Research Interests

Performing multiwavelength study of blazars:
Blazars are extremely bright across the electromagnetic spectrum, from radio to very-high-energy gamma-rays. Contemporaneous multiwavelength studies are key to unraveling many blazar mysteries. I have first-hand observing and data-handling experience with the Metsähovi Radio Observatory, Nordic Optical Telescope, and the MAGIC gamma-ray telescopes. I am also the PI of Nordic Optical Telescope's blazar polarization monitoring program, which has lead to tens of papers in collaboration with the Imaging X-ray Polarimetry Explorer (IXPE) satellite (see polarization below).

Understanding blazar variability and flaring:
While stochastic in nature, blazar variability is telltale of underlying jet processes which are not entirely understood. I obtained optical light curves for ~7700 blazars using all-sky surveys CRTS, ATLAS, and ZTF, which will be publicly released in our upcoming CAZ catalog paper. I developed methods to identify and characterize their flaring behavior. These will be used in several other upcoming studies and can serve as a basis for handling next-generation data, like, LSST's.

Polarization

Understanding acceleration mechanisms in blazars:
Blazars exhibit extreme non-thermal emissions coming from highly relativistic particles gyrating in the magnetic fields of their jet. It is not clear how the particles are accelerated to such extreme energies. I recently lead the IXPE collaboration paper on the multiwavelength campaign of the high-synchrotron peaked blazar PKS 2155−304 in Kouch et al. (2024, A&A, 689, A119). We contemporaneously took photo-polarimetric data from the radio to X-ray bands with maximal cadence for ~10 days in order to understand the nature of the high-energy emission of the jet and and the orientation of its magnetic field. Our results favored shock acceleration over turbulent or magnetic reconnection processes as the main acceleration mechanism.

Multi-messenger astronomy

Are blazars emitting high-energy neutrinos?
Ever since the IceCube Neutrino Observatory started detecting high-energy neutrinos from astrophysical sources (~15 per year), blazars have been suspected as their origin. However, apart from a few individual associations, a large-scale population based correlation between blazars and neutrinos has not been confidently established (at best ~3σ). In Kouch et al. (2024, A&A, 690, A111), I lead a spatio-temporal correlation study between the first catalog of high-energy neutrino events (IceCat-1) and ~1000 blazars in the radio and optical bands. With our novel weighting scheme, we found a ~2σ correlation.

Optimizing the hunt for cosmic neutrinos:
A possibility for the weak blazar-neutrino correlations is the lack of sufficient detection power. To address this, I performed extensive simulations in Kouch et al. (2025, A&A, 696, A73), identifying the most optimal test strategy. I then lead another paper (upcoming in A&A) where the spatio-temporal correlation of 356 updated IceCat-1 neutrinos is tested against the CAZ light curves of 5880 blazars. We found that, even with substantially more blazar and neutrino data, the correlation remains rather weak. Thus, the mystery continues...