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 J0513-6935 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~1037

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 stateOptical 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 A0538-66

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)

• TBB ~ 20-50 eV

• Lbol ~ 1037 - 1038 erg s-1

• Supersoft emission < 0.5 keV

• SSS system : WD + Sub-giant companion High accretion rate > 10-7 Msun yrs-1

• WD burns H steadily at its surface

• Orbital period : Porb< ~1 d

Long-term MACHO and OGLE light curves

CAL 83Timescale ~ 450 d

Optical minima duration : ~ 200 d

RXJ 0513.9-6951Timescale ~ 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 Porb= 1.04752 +/- 0.00001

RX J0513.9-6951 Porb= 0.76295 +/- 0.00001 d

Rajoelimanana, Charles & Udalski ., 2011 (in prep)

EPIC-PN spectra fitted by blackbody model (using Xspec)

nH=6.5 x 1020cm-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

Tbb 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 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

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.

Thank you