Issue |
A&A
Volume 407, Number 2, August IV 2003
|
|
---|---|---|
Page(s) | 453 - 460 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20030915 | |
Published online | 17 November 2003 |
X-ray and optical observations of BL Lac objects: 3C 66A (B0219+428) and ON 325 (B1215+303)
1
Dipartimento di Fisica, Università “La Sapienza”, Piazzale A. Moro 2, 00185 Roma, Italy
2
ASI Science Data Center, c/o ESA-ESRIN, via G. Galilei, 00044 Frascati, Italy
3
Istituto di Astrofisica Spaziale e Fisica Cosmica, CNR, via del Fosso del Cavaliere 100, 00133 Roma, Italy
4
Osservatorio Astronomico di Brera, via Bianchi 46, 22055 Merate, Italy
5
Department of Physics and Astronomy, Georgia State University, Atlanta GA, USA
Corresponding author: M. Perri, perri@asdc.asi.it
Received:
24
February
2003
Accepted:
10
June
2003
We report the results of new observations of the two BL Lac objects 3C 66A and
ON 325 performed with BeppoSAX and of nearly simultaneous photometric measurements
in the bandpasses from I to B.
3C 66A was observed in January 1999 and in July 2001: its X-ray flux was
erg cm-2 s-1
in January 1999 and
erg cm-2 s-1 in July 2001.
In both observations the X-ray spectrum can be fitted by a single power law with an
energy index
, steeper than that measured in the optical, equal
to
.
The BeppoSAX observation of ON 325 was performed in December 1998 when its X-ray
flux was
erg cm-2 s-1.
The X-ray spectrum cannot be fitted by a single power law, but it is found to be well represented
by a broken power law with a break energy at around 4 keV and energy indices
equal to
and
.
Both sources are characterised by a synchrotron-dominated emission at
energies lower than a few keV, with a sharp flattening toward higher energies
due to the inverse Compton component.
We obtained satisfactory modelling of the overall spectral energy
distributions, from the optical to low energy X-rays, with log-parabolic
laws.
Key words: radiation mechanisms: non-thermal / galaxies: active / BL Lacertae objects: individual: 3C 66A, ON 325 / X-rays: galaxies
© ESO, 2003
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