New INTEGRAL High Mass Xray Binaries

1
New INTEGRAL High Mass X-ray Binaries

• Lara Sidoli
• (INAF-IASF, Milano)

Simbol-X Bologna, 2007, 14-16 May
2
Overview

• 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

3
Sources detected with ISGRI during the first 4
years of observations
from Bodaghee et al., 2007, astro-ph/0703043
4
Sources detected with ISGRI during the first 4
years of observations
from Bodaghee et al., 2007, astro-ph/0703043
5
About 30 of the new IGRs are HMXRBs

• 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 gt 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)
• Optical Identification with Blue Supergiants or
  Be stars (e.g. Masetti et al. 2005, 2006, Reig et
  al. 2005)
• They are mainly located in the direction of the
  spiral arms of our galaxy

6
The prototype of the highly obscured IGR sources
IGR J16318-4848
IGR J16318-4848 with XMM-Newton INTEGRAL
from Ibarra et al. 2006
7
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
8
An updated summary of IGR HMXBs with known Pspin
or Porb, or both
9
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
10
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 gt Be/XRB ???
11
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 gt Be/XRB
??? Negueruela et al. 2005 Optical
counterpart is an O-type supergiant (O8 I ) -gt
dist 2 kpc gt a new class of transient
sources!?!?!
12
INTEGRAL discoveries and observationsSupergiant
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 peak254 mCrab
from Sguera et al. 2005

• OUTBURST DURATION few hours, less than a
  day
• RECURRENT OUTBURSTS
• HARD AND HIGHLY ABSORBED X-RAY SPECTRUM
• reminiscent of an X-ray pulsar
• OPTICAL COUNTERPART
  highly reddened O B
  supergiants

13
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

from Negueruela et al. 2005 Sguera et al. 2005,
2006
Source Dist Sp.Type Peak flux
(20-40) (kpc) ISGRI
(erg/cm2/s) IGR J17391-3021/XTE J1739-302 2-3
O8Iab 6.5
E-09 IGR J17544-2619
3 O9Ib 3.0
E-09 SAX J1818.6-1703
? supergiant earlier than B3 1.3 E-09 IGR
J16479-4514 ? ?
2MASS source 2.4 E-10 IGR
J18410-0535/AX J1841.0-0536 10 B0I
9.0 E-10 IGR J17407-2808
(SBM10) ? 10 ? -
6.0 E-09 IGR J16195-4945/AXJ1619
29-4945 ? 5 -
3.0 E-10 AX J1749.1-2733 ?
- -
3.0 E-10 XTE J1743-363 ?
- -
3.0 E-10 IGR J16418-4532 ?
- supergiant??
6.0 E-10 IGRJ18450-0435/AX
J1845.0-0433 3.6 O 9.5 I
6.0E-10 IGR J08408-4503
? Ob5Ib
6.0E-09 IGR J11215-5952
Other possible candidates IGR
J10043-8702, IGR J10500-6410, IGR J15283-4443,
IGR J18159-3353, IGR J18159-3353, IGR J
201883647, IGR J211173427,IGR J17354-3255
14
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

from Negueruela et al. 2005 Sguera et al. 2005,
2006 et al.
Source Dist Sp.Type Peak flux
(20-40) (kpc) ISGRI
(erg/cm2/s) IGR J17391-3021/XTE J1739-302 2-3
O8Iab 6.5
E-09 IGR J17544-2619
3 O9Ib 3.0
E-09 SAX J1818.6-1703
? supergiant earlier than B3 1.3 E-09 IGR
J16479-4514 ? ?
2MASS source 2.4 E-10 IGR
J18410-0535/AX J1841.0-0536 10 B0I
9.0 E-10 IGR J17407-2808
(SBM10) ? 10 ? -
6.0 E-09 IGR J16195-4945/AXJ1619
29-4945 ? 5 -
3.0 E-10 AX J1749.1-2733 ?
- -
3.0 E-10 XTE J1743-363 ?
- -
3.0 E-10 IGR J16418-4532 ?
- supergiant??
6.0 E-10 IGRJ18450-0435/AX
J1845.0-0433 3.6 O 9.5 I
6.0E-10 IGR J08408-4503
? Ob5Ib
6.0E-09 IGR J11215-5952
Other possible candidates IGR
J10043-8702, IGR J10500-6410, IGR J15283-4443,
IGR J18159-3353, IGR J18159-3353, IGR J
201883647, IGR J211173427,IGR J17354-3255
Hard X-ray spectra with high energy cut off at
10-30 keV L outburst / L quiesc.
1E3-1E4 (from ASCA archival, or XMM or
Chandra obs) but only from few sources!
15
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
16
IGR J17544-2619
in't Zand 2005 Chandra obs
17
SFXTs properties absorbing column density from
X-ray spectra
NH NH Gal (1E22 cm-2)
Total NH Galactic (1E22 cm-2) towards the sources
18
SFXTs properties X-ray luminosity during the
short flares
19
HMXRB classes a summary
Persistent wind fed accreting X-ray pulsars
with supergiant companions typical HMXRBs,
Vela X-1 like
A new class -gt Supergiant Fast X-ray
Transients with supergiant companions transient
emission, with short duration outbursts,
typically few hours, less than Be/XRBs
outbursts
highly absorbed HMXRBs discovered with INTEGRAL
a growing number of members have been discovered
with INTEGRAL
Be/X-ray binaries typically Transient X-ray
sources with Be companions
Bright persistent disk-fed massive X-ray binaries
(Cen X-3 like) in close orbits
20
Supergiant Fast X-ray Transientsproposed
interpretations (I)

• 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
• Owocki et al. 1997, Lamers Cassinelli 1999
  line-driven winds from supergiant stars are
  highly variable

21
Supergiant Fast X-ray Transientsproposed
interpretations (II)

• A new kind of supergiant HMXRBs in wide eccentric
  orbits? (wider than normal supergiants HMXRBs,
  like Vela X-1, in nearly circular orbits) also
  to 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 wind1
terminal wind velocity1800 km/s Porb200
days Wind mass loss rate2 E-6 Msun/yr
22
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)
23
The INTEGRAL lightcurve shows a periodicity of
330 days in the recurrence of the outbursts
(Sidoli, Paizis Mereghetti, 2006, AA, 450,
L9 astro-ph/0603081).
330 days !
330 days !
1st outburst 3-4 July 2003
2nd outburst 26-27 May 2004
3rd outburst 22 Apr 2005
ISGRI lightcurves (17-40 keV)
330 days likely orbital period
24
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/
25
IGR J11215-5952 INTEGRAL spectra
1st outburst
2nd outburst
2004
2003
JEM-X
IBIS/ISGRI
IBIS/ISGRI
5
100
100
20
Energy (keV)
Energy (keV)
ph.index 2.6 1.8 -0.6
ph.index 0.5 0.4 -0.6
E cutoff 15 /-5 keV
F 2.5 E -10 erg/cm2/s (20-100 keV)
F 6.2 E -10 erg/cm2/s (5-100 keV)
L 3E36 erg/s (5-100 keV)
26
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 5th outburst in Feb
2007 (Swank et al. ATel 999) Pspin186.78 /-
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 !!!
Porb329 days seem to suggest that outbursts in
SFXTs might be related to wide highly eccentric
orbits and not to clumpy winds
27
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 (AA in press astro-ph/0704.0543)
28
Final lightcurve from Swift / XRT observations of
IGR J11215-5952
9th February 2007
Romano et al. 2007
29
1st fact the accretion phase in SFXTs lasts
longer than originally thought based on less
sensitive instruments
30
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
31
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
32
NH1.11E22 (0.79 -0.49) G0.91 (0.42 -0.32)
NH0.85E22 (0.46 -0.32) G0.94 (0.31 -0.28)
NH2.02E22 (1.01 -0.79) G1.51 (0.58 -0.53)
NH0.88E22 (0.38 -0.31) G1.03 (0.32 -0.31)
NH0.83E22 (0.62 -0.42) G0.82 (0.44 -0.40)
33
The total Galactic absorption towards the source
is 0.8 E22 cm-2
34
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
35
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!)
36
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.....
37
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
38
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
39
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
40
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
41
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 lt 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 NhmH / h r
1E-14 cm-3
h
42
variable wind density along the orbit
disk wind
polar wind
43
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
Pspin187 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
44
(No Transcript)
45
few further questions ....
46
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
47
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
48

• Conclusions
• INTEGRAL observations opened a new view on High
  Mass X-ray Binaries
• 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
• 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