A suzaku discovery of a slowly varying hard X-ray continuum from the type i Seyfert Galaxy NGC 3516

Hirofumi Noda, Kazuo Makishima, Kazuhiro Nakazawa, Shin'Ya Yamada

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10 Citations (Scopus)


The bright type I Seyfert galaxy NGC 3516 was observed by Suzaku twice, in 2005 October 12-15 and 2009 October 28-November 2, for a gross time coverage of 242 and 544 ks and a net exposure of 134 and 255 ks, respectively. The 2-10 keV luminosity was 2.8 × 1041 erg s-1 in 2005 and 1.6 × 1041 erg s-1 in 2009. The 1.4-1.7 keV and 1.7-10 keV count rates both exhibited peak-to-peak variations of a factor of ∼2 in 2005 and ∼4 in 2009. In both observations, the 15-45 keV count rate was less variable. The 2-10 keV spectrum in 2005 was significantly more convex than that in 2009. Through a count-count plot technique, the 2-45 keV signals in both sets of data were successfully decomposed in a model-independent way into two distinct broadband components. One is a variable emission with a featureless spectral shape, and the other is a non-varying hard component accompanied by a prominent Fe-K emission line at 6.33 keV (6.40 keV in the rest frame). The former was successfully fitted by an absorbed power-law model, while the latter requires a new hard continuum in addition to a reflection component from distant materials. The spectral and variability differences between the two observations are mainly attributed to long-term changes of this new hard continuum, which was stable on timescales of several hundreds of kiloseconds.

Original languageEnglish
Article number100
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 2013 Jul 10


  • X-rays: galaxies
  • galaxies: Seyfert
  • galaxies: active
  • galaxies: individual (NGC 3516)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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