NuSTAR Hard X-Ray Survey of the Galactic Center Region I Hard X-Ray Morphology and Spectroscopy of the Diffuse Emission

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 Gamma ~ 1.3--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 Kalpha fluorescence line emission associated with two Sgr A molecular clouds MC1 and the Bridge. Broadband X-ray spectral analysis with a Monte-Carlo based X-ray reflection model self-consistently determined their intrinsic column density (~10<SUP>23</SUP> cm<SUP>-2</SUP>), primary X-ray spectra (power-laws with Gamma ~ 2) and set a lower limit of the X-ray luminosity of Sgr A* flare illuminating the Sgr A clouds to L<SUB>X</SUB> ≳ 10<SUP>38</SUP> erg s<SUP>-1</SUP>. 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<SUB>WD</SUB> ~ 0.9 M<SUB>&sun;</SUB>. 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.