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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)
MACHO and OGLE light curves
(Rajoelimanana, Charles & Udalski ., 2011,MNRAS, 413,1600)
V vs. V-R diagram
SXP18.3
Loop-like structure.
• Disk-less phase
• Disk formation
• Disk dissipation
“Be – Normal B – Be” star
transitions.
SALT/RSS Broad-band Spectra
Optical high state
Optical low state
Be star
Normal B-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
Disk-less phase
Outburst
phase=1.0
Before
phase=0.87
After
phase=1.24
Orbital and super-orbital period correlation
Shorter period :
truncated at
smaller radius
Rajoelimanana, Charles & Udalski ., 2011,MNRAS, 413,1600
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 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))
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)
XMM-Newton spectra 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))
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


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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


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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