Unveiling the hard x ray galactic sky with ibis
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5 th Science AGILE Workshop, ASDC, Frascati,12-13 Jun 2008. Unveiling the hard X-ray Galactic sky with IBIS. Vito Sguera INAF/IASF Bologna On behalf of the IBIS Survey Team. OUTLINE. General overview of the third IBIS catalog HMXBs in the INTEGRAL era:

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Unveiling the hard X-ray Galactic sky with IBIS

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5th Science AGILE Workshop, ASDC, Frascati,12-13 Jun 2008

Unveiling the hard X-ray Galactic sky with IBIS

Vito Sguera


On behalf of the IBIS Survey Team


  • General overview of the third IBIS catalog

  • HMXBs in the INTEGRAL era:

    Supergiant Fast X-ray Transients (SFXTs)

    Obscured HMXBs

  • Possible associations with MeV-TeV sources

Input dataset third IBIS catalog

  • All public and Core Programme data

    revolutions 12 to 429

  • Spans a range from Nov 2002 to May 2006

    ~ 3.5 years

  • 24,075 pointed Science Windows

  • Total telescope time of ~ 57 Ms

Sky coverage

All-sky galactic projection - contours at 500ks intervals


light curves


The third IBIS catalog lists 421 soft gamma-ray sources

Source populations

HMXBs distribution

Bodaghee et al. 2007


About35% of HMXBs in the IBIS catalog areBe X-ray binaries

  • neutron star

  • main sequence Be star

  • wind accretion from the dense

  • equatorial disk

  • long orbital periods (20-300 days)

  • particularly eccentric orbits

  • mostly transient systems

  • several weeks or months

about 65% of HMXBs in the third IBIS cat areSGXBswithmassivesupergiant early type (OB) companion donor

SGXBs before the INTEGRAL era

  • bright and persistentX-ray sources, not strongly absorbed

  • X-ray luminosities in the range1036-1038 erg s-1

  • orbital period in the range 1.4-14 days

  • nearlycircularorbit

because of the evolutionary timescale involved, up to recently SGXBs were believed to be very rare objects, a dozen SGXBs have been discovered in our Galaxy in almost 40 years of X-ray astronomy! (Liu et al. 2000)

SGXBs in the INTEGRAL era

Since its launch in 2002, in just a few years INTEGRAL tripled the population of SGXBs in our Galaxy!

The majority of newly discovered SGXBs are persistent hard X-ray sources which escaped previous detections because of their strongly obscured nature, NH ≥ 1023 cm-2

population of persistent strongly absorbed SGXBs

(i.e. Walter et al. 2006, Chaty et al. 2006)

The remaining are not strongly absorbed. They escaped previous detections because of theirfast X-ray transient nature, a characteristic never seen before from “classical persistent SGXBs”

new class: Supergiant Fast X-ray Transients, SFXTs

(i.e. Sguera et al. 2005, 2006, 2007, Negueruela et al. 2005,2006)

IGR J16318-4848, prototype of highly absorbed and persistent SGXBs

Courvoisier et al. 2003, Walter et al. 2003

NH ~ 1024 cm-2

Fe Kα ~6.4 keV, Fe Kβ~7.1 keV

Lx ~1036 erg s-1(20-100 keV, 5 kpc )

Supergiant Fast X-ray Transients

  • most of the time in quiescence,

  • luminosity values or upper limits in the range 1032 – 1033 erg s-1

  • fast X-ray flares lasting less than a day, typically few hours

  • peak luminosity of 1036 – 1037 erg s-1

  • dinamical range 103 - 104

  • To date, in just a few years 9 SFXTs reported in the literature

  • 5 SFXTs are newly discovered sources by INTEGRAL

  • The remaining 4 SFXTs were previously discovered by other X-ray satellites (ASCA, BeppoSAX, RXTE), however INTEGRAL detected several fast hard X-ray outbursts unveiling or strongly confirming their fast X-ray transient nature

XTE J1739-302, prototype of SFXTs

Sguera et al. 2005

Duration~ 2 hoursOutburstluminosity ~ 2x1036 erg s-1 (20-60 keV)

Quiescent luminosity ~ 5x1032 erg s-1


In the last years, gamma-ray HMXBs became subjects of very major interest in VHE astronomy.To date, 4 HMXBs have been detected at TeV energies Albert et al. (2007,2006), Aharonian et al. (2005a,2005b)

LS I+61 303

LS 5039

9.5σ, 20-100 keV

10σ, 20-100 keV

PSR B1259-63

Cygnus X-1

5σ, 30-50 keV

4400σ, 20-100 keV

  • different mechanisms to explain VHE emission from HMXBs:

  • leptonic and hadronic jet models (Romero et al. 2005, Paredes et al. 2006, Dermer et al. 2006, Bosch-Ramon et al. 2006)

  • interaction between the relativistic wind of a young NS and the stellar wind (Maraschi et al. 1981, Dubus et al. 2006)

  • Cheng-Ruderman mechanism in the magnetosphere of an accreting NS (Orellana et al. 2007)

HESS J1841-055 & AX J1841.0-0535

  • Aharonian et al. (2008)

  • HESS J1841-055

  • extended morphology

  • (semi-major axis 24 arcminutes)

  • bipolar morphology with two peaks (possibly three)

  • HESS J1841-055 could be the blend of more than one source

  • from catalog research, Aharonian et al. (2008) reported a

  • positional correlation with: PSR J1841-0524, PSR J1838-0549,

  • SNR G26.6-0.1, AX J1841.0-0535 (SFXT)

  • AX J1841.0-0535 (SFXT)

  • neutron star 4.7 sec

  • quiescent Lx ~ 2x1034 erg s-1

  • peak Lx ~ 5x1036 erg s-1

  • point-like nature and transient behaviour of

  • AX J1841.0-0535 do not agree with the

  • extended HESS emission

  • it could eventually be responsible for a

  • fraction of the entire TeV emission

10σ, 20-100 keV, ~  3 Ms exposure

IGR J20188+3647 & AGILE transient in Cygnus

Sguera et al. 2007

IBIS significance image (17-30 keV, 2,000 s exposure ) of the transient IGR J20188+3647(7σdetection), 30 minutes activity, flux 33 mCrab, upper limit 1 mcrab (1Ms)

  • 3EGJ2016+3657 green probability contours (50%, 68%, 95% and 99%) with its associated blazar (cross point)

  • 3EG J2021+3716 purple probability contours (50%, 68%, 95% and 99%) with its associated pulsar (diamond)

  • MILAGRO TeV source MGRO J2019+37 (yellow circle) (Abdo et al. 2007)

  • AGILEtransient (white circle): strongly variable, lasting only 1 day(Chen et al. 2007)

HESS J1632-478 & IGR J16320-4751

  • HESS J1632-478(Aharonian et al. 2006)

  • elongated shape (semi-major axis 12 arcmin, semi-minor axis 3 arcmin)

  • flux above 200 GeV about 12% of the flux from the Crab

  • from catalog research, positional correlation

  • with AX J163252-4746 an IGR J16320-4751(Aharonian et al. 2006)

  • IGR J16230-4751

  • persistent SGXB, Lx~ 1036 erg s-1 20-100 keV

  • highly absorbed, NH~ 1023 cm-2

  • NS 1300 s, 9 days

  • the point like nature of IGR do not agree with the

  • extended HESS emission

  • it could eventually be responsible for a

  • fraction of the entire TeV emission

18σ, 20-100 keV, ~ 3.2 Ms

Example of another important and unexpected INTEGRAL discovery

Hard X-ray emission from Anomalous X-ray Pulsars

  • X-ray luminosities 1034 – 1036 , steady source but outbursts also detected (transient AXPs)

  • spin periods (5-12 seconds)

  • no rotation powered, no accretion powered (no apparent optical counterpart)

  • the so called magnetar model (decay of a very strong magnetic field, 1014 - 1015 G)

  • is able to explain the observed characteristics of AXPs

  • AXPs were traditionally considered as soft X-ray sources (0.5-10 keV) with thermal

  • like spectra (kT ~ 0.4- 0.7 keV) plus a steep power law component (Г~ 3- 4)

Recently, INTEGRAL discovered hard X-ray tails from AXPs, described by a power law models with Г~1-1.5 and no sign of break up to ~150 keV, but there must be a break somewhere between 150-750 keV. (Kuiper et al. 2004,2006)

A new energy window (E>10 keV) has been opened providing an important dagnostic to study magnetars

(Kuiper et al. 2006)

This is not the end of the story….

fourth IBIS catalog on going

Input dataset ~ 40,000 pointed science windows, i.e. twice the

previous IBIS cat; the rate of discovery of HMXBs could

hugely increase

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