

• Sporadic outbursts lasting minutes to hours Luminosity of the peak ~ Luminosity in quiescence ~

• Spectra: HMXB A flat hard power law below 10keV a high energy cut-off at about 15-30keV

• IR/optical observation: OB supergiant companion wind accretion (Halpern et al. 2004, Pellizza et al. 2006, Masetti et al. 2006)

36 3710 1031 3310 10

• Sodoli et al. 2006 arxiv:0610890v1

Something extra :IGR J11215-5952

• X-ray pulsar: Ps=186.78s• Outbursts: Period ~329 days 3-4 July 2003 26-27 May 2004 (Sguera et al. arxiv:0603756)

Spaced ~330 days 16-17 March 2006 (smith et al. The Astronomer’s Telegram 766)

9 February 2007 (Romano et al. 2007)

Models

• Clumpy winds

• Anisotropic winds

• Gated mechanisms

Clumpy winds

Outbursts from spherically symmetric clumpy winds

• The mass loss rate in the form of wind clump:

Walter & Zurita Heras. 2007 Arxiv:0710.2542v1 Result match Oskinova et al. 2007

• The problem of the model

• Accretion process complex:Centrifugal effect of a neutron star’s magnetic field Lx and the dense of the wind (Grebenev & Sunyaev 2007)

Outbursts from spherically symmetric clumpy winds

Model: Oskinova et al. 2007

Negueruela et al. 2008Arxiv: 0801.3863v1

Oskinova et al. 2007 arxiv:0704.2390v2

Anisotropic winds

• The problem of the model (IRG J11215-5952)

Sidoli et al. 2007 arxiv:0710.1175v1

Outbursts from anisotropic winds: a preferential plane for the outflowing wing

• Problem of the clumpy wind model:

• &

• The density and/or velocity contrasts in the wind can be eased if there is a barrier that remains closed during quiescence

MrelV

Gated mechanisms

Gated mechanisms• Definition of 3 radius:• Ra: the accretion radius Gravitationally focuesd• Rm: the magnetospheric radius The pressure of the magnetic field > the ram pr

essure of the inflowing matter• Rco: the corotation radius the angular velocity of NS = Keplerian angular ve

locity

Rm>Ra: the magnetic inhibition of accretion

• Rm>Ra,Rco• The superKeplerian • magnetic inhibition regime

• Rco>Rm>Ra• The subKeplerian • magneitc inhibition regime

Rm<Ra: propeller

• Rco<Rm<Ra• The supersonic propeller

regime

• Rm<Ra,Rco & • Tne subsonic propeller re

gime

limwM M

• Rm<Ra,Rco &

• The direct accretion regime

limwM M& &

Transitions

• Long spin period systems require magnetar-like B-fields

• Shorter spin period systems must posses lower magnetic fields

• Few or no transitions with either high magnetic fields and short spin periods, or systems with lower magnetic fields and long spin periods

Application to IGR J17544-2619

• Quiescent

• Rise

• Outburst peak

• Tail

32 12 10xL ergs

34 11.5 10xL ergs

37 14 10xL ergs

36 12 10xL ergs

Ps=1300s, strong B• Quiescent superKeplerian magnetic inhibition• Rise subKeplerian magntic inhibition• Outburst peak direct accretion • Tail direct accretion Mdot decrease

Ps=400s, weak B

• Quiescent supersonic propeller• Rise subsonic propeller• Outburst peak direct accretion • Tail direct accretion Mdot decrease

• Problem of the model

• Both explanation require B>10^15G and >10^13G, in the magnetar range

Thanks