* Astronomy

Title: Multi-wavelength Observations of the Giant X-ray Flare Galaxy NGC 5905: signatures of tidal disruption
Authors: H.Raichur, M.Das, A.Alonso Herrero, P.Shastri, N.G.Kantharia

NGC 5905 is one of the few galaxies in which an X-ray flare was discovered by the ROSAT All Sky Survey (RASS). This flare was supposed to have occurred due to tidal disruption of a star by the central black hole. In this work we present analysis of multi-wavelength follow-up observations made in X-ray, mid-infrared and radio using data obtained from the Chandra X-ray observatory, Spitzer and Giant Meter wave Radio telescope (GMRT) respectively. The archival Chandra 2007 observations show that the X-ray luminosity in the energy band of 0.5-2.0 keV has decreased by a factor of 200 since the peak of the X-ray flare observed in 1990. The X-ray image reveals no centrally bright core expected in the presence of an AGN. Diffuse X-ray emission lying close to the circum-nuclear star forming ring is observed. The radio flux density observed with the GMRT data is similar to the flux density derived using the VLA FIRST observation in 1997 which indicates that the radio emission is probably unaffected by the 1990 X-ray flare. The archival Spitzer 2006 mid-infrared spectrum shows strong evidence of nuclear star formation but does not show any clear signatures of AGN activity. Therefore, we conclude, that there is no central AGN in NGC 5905 and reaffirm that the 1990 X-ray flare observed in this galaxy was a tidal disruption event and not due to AGN variability. NGC 5905 represents one of the few direct evidences that non-accreting black holes exist and hence provides an opportunity to study the post-outburst evolution of a tidal disruption event in the nucleus of a giant low surface brightness galaxy.

Read more (609kb, PDF)