Issue |
A&A
Volume 374, Number 3, August II 2001
|
|
---|---|---|
Page(s) | 895 - 906 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20010798 | |
Published online | 15 August 2001 |
Temporal and spectral gamma-ray properties of Mkn 421 above 250 GeV from CAT observations between 1996 and 2000
1
Laboratoire de Physique Nucléaire des Hautes Énergies, École Polytechnique, Palaiseau, France (IN2P3/CNRS)
2
Physique Corpuscul aire et Cosmologie, Collège de France et Université Paris VII, France (IN2P3/CNRS)
3
Laboratoire de Physique Nucléaire et de Hautes Energies, Universités Paris VI/VII, France (IN2P3/CNRS)
4
Centre d'Études Spatiales des Rayonnements, Université Paul Sabatier, Toulouse, France (INSU/CNRS)
5
Groupe de Physique Fondamentale, Université de Perpignan, France
6
Service d'Astrophysique, Centre d'Études de Saclay, France (CEA/DSM/DAPNIA)
7
Nuclear Center, Charles University, Prague, Czech Republic
Corresponding author: F. Piron, piron@in2p3.fr
Received:
10
April
2001
Accepted:
30
May
2001
The γ-ray emission above from the BL Lac object Markarian 421
was observed by the CAT Cherenkov imaging telescope between December, 1996, and June, 2000.
In 1998, the source produced a series of small flares, making it the second extragalactic source detected
by CAT. The time-averaged differential spectrum has been measured from 0.3 to
, which is well fitted
with a power law:
.
In 2000, the source showed an unprecedented activity, with variability time-scales as short as one hour, as for
instance observed during the night between 4 and 5 February.
The 2000 time-averaged spectrum measured is compatible
with that of 1998, but some indication of a spectral curvature is found between 0.3 and
.
The possibility of
spectral hardening during flares is also discussed, and the results are compared to those obtained on
the other
BL Lac, Markarian 501.
Key words: galaxies: active / galaxies: nuclei / BL Lacertæobjects: individual: Mkn 421 / gamma-rays: observations
© ESO, 2001
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