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

Kaya Mori, Charles J. Hailey, Roman Krivonos, Jaesub Hong, Gabriele Ponti, Franz Bauer, Kerstin Perez, Melania Nynka, Shuo Zhang, John A. Tomsick, David M. Alexander, Frederick K. Baganoff, Didier Barret, Nicolas Barriere, Steven E. Boggs, Alicia M. Canipe, Finn Erland Christensen, William W. Craig, Karl Forster, Paolo GiommiBrian W. Grefenstette, Jonathan E. Grindlay, Fiona A. Harrison, Allan Hornstrup, Takao Kitaguchi, Jason E. Koglin, Vy Luu, Kristen K. Madsen, Peter H. Mao, Hiromasa Miyasaka, Matteo Perri, Michael J. Pivovaroff, Simonetta Puccetti, Vikram Rana, Daniel Stern, Niels J. Westergaard, William W. Zhang, Andreas Zoglauer

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    Abstract

    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 similar to 1.3-2.3 up to similar 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. Broadband X-ray spectral analysis with a Monte-Carlo based X-ray reflection model self-consistently determined their intrinsic column density (similar to 10(23) cm(-2)), primary X-ray spectra (power-laws with Gamma similar to 2) and set a lower limit of the X-ray luminosity of Sgr A* flare illuminating the Sgr A clouds to L-X >= 10(38) erg s(-1). Above similar to 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-WD similar to 0.9M(circle dot). 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.
    Original languageEnglish
    Article number94
    JournalAstrophysical Journal
    Volume814
    Issue number2
    Number of pages24
    ISSN0004-637X
    DOIs
    Publication statusPublished - 2015

    Keywords

    • Galaxy: center
    • Radiation mechanisms: non-thermal
    • X-rays: general
    • X-rays: ISM

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