Astronomy and Astrophysics, volume 371, 512-526 (2001/5-4)
Extreme synchrotron BL Lac objects. Stretching the blazar sequence.
COSTAMANTE L., GHISELLINI G., GIOMMI P., TAGLIAFERRI G., CELOTTI A., CHIABERGE M., FOSSATI G., MARASCHI L., TAVECCHIO F., TREVES A. and WOLTER A.
Abstract (from CDS):
We performed an observational program with the X-ray satellite BeppoSAX, to study objects with extreme synchrotron peak frequencies (νpeak>1keV). Of the seven sources observed, five revealed or confirmed their extreme nature. Four showed peak frequencies in the range 1-5keV, while one (1ES 1426+428) displayed a flat power law spectrum (αx=0.92±0.04) which locates its synchrotron peak at or above 100keV. This is the third source of this type ever found, after Mkn 501 and 1ES 2344+514. In the context of the whole blazar class, the broad band properties of these objects confirm the scenario of a synchrotron peak smoothly spanning the IR - X-ray range, which explains the multi-frequency properties of the blazar class. Our data also confirm the large νpeak variability which seems to characterize this class of sources, compared with lower νpeak objects. Given the high synchrotron peak energies, which flag the presence of high energy electrons, these extreme BL Lacs are also good candidates for TeV emission, and therefore good probes of the IR background.
BL Lacertae objects: individual: 1ES 0033+595, 1ES 0120+340, PKS 0548-322, GB 1114+203, 1ES 1218+304, 1ES 1426+428, H 2356-309 - X-rays: general - TeV: general
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