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Register a new user15 years of Galactic surveys and hard X-ray Background measurements
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The INTEGRAL hard X-ray surveys have proven to be of fundamental importance. INTEGRAL has mapped the Galactic plane with its large field of view and excellent sensitivity. Such hard X-ray snapshots of the whole Milky Way on a time scale of a year are beyond the capabilities of past and current narrow-FOV grazing incidence X-ray telescopes. By expanding the INTEGRAL X-ray survey into shorter timescales, a productive search for transient X-ray emitters was made possible. In more than fifteen years of operation, the INTEGRAL observatory has given us a sharper view of the hard X-ray sky, and provided the triggers for many follow-up campaigns from radio frequencies to gamma-rays. In addition to conducting a census of hard X-ray sources across the entire sky, INTEGRAL has carried out, through Earth occultation maneuvers, unique observations of the large-scale cosmic X-ray background, which will without question be included in the annals of X-ray astronomy as one of the missions most salient contribution to our understanding of the hard X-ray sky.
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We briefly review the synergy between X-ray and infrared observations for Active Galactic Nuclei (AGNs) detected in cosmic X-ray surveys, primarily with XMM-Newton, Chandra, and NuSTAR. We focus on two complementary aspects of this X-ray-infrared synergy (1) the identification of the most heavily obscured AGNs and (2) the connection between star formation and AGN activity. We also briefly discuss future prospects for X-ray-infrared studies over the next decade.
The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) continues to successfully work in orbit after its launch in 2002. The mission provides the deepest ever survey of hard X-ray sources throughout the Galaxy at energies above 20 keV. We report on a catalogue of new hard X-ray source candidates based on the latest sky maps comprising 14 years of data acquired with the IBIS telescope onboard INTEGRAL in the Galactic Plane (|b|<17.5 deg). The current catalogue includes in total 72 hard X-ray sources detected at S/N>4.7 sigma and not known to previous INTEGRAL surveys. Among them, 31 objects have also been detected in the on-going all-sky survey by the BAT telescope of the Swift observatory. For 26 sources on the list, we suggest possible identifications: 21 active galactic nuclei, two cataclysmic variables, two isolated pulsars or pulsar wind nebulae, and one supernova remnant; 46 sources from the catalogue remain unclassified.
We present the first sub-arcminute images of the Galactic Center above 10 keV, obtained with NuSTAR. NuSTAR resolves the hard X-ray source IGR J17456-2901 into non-thermal X-ray filaments, molecular clouds, point sources and a previously unknown central component of hard X-ray emission (CHXE). NuSTAR detects four non-thermal X-ray filaments, extending the detection of their power-law spectra with $Gammasim1.3$-$2.3$ up to ~50 keV. A morphological and spectral study of the filaments suggests that their origin may be heterogeneous, where previous studies suggested a common origin in young pulsar wind nebulae (PWNe). NuSTAR detects non-thermal X-ray continuum emission spatially correlated with the 6.4 keV Fe K$alpha$ fluorescence line emission associated with two Sgr A molecular clouds: MC1 and the Bridge. Broad-band X-ray spectral analysis with a Monte-Carlo based X-ray reflection model self-consistently determined their intrinsic column density ($sim10^{23}$ cm$^{-2}$), primary X-ray spectra (power-laws with $Gammasim2$) and set a lower limit of the X-ray luminosity of Sgr A* flare illuminating the Sgr A clouds to $L_X stackrel{>}{sim} 10^{38}$ erg s$^{-1}$. Above ~20 keV, hard X-ray emission in the central 10 pc region around Sgr A* consists of the candidate PWN G359.95-0.04 and the CHXE, possibly resulting from an unresolved population of massive CVs with white dwarf masses $M_{rm WD} sim 0.9 M_{odot}$. Spectral energy distribution analysis suggests that G359.95-0.04 is likely the hard X-ray counterpart of the ultra-high gamma-ray source HESS J1745-290, strongly favoring a leptonic origin of the GC TeV emission.
We present the 3-8 keV and 8-24 keV number counts of active galactic nuclei (AGN) identified in the NuSTAR extragalactic surveys. NuSTAR has now resolved 33-39% of the X-ray background in the 8-24 keV band, directly identifying AGN with obscuring columns up to approximately 1e25 /cm2. In the softer 3-8 keV band the number counts are in general agreement with those measured by XMM-Newton and Chandra over the flux range 5e-15 < S(3 - 8 keV)/(erg/cm2/s) < 1e-12 probed by NuSTAR. In the hard 8-24 keV band NuSTAR probes fluxes over the range 2e-14 < S(8-24 keV)/(erg/cm2/s) < 1e-12, a factor of approximately 100 fainter than previous measurements. The 8-24 keV number counts match predictions from AGN population synthesis models, directly confirming the existence of a population of obscured and/or hard X-ray sources inferred from the shape of the integrated cosmic X-ray background. The measured NuSTAR counts lie significantly above simple extrapolation with a Euclidian slope to low flux of the Swift/BAT 15-55 keV number counts measured at higher fluxes S(15-55 keV) > 1e-11 erg/cm2/s, reflecting the evolution of the AGN population between the Swift/BAT local (z<0.1) sample and NuSTARs z~1 sample. CXB synthesis models, which account for AGN evolution, lie above the Swift/BAT measurements, suggesting that they do not fully capture the evolution of obscured AGN at low redshifts.
This paper reports the analysis procedure and results of simultaneous spectral fits of the Suzaku archive data for Sagittarius (Sgr) A East and the nearby Galactic center X-ray emission (GCXE). The results are that the mixed-morphology supernova remnant Sgr A East has a recombining plasma (RP) with Cr and Mn He$alpha$ lines, and a power-law component (PL) with an Fe I K$alpha$ line. The nearby GCXE has a $sim$1.5-times larger surface brightness than the mean GCXE far from Sgr A East, although the spectral shape is almost identical. Based on these results, we interpret that the origins of the RP and the PL with the Fe I K$alpha$ line are past big flares of Sgr A$^*$.
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