New Paper "Evidence for a quasi-periodic modulation in a gamma-ray blazar"
Accretion onto supermassive black holes in Active Galactic Nuclei (AGN)
is sometimes associated with an ejection of two opposit relativistic
jets. Radiation from the jets is boosted in the direction of motion
such that the source will appear very bright if a jet is pointing close to
our line of sight. These sources are known as blazars. Observations with
the Fermi-LAT gamma-ray telescope over 7 years has revealed what appears
to be a 2-year periodic modulation in the blazar PG 1553+113. A possible
explanation is that these variations are driven by a quasi-periodic
oscillation in (or of) the accretion disk surrounding the black hole.
An alternative and even more exciting explanaition is two supermassive
black holes orbiting each other causing a precession of the blazar jets.
The study of PG 1553+113 was performed by a Fermi-LAT team lead by
Stefano Ciprini, Sara Cutini (both at ASDC, Rome) together with
Stefan Larsson in our group.
The results were published in Ap.J Letters on 10 November and was also
the topic of a NASA press release,
"NASA's Fermi Mission Finds Hints of Gamma-ray Cycle in an Active Galaxy".