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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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  • 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
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
Sky coverage

All-sky galactic projection - contours at 500ks intervals



light curves


The third IBIS catalog lists 421 soft gamma-ray sources

hmxbs distribution
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
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