Unveiling the hard X-ray Galactic sky with IBIS

Vito SgueraINAF/IASF Bologna

On behalf of the IBIS Survey Team

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

OUTLINE 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

spectra

images

The third IBIS catalog lists 421 soft gamma-ray sources

Source populations

AGN32%

CV5%HMXB

18%

LMXB21%

Pulsars3%

Unknown19%

SNR2%

HMXBs distribution

Bodaghee et al. 2007

Be HMXBsAbout 35% of HMXBs in the IBIS catalog are Be 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 are SGXBs

with massive supergiant early type (OB)

companion donor

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)

• bright and persistent X-ray sources, not strongly absorbed

X-ray luminosities in the range 1036-1038 erg s-1

• orbital period in the range 1.4-14 days

• nearly circular orbit

SGXBs before the INTEGRAL era

SGXBs in the INTEGRAL eraSince 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 their fast 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

Duration ~ 2 hours Outburst luminosity ~ 2x1036 erg s-1 (20-60 keV)

Quiescent luminosity ~ 5x1032 erg s-1

Sguera et al. 2005

XTE J1739-302, prototype of SFXTs

TeV HMXBsIn 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 5039LS I+61 303

Cygnus X-1 PSR B1259-63

9.5σ, 20-100 keV 10σ, 20-100 keV

4400σ, 20-100 keV 5σ, 30-50 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 J1841.0-0535Aharonian 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

• 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)

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

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

Sguera et al. 2007

HESS J1632-478 & IGR J16320-4751

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

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)

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