Michal Dovčiak

email: dovciak@astro.cas.cz
phone: +420 226 258 425

Michal Dovčiak is a leading researcher in high-energy astrophysics, specializing in black holes and their immediate environments. Based at the Astronomical Institute of the Czech Academy of Sciences, his work focuses on the study of X-ray emission, polarimetry, and reverberation from accretion discs around black holes. His research spans both observational and theoretical astrophysics, involving close collaborations with researchers worldwide.

Michal works at the Astronomical Institute of the Academy of Sciences (ASU) since 2003, currently as a senior research scientist. Since 2017 he serves as a Deputy Director for Foreign relations at the ASU and since 2022, he is a member of Board of the Institute.

Key Research Areas:

X-ray Polarimetry of accreting black holes

A signiﬁcant portion of Michal’s recent research is dedicated to X-ray polarimetry, with a focus on how the strong gravitational
ﬁelds near black holes aﬀect the polarization of emitted light. His models are essential for interpreting data from X-ray polarimetric missions (IXPE, eXTP, etc.). His work helps determine the structure of the X-ray corona and the geometry of the inner accretion ﬂow near the event horizon. He is a member of the Imaging X-ray Polarimetry Explorer (IXPE) mission lead by NASA (USA) and ASI (Italy) that was launched in December 2021. He servers there as a chair of the topical working group “Accreting Stellar-Mass Black Holes”. Except co-ordinating and participating at X-ray polarimetric observations of black holes with this mission, he contributed to the development of

spectro-polarimetric STOKES tables and models of reprocessed emission from a slab illuminated by X-ray power-law radiation,
relativistic spectro-polarimetric KYNstokes model of reprocessed emission from an accretion disc illuminated by an X-ray source with power-law emission,
spectro-polarimetric model for black-hole accretion disc emission (not available publicly yet).

These works are mainly in collaboration with Jakub Podgorný and Vladimír Karas (ASU), René Goosmann and Frédéric Marin (Observatoire Astronomique de Strasbourg), Giorgio Matt (Università degli Studi Roma Tre), Fabio Muleri (INAF), and Roberto Taverna and Lorenzo Mara (Università degli Studi di Padova).

X-ray Lags and Reverberation Mapping

In the study of reverberation mapping and X-ray time lags, Michal has explored the time delays between the primary X-ray emission and its reprocessed light as it reﬂects oﬀ the accretion disc. These time lags provide crucial information about the disc-corona geometry. He also created an animation illustrating the X-ray reverberation in active galactic nuclei (AGN).

Michal has also extended this approach to study optical/UV reverberation, providing insights into how the disc and corona interacts in AGN and how this interaction manifests itself in variability across multiple wavelengths.

Michal has developed several reverberation codes:

relativistic reverberation KYNreverb package, which contains the KYNrefrev and KYNxilrev models that provide the response
function from an acrretion disc illuminated by an X-ray corona (based on REFLIONX and XILLVER tables),
relativistic reverberation KYNxiltr model, which provides the response function from an acrretion disc illuminated by an X-ray
corona (based on the spectral KYNSED model).

These works are mainly in collaboration with Iossif Papadakis (University of Crete) and Elias Kammoun (California Institute of
Technology).

Corona geometry

Michal is also studying the geometry and size of the corona in black hole systems, a region responsible for producing high-energy
X-rays through inverse Compton scattering of photons from the accretion disc on hot coronal electrons. To this purpose, MONK has
been developed at ASU. In collaboration with the main developer of the model, Wenda Zhang (National Astronomical
Observatories, Chinese Academy of Sciences), and Michal Bursa and Sudeb Datta (ASU), he studies how the geometry and height
of the corona above the accretion disc inﬂuence the observed X-ray spectra, time lags, and reverberation signals. This research is
crucial for understanding the energy release mechanisms and the dynamics of matter in extreme gravitational ﬁelds.