New INTEGRAL New INTEGRAL High Mass X-ray BinariesHigh Mass X-ray Binaries

Lara Sidoli

(INAF-IASF, Milano)

Simbol-X Bologna, 2007, 14-16 May

● 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

Overview

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

Sources detected with ISGRI during the first 4 years of observations

● 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)

● 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

About 30% of the new IGRs are HMXRBs

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-2cutoffpl :

ph. index = 1.6Ec = 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 observationsSupergiant Fast X-ray Transients

unusually SHORT outbursts, significantly shorter than Be/NS binaries

● 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

ISGRI SWs (~2 ks) image sequence (20-30 keV)flux at peak=254 mCrab

from Sguera et al. 2005

IGR J17391-3021/XTE J1739-302

A growing number of observationsand a growing number of sources mainly thanks to INTEGRAL !

SFXTs and SFXT candidatesinitially selected because of the short outbursts, then possibly confirmed based

on the optical counterpart from Negueruela et al. 2005Sguera 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-09IGR J17544-2619 3 O9Ib 3.0 E-09SAX J1818.6-1703 ? supergiant earlier than B3 1.3 E-09IGR J16479-4514 ? ? 2MASS source 2.4 E-10IGR J18410-0535/AX J1841.0-0536 10 B0I 9.0 E-10IGR J17407-2808 (=SBM10) ? 10 ? - 6.0 E-09IGR J16195-4945/AXJ161929-4945 ? 5 - 3.0 E-10AX J1749.1-2733 ? - - 3.0 E-10XTE J1743-363 ? - - 3.0 E-10IGR J16418-4532 ? - supergiant?? 6.0 E-10IGRJ18450-0435/AX J1845.0-0433 3.6 O 9.5 I 6.0E-10IGR 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 20188+3647, IGR J21117+3427,IGR J17354-3255

A growing number of observationsand a growing number of sources mainly thanks to INTEGRAL !

SFXTs and SFXT candidatesinitially selected because of the short outbursts, then possibly confirmed based

on the optical counterpart from Negueruela et al. 2005Sguera 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-09IGR J17544-2619 3 O9Ib 3.0 E-09SAX J1818.6-1703 ? supergiant earlier than B3 1.3 E-09IGR J16479-4514 ? ? 2MASS source 2.4 E-10IGR J18410-0535/AX J1841.0-0536 10 B0I 9.0 E-10IGR J17407-2808 (=SBM10) ? 10 ? - 6.0 E-09IGR J16195-4945/AXJ161929-4945 ? 5 - 3.0 E-10AX J1749.1-2733 ? - - 3.0 E-10XTE J1743-363 ? - - 3.0 E-10IGR J16418-4532 ? - supergiant?? 6.0 E-10IGRJ18450-0435/AX J1845.0-0433 3.6 O 9.5 I 6.0E-10IGR 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 20188+3647, IGR J21117+3427,IGR J17354-3255

Hard X-ray spectrawith 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!

1997, Aug, XTE obs 2004, Aug, ISGRI obs

Flux (20-40 keV) at the peak of the outburst, together with the “quiescent” level

quiescent levelmeasured well far away from the outbursts

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

Be/X-ray binariestypically Transient X-ray sourceswith Be companions

A new class -> Supergiant Fast X-ray Transientswith supergiant companionstransient emission, withshort duration outbursts, typically few hours, less than Be/XRBs outbursts

highly absorbed HMXRBsdiscovered with INTEGRAL

a growing number of membershave been discovered

with INTEGRAL

Bright persistent disk-fedmassive X-ray binaries (Cen X-3 like) in close orbits

Supergiant Fast X-ray Transients:proposed 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

Supergiant Fast X-ray Transients:proposed 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 orbitaround a supergiant with a spherical homogeneous windin the case:30 Msun companion starbeta wind=1 terminal wind velocity=1800 km/sPorb=200 daysWind mass loss rate=2 E-6 Msun/yr

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)

ISGRI lightcurves (17-40 keV)

1st outburst 3-4 July 2003 2nd outburst

26-27 May 2004

3rd outburst22 Apr 2005

~ 330 ~ 330 days !days !

~ 330 ~ 330 days !days !

330 days = likely orbital period 330 days = likely orbital period

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).

44thth outburst lightcurve outburst lightcurve (Smith et al. 2006, ATel 766 and ATel 773)

from http://scipp.ucsc.edu/~dsmith/atel/atel0306/

XTE/PCA

extreme variability

X-ray spectrum: hard and quite constant through the outburstPh. 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

IGR J11215-5952: INTEGRAL spectra

1st outburst 2nd outburst

JEM-X

IBIS/ISGRI IBIS/ISGRI

Energy (keV)5 100 Energy (keV) 10020

ph.index = 2.6 +1.8 -0.6ph.index = 0.5 +0.4 -0.6

F = 2.5 E -10 erg/cm2/s (20-100 keV)F = 6.2 E -10 erg/cm2/s (5-100 keV)

E cutoff = 15 +/-5 keV

2003 2004

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

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)

The The periodicperiodic nature of the nature of the outburstsoutbursts from from IGR J11215-5952IGR J11215-5952 allowed us to plan & perform for the first time a allowed us to plan & perform for the first time a

sensitive and complete monitoring sensitive and complete monitoring of the of the entire outburst from a SFXTentire outburst from a SFXT,,

during the latest outburst, expected on during the latest outburst, expected on 2007, 92007, 9thth February Februarywith with Swift/XRTSwift/XRT

Final lightcurve from Swift / XRT observations of IGR J11215-5952IGR J11215-5952

9th February 2007Romano et al. 2007

1st fact: the accretion phase in SFXTs lasts longer than originally thought basedon 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)=0.94 (+0.31 -0.28)

NH=1.11E22 (+0.79 -0.49)=0.91 (+0.42 -0.32)

NH=0.83E22 (+0.62 -0.42)=0.82 (+0.44 -0.40)

NH=0.88E22 (+0.38 -0.31)=1.03 (+0.32 -0.31)

NH=2.02E22 (+1.01 -0.79)=1.51 (+0.58 -0.53)

The total Galactic absorption towards the source is 0.8 E22 cm-2

Model of accretion from a spherical homogeneous wind in an eccentric orbit around the HD star

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

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 homogeneousthen.....

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 homogeneousthen.....

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 ratecompared to the “polar wind component”

from Ud-Doula, Townsend & Owocki, 2006, ApJ, 640, L191

Simulation of the radiatively driven outflow from a rotating hot star with a dipole magnetic field

Log (wind density)

The proposed geometry to explain the short SFXT outbursts:

The thin equatorial disk of the B-supergiantis 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

ns

OB supergiant

Sidoli et al., 2007, in preparation

The thickness “h” of the densest region of this disk

h

orbital plane

“h” can be estimated from the duration of the outburst:the duration t of the brightest part of the outburstis 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)

The thickness “h” of the densest region of the disk

h

orbital plane

“h” can be estimated from the duration of the outburst:the duration t of the brightest part of the outburstis 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-2Assuming about 1E22 cm-2 is local and mainly due to the supergiant disk, a

rough estimate of the density of the supergiant disk is:

Nh*mH / h =cm

“disk” wind

“polar” wind

variable wind density along the orbit

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/yrterminal velocity (“polar wind”) = 1800 km/sbeta law exponent = 1.0Porb = 329 dayse = 0.4

Note that along the orbit, the centrifugal barrieris always open (with B ~ 1E12 G, and Pspin=187 s)

“disk wind”with Mdot_wind = 100 * Mdot_polarterminal velocity = 900 km/s

“disk wind”with Mdot_wind = 30 * Mdot_polarterminal velocity = 1600 km/s

few further questions ....

how to explain other SFXTs where a clear periodicity in the outburstshas not been found yet?

probably a different eccentricity & a different geometry of the thin disk withrespect to the orbital plane

how to explain other SFXTs where a clear periodicity in the outburstshas not been found yet?

probably a different eccentricity & a different geometry of the thin disk withrespect to the orbital plane

how to explain the persistent Vela X-1-like HMXBs withsupergiant 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

●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