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A UV Flare at the Center of the Elliptical Galaxy NGC 4552

Published online by Cambridge University Press:  25 May 2016

Lucio M. Buson ,
Francesco Bertola ,
David Burstein ,
Michele Cappellari ,
Sperello di Serego Alighieri ,
Laura Greggio  and
Alvio Renzini
Lucio M. Buson
Affiliation:
Osservatorio di Capodimonte, Napoli, Italy
Francesco Bertola
Affiliation:
Dipartimento di Astronomia, Università di Padova, Padova, Italy
David Burstein
Affiliation:
Department of Physics & Astronomy, Arizona State University, Tempe, AZ, USA
Michele Cappellari
Affiliation:
Dipartimento di Astronomia, Università di Padova, Padova, Italy
Sperello di Serego Alighieri
Affiliation:
Osservatorio di Arcetri, Firenze, Italy
Laura Greggio
Affiliation:
Dipartimento di Astronomia, Università di Bologna, Bologna, Italy Sternwarte der Universität München, München, Germany
Alvio Renzini
Affiliation:
European Southern Observatory, Garching bei München, Germany

Abstract

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A self-consistent analysis of near-UV, HST/FOC images of the elliptical galaxy NGC 4552 is used to show that its central spike has brightened by a factor ˜ 4.5 between 1991 and 1993, and has decreased its luminosity by a factor ˜ 2.0 between 1993 and 1996. A strong UV continuum over the energy distribution of the underlying galaxy is concurrently revealed shortward of λ ˜ 3200 Å by our FOS spectra extending from the near-UV to red wavelengths. Nuclear emission-line profiles of both permitted and forbidden lines are best modelled with a combination of broad and narrow components, with FWHM of ˜ 3000 km s−1 and ˜ 700 km s−1, respectively. Current diagnostics based on the emission line intensity ratios definitely places the spike among AGNs, just at the border between Seyferts and LINERs. This evidence argues for the variable central spike being produced by a modest accretion event onto a central massive black hole (BH), with the accreted material having possibly being stripped from a star in a close fly-by with the BH. In this regard, one has to look at NGC 4552 as the faintest known AGN.

Type
IV. AGN Related Phenomena
Information
Symposium - International Astronomical Union , Volume 194: Activity in Galaxies and Related Phenomena , 1999 , pp. 389 - 393
Copyright
Copyright © Astronomical Society of the Pacific 1999 

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