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Astron. Astrophys. 351, 59-64 (1999)

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Synchrotron and inverse Compton variability in the BL Lacertae object S5 0716+714

P. Giommi 1, E. Massaro 2, L. Chiappetti 3, E.C. Ferrara 4, G. Ghisellini 5, Minhwan Jang 6, M. Maesano 2, H.R. Miller 4, F. Montagni 2, R. Nesci 2, P. Padovani **  7, E. Perlman 7, C.M. Raiteri 8, S. Sclavi 2, G. Tagliaferri 5, G. Tosti 9 and M. Villata 8

1 BeppoSAX Science Data Center, ASI, Via Corcolle 19, 00131 Roma, Italy
2 Istituto Astronomico, Universita' "La Sapienza", Via Lancisi 29 00161 Roma, Italy
3 IFC, CNR, Via Bassini 15, Milan, Italy
4 Department of Physics and Astronomy, Georgia State University Atlanta, GA 30303, USA
5 Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate, Italy
6 Department Astronomy and Space Science, Kyung Hee University, Yongin, Kyungki-Do 449-701, Korea
7 Space Telescope Science Institute 3700 San Martin Drive, Baltimore, MD 21218, USA
8 Osservatorio Astronomico di Torino, Strada Osservatorio 20 10025 Pino Torinese, Italy
9 Osservatorio Astronomico, Universita' di Perugia, Perugia, Italy

Received 23 June 1999 / Accepted 6 September 1999


We report intensity variations of different spectral components in the BL Lac object S5 0716+714 detected during coordinated BeppoSAX and optical observations in 1996 and 1998. The transition between synchrotron and inverse Compton emission has been clearly detected as sharp X-ray spectral breaks at around 2-3 keV on both occasions. Correlated optical and soft X-ray variability was found during the second BeppoSAX pointing when intensive optical monitoring could be arranged. The hard (Compton) component changed by a factor of 2 between the two observations, but remained stable within each exposure. During events of rapid variability S5 0716+714 showed spectral steepening with intensity, a behaviour rarely observed in BL Lacs. We interpret these findings as the probable consequence of a shift of the synchrotron peak emission from the IR/optical band to higher energies, causing the synchrotron tail to push into the soft X-ray band more and more as the source brightens.

Key words: radiation mechanisms: non-thermal – galaxies: active – galaxies: BL Lacertae objects: individual: S5 0716+714 – X-rays: galaxies

* Affiliated to the Astrophysics Division, Space Science Department, European Space Agency
** On leave of absence from Dipartimento di Fisica, II Università di Roma "Tor Vergata", Italy

Send offprint requests to: P. Giommi

© European Southern Observatory (ESO) 1999

Online publication: November 2, 1999