Letter to the Editor

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

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

Abstract

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.