The Nuclear Spectroscopic Telescope Array (NuSTAR) mission, launched on 2012 June 13, is the first focusing high-energy X-ray telescope in orbit. NuSTAR operates in the band from 3 to 79 keV, extending the sensitivity of focusing far beyond the ∼10 keV high-energy cutoff achieved by all previous X-ray satellites. The inherently low background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than 100-fold improvement in sensitivity over the collimated or coded mask instruments that have operated in this bandpass. Using its unprecedented combination of sensitivity and spatial and spectral resolution, NuSTAR will pursue five primary scientific objectives: (1) probe obscured active galactic nucleus (AGN) activity out to the
We present results of an all-sky hard X-ray survey based on almost four years of observations with the IBIS telescope onboard the INTEGRAL observatory. The dead time-corrected exposure of the survey is ∼33 Ms. Approximately 12% and 80% of the sky has been covered to limiting fluxes lower than 1 and 5 mCrab, respectively. Our catalog of detected sources includes 403 objects, 316 of which exceed a 5σ detection threshold on the time-averaged map of the sky, and the rest were detected in various subsamples of exposures. Among the identified sources, 219 are Galactic (90 low-mass X-ray binaries, 76 high-mass X-ray binaries, 21 cataclysmic variables, 6 coronally active stars, and other types) and 137 are extragalactic, including 130 active galactic nuclei (AGNs) and 3 galaxy clusters. We derived number-flux functions of AGNs and Galactic sources. The log N-log S relation of non-blazar AGNs is based on 68 sources located at Galactic latitudes |b| > 5• , where the survey is characterized by high identification completeness, with fluxes higher than S lim = 1.1 × 10 −11 erg s −1 cm −2 (∼0.8 mCrab) in the 17−60 keV energy band. The cumulative AGN number-flux function can be described by a power law with a slope of 1.62 ± 0.15 and normalization of (5.7 ± 0.7) × 10 −3 sources per deg 2 at fluxes >1.43 × 10 −11 erg s −1 cm −2 (>1 mCrab). Those AGNs with fluxes higher than S lim make up ∼1% of the cosmic X-ray background at 17−60 keV. We present evidence of strong inhomogeneity in the spatial distribution of nearby ( < ∼ 70 Mpc) AGNs, which reflects the large-scale structure in the local Universe.
We use NuSTAR observations of the Galactic Center to search for X-ray lines from the radiative decay of sterile neutrino dark matter. Finding no evidence of unknown lines, we set limits on the sterile neutrino mass and mixing angle. In most of the mass range 10-50 keV, these are now the strongest limits, at some masses improving upon previous limits by a factor of ∼ 10. In the νMSM framework, where additional constraints from dark matter production and structure formation apply, the allowed parameter space is reduced by more than half. Future NuSTAR observations may be able to cover much of the remaining parameter space. P r e v io u s X -r a y c o n s t r a in t s M W s a t e ll it e c o u n t s a n d p h a s e s p a c e c o n s t r a in t sNuSTAR GC 2016 FIG. 1. Simplified overview of constraints on νMSM sterile neutrino dark matter in the plane of mass and mixing angle; details are described in Sec. IV, and the experimental constraints included are listed in Fig. 8. For parameters between the gray regions, the observed dark matter abundance can be produced through resonant production in the νMSM. Most of this region is ruled out by constraints from structure formation (blue) or astrophysical X-ray observations (green). Our new constraint (red line and hatched region) is obtained from NuSTAR observations of the GC, and rules out about half of the previously allowed parameter space (white region).
Aims. We study the hard X-ray luminosity function and absorption distribution of local (z 0.1) active galactic nuclei (AGN) and discuss the implications for AGN cosmological evolution and for the cosmic X-ray background (CXB). Methods. We use the INTEGRAL all-sky hard X-ray survey to perform a statistical study of a representative sample of nearby AGN. Our entire all-sky sample consists of 127 AGN, of which 91 are confidently detected (>5σ) on the time-averaged map obtained with the IBIS/ISGRI instrument and 36 are detected only during single observations. Among the former there are 66 non-blazar AGN located at |b| > 5• , where the survey's identification completeness is ∼93%, which we use for calculating the AGN luminosity function and X-ray absorption distribution. Results. In broad agreement with previous studies, we find that the fraction f a of obscured (log N H > 22) objects is much higher (∼70%) among the low-luminosity AGN (L hx < 10 43.6 erg s −1 ) than among the high-luminosity ones (L hx > 10 43.6 erg s −1 ), f a ∼ 25%, where L hx is the luminosity in the 17-60 keV energy band. We also find that locally the fraction of Compton-thick AGN is less than 20% unless there is a significant population of AGN that are so strongly obscured that their observed hard X-ray luminosities fall below ∼1040 -10 41 erg s −1 , the effective limit of our survey. The constructed hard X-ray luminosity function has a canonical, smoothly broken power-law shape in the range 40 < log L hx < 45.5 with a characteristic luminosity of log L * = 43.40 ± 0.28. The estimated local luminosity density due to AGN with log L hx > 40 is (1.4 ± 0.3) × 10 39 erg s −1 Mpc −3 (17-60 keV). We demonstrate that the spectral shape and amplitude of the CXB are consistent with the simple scenario in which the N H distribution of AGN (for a given L hx /L * (z) ratio) has not changed significantly since z ∼ 1.5, while the AGN luminosity function has experienced pure luminosity evolution.
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