Download X-ray pulsars in wind-fed accretion systems

X-ray pulsars in wind-fed
accretion systems
王
伟
(NAOC)
July 2009, Pulsar Summer School Beijing
Neutron star accretion in binary systems
 Disk accretion:
Roche lobe filling; outflow
Companion:
low mass stars; massive stars; white dwarfs
 Wind accretion:
Roche lobe under-filled
Companion:
massive stars (>10M⊙)
with strong stellar winds
NS
Wind-fed accretion neutron stars
• X-ray luminosity (1034-37 erg/s) lower than those (103839 erg/s) of disk-fed accretion
• Higher column density (NH>1022 cm-2)
maybe absorption in soft X-rays (<3 keV);
hard X-ray observations (10-100 keV) better
• BASTE (20-60 keV) aboard CGRO discovered >10
these systems
companion: Be stars (main-sequence/under-filled) - circumstellar
decretion disk – X-ray transients;
Supergiants (evolved; strong winds) , direct wind accretion
INTEGRAL hard X-ray all-sky surveys
(20-200 keV)
Exposure Map of present observations
INTEGRAL discoveries of supergiant fast X-ray transients (SFXTs)
wind-fed accretion systems
IGRJ18450-0435
IGR J17544−2619
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•
•
IGR J17391−3021
IGR J17544−2619
IGR J18410−0535
IGR J18410−0535
About 12 systems identified, wind-fed, supergiant companion
Outburst, L=1036 erg/s; otherwise L<1034 erg/s
Origin unknown; proposed - clumps in supergiant winds
INTEGRAL hard X-ray all-sky surveys
(20-200 keV)
Exposure Map of present observations
First sky region we studied – Cas A region
Hard X-ray views around Cas A region (20 – 60 keV)
18 sources: 2 SNRs, 1 AXP, 1 AGN, CV, X-ray binaries, transients, unidentified
Three sources studied here: known wind-fed systems 2S 0114+65; 4U 2206+54
unidentified IGR J01583+6713
2S 0114+65
• Supergiant X-ray binary, distance 7.2 kpc
• Pspin=2.7 hr (around 2000); Porb=11.6 day
• Neutron star is spinning up
2S 0114+65
Finley 1992
6.9x10-7
Hall 2000
8.9x10-7
Bonning 2005
(INTEGRAL)
Spin-up rate:
1.2x10-6 s/s
Wang & Jiang 2009
INTEGRAL
Farrell 2008
RXTE
1.6x10-6
2S 0114+65
• Supergiant X-ray binary, distance 7.2 kpc
• Pspin=2.7 hr (around 2000); Porb=11.6 day
• Neutron star is spinning up
not in accretion equilibrium
• Formation mechanism of super-long pulsation
unclear at present
(1) Li & van den Heuvel (1999) : an initial magnetar (>1014 G)
decaying to current 1012 G, allowing the spin period down to >1000
s within lifetime of companion.
magnetic field strength of 2S 0114+54 is unknown
(2) Ikhsanov (2007): angular momentum transfer in propeller phase
2S 0114 light curve 2003 – 2006 by INTEGRAL
Ecyc = 66±5 keV
B=7x1012 G
Magnetic neutron star in
2S 0114+65
Wang & Jiang 2009
2S 0114 light curve 2003 – 2006 by INTEGRAL
4U 2206+54
• Low luminosity X-ray binary: 1033 – 1035 erg s-1 (1-10 keV)
• Donor: a main-sequence star, O9.5V star, d=3 kpc
the only permanent wind-fed HMXB with a main-sequence donor
• compact object of unknown nature, and most think it is a NS
INTEGRAL observations (20 -40 keV)
2003 Dec
2005 Dec 5-13
2005 Dec 15
2005 Dec 18 -25
Light curve from Dec 11 – 19 2005
Peak =Burst ?
Cyclotron absorption line
29.6±2.8 keV and
59.5 ±2.1 keV
a magnetic field of
3.3x1012 G
Wang 2009a
Light curves of the peak
Pulse period
5500 -5600 s
Reig et al. (2009) found a
pulsation of around 5560 s
using RXTE/PCA data
P=5600 s
4U 2206+54 identified as a
magnetic neutron star of long
pulsation!
2005 Dec - 4U 2206+54 - INTEGRAL+RXTE/ASM
INTEGRAL Julian Date (IJD, starting at 2000 January 1)
Exponential-like
decay –
Type 1 X-ray
bursts
1 Crab = 2.2x10-8 erg cm-2 s-1 (1.5 -12 keV) ; 7.6x10-9 erg cm-2 s-1 (20-40 keV)
First peak by ASM: Lx =3.6x1036 erg/s
(1.5-12 keV);
Second by IBIS:
Lx(mean)=1036 erg/s (20-40 keV)
The first peak of the burst
Hardness Ratio evolution
HR reaches a peak of 8-9, much higher than HR
of Type 1 burst and superbursts (typical 1-3).
Unknown origin: thermonuclear burst ? bright
accretion flares? …
Lightcurves in three bands: only detected above 5 keV of duration 15 hr; a hard X-ray
burst, the spectra harder than Type 1 X-ray bursts (kT<3 keV, occuring in LMXBs).
X-ray Transient IGR J01583-67
Transient discovered on Dec 6 2005 by INTEGRAL surveys
2005 Dec 6-7
Outburst
2005 Dec 8-10
Flux decaying
2005 Dec 11-13
undetected
We first identified it as a transient X-ray pulsar !
(with a magnetic neutron star)
Wang 2009b
outbursts
Transient X-ray pulsar IGR J01583-67
35 keV
Magnetic field 4x1012 G
Decaying phase
(7σ )
Γ～2.5
5.47 hr modulation period
62 -70 keV
Summary
• Long pulsation of magnetic NS (>1012 G):
1.57 hr (4U 2206+54); 2.7 hr (2S 0114+65); 5.47 hr (IGR J01583-67)
• Spin-up rate of Supergiant binary 2S 0114+65
accelerates: evolving to equilibrium ?
• A hard X-ray burst in 4U 2206+54
2-day duration; exponential-decay profile; hard spectra; origin unclear
• Transient X-ray pulsar IGR J01583-67 would be windfed system too
• SFXTs would be nature of wind-accretion magnetic
neutron stars
NS X-ray binaries
Pspin – Porbit diagram (Corbet diagram)
wind accretion
SFXTs
decretion disk
from winds
accretion disk