The Be/X-ray binary V

Transcription

1 The Be/X-ray binary V C. Ferrigno, V. Savchenko, M. Kühnel, L. Ducci,. P. Kretschmar, K. Pottschmidt, J. Wilms, E. Bozzo, C. Malacaria, A. Santangelo, G. Schönherr 1

2 Introduction High mass X-ray binaries are young systems, where NS has a high B-field ( G) wind-fed systems but with formation of transient accretion disk transients or persistent Be/X-ray binaries become very bright during outbursts and give high S/N: an ideal laboratory. L outburst X L quiescence X

3 A giant outburst ten years later INTEGRAL Swift-BAT MAXI Flux (Crab) The outburst followed a predictable decay pattern Time (MJD) courtesy M. Kühnel Modulation at the orbital period (34 days). Three INTEGRAL observations: 85 ks, 147 ks, 73 ks. 3

4 Emission mechanisms in a high magnetic field The accreting matter acquires a high kinetic energy v~c/2 which is partially dissipated close to the compact object surface and emitted in the form of X and Gamma-rays. If the neutron star has a considerable magnetic field, the accreting matter is channeled at the magnetic poles along the field lines and accretes on the poles. For high accretion rates, radiation dominates: a radiative shock and an accretion column form. Seed photons coming from thermal mound and electron breemstrahlung, in the high B-field, are Compton scattered. Becker & Wolff (2007) 4

5 Kreikenbohm et al. (2005) Cyclotron scattering absorption features Electrons are exited to the first Landau level and then re-emit To be observed in the X-ray domain, a B-field of G is required G Discovered on the spectrum of Her X-1 (Trumper 1977, 1978) Cyclotron lines Trumper et al. (1978) V Isenberg et al. (1998) 5

6 Luminosity dependent cyclotron line Tsygankov et al (2009) INTEGRAL RXTE/PCA Mowlavi et al. (2006) Only clear example of anticorrelation 6

7 Formation site of cyclotron lines Schwarm et al. (2013) Poutanen et al. (2013) The surface layers of the column The neutron star surface 7

8 From OSA 10 to 11 for IBIS OSA 10 OSA 11, preliminary Fit OSA 11 plot residuals OSA 10. Huge difference below 50 kev and above 80 kev. same kev. 8

9 OSA 11 improvements Work by V. Savchenko in the IBIS/ISGRI team in APC (Paris) Account for drifting gain and energy resolution degradation. New lowenergy reconstruction. Response matrix computed from MC simulations. 9

10 Cyclotron line energy E1 [kev] E2 [kev] IBIS+JEM-X (2005) IBIS+JEM-X (2015) SPI+JEM-X (2005) SPI+JEM-X (2015) No JEM-X Preliminary log 10 Flux ( kev) [erg/s/cm 2 ] Different line model (gabs) from previous slide (cyclabs, +~1 kev). Some differences from 2005, but similar trend. IBIS OSA11 is preliminary! 10

11 Pulse profiles Assuming isotropic emission from the base of a filled or hollow column plus a halo at the base Strong energy dependence (right figure) Sharp structures due to self-obscuration from the flow 11

12 Pulse decomposition Assuming that there are two identical poles, placed asymmetrically on the NS and using several observations, it is possible to reconstruct the geometry and the energy dependent emission pattern. Sasaki et al.(2012) 12

13 Pulse profiles High lum. Low lum. Double-peak structure disappearing at the lowest luminosity in correspondence of the cyclotron line absorption features Need more modeling to understand the details of the emission pattern close to the neuron star. 13

14 Energy Column beam pattern Luminosity More isotropic emission at lower luminosity Double peaked emission at the maximum: hollow column? 14

15 Geometries High Lum. Low Lum. Coupling between disk and magnetosphere 15

16 Energy-phase matrix NRT

17 Pulse profile Dramatic luminosity dependency at the energy of the cyclotron line. 17

18 Conclusions The outburst followed the same decay pattern of 2005 after a shallower rise. This will be used to study the interaction pattern between the NS and the Be star outflow. The luminosity dependency of the cyclotron line energy is present also in this second outburst of the source, but the hard X-ray flux is different (under investigation). The spin-phase dependent analysis confirms a change of the structure in the accretion stream near the neutron star at different luminosities. Another team will exploit NuSTAR data to study this source. 18

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20 SPIROS and SPIDAI SPIDAI (Toulouse) SPIROS (OSA) ~15% different normalization, but same shape. 20