Документ взят из кэша поисковой машины. Адрес оригинального документа : http://hea.iki.rssi.ru/conf/hea2007/presentations/26.12.2007/07-postnov.pdf Дата изменения: Wed Jan 30 21:47:17 2008 Дата индексирования: Tue Oct 2 01:11:45 2012 Кодировка: Поисковые слова: m 5

A0535+26

.. ( ) In collaboration with:
R.Staubert, A.Santangelo, P.Kretschmar, I.Caballero, D.Klochkov IAAT, U. of Tuebingen


Introduction

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Error bars: 90% CL

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outburst pre-flares

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Error bars: 90% CL

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Summary of the RXTE/INTEGRAL analysis

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Swift BAT light curves
Giant o. Apr/May 05 Look-up

1st normal o. Aug/Sep 05

2nd normal o. Dec 05

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Rising of the Aug/Sep 2005 outburst

t=104 - 3 104 s
Typical mass in X-ray flares: M= E /(0.1c 2 ) 3 1020 - 1021 g
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Disk-magnetospheric interaction
Boundary layer: <20cs / K (Anzer & Boerner, 1983) ~5cs /
K

(Lovelace et al. 1995)

Lovelace et al. 1995

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Estimate of mass in the boundary layer: h ~ 0.1Rm Standard Shakura-Sunyaev accretion disk: M= (2 R m ) 2h ;
7/ (2 1019 g) rm,5 9 - 4/5

M

3/ 5 - 10

(1 - )

3/ 5

= j / jin ,

j = M GMr

At the beginning of outburst 0 ~ 0.01, M - 10 ~ 3 M~1021g
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Linear analysis (Arons & Lea, 1976, Baan 1977, 79):

: exp( t ),
2 = kg
eff

tanh(kz )

The effective acceleration near the equatorial plane: g
eff

GM (k ) 2 u 3µ 2 k µ 2 rm dV 2 2 - rm - - - - 6 6 6 rm 4 m krm 4 m Rc rm 4 m rm 4 dz

rm

Centrifug. force

m.f.line curvature 1st-order correction due to current sheet

Bending of field lines due to instability
g g
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eff eff

> 0 instability; low-modes (large k) first instable < 0 stability
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At small M, accretion is centrifugally prohibited (R m > rcor = (GM / *2 )1/ 3 ). g When M increases, R m M
eff



GM 2 (1 - *2 / K ) < 0 2 Rm decreases

- 2/7

A the onset of accretion (when R m < Rcor ) g eff can be positive unstable magnetospheric accretion can occur (like in the rapid burster MXB 1730-335)

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How does this explain the observed features of Aug/Sep 05 outburst?
1) X-ray luminosity of flares are due to spasmodic accretion of matter from unstable NS magnetosphere
2) Blobs with M 1021 g produce very small spin-up P P =
max

M GMRm 7 10- 6 , 2 I

within period measurement errors

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3) Plasma entering magnetosphere through KS-instability can be frozen closer to NS and falls along different lines difference in the CRSF in flares and the main outburst

4) Independence of Ec on luminosity during the main outburst suggests the absence of radiation-dominated accretion column (like in Her X-1, Staubert et al. 2007). Ec/Ec~10% in the flare B/B~10% R/R~3% R~300 m! Emission during the flare comes almost from the NS surface.

Explanation of the different pulse profile evolution
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5) Smooth p.p. change with energy in the flare suggests pencil-beam emission diagram in the flares. In the main outburst accretion column is higher and can have additional fan-beam formed by e-photons.
E = Ec :

Only pencil-beam ? Fan-beam due to e-photons disappears after crossing Ec

P ; T ( E / Ec ) 2 (e)
; T in 2 + cos 2 ( E / Ec ) 2 (o) s P = @ ~ /2
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E Ec :



~ P@ ~ /2
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Pencil-beam

Pencil-beam B

Fan beam

Flares

Main outburst

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6. The amplitude of X-ray flares are strongly reduced when the NS spin-up starts, because then =j/jin -> 1 and the mass in the boundary layer decreases (M~(1- )3/5). When spin-up stops, flaring activity appears again (after Sep. 14, see the BAT light curve)

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Other X-ray transients: 1) 2S 1845-024

Finger et al. 1999
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2) EXO 2030+375

Camero Arranz et al 2005
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Conclusions
· X-ray flares at the beginning of X-ray outbursts in A0535+26 can be due to magnetospheric instability · Spasmodic accretion on top of quasi-stationarily increasing accretion rate explains all features observed in Aug/Sep 2005 outburst of A0535+26 · Such behavior is expected at some critical accretion rate and is observed in other sources (e.g. 2S 1845-024 (Finger et al. 1999), EXO 2030+375 (Camero et al. 2005)). · Further studies are under way searching for cyclotron line energy in other flares of A0535+26 and in other sources

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