EDP Sciences
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Volume 443, Number 3, December I 2005
Page(s) L33 - L36
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200500198

A&A 443, L33-L36 (2005)
DOI: 10.1051/0004-6361:200500198


Multiband photometry of the blazar PKS 0537-441: a major active state in December 2004-March 2005

A. Dolcini1, S. Covino2, A. Treves1, E. Palazzi3, E. Pian4, E. Molinari2, G. Chincarini2, 5, F. M. Zerbi2, M. Rodonó6, 7, V. Testa8, G. Tosti9, F. Vitali8, L. A. Antonelli8, P. Conconi2, G. Cutispoto6, A. Monfardini10, 11, M. Stefanon12, P. D'Avanzo1, 2, J. Danziger4, A. Fernandez-Soto13 and E. Meurs14

1  Università dell'Insubria, Dipartimento di Fisica e Matematica, via Valleggio 11, 22100 Como, Italy
2  INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (Lc), Italy
    e-mail: covino@merate.mi.astro.it
3  IASF/CNR, Sezione di Bologna, via Gobetti 101, 40129 Bologna, Italy
4  INAF, Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34131 Trieste, Italy
5  Università degli studi di Milano-Bicocca, Dipartimento di Fisica, Piazza delle Scienze 3, 20126 Milan, Italy
6  INAF, Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
7  Dipartimento di Fisica e Astronomia Università di Catania, v. S. Sofia 78, 95123 Catania, Italy
8  INAF, Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
9  Dipartimento di Fisica e Osservatorio Astronomico, Università di Perugia, Italy
10  Astrophysics Research Institute, Liverpool JMU, UK
11  ITC-IRST and INFN, Trento, Italy
12  European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
13  Observatori Astronomic, Universitat de Valencia, Aptdo. Correos 22085, Valencia 46071, Spain
14  Dunsink Observatory, Castleknock, Dublin 15, Ireland

(Received 15 July 2005 / Accepted 5 October 2005)

Multiband VRIJHK photometry of the Blazar PKS 0537-441 obtained with the REM telescope from December 2004 to March 2005 is presented. A major period of activity is found with more than four magnitudes variability in the V filter in 50 days and of 2.5 in 10 days. In intensity and duration the activity is similar to that of 1972 reported by Eggen (1973, ApJ, 186, 1), but it is much better documented. No clear evidence of variability on time-scale of minutes is found. The spectral energy distribution is roughly described by a power-law, with the weaker state being the softer.

Key words: galaxies: active -- galaxies: BL Lacertae objects: PKS 0537-441

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