Transcript New INTEGRAL High Mass X

New INTEGRAL
High Mass X-ray Binaries
Lara Sidoli
(INAF-IASF, Milano)
Simbol-X Bologna, 2007, 14-16 May
Overview
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A biased introduction to the INTEGRAL discoveries in the
HMXB field: highly obscured Galactic sources and...
....The mistery of the Supergiant Fast X-ray Transients
IGR J11215-5952: a unique SFXT !
A possible solution to the SFXTs puzzle
Sources detected with ISGRI during the first 4 years of observations
from Bodaghee et al., 2007, astro-ph/0703043
Sources detected with ISGRI during the first 4 years of observations
from Bodaghee et al., 2007, astro-ph/0703043
About 30% of the new IGRs are HMXRBs
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X-ray pulsations (slow pulsators, with periods ~
few hundred seconds)
Hard and highly absorbed X-ray spectra
sometimes with strong Fe emission lines (Ph.Index ~0.5-1;
absorbing column densities NH > 1E23 cm-2)
– the first (discovered on 2003, Jan 29) of these heavily
absorbed sources was IGR J16318-4848 (Walter et al 2003,
Matt & Guainazzi 2003, Ibarra et al. 2006)
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Optical Identification with Blue Supergiants or Be stars
(e.g. Masetti et al. 2005, 2006, Reig et al. 2005)
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They are mainly located in the direction of the spiral
arms of our galaxy
The prototype of the highly obscured IGR sources: IGR J16318-4848
IGR J16318-4848 with XMM-Newton & INTEGRAL
from Ibarra et al. 2006
Simulation of a IGR J16318-4848-like spectrum with Simbol-X
Simulated spectrum (50 ks)
Nh = 2E24 cm-2
cutoffpl :
ph. index = 1.6
Ec = 60 keV
3 gaussians at 6.4 keV, 7.099 keV and 7.45 keV
An updated summary of IGR
HMXBs with known Pspin or Porb, or both :
Thanks to the Galactic Plane monitoring with INTEGRAL:
heavily obscured sources
& transients with short outburst
have been discovered in the first 4 years of observations
The story of the SFXTs begins with
XTE J1739-302 ..... an unusual new x-ray transient
Smith et al. 1998:
RossiXTE obs. 1997 Aug 12 – discovery of a new transient,
active only 1 day !
~ 3E-9 erg/cm2/s (2-25 keV): the brightest source in the direction of the
Galactic Center region on that one day
Thermal bremsstrahlung spectrum kT ~ 21 keV
=> Be/XRB ???
XTE J1739-302 ..... an unusual new x-ray transient
Smith et al. 1998:
RossiXTE obs. 1997 Aug 12 – discovery of a new transient,
active only 1 day !
~ 3E-9 erg/cm2/s (2-25 keV): the brightest source in the direction of the
Galactic Center region on that one day
Thermal bremsstrahlung spectrum kT ~ 21 keV
=> Be/XRB ???
Negueruela et al. 2005:
Optical counterpart is an O-type supergiant (O8 I ) -> dist ~ 2 kpc
=> a new class of transient sources!?!?!
INTEGRAL discoveries and observations
Supergiant Fast X-ray Transients
unusually SHORT outbursts, significantly shorter than Be/NS binaries
IGR J17391-3021/XTE J1739-302
ISGRI SWs (~2 ks)
image sequence
(20-30 keV)
flux at peak=254 mCrab
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OUTBURST DURATION:
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RECURRENT OUTBURSTS
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HARD AND HIGHLY ABSORBED X-RAY SPECTRUM
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~ few hours, less than a day
reminiscent of an X-ray pulsar
OPTICAL COUNTERPART:
highly reddened O B supergiants
from Sguera et al. 2005
A growing number of observations
and a growing number of sources mainly thanks to INTEGRAL !
SFXTs and SFXT candidates
initially selected because of the short outbursts, then possibly confirmed based
on the optical counterpart
Source
Dist Sp.Type
(kpc)
Peak flux (20-40)
ISGRI (erg/cm2/s)
IGR J17391-3021/XTE J1739-302 2-3
O8Iab
6.5 E09
IGR J17544-2619
3
O9Ib
3.0 E09
SAX J1818.6-1703
? supergiant earlier than B3 1.3 E09
IGR J16479-4514 ?
? 2MASS source
2.4 E10
IGR J18410-0535/AX J1841.0-0536 10
B0I
9.0 E10
IGR J17407-2808 (=SBM10) ?
10 ?
6.0 E09
IGR J16195-4945/AXJ161929-4945 ? 5
3.0 E10
AX J1749.1-2733 ?
3.0 E10
XTE J1743-363 ?
3.0 E10
from Negueruela et al. 2005
Sguera et al. 2005, 2006
A growing number of observations
and a growing number of sources mainly thanks to INTEGRAL !
SFXTs and SFXT candidates
initially selected because of the short outbursts, then possibly confirmed based
on the optical counterpart
Source
Dist Sp.Type
(kpc)
from Negueruela et al. 2005
Sguera et al. 2005, 2006 et al.
Peak flux (20-40)
ISGRI (erg/cm2/s)
IGR J17391-3021/XTE J1739-302 2-3
O8Iab
6.5 E09
Hard X-ray spectra
IGR J17544-2619
3
O9Ib
3.0 Ewith high energy cut off
09
SAX J1818.6-1703
? supergiant earlier than B3 1.3 E-at ~ 10-30 keV
09
IGR J16479-4514 ?
? 2MASS source
2.4 EL outburst / L quiesc.
10
IGR J18410-0535/AX J1841.0-0536 10
B0I
9.0 E~ 1E3-1E4
10
(from ASCA archival, or XMM or Chandra obs)
IGR J17407-2808 (=SBM10) ?
10 ?
6.0 E-but only from few sources!
09
IGR J16195-4945/AXJ161929-4945 ? 5
3.0 E10
AX J1749.1-2733 ?
3.0 E10
XTE J1743-363 ?
3.0 E10
Flux (20-40 keV) at the peak of the outburst, together with the “quiescent” level
quiescent level
measured well far away from
the outbursts
1997, Aug, XTE obs
2004, Aug, ISGRI obs
IGR J17544-2619
in't Zand 2005 Chandra obs
SFXTs properties: absorbing column density from X-ray spectra
NH – NH Gal (1E22 cm-2)
Total NH Galactic (1E22 cm-2) towards the sources
SFXTs properties: X-ray luminosity during the short flares
HMXRB classes: a summary
Persistent
wind fed accreting X-ray pulsars
with supergiant companions
“typical” HMXRBs, Vela X-1 like
highly absorbed HMXRBs
discovered with INTEGRAL
Bright persistent disk-fed
massive X-ray binaries
(Cen X-3 like) in close orbits
A new class ->
Supergiant Fast X-ray Transients
with supergiant companions
transient emission, with
short duration outbursts, typically
few hours, less than Be/XRBs
outbursts
Be/X-ray binaries
typically Transient X-ray sources
with Be companions
a growing number of members
have been discovered
with INTEGRAL
Supergiant Fast X-ray Transients:
proposed interpretations (I)
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Outbursts produced by short ejections from the donor stars in XRBs? or
clumpy winds? (in 't Zand 2005) this suggestion is based on optical observations of the clumping
nature of the wind from early type stars:
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Owocki et al. 1997, Lamers & Cassinelli 1999: line-driven winds from supergiant stars are highly variable
Supergiant Fast X-ray Transients:
proposed interpretations (II)
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A new kind of supergiant HMXRBs in wide eccentric orbits? (wider than
“normal” supergiants HMXRBs, like Vela X-1, in nearly circular orbits)
explain the large Lmax / Lmin (Negueruela et al. 2005)
Lx expected from an eccentric orbit
around a supergiant with a
spherical homogeneous wind
in the case:
30 Msun companion star
beta wind=1
terminal wind velocity=1800 km/s
Porb=200 days
Wind mass loss rate=2 E-6 Msun/yr
also to
IGR J11215-5952: a unique SFXT
Fast transient discovered on April 22, 2005 (Lubinski et al. 2005):
detected with ISGRI in 2 consecutive pointings,
reaching 75 mCrab at peak (20-60 keV)
The companion is a B-type Supergiant: HD 306414 (Negueruela et al. 2005; Masetti et al. 2006)
The INTEGRAL lightcurve shows a periodicity of ~ 330 days in the recurrence of the
outbursts (Sidoli, Paizis & Mereghetti, 2006, A&A, 450, L9; astro-ph/0603081).
~ 330 days
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1st outburst
3-4 July 2003
~ 330 days
!
2nd outburst
26-27 May 2004
3rd outburst
22 Apr 2005
ISGRI lightcurves (17-40 keV)
330 days = likely orbital period
4th outburst lightcurve (Smith et al. 2006, ATel 766 and ATel 773)
XTE/PCA
extreme variability
X-ray spectrum:
hard and quite constant through the outburst
Ph. index ~ 1.7 +/- 0.2 (2.5-15 keV)
NH ~ 11 +/- 3 E22 cm-2 (higher than Galactic)
Flux at peak ~ 2 x 10-10 erg/cm2/s
roughly consistent with previous outbursts
from http://scipp.ucsc.edu/~dsmith/atel/atel0306/
IGR J11215-5952: INTEGRAL spectra
2nd outburst
1st outburst
2004
2003
JEM-X
IBIS/ISGRI
IBIS/ISGRI
5
Energy (keV)
100
20
Energy (keV)
100
ph.index = 0.5 +0.4 -0.6
E cutoff = 15 +/-5 keV
ph.index = 2.6 +1.8 -0.6
F = 6.2 E -10 erg/cm2/s (5-100 keV)
F = 2.5 E -10 erg/cm2/s (20-100 keV)
L = 3E36 erg/s (5-100 keV)
IGR J11215-5952 is a slow X-ray pulsator in a wide orbit
XTE/PCA pointings performed during the 4th outburst in 2006 showed variability which suggested a pulsation
period of approximately 195 +/- 10 s (Smith et al. 2006).
The pulsations have been confirmed during the 5 th outburst in Feb 2007 (Swank et al. ATel # 999): Pspin=186.78
+/- 0.3 s
This would imply an X-ray pulsar with:
Porb ~ 329 days
P spin ~ 190 s
thus an accreting pulsar lying in the Be\XRB region of the Corbet diagram ??
BUT the companion is a supergiant! so it is not a Be/NS system !!!
Porb=329 days seem to suggest that outbursts in SFXTs
might be related to wide highly eccentric orbits and not to clumpy winds
The periodic nature of the outbursts
from IGR J11215-5952 allowed us to plan & perform for the first time a
sensitive and complete monitoring
of the entire outburst from a SFXT,
during the latest outburst, expected on 2007, 9th February
with Swift/XRT
Monitoring campaign strategy:
- 2 ks / day at the beginning (starting on 4th February)
- then exposure up to 10 ks / day during outburst
- Monitoring end planned for 14th February (actually, IGR11215
was kindly observed up to 26th February)
- Thanks to Neil Gehrels and to the Swift Team
Results in Romano, Sidoli, Mangano, Mereghetti & Cusumano ,
2007 (A&A in press; astro-ph/0704.0543)
Final lightcurve from Swift / XRT observations of IGR J11215-5952
9th February 2007
Romano et al. 2007
1st fact:
the accretion phase in SFXTs lasts longer than originally thought based
on less sensitive instruments
Note that INTEGRAL would have seen ONLY the bright “orange” region of the lightcurve,
lasting less than 1 day and composed of several ``short flares”
9th February 2007
Close-up view of the brightest part of the outburst (9th Feb)
2nd fact:
a large variability is present, and the outburst event is composed of short flares, lasting few hours or less
NH=0.85E22 (+0.46 -0.32)
G=0.94 (+0.31 -0.28)
NH=1.11E22 (+0.79 -0.49)
G=0.91 (+0.42 -0.32)
NH=2.02E22 (+1.01 -0.79)
G=1.51 (+0.58 -0.53)
NH=0.83E22 (+0.62 -0.42)
G=0.82 (+0.44 -0.40)
NH=0.88E22 (+0.38 -0.31)
G=1.03 (+0.32 -0.31)
The total Galactic absorption towards the source is 0.8 E22 cm-2
How to explain the outburst?
The recurrence time of 329 days is the underlying clock of the phoenomenon,
which can be interpreted in a natural way as the orbital period of the binary system
Model of accretion from a spherical homogeneous wind in an eccentric orbit around the HD star
A sorta fairytale
3rd fact: the lightcurve is too narrow and steep to be explained within a model
of Bondi accretion from a spherical and homogeneous wind in an eccentric binary
(even with extreme eccentricities!)
Using the neutron star as a probe of the supergiant wind,
the shape of the X-ray lightcurve
implies
that the wind from the B supergiant is
NOT spherical nor homogeneous
then.....
Using the neutron star as a probe of the supergiant wind,
the shape of the X-ray lightcurve
implies
that the wind from the B supergiant is
NOT spherical nor homogeneous
then.....
our idea is that there is a second wind component in a
“thin equatorial disk”
with lower wind velocity and a higher wind mass loss rate
compared to the “polar wind component”
Simulation of the radiatively driven outflow from a rotating hot star with a dipole magnetic field
Log (wind density)
from Ud-Doula, Townsend & Owocki, 2006, ApJ, 640, L191
The proposed geometry to explain the short SFXT outbursts:
OB supergiant
ns
The thin equatorial disk of the B-supergiant
is inclined with respect to the orbital plane
The star has also a polar wind with higher velocity and lower mass loss rate (~0.01 * Mass loss rate in the disk)
thus, in order to explain the low X-ray emission level out of the outburst, we need anyway a not circular orbit
Sidoli et al., 2007, in preparation
The thickness “h” of the densest region of this disk
orbital plane
“h” can be estimated from the duration of the outburst:
the duration t of the brightest part of the outburst
is t ~ 1 day,
the ns velocity near periatron is roughly vns ~ 100-200 km/s
thus:
h ~ 8E11 – 1.7 E12 cm
(0.3-0.6 Ropt, if Ropt ~ 40 Rsun)
h
The thickness “h” of the densest region of the disk
orbital plane
“h” can be estimated from the duration of the outburst:
the duration t of the brightest part of the outburst
is t ~ 1 day,
the ns velocity near periatron is roughly vns ~ 100-200 km/s
thus:
h ~ 8E11 – 1.7 E12 cm
(0.3-0.6 Ropt, if Ropt ~ 40 Rsun)
Nh galactic < 0.8 E 22 cm-2; Nh from X-ray spectra ~1-2 * 1E22 cm-2
Assuming about 1E22 cm-2 is local and mainly due to the supergiant disk, a
rough estimate of the r density of the supergiant disk is:
Nh*mH / h = r
~ 1E-14 cm-3
h
variable wind density along the orbit
“disk” wind
“polar” wind
Example of the model of wind accretion
with the following parameters:
B-supergiant mass = 39 Msun
“polar wind” mass loss rate = 3.7 E-6 Msun/yr
terminal velocity (“polar wind”) = 1800 km/s
beta law exponent = 1.0
Porb = 329 days
e = 0.4
Note that along the orbit,
the centrifugal barrier
is always open
(with B ~ 1E12 G, and
Pspin=187 s)
“disk wind”
with Mdot_wind = 100 * Mdot_polar
terminal velocity = 900 km/s
“disk wind”
with Mdot_wind = 30 * Mdot_polar
terminal velocity = 1600 km/s
few further questions ....
how to explain other SFXTs where a clear periodicity in the outbursts
has not been found yet?
probably a different eccentricity & a different geometry of the thin disk with
respect to the orbital plane
how to explain other SFXTs where a clear periodicity in the outbursts
has not been found yet?
probably a different eccentricity & a different geometry of the thin disk with
respect to the orbital plane
how to explain the persistent Vela X-1-like HMXBs with
supergiant donors?
probably the “equatorial disk” of the supergiant in the persistent systems lies on
the orbital plane and the ns always moves inside the disk
Conclusions
INTEGRAL observations opened a new view on High Mass X-ray Binaries
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The new class of SFXTs has been discovered
●The SFXT IGRJ11215-5952 is a key system to understand this new class of X-ray sources
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We proposed a new hypothesis to explain the properties of the SFXTs, where the supergiant has an
equatorial component of the wind, besides the “standard” “polar” high velocity wind.
●The enhanced accretion rate when the neutron star cross this disk produces the short duration
X-ray
outburst
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