THE NATURE OF UNIDENTIFIED HIGH-ENERGY SOURCES DETECTED WITH INTEGRAL

Transcription

1 THE NATURE OF UNIDENTIFIED HIGH-ENERGY SOURCES DETECTED WITH INTEGRAL Nicola Masetti (INAF/IASF di Bologna, Italy) on behalf of a large collaboration

2 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

3 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).

4 HARD X-RAY SURVEYS - II INTEGRAL/IBIS 4 th IBIS Survey ( 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)

5 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.

6 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 J ESO 3.6m

7 NEED FOR SUBARCSEC POSITIONS Swift Torres et al. (2006) Tomsick et al. (2013) IGR J Sometimes we need very accurate subarcsec localizations to remove the ambiguity in crowded fields. At present, only Chandra and VLA allow this accuracy.

8 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)

9 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)

10 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 J (BL Lac) IGR J (Sy1 AGN) IGR J (Sy1 AGN) IGR J (Sy2 AGN) IGR J (NLSy1 AGN) IGR J (Sy1 AGN) Chaty et al. Optical and NIR identifications of HMXBs and AGNs: Negueruela et al. IGR J (SgXRB) Pellizza et al. IGR J (Be/X) Reig et al. IGR J (Sy1 AGN) Hannikainen et al. IGR J (SgXRB) Zurita Heras et al. IGR J (SFXT) Smith et al. XTE J (SFXT) XTE J (SyXB) IGR J (SFXT) IGR J (SgXRB) Halpern et al. Optical identifications of HMXBs and AGNs: Goncalves et al. IGR J (SFXT) IGR J (SFXT) IGR J (Sy2 AGN) Nespoli et al. Optical identifications of HMXBs: IGR J (SgXRB) Sturm et al. Optical identifications of HMXBs: IGR J (Be/X) Ratti et al. Optical identifications of X-ray binaries: IGR J (IMXB) Rodes-Roca et al. Optical identifications of HMXBs: AX J (SgXRB)

11 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 J (SgB[e]) IGR J (LMXB) IGR J (Oe/Be) IGR J (O9.7e Iab) IGR J (BN0.5 Ia) IGR J (O8 Iafpe) IGR J (SgB[e]; or SyXB?) IGR J (Be IV-V) IGR J (BN0.5 Ia) IGR J (O8.5 Ie) IGR J (LMXB?) IGR J (O8.5 Ie) IGR J (O9 Iab) IGR J (Be; or LMXB?) IGR J (early Sg) IGR J (LMXB?) Chaty et al. (2008) Rahoui et al. (2008) Coleiro et al. (2013)

12 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 J 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 ms seen with RXTE (Renaud et al. 2010) Energetic, young (<10 3 yrs) and distant (~7 kpc) PWN

13 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 ~ 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 J XRT Masetti et al. (2007) Nespoli et al. (2010) Smith et al. (2011)

14 HIGH-REDSHIFT BLAZARS The joint use of INTEGRAL/IBIS and Swift/XRT allowed the discovery of powerful gamma-ray loud blazars IGR J and IGR J 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 J Swift/XRT image Bassani et al. (2007) Masetti et al. (2012) Bassani et al. (2012)

15 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.

16 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.

17 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)

18 Catalogue of optically/nir identified IGR sources: THANK YOU!