SirWilliam Herschel already recognised them as a 'double nebula'[citation needed] and they were jointly listed asHolm 187 in theCatalogue of Double and Multiple Galaxies and asArp 94 in theAtlas of Peculiar Galaxies. Amateur telescopes can discern them but require magnification of about 100 times. They are situated 50′ east of the well-known double star systemGamma Leonis (i.e. Algieba).
Onesupernova has been observed in NGC 3227: SN 1983U (type Ia, mag. 12) was discovered by Vladimir Pronik on 4 November 1983.[5][6]
As is typical of many AGN, the nucleus of NGC 3227 has been identified as a source of variableX-ray emission.[9][10][11][12][13] This variability occurs on time scales ranging from a few hours to a few months.[9][11][12][13] The variability may be caused by variations in the density orionization of gas and dust near the AGN that absorb the X-ray emission.[10][11][12][13] A substantial amount of the X-ray-absorbing gas may lie within 0.4parsec (1.3light-years) of the nucleus.[13] An observed change in the shape of the X-rayspectrum in 2000 and 2001 suggests that some of the X-ray absorbing gas is located within 10–100light-days of the nucleus.[14]
The luminosity of the nucleus reached a maximum in 1977 when evidence suggesting long-lived one-sided or two-sided gas streams was obtained. X-ray radiation of the central accretion disc is reprocessed in one to two days to be re-emitted in the optical spectrum. Infra-redlight emission from the hot dust torus lags optical light emission from the nucleus by about 20 days in NGC 3227. The temperature of the dust torus is estimated at 1500 K to 1800 K in NGC 3227 and similar galaxies.
Catalogue of Double and Multiple Galaxies, Erik Holmberg, 1937
A catalogue of dwarf galaxy candidates around interacting galaxies, Astron. Astrophys., Suppl. Ser., 129, 455-462 (1998) - May(I) 1998, Deeg, H.J. et al.
Long-term variability of the optical emission lines in the nuclear spectrum of the Seyfert galaxy NGC 3227,Active Galaxies Newsletter, No 98, Pronik I., Metik L., May 2005
Reverberation Measurements of the Inner Radius of the Dust Torus in Nearby Seyfert 1 Galaxies, M. Suganuma et al., Astrophysical Journal, vol 639, March 2006
^Graham, Alister W. (November 2008), "Populating the Galaxy Velocity Dispersion - Supermassive Black Hole Mass Diagram: A Catalogue of (Mbh, σ) Values",Publications of the Astronomical Society of Australia,25 (4):167–175,arXiv:0807.2549,Bibcode:2008PASA...25..167G,doi:10.1071/AS08013,S2CID89905.
