Rapid variability in TeV blazars: the case of PKS2155-304
Abstract
Recent Cherenkov observations of BL Lacertae (BL Lac) objects showed that the TeV (teraelectron volt) flux of PKS2155-304 changed by a factor of 2 in just 3-5min. This fast variability can be accounted for if the emitting region is moving with a bulk Lorentz factor Γ ~ 50 and a similar relativistic Doppler factor. If this Γ is adopted, several models can fit the data, but, irrespective of the chosen model, the jet is matter dominated. The Doppler factor requires viewing angles of the order of 1° or less: if the entire jet is as narrow as this, then we have problems with current unification schemes. This suggests that there are small active regions, inside a larger jet, moving faster than the rest of the plasma, occasionally pointing at us. Coordinated X-ray/TeV variability can discriminate between the different scenarios.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- May 2008
- DOI:
- 10.1111/j.1745-3933.2008.00454.x
- arXiv:
- arXiv:0801.2569
- Bibcode:
- 2008MNRAS.386L..28G
- Keywords:
-
- radiation mechanisms: general;
- galaxies: active;
- BL Lacertae objects: individual: PKS2155-304;
- galaxies: jets;
- gamma-rays: observations;
- Astrophysics
- E-Print:
- Minor changes, accepted for publication in MNRAS Letters