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Register a new userInvestigating the true nature of three hard X-ray sources
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Many of the new high energy sources discovered both by INTEGRAL/IBIS and Swift/BAT have been characterised thanks to extensive, multi-band follow-up campaigns, but there are still objects whose nature remains to be asserted. In this paper we investigate the true nature of three high energy sources, IGR J12134-6015, IGR J16058-7253 and Swift J2037.2+4151, employing multiwavelength data from the NIR to the X-rays. Through Gaia and ESO-VLT measurements and through Swift/XRT X-ray spectral analysis, we re-evaluate the classification for IGR J12134-6015, arguing that the source is a Galactic object and in particular a Cataclysmic Variable. We were able to confirm, thanks to NuSTAR observations, that the hard X-ray emission detected by INTEGRAL/IBIS and Swift/BAT from IGR J16058-7253 is coming from two Seyfert 2 galaxies which are both counterparts for this source. Through optical and X-ray spectral analysis of Swift J2037.2+4151 we find that this source is likely part of the rare and peculiar class of Symbiotic X-ray binaries and displays flux and spectral variability as well as interesting spectral features, such as a blending of several emission lines around the iron line complex.
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The Gamma ray Burst Monitor (GBM) on board Fermi Gamma-ray Space Telescope has been providing continuous data to the astronomical community since 2008 August 12. We will present the results of the analysis of the first three years of these continuous data using the Earth occultation technique to monitor a catalog of 209 sources. Although the occultation technique is in principle quite simple, in practice there are many complications including the dynamic instrument response, source confusion, and scattering in the Earths atmosphere, which will be described. We detect 99 sources, including 40 low-mass X-ray binary/neutron star systems, 31 high-mass X-ray binary/neutron star systems, 12 black hole binaries, 12 active galaxies, 2 other sources, plus the Crab Nebula and the Sun. Nine of these sources are detected in the 100-300 keV band, including seven black-hole binaries, the active galaxy Cen A, and the Crab. The Crab and Cyg X-1 are also detected in the 300-500 keV band. GBM provides complementary data to other sky monitors below 100 keV and is the only all-sky monitor above 100 keV. In our fourth year of monitoring, we have already increased the number of transient sources detected and expect several of the weaker persistent sources to cross the detection threshold. I will briefly discuss these new sources and what to expect from our five year occultation catalog.
The INTEGRAL archive developed at INAF-IASF Milano with the available public observations from late 2002 to 2016 is investigated to extract the X-ray properties of 58 High Mass X-ray Binaries (HMXBs). This sample consists of sources hosting either a Be star (Be/XRBs) or an early-type supergiant companion (SgHMXBs), including the Supergiant Fast X-ray Transients (SFXTs). INTEGRAL light curves (sampled at 2 ks) are used to build their hard X-ray luminosity distributions, returning the source duty cycles, the range of variability of the X-ray luminosity and the time spent in each luminosity state. The phenomenology observed with INTEGRAL, together with the source variability at soft X-rays taken from the literature, allows us to obtain a quantitative overview of the main sub-classes of massive binaries in accretion (Be/XRBs, SgHMXBs and SFXTs). Although some criteria can be derived to distinguish them, some SgHMXBs exist with intermediate properties, bridging together persistent SgHMXBs and SFXTs.
IGR J17454-2919 is a hard X-ray transient discovered by INTEGRAL on 2014 September 27. We report on our 20ks Chandra observation of the source, performed about five weeks after the discovery, as well as on INTEGRAL and Swift monitoring long-term observations. X-ray broad-band spectra of the source are compatible with an absorbed power-law, $Gammasim$1.6-1.8, ${rm N_H}sim$(10-12)$times 10^{22},{rm cm}^{-2}$, with no trace of a cut-off in the data up to about 100keV, and with an average absorbed 0.5-100keV flux of about (7.1-9.7)${times 10^{-10}~erg~cm^{-2}~s^{-1}}$. With Chandra, we determine the most accurate X-ray position of IGR J17454-2919, $alpha_{J2000}$=17$^{h}$ 45$^{m}$ 27$^{s}$.69, $delta_{J2000}$= $-$29$^{circ}$ 19$^{prime}$ 53$^{prime prime}$.8 (90% uncertainty of 0$^{primeprime}$.6), consistent with the NIR source 2MASS J17452768-2919534. We also include NIR investigations from our observations of the source field on 2014 October 6 with GROND. With the multi-wavelength information at hand, we discuss the possible nature of IGR J17454-2919.
We analyse very deep X-ray and mid-IR surveys in common areas of the Lockman Hole and the HDF North to study the sources of the X-ray background (XRB) and to test the standard obscured accretion paradigm. We detect with ISO a rich population of X-ray luminous sources with red optical colours, including a fraction identified with Extremely Red Objects (R-K > 5) and galaxies with SEDs typical of normal massive ellipticals or spirals at z ~ 1. The high 0.5-10 keV X-ray luminosities of these objects (1E43-1E45 erg/s) indicate that the ultimate energy source is gravitational accretion, while the X-ray to IR flux ratios and the X-ray spectral hardness show evidence of photoelectric absorption at low X-ray energies. An important hint on the physics comes from the mid-IR data at 6.7 and 15 um, well reproduced by model spectra of completely obscured quasars under standard assumptions and l.o.s. optical depths tau ~ 30-40. Other predictions of the standard XRB picture, like the distributions of intrinsic bolometric luminosities and the relative fractions of type-I and -II objects (1:3), are also consistent with our results. Obscured gravitational accretion is then confirmed as being responsible for the bulk of the X-ray background, since we detect in the IR the down-graded energy photoelectrically absorbed in X-rays: 63% of the faint 5-10 keV XMM sources are detected in the mid-IR by Fadda et al. (2001). However, although as much as 90% of the X-ray energy production could be converted to IR photons, no more than 20% of the Cosmic IR Background can be attributed to X-ray loud AGNs.
We present the results from Suzaku observations of the hottest Abell galaxy cluster A2163 at $z=0.2$. To study the physics of gas heating in cluster mergers, we investigated hard X-ray emission from the merging cluster A2163, which hosts the brightest synchrotron radio halo. We analyzed hard X-ray spectra accumulated from two-pointed Suzaku observations. Non-thermal hard X-ray emission should result from the inverse Compton (IC) scattering of relativistic electrons by the CMB photons. To measure this emission, the dominant thermal emission in the hard X-ray band must be modeled in detail. To this end, we analyzed the combined broad-band X-ray data of A2163 collected by Suzaku and XMM-Newton, assuming single- and multi-temperature models for thermal emission and the power-law model for non-thermal emission. From the Suzaku data, we detected significant hard X-ray emission from A2163 in the 12-60 keV band at the $28sigma$ level (or at the $5.5sigma$ level if a systematic error is considered). The Suzaku HXD spectrum alone is consistent with the single-T thermal model of gas temperature $kT=14$ keV. From the XMM data, we constructed a multi-T model including a very hot ($kT=18$ keV) component in the NE region. Incorporating the multi-T and the power-law models into a two-component model with a radio-band photon index, the 12-60 keV energy flux of non-thermal emission is constrained within $5.3 pm 0.9 (pm 3.8)times 10^{-12}~{rm erg, s^{-1} cm^{-2}}$. The 90% upper limit of detected IC emission is marginal ($< 1.2times 10^{-11}~{rm erg, s^{-1} cm^{-2}}$ in the 12-60 keV). The estimated magnetic field in A2163 is $B > 0.098~{rm mu G}$. While the present results represent a three-fold increase in the accuracy of the broad band spectral model of A2163, more sensitive hard X-ray observations are needed to decisively test for the presence of hard X-ray emission due to IC emission.
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