Discovery of superstrong, fading, iron line emission and double-peaked Balmer lines of the galaxy SDSS J095209.56+214313.3: the light echo of a huge flare

摘要: We report the discovery of superstrong, fading, high-ionization iron line emission in galaxy SDSS J095209.56+214313.3 (SDSS J0952+2143 hereafter), which must have been caused by an X-ray outburst large amplitude. is unique its strong multiwavelength variability; such a broadband emission-line and continuum response has not observed before. The accompanied unusual Balmer with broad base, narrow core, double-peaked horns, He II emission. These lines, while spectrum taken 2005, faded away significantly new spectra 2007 December. Comparison SDSS, 2MASS, GALEX, follow-up GROND photometry reveals variability NUV, optical, NIR band. Taken together, these observations can be explained giant EUV-X-ray band, detected even optical NIR. intense variable iron, helium, lines represent "light echo" flare, as it traveled through circumnuclear material. may tidal disruption star supermassive black hole. Spectroscopic surveys are well suited to detect light echoes rare flare events. Reverberation-mapping then used efficient probe physical conditions material nonactive or active galaxies.