THE GROUP
The Helmholtz-University Young Investigator Group on
"Multi-messenger studies of point sources of cosmic rays
using data from IceCube"
is working at DESY and focuses on the study of the very high energy emission of
individual astrophysical sources by participating to two astrophysical projects:
the IceCube neutrino telescope at the South Pole and the MAGIC gamma-ray telescope in La Palma.
The idea is to extend the "multi-wavelength" concept to the observation
of neutrinos and ultimately develop a "multi-messenger" approach. The
goal is to increase the discovery potential of IceCube, confirm the
hadronic nature of cosmic accelerators, and allow to alert electromagnetic
observations by neutrino signals, i.e. providing a clear "hadron trigger".
The main topics of activity of the group are the analysis of data
from IceCube (neutrino
telescope) and from gamma-ray telescopes (public data from
different gamma-ray telescopes and active participation in the analysis
of MAGIC data)
along three different
lines of study:
- Optimization of the sensitivity of the IceCube telescope to point sources of neutrinos
and analysis of data from AMANDA and IceCube.
-
Identification of the
most promising periods and sources to search for coincident neutrinos
based on data from gamma-ray telescopes.
-
Development of common Target Of Opportunity strategies with the gamma-ray community.
-
Analysis of MAGIC data from AGN monitoring
This project belongs to the Young
Investigators programm of the Helmholtz Association.
COSMIC RAYS
being built...
NEUTRINO ASTRONOMY
being built...
GAMMA-RAY ASTRONOMY
Gamma-rays are produced by a variety of Galactic and extra-galactic objects.
As for neutrinos, the directional information is not lost, so that gamma-rays
point back to their production site, which can help us unveiling the origin of
Cosmic Rays.
What we define as gamma-rays is electro-magnetic radiation with energies above
1MeV. The High Energy (HE) gamma-ray regime extends
from 100MeV to several tens of GeV.
Beyond a few tens of GeV it is general consensus to talk about
Very High Energy (VHE) gamma-rays.
HE gamma-rays from 271 pointsources as well as diffuse emission from the
Galactic plane have been observed with the EGRET satellite onboard the
Compton Gamma-Ray Observatory. The successor experiment GLAST is expected
to increase the number of known HE gamma-ray sources by a factor of 10.
Due to the flux falling off with a power-law to higher energies,
large detection areas are needed in the VHE regime. This is achieved
with Cherenkov Telescopes (CTs) that use the atmosphere as a calorimeter.
A primary gamma-ray hitting the atmosphere produces an extended air-shower.
The secondary shower particles produce Cherenkov radiation that is imaged by
the CTs on the ground. The imaging atmospheric Cherenkov technique was
pioneered by the Whipple collaboration that could, for the first time ever,
detect VHE gamma-rays from a point source in our galaxy, the Crab-Nebula.
This technique was subsequently adopted by several experiments, including
HEGRA (that pioneered the stereoscopic technique), CAT, CANGAROO in the
first generation, and H.E.S.S., MAGIC, VERITAS and CANGAROO-II/III in the second
generation. With many new point-sources as well as extended and
diffuse emission detected by H.E.S.S. and also first results from MAGIC,
the field is currently flourishing.
The most popular models explaining the observed gamma-ray emission
are mainly based on two production mechanisms:
-
leptonic:
accelerated electrons inverse-Compton (IC) scatter off photons from
a local radiation field. Thereby, energy is transferred from the
electrons to the photons, boosting the electromagnetic radiation
to the VHE regime. The local radiation field can be either external
(e.g. infra-red radiation from the surrounding medium, cosmic micro-wave
background radiation) or internal (e.g. synchrotron emission from the
accelerated electrons moving in a magnetic field).
-
hadronic:
in the frame of shock-front acceleration (fermi second order), hadrons
are accelerated and interact with the surrounding medium. Neutral pions
are then produced in hadron-hadron interactions or via photo-pion production.
The neutral pions then decay into gamma-rays. Neutrinos from the decay
of charged mesons are also produced in this process (see above).
-
gin tonic:
try it out. Anything will feel accelerated.