Scientific article
English

Hitomi observation of radio galaxy NGC 1275: The first X-ray microcalorimeter spectroscopy of Fe-Kα line emission from an active galactic nucleus

Publication date2018
First online date2018-04-11
Abstract

The origin of the narrow Fe-Kα fluorescence line at 6.4 keV from active galactic nuclei has long been under debate; some of the possible sites are the outer accretion disk, the broad line region, a molecular torus, or interstellar/intracluster media. In 2016 February–March, we performed the first X-ray microcalorimeter spectroscopy with the Soft X-ray Spectrometer (SXS) on board the Hitomi satellite of the Fanaroff–Riley type I radio galaxy NGC 1275 at the center of the Perseus cluster of galaxies. With the high-energy resolution of ∼5 eV at 6 keV achieved by Hitomi/SXS, we detected the Fe-Kα line with ∼5.4 σ significance. The velocity width is constrained to be 500–1600 km s−1 (FWHM for Gaussian models) at 90% confidence. The SXS also constrains the continuum level from the NGC 1275 nucleus up to ∼20 keV, giving an equivalent width of ∼20 eV for the 6.4 keV line. Because the velocity width is narrower than that of the broad Hα line of ∼2750 km s−1, we can exclude a large contribution to the line flux from the accretion disk and the broad line region. Furthermore, we performed pixel map analyses on the Hitomi/SXS data and image analyses on the Chandra archival data, and revealed that the Fe-Kα line comes from a region within ∼1.6 kpc of the NGC 1275 core, where an active galactic nucleus emission dominates, rather than that from intracluster media. Therefore, we suggest that the source of the Fe-Kα line from NGC 1275 is likely a low-covering-fraction molecular torus or a rotating molecular disk which probably extends from a parsec to hundreds of parsecs scale in the active galactic nucleus system.

Funding
  • Ministry of Education, Culture, Sports, Science and Technology [15J02737]
  • National Aeronautics and Space Administration [NNX15AC76G]
  • Science and Technology Facilities Council [ST/L00075X/1]
  • Science and Technology Facilities Council [ST/J003697/2]
  • National Aeronautics and Space Administration [PF6-170160]
  • European Commission - ACCRETING BLACK HOLES AND COSMIC FEEDBACK [340442]
Citation (ISO format)
AUDARD, Marc, FERRIGNO, Carlo, PALTANI, Stéphane. Hitomi observation of radio galaxy NGC 1275: The first X-ray microcalorimeter spectroscopy of Fe-Kα line emission from an active galactic nucleus. In: Publications of the Astronomical Society of Japan, 2018, vol. 70, n° 2, p. 13. doi: 10.1093/pasj/psx147
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Article (Published version)
accessLevelRestricted
Identifiers
Journal ISSN0004-6264
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