Research on Physics of jets and their gamma-ray emission

In radio- and gamma-ray loud AGNs, the emission from a relativistic jet beamed in the direction of motion dominates the energy output. In spite of many years of research, the basic questions on the location of the gamma-ray emitting region and on the particle acceleration mechanisms remain unanswered. We have recently used the Fermi/LAT data to study GeV spectra on bright blazars, demonstrating that they consistently show breaks at similar energies (Stern & Poutanen 2014; see Fig. 1), which can be interpreted as a result of gamma-gamma pair production absorption within the broad-line region (BLR; see Poutanen & Stern 2010). This has profound implication on the location of the gamma-ray emitting region, univocally proving it being with the BLR. We also conduct theoretical studies of gamma-ray emission mechanisms and have proposed a novel particle acceleration mechanism−"photon breeding"−operating in relativistic jets in blazars (Stern & Poutanen 2006, 2008).



Figure 1: Redshift corrected Fermi/LAT spectra of individual bright blazars. The dashed line shows the log-normal model, while the solid line includes also the photon-photon pair production absorption on BLR photons.

Selected publications:


Working groups

X-ray binaries

Description of the group activity.
Group meetings take place on Wednesdays (first and third of each month), 15.00 in the coffee room.

Stellar explosions

Description of the group activity.
Group meetings take place on Mondays, 15.00 in the coffee room.

AGNs and Very High Energy Astrophysics

Description of the group activity.
Group meetings take place on Wednesday (second and fourth of each month), 15.00 in the coffee room.