THE NATURE OF UNIDENTIFIED HIGH-ENERGY SOURCES DETECTED WITH INTEGRAL Nicola Masetti (INAF/IASF di Bologna, Italy) on behalf of a large collaboration
OUTLINE The INTEGRAL hard X-ray surveys The quest for unidentified sources Catalogue cross-correlations Soft X-ray and optical followups The contribution at other wavelengths How to use this information? The VVV near-ir survey of the Galactic Bulge
HARD X-RAY SURVEYS In the past decade, several surveys of the hard X-ray sky were collected, most of them with the INTEGRAL satellite. These allowed the sky above 20 kev to be mapped with unprecedented detail in terms of sensitivity (<1 mcrab) and positional accuracy (better than few arcmin).
HARD X-RAY SURVEYS - II INTEGRAL/IBIS 4 th IBIS Survey (20-100 kev): sensitivity <1 mcrab, 723 sources, 29% unidentified (Bird et al. 2010) 7-year all-sky survey (17-60 kev): sensitivity ~0.3 mcrab, 521 sources, 8% unidentified (Krivonos et al. 2010) 9-year Galactic Plane survey (17-80 kev): sensitivity ~0.3 mcrab, 402 sources, 8% unidentified (Krivonos et al. 2012)
X-RAYS FROM THE UNKNOWN! IBIS 4 th survey These surveys thus contain a number of unidentified or poorly known hard X-ray sources which need multiwavelength studies to be properly characterized.
FOLLOW-UP METHODS Stephen et al. (2005, 2006) demonstrated that if a soft X-ray source is present within the hard X-ray error circle, it is the corresponding softer counterpart, marking the object position at arcsec-sized level. This greatly facilitates spectroscopic followup in optical/nir bands. Masetti et al. (2008) Ly α z = 2.40 SIV CIV CIII] XRT SWIFT J1656.3-3302 ESO 3.6m
NEED FOR SUBARCSEC POSITIONS Swift Torres et al. (2006) Tomsick et al. (2013) IGR J17497-2821 Sometimes we need very accurate subarcsec localizations to remove the ambiguity in crowded fields. At present, only Chandra and VLA allow this accuracy.
WHAT WE DID UP TO NOW Our group started in July 2004 with spectroscopy of 3 INTEGRAL sources at Loiano (two AGNs and one CV). Masetti et al. (2004) Across the last 9 years, we set up an international collaboration involving more than 20 people from 12 institutes in 6 different countries (Italy, United Kingdom, Chile, Mexico, South Africa, Argentina). Our group used 12 facilities worldwide and two online catalogues (6dF and SDSS) for the optical spectroscopic identification work, and pinpointed the nature of more than 200 INTEGRAL sources. Masetti et al. (2004, 2006abcd, 2007, 2008, 2009, 2010, 2012, 2013)
OBSERVATIONAL FACILITIES 1.5m «G.D. Cassini» in Loiano (Italy) 1.5m CTIO in Cerro Tololo (Chile) 1.8m «Copernicus» in Asiago (Italy) 1.9m «Radcliffe» at SAAO (South Africa) 2.1m OAN in San Pedro Mártir (Mexico) 2.15m «Jorge Sahade» at CASLEO (Argentina) 3.58m TNG in La Palma (Spain) 3.58m ESO-NTT in La Silla (Chile) 3.6m ESO in La Silla (Chile) 4.2m WHT in La Palma (Spain) 10.4m GTC telescope in La Palma (Spain) 11m SALT telescope at SAAO (South Africa)
Other optical/nir identifications of IGR sources Bikmaev et al. Burenin et al. Krivonos et al. Lutovinov et al. Sazonov et al. Optical identifications of AGNs: RX J0137.7+5814 (BL Lac) IGR J18259-0706 (Sy1 AGN) IGR J18538-0102 (Sy1 AGN) IGR J20216+4359 (Sy2 AGN) IGR J21277+5656 (NLSy1 AGN) IGR J23206+6431 (Sy1 AGN) Chaty et al. Optical and NIR identifications of HMXBs and AGNs: Negueruela et al. IGR J00370+6122 (SgXRB) Pellizza et al. IGR J01363+6610 (Be/X) Reig et al. IGR J09026-4812 (Sy1 AGN) Hannikainen et al. IGR J16283-4838 (SgXRB) Zurita Heras et al. IGR J16465-4507 (SFXT) Smith et al. XTE J1739-302 (SFXT) XTE J1743-363 (SyXB) IGR J17544-2619 (SFXT) IGR J19140+0951 (SgXRB) Halpern et al. Optical identifications of HMXBs and AGNs: Goncalves et al. IGR J18410-0535 (SFXT) IGR J18450-0435 (SFXT) IGR J20187+4041 (Sy2 AGN) Nespoli et al. Optical identifications of HMXBs: IGR J16493-4348 (SgXRB) Sturm et al. Optical identifications of HMXBs: IGR J05414-6858 (Be/X) Ratti et al. Optical identifications of X-ray binaries: IGR J19308+0530 (IMXB) Rodes-Roca et al. Optical identifications of HMXBs: AX J1910.7+0917 (SgXRB)
NIR/MIR IDENTIFICATIONS NIR spectrophotometry of the counterparts of about 30 INTEGRAL sources, together with MIR and optical photometric followup, revealed that some of them are heavily obscured HMXBs. 16 objects were identified as follows on the basis of their spectra (red) or photometry (green). Tentative identifications are given in black. IGR J10101-5654 (SgB[e]) IGR J11187-5438 (LMXB) IGR J14488-5942 (Oe/Be) IGR J16195-4945 (O9.7e Iab) IGR J16320-4751 (BN0.5 Ia) IGR J16328-4726 (O8 Iafpe) IGR J16358-4726 (SgB[e]; or SyXB?) IGR J16393-4643 (Be IV-V) IGR J16418-4532 (BN0.5 Ia) IGR J16479-4514 (O8.5 Ie) IGR J17091-3624 (LMXB?) IGR J17252-3616 (O8.5 Ie) IGR J17354-3255 (O9 Iab) IGR J17404-3655 (Be; or LMXB?) IGR J17586-2129 (early Sg) IGR J17597-2201 (LMXB?) Chaty et al. (2008) Rahoui et al. (2008) Coleiro et al. (2013)
ALTERNATIVE TECHNIQUES When no information can be extracted from opt/ir observations (due to e.g. huge absorption or intrinsic faintness) the combined use of multiwavelength data can provide the object s nature. For instance: IGR J14003-6326 extended X-ray emission seen with Chandra (Tomsick et al. 2009) extended radio counterpart; no GeV emission (Renaud et al. 2010) X-ray pulsations at 31.18 ms seen with RXTE (Renaud et al. 2010) Energetic, young (<10 3 yrs) and distant (~7 kpc) PWN
Symbiotic X-ray Binaries (SyXBs) These objects are binary systems composed of a red giant and a long spin period (10 2 to 10 4 s) NS accreting form its wind; L X ~ 10 32-10 34 erg/s. Optical spectroscopy shows that in general the optical counterpart is a normal red giant of spectral type M III. SyXBs are very rare Low-Mass X-ray Binaries (only 7 are firmly identified to date). Three were identified starting from INTEGRAL data. ROSAT IGR J16194-2810 XRT Masetti et al. (2007) Nespoli et al. (2010) Smith et al. (2011)
HIGH-REDSHIFT BLAZARS The joint use of INTEGRAL/IBIS and Swift/XRT allowed the discovery of powerful gamma-ray loud blazars IGR J12319-749 and IGR J22517+2218 at z = 3.12 and z = 3.668, respectively. These objects also have an unusual Spectral Energy Distribution, with a Compton peak located in the hard X-ray/soft gamma-ray band. These are also the two farthest persistently-emitting X-ray objects detected with INTEGRAL. IGR J22517+2218 Swift/XRT image Bassani et al. (2007) Masetti et al. (2012) Bassani et al. (2012)
HARD X-RAY AGNs IN THE HIGH-z UNIVERSE Our latest sets of identifications show a non-negligible fraction of high-z AGNs among the unidentified sources with faint optical counterparts. Their average redshift is ~0.5 compared with that (~0.14) of identified objects in the INTEGRAL surveys. Masetti et al. (2012) The Eddington ratio of many of these sources is possibly larger than 0.1, suggesting an extreme blazar nature for them. Deep hard X-ray surveys are possibly complementary to GeV observations to explore these objects.
SOME STATISTICS... 4 th IBIS/INTEGRAL survey (442 known objects): Opt-NIR identified IGR sources (247 objects): 209 AGNs (47%); 174 X-ray Binaries (39%); of these, 52% are LMXBs and 48% are HMXBs; 35 CVs (8%); 24 others (6%). 147 AGNs (59.6%); 67 X-ray Binaries (27.1%); of these, 22% are L/IMXBs and 78% are HMXBs; 29 CVs (11.7%); 4 active stars (1.6%). This suggests that: 1) INTEGRAL is contributing to the discovery of new classes of absorbed HMXBs in the Galactic Plane; 2) INTEGRAL is giving fundamental insights to detect AGNs in the Zone of Avoidance along the Galactic Plane as well as at high redshift; 3) INTEGRAL is able to detect a substantial fraction of (magnetic) CVs.
THE VVV SURVEY VISTA Variables in the Via Lactea (VVV) is a public IR variability survey of the Milky Way bulge and an adjacent section of the mid-plane. It is being acquired at the VISTA telescope in Cerro Paranal (Chile) and, until 2014, it will cover ~109 point sources within an area of 520 deg2. The final products will be a deep IR atlas in 5 passbands (YZJHK) and a catalogue of ~106 variable point sources. Given its unprecedented sensitivity, it is an invaluable help for the search of NIR counterparts of hard X-ray sources falling in this area. vvvsurvey.org Minniti et al. (2010)
Catalogue of optically/nir identified IGR sources: http://www.iasfbo.inaf.it/extras/igr/main.html THANK YOU!