Unveiling the hard X-ray Galactic sky with IBIS

1
Unveiling the hard X-ray Galactic sky with IBIS
5th Science AGILE Workshop, ASDC, Frascati,12-13
Jun 2008
Vito Sguera INAF/IASF Bologna On behalf of the
IBIS Survey Team
2
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

3
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

4
Sky coverage
All-sky galactic projection - contours at 500ks
intervals
5
The third IBIS catalog lists 421 soft gamma-ray
sources
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 (20-300 days)
• particularly eccentric orbits
• mostly transient systems
• several weeks or months

9
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 1036-1038 erg
  s-1
• orbital period in the range 1.4-14 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 1024 cm-2 Fe Ka 6.4
keV, Fe Kß 7.1 keV Lx 1036 erg s-1 (20-100
keV, 5 kpc )
12
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

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
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 I61 303
LS 5039
9.5s, 20-100 keV
10s, 20-100 keV
PSR B1259-63
Cygnus X-1
4400s, 20-100 keV
5s, 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)

15
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

10s, 20-100 keV,   3 Ms exposure
16
IGR J201883647 AGILE transient in Cygnus
Sguera et al. 2007
IBIS significance image (17-30 keV, 2,000 s
exposure ) of the transient IGR J201883647
(7s detection), 30
minutes activity, flux 33 mCrab, upper
limit 1 mcrab (1Ms)

• 3EGJ20163657 green probability contours (50,
  68, 95 and 99) with its associated blazar
  (cross point)
• 3EG J20213716 purple probability contours (50,
  68, 95 and 99) with its associated pulsar
  (diamond)
• MILAGRO TeV source MGRO J201937 (yellow circle)
  (Abdo et al. 2007)
• AGILE transient (white circle) strongly
  variable, lasting only 1 day (Chen et al. 2007)

17
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

18s, 20-100 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, 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 (? 3- 4)

Recently, INTEGRAL discovered hard X-ray tails
from AXPs, described by a power law models with
?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 (Egt10 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

20
(No Transcript)
21
(No Transcript)
22
(No Transcript)