First hard X-ray detection of the non-thermal emission around the Arches cluster: morphology and spectral studies with NuSTAR

Roman A. Krivonos, John A. Tomsick, Franz E. Bauer, Frederick K. Baganoff, Nicolas M. Barriere, Arash Bodaghee, Steven E. Boggs, Finn Erland Christensen, William W. Craig, Brian W. Grefenstette, Charles J. Hailey, Fiona A. Harrison, JaeSub Hong, Kristin K. Madsen, Kaya Mori, Melania Nynka, Daniel Stern, William W. Zhang

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Abstract

The Arches cluster is a young, densely packed massive star cluster in our Galaxy that shows a high level of star formation activity. The nature of the extended non-thermal X-ray emission around the cluster remains unclear. The observed bright Fe Ku line emission at 6.4 keV from material that is neutral or in a low ionization state can be produced either by X-ray photoionization or by cosmic-ray particle bombardment or both. In this paper, we report on the first detection of the extended emission around the Arches cluster above 10 keV with the NuSTAR mission, and present results on its morphology and spectrum. The spatial distribution of the hard X-ray emission is found to be consistent with the broad region around the cluster where the 6.4 keV line is observed. The interpretation of the hard X-ray emission within the context of the X-ray reflection model puts a strong constraint on the luminosity of the possible illuminating hard X-ray source. The properties of the observed emission are also in broad agreement with the low-energy cosmic-ray proton excitation scenario.
Original languageEnglish
Article number107
JournalAstrophysical Journal
Volume781
Issue number2
Number of pages11
ISSN0004-637X
DOIs
Publication statusPublished - 2014

Keywords

  • ASTRONOMY
  • SGR-A-ASTERISK
  • XMM-NEWTON OBSERVATION
  • GALACTIC-CENTER REGION
  • MOLECULAR CLOUDS
  • LINE EMISSION
  • STELLAR CLUSTERS
  • BRIGHTEST FLARE
  • MASSIVE STARS
  • DISCOVERY
  • CHANDRA

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