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Nature of X-ray transients in the Magellanic Clouds : (Be/X-ray pulsars, and Supersoft sources)

Nature of X-ray transients in the Magellanic Clouds : (Be/X-ray pulsars, and Supersoft sources) . Andry RAJOELIMANANA 1 , 2 ‏ Supervisor : Prof Phil CHARLES 3 Co-supervisor : Prof Brian Warner 1.

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Nature of X-ray transients in the Magellanic Clouds : (Be/X-ray pulsars, and Supersoft sources)

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  1. Nature of X-ray transients in the Magellanic Clouds : (Be/X-ray pulsars, and Supersoft sources) Andry RAJOELIMANANA 1 , 2 ‏ Supervisor : Prof Phil CHARLES 3 Co-supervisor : Prof Brian Warner 1 1 University of Cape Town (UCT), 2 South African Astronomical Observatory (SAAO) 3School of Physics and Astronomy, Southampton University

  2. Outline • Be/X-ray transients • Introduction • Long-term properties • SALT/RSS spectroscopy. • Supesoft sources : CAL83 and RX J0513-6935 • Long-term properties • Orbital periodicities. • X-ray spectroscopy. • X-ray/optical anti-correlation. • Summary

  3. Be/X-ray pulsar (BeX) • Be Star + X-ray pulsar • Transient X-ray sources (Lx~1037 erg.s-1) • Wide and eccentric orbit (0.1<e<0.9) • Accretion from the Be equatorial disc

  4. Long-term variations (18 yrs observation) MACHO and OGLE light curves (Rajoelimanana, Charles & Udalski ., 2011,MNRAS, 413,1600)

  5. V vs. V-R diagram SXP18.3 Loop-like structure. • Disk-less phase • Disk formation • Disk dissipation “Be – Normal B – Be” star transitions.

  6. SALT/RSS Broad-band Spectra Optical high state Optical low state Be star Normal B-star

  7. SALT/RSS High resolution Blue Spectra • Spectral classification (temperature criteria). • Rotational velocities.

  8. Outbursts amplitude vs. brightness • The strength of the outburst increases with the brightness of the source.

  9. Evolution of the line profiles in A0538-66 Disk-less phase Outburst phase=1.0 Before phase=0.87 After phase=1.24

  10. Orbital and super-orbital period correlation Shorter period : truncated at smaller radius Rajoelimanana, Charles & Udalski ., 2011,MNRAS, 413,1600

  11. Supersoft X-ray sources (SSS)

  12. SupersoftX-ray sources (SSS)‏ • TBB~ 20-50 eV • Lbol ~ 1037 - 1038erg s-1 • Supersoft emission < 0.5 keV • SSS system : • WD + Sub-giant companion • High accretion rate > 10-7Msun yrs-1 • WD burns H steadily at its surface • Orbital period : Porb< ~1 d

  13. Long-term MACHO and OGLE light curves CAL 83 Timescale ~ 450 d Optical minima duration : ~ 200 d RXJ 0513.9-6951 Timescale ~ 170 d Optical minima duration : ~ 30 d (Rajoelimanana, et al 2011 (in prep))

  14. Orbital periodicity Detrend: subtract a linear fit. Refinement of the orbital periods using 18 yrs light curves CAL 83 Porb= 1.04752 +/- 0.00001 RX J0513.9-6951 Porb= 0.76295 +/- 0.00001 d Rajoelimanana, Charles & Udalski ., 2011 (in prep)

  15. XMM-Newtonspectra of CAL83 • EPIC-PN spectra fitted by blackbody model (using Xspec) • nH=6.5 x 1020cm-3 (frozen, HST) (Rajoelimanana, et al 2011 (in prep))

  16. X-ray / Optical anti-correlation in CAL83 Optical low X-ray on Optical high X-ray off or very weak Tbbfrom 40 keV to 25 keV (Rajoelimanana, et al 2011 (in prep))

  17. X-ray / Optical anti-correlation Optical low X-ray on Optical high X-ray off or very weak • Contraction model : (Southwell et al., 1996)‏ • Accretion rate drops Rwd decreases (Optical brightness decreases) • rise in effective temperature (from ~ 25 keV to 40 keV) • increase in X-ray luminosity No X-ray emissions detected during optical high state peak of the emission is SHIFTED from the supersoft X-ray to the UV

  18. Summary • Be/X-ray transients • Loop-like structure in the colour magnitude diagram. • Disk-less, disk formation, disk dissipation phases. • Broad-band spectra : “Be – Normal B – Be star” transitions. • High resolution spectra : Spectral classifications and rotational velocities. • Correlation between orbital and super-orbital periodicities • Supesoft sources : CAL83 and RX J0513-6935 • Long-term variations on timescales of 450 d and 170 d, respectively • Refinement of their orbital periodicities. • Anti-correlation between X-ray count rate and optical brightness. • Anti-correlation between blackbody temperatures/luminosities and optical brightness (Contraction model). • The peak of the emission is shifted from supersoft X-ray into the UV during optical high state.

  19. Thank you

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