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Astron. Astrophys. 332, L1-L4 (1998)

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Letter to the Editor

Intraday variability of BL Lacertae in the great 1997 outburst

R. Nesci 1, M. Maesano 1, E. Massaro 1, F. Montagni 1, G. Tosti 2 and M. Fiorucci 2

1 Istituto Astronomico, Unitá GIFCO-CNR Roma1, Universitá di Roma "La Sapienza", via Lancisi 29, I-00161 Roma, Italy
2 Osservatorio Astronomico, Universitá di Perugia, via Bonfigli, I-06126 Perugia, Italy

Received 23 October 1997 / Accepted 15 January 1998


We report intranight observations performed during the Summer 1997 outburst of BL Lac, in the B, V, [FORMULA] and [FORMULA] bands. The source was never found to be stable, but always showed a variability of at least 0.04 mag/hour, often with superimposed fast fluctuations on time scales of about an hour and with amplitudes of about 0.1 mag. The amplitude of the flux variations was always larger at shorter wavelengths. No time lag between different bands could be unambiguously detected.

Key words: BL Lacertae objects: general – BL Lacertae objects: individual: BL Lac

Send offprint requests to: R. Nesci

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© European Southern Observatory (ESO) 1998

Online publication: March 10, 1998