1. Unveiling the hard X-ray Galactic sky with IBIS
5th 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

2. OUTLINE Obscured HMXBs Possible associations with MeV-TeV sources
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
Telescope time = SUM OF ONTIMEs

3. Input dataset third IBIS catalog
All public and Core Programme data
revolutions 12 to 429
Spans a range from Nov to May 2006
~ 3.5 years
24,075 pointed Science Windows
Total telescope time of ~ 57 Ms
Telescope time = SUM OF ONTIMEs

4. Sky coverage
All-sky galactic projection - contours at 500ks intervals

5. The third IBIS catalog lists 421 soft gamma-ray sources
images
light curves
spectra

6. Source populations

7. HMXBs distribution
Bodaghee et al. 2007

8. Be HMXBs About 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 ( days)
particularly eccentric orbits
mostly transient systems
several weeks or months

9. SGXBs before the INTEGRAL era
about 65% of HMXBs in the third IBIS cat are SGXBs with massive supergiant early type (OB) companion donor
SGXBs before the INTEGRAL era
bright and persistent X-ray sources, not strongly absorbed
X-ray luminosities in the range erg s-1
orbital period in the range days
nearly circular orbit
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)

10. 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 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)

11. IGR J16318-4848, prototype of highly absorbed and persistent SGXBs
Courvoisier et al. 2003, Walter et al. 2003
NH ~ cm-2
Fe Kα ~ 6.4 keV, Fe Kβ~ 7.1 keV
Lx ~ erg s-1 ( keV, 5 kpc )

12. Supergiant Fast X-ray Transients
most of the time in quiescence,
luminosity values or upper limits in the range 1032 – erg s-1
fast X-ray flares lasting less than a day, typically few hours
peak luminosity of – 1037 erg s-1
dinamical range
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

13. XTE J1739-302, prototype of SFXTs
Sguera et al. 2005
Duration ~ 2 hours Outburst luminosity ~ 2x1036 erg s-1 (20-60 keV)
Quiescent luminosity ~ 5x1032 erg s-1

14. TeV HMXBs LS I+61 303 LS 5039 PSR B1259-63 Cygnus X-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
LS 5039
9.5σ, keV
10σ, keV
PSR B
Cygnus X-1
4400σ, keV
5σ, 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)

15. HESS J1841-055 & AX J1841.0-0535 HESS J1841-055 AX J1841.0-0535 (SFXT)
Aharonian et al. (2008)
HESS J
extended morphology
(semi-major axis 24 arcminutes)
bipolar morphology with two peaks (possibly three)
HESS J could be the blend of more than one source
from catalog research, Aharonian et al. (2008) reported a
positional correlation with: PSR J , PSR J ,
SNR G , AX J (SFXT)
AX J (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 J do not agree with the
extended HESS emission
it could eventually be responsible for a
fraction of the entire TeV emission
10σ, keV, ~  3 Ms exposure

16. 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 J (7σ detection), 30 minutes activity, flux 33 mCrab, upper limit 1 mcrab (1Ms)
3EGJ green probability contours (50%, 68%, 95% and 99%) with its associated blazar (cross point)
3EG J purple probability contours (50%, 68%, 95% and 99%) with its associated pulsar (diamond)
MILAGRO TeV source MGRO J (yellow circle) (Abdo et al. 2007)
AGILE transient (white circle): strongly variable, lasting only 1 day (Chen et al. 2007)

17. HESS J & IGR J
HESS J (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 J an IGR J (Aharonian et al. 2006)
IGR J
persistent SGXB, Lx ~ 1036 erg s 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, keV, ~ 3.2 Ms

18. 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, G)
is able to explain the observed characteristics of AXPs
AXPs were traditionally considered as soft X-ray sources ( keV) with thermal
like spectra (kT ~ 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 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)

19. 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