EDP Sciences
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Volume 400, Number 2, March III 2003
Page(s) 477 - 486
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20021916

A&A 400, 477-486 (2003)
DOI: 10.1051/0004-6361:20021916

The BL Lacertae objects OQ 530 and S5 0716+714

Simultaneous observations in the X-rays, radio, optical and TeV bands
G. Tagliaferri1, M. Ravasio1, G. Ghisellini1, P. Giommi2, E. Massaro3, R. Nesci3, G. Tosti4, M. F. Aller5, H. D. Aller5, A. Celotti6, L. Maraschi7, F. Tavecchio1 and A. Wolter7

1  INAF - Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate, Italy
2  ASI Science Data Center, Via Galileo Galilei, 00044 Frascati, Italy
3  Dipartimento di Fisica, Università La Sapienza, P.le Aldo Moro 2, 00185 Roma, Italy
4  Dipartimento di Fisica e Osservatorio Astronomico, Università di Perugia, Perugia, Italy
5  Department of Astronomy, University of Michigan, Dennison Building, Ann Arbor MI 48109-1090, USA
6  SISSA/ISAS, via Beirut 2-4, 34014 Trieste, Italy
7  INAF - Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milano, Italy

(Received 25 October 2002 / Accepted 20 December 2002 )

We present the results of the BeppoSAX observations of two BL Lacs, OQ 530 and S5 0716+714, as part of a ToO program for the simultaneous observation at radio, optical, X-ray and TeV energies. Both sources are detected in the LECS and MECS, with S5 0716+714 visible also in the PDS band, up to about ~60 keV. The X-ray spectra of both sources are better fitted by a double power-law model, with a steep soft X-ray component flattening at harder energies, with breaks at 0.3 and 1.5 keV, respectively. The concave shape of the spectra in both objects is consistent with soft X-rays being produced by the synchrotron and harder X-rays by the inverse Compton processes. Also the X-ray variability properties confirm this scenario; in particular, for S5 0716+714 our observation shows variations by about a factor of 3 over one hour below ~3 keV and no variability above. Their simultaneous broad-band energy spectral distributions can be successfully interpreted within the frame of a homogeneous synchrotron and inverse Compton model, including a possible contribution from an external source of seed photons with the different spectral states of S5 0716+714 being reproduced by changing the injected power. The resulting parameters are fully consistent with the two sources being intermediate objects within the "sequence" scenario proposed for blazars.

Key words: BL Lacertae objects: general -- X-rays: galaxies -- BL Lacertae objects: individual: OQ 530, S5 0716+714

Offprint request: G. Tagliaferri, gtagliaf@merate.mi.astro.it

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