Blazars, neutrinos & jet emission processes

Blazars are a subclass of active galactic nuclei (AGN). AGN sometimes exhibit relativistic outflows of plasma originating close to the supermassive black hole in the center of the host galaxy. We study blazars, as in those sources, the jet points at Earth, and we can directly ‘look into the jet’. I have used a sample of ~100 southern blazars from the TANAMI sample to study their multiwavelength and multimessenger behavior. I combine data from various instruments to construct broadband spectral energy distributions (SED). These allow us to take a closer look at the physical mechanisms involved in producing powerful AGN jets. The underlying emission mechanism of the high-energy peak is unclear. AGN are possible sources of Ultra-High Energy Cosmic Rays (UHECR). In this case the high energy hump could be produced through photopion production.

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TANAMI VLBI images show the inner regions of the jet; these images are used for morphology and kinematic studies. We combined the information at radio wavelength with other frequencies to build a multiwavelength picture for each source.

Broadband spectra of blazars typically show a double-humped structure, with the first peak originating in synchrotron emission. Hadronic and leptonic scenarios are available for the second peak. A detection of neutrinos from a blazar jet would provide unambiguous evidence of hadronic processes. In a first study I was able to show that blazars as a class are able to produce the observed IceCube neutrinos. In a follow-up study we found a coincidence in time and position of a blazar outburst with an astrophysical neutrino (marked in red in the light curve). This outburst has been one of the most dramatic outbursts of all LAT blazars. At the end of 2017, another blazar outburst coincided with a neutrino event from IceCube.

Multiwavelength SEDs of blazars

I study simultaneous radio to γ-ray spectral energy distributions (SEDs) from the southern blazars of the TANAMI sample, with over 80 SEDs for 22 sources. The large amount of monitoring data from the TANAMI project allows us to construct dynamic SEDs, highlighting spectral changes in varying flux states.

Changes in Fermi/LAT flux are not always seen as strongly in the X-rays, but often in the optical. Fermi/LAT light curves with a Bayesian Block algorithm allow me to segment the data into times of statistically constant flux. These time ranges can be used to construct broadband SEDs. The SEDs allow us to study the blazar sequence, Compton dominance, the fundamental plane of black hole and the big blue bump over varying flux states of the blazars.

Peculiar AGN

Another research focus are peculiar AGN, including young radio galaxies. From these objects we can learn more about jet evolution and emission mechanisms.

Two examples of peculiar AGN are PMN J1603–4904 and IC 310. PMN J1603–4904 is peculiar in its SED as it shows a blackbody-like emission in the infrared wavelengths, possibly related to a hot torus. Additionally, its radio and X-ray properties are not blazar like. Unlike in blazars, no changes are observed in the jet. It is also a strong γ-ray emitter and is part of the 1FHL catalog. It has been found to be a compact symmetric object (CSO), one of the first ones to be detected at γ-ray energies.

IC 310 shows blazar like behavior, including rapid variability, as seen in the MAGIC light curve, but the angle between the jet and the line of sight has been constrained between 10° and 20°. One model to explain such emission involves acceleration of particles in a magnetospheric gap.

Supernovae Ia

In collaboration with the working group of Prof. Roepke, I was involved in a project studying the different explosion mechanisms of supernovae of type Ia, which produce different amounts of iron. This could be used to differentiate between the explosion channels using the detection and flux measurements of X-ray line emission.

Further Research Interests

As a member of the Fermi/LAT and the CTA collaborations, I’m interested in the astroparticle physics aspect in AGN and other sources. I’m also interested in accretion and the contribution of the accretion disk to the thermal emission seen in blazars and other AGN.