NGC 7213 (also ESO 288-43, AM 2206-472, IRAS 22061-4724 and PGC 68165) is a magnitude +10.1 face-on Seyfert spiral galaxy located ~72 million light-years away in the constellation Grus. NGC 7213 is about 16' southeast of Alpha Gruis. The galaxy is both a LINER and a Type I Seyfert galaxy.
The galaxy was discovered by British astronomer John Herschel using a 47.5 cm (18.7 inch) f/13 speculum reflector at the Cape of Good Hope on the 30th September 1834
Right Ascension 22h 9m 16.2s, Declension -47° 10' 1"
Title: The 'harder when brighter' X-ray behaviour of the low luminosity active galactic nucleus NGC 7213 Authors: D. Emmanoulopoulos, I. E. Papadakis, I. M. McHardy, P. Arevalo, D. E. Calvelo, P.Uttley
We present the first robust evidence of an anti-correlation between the X-ray photon index, \Gamma, and the X-ray luminosity in a single low luminosity active galactic nuclei (LLAGN), NGC 7213. Up to now, such anti-correlation trends have been seen only in large samples of LLAGN that span a wide range of X-ray fluxes, although the opposite behaviour (i.e. a positive correlation between \Gamma and X-ray luminosity) has been extensively studied for individual X-ray bright active galactic nuclei. For NGC 7213, we use the long-term X-ray monitoring data of Rossi X-ray Timing Explorer (RXTE), regularly obtained on average every two days from March 2006 to December 2009. Based on our X-ray data, we derive the \Gamma versus flux and the hardness ratio versus flux relations, indicating clearly that NGC 7213 follows a 'harder when brighter' spectral behaviour. Additionally, by analysing radio and optical data, and combining data from the literature, we form the most complete spectral energy distribution (SED) of the source across the electromagnetic spectrum yielding a bolometric luminosity of 1.7*10^43 erg s^-1. Phenomenologically, the SED of NGC 7213 is similar to that of low-ionisation nuclear emission-line region. The robust anti-correlation trend that we find between \Gamma and X-ray luminosity together with the low accretion rate of the source, 0.14 per cent that of Eddington limit, make NGC 7213 the first LLAGN exhibiting a similar spectral behaviour with that of black hole X-ray binaries in 'hard state'.