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) 3 School of Physics and Astronomy, Southampton University

Outline  Be/X-ray transients  Introduction  Long-term properties  SALT/RSS spectroscopy.  Supesoft sources : CAL83 and RX J  Long-term properties  Orbital periodicities.  X-ray spectroscopy.  X-ray/optical anti-correlation.  Summary

Be/X-ray pulsar (BeX) Be Star + X-ray pulsar Transient X-ray sources (Lx~10 37 erg.s -1 ) Wide and eccentric orbit (0.1<e<0.9) Accretion from the Be equatorial disc

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

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

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

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

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

Evolution of the line profiles in A Outburst Before After phase=1.0 phase=1.24 phase=0.87 Disk-less phase

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

Supersoft X-ray sources (SSS)

Supersoft X-ray sources (SSS)‏ T BB ~ eV L bol ~ erg s -1 Supersoft emission < 0.5 keV SSS system :  WD + Sub-giant companion  High accretion rate > M sun yrs -1 WD burns H steadily at its surface Orbital period : P orb < ~1 d

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

Orbital periodicity Detrend: subtract a linear fit. Refinement of the orbital periods using 18 yrs light curves CAL 83 P orb = / RX J P orb = / d Rajoelimanana, Charles & Udalski., 2011 (in prep)

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

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

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 R wd 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

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 J  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.

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