Proposed subjects of PhD theses for the year 2015

 

 

 

Subject: Pulsar astrophysics

Advisor: Dr hab. Jarosław Dyks (jinx@ncac.torun.pl)


Selection of projects within the field of pulsar astrophysics: pulsar data analysis, physical interpretation of data, numerical modeling of radiative processes in pulsar magnetospheres. Projects possible both in the radio band (interpretation of pulse profiles, polarisation, single-pulse effects: subpulse drift, nulling) as well as in the high-energy domain (modeling of gamma-ray spectra and pulse profiles).

 

 

Subject: Relativistic astrophysics

Advisor: Prof. Włodek Kluźniak (wlodek@camk.edu.pl)

 

PhD studies in a range of topics in theoretical astrophysics are offered including, but not limited to, the astrophysics of black holes and neutron stars. These include phenomena as diverse as TeV emission, gamma-ray bursts (GRBs), gravitational waves, the (magneto)hydrodynamics of accretion disks and jets, and binary evolution. Work on these topics will be relevant to ongoing and future observations with several modern and planned instruments, including H.E.S.S., CTA, LOFT and a host of optical, radio and X-ray telescopes.

Among specific topics of current interest are studies of the variability and stability of accretion disks in the presence of strong radiation fields. Prospective graduate students would be welcome to perform radiative MHD simulations of accretion disks with existing codes, as well as to work on improving radiation routines. The student working on radiative MHD simulations is expected to visit Harvard University and/or MIT (Massachusetts Institute of Technology) to collaborate with Professor Ramesh Narayan and Dr. Aleksander Sądowski.

 

 

Subject: Energetics and magnetization of jets in quasars and radio galaxies

Advisor: Prof. Marek Sikora (sikora@camk.edu.pl)

 

In many Active Galactic Nuclei (AGN) accretion of matter onto black hole is accompanied by production of narrow streams of matter called 'jets'. These jets are often relativistic and reach powers comparable to the accretion power. Their launching via Blandford-Znajek mechanism must involve  fast rotating black holes and  so strong magnetic fields that they  may  dynamically dominate over  innermost portions of the accretion flow. This challenges the standard accretion disk models and supports the magnetically-arrested-disk scenario. The main purpose of the project is to verify consistency of  such a scenario by studies of the jet energetics and magnetization at different distances from the black hole.

 

 

Subject: Comptonization of external, anisotropic radiation in blazars

Advisor: Prof. Marek Sikora (sikora@camk.edu.pl)

 

The project would focus on showing, how strongly jet properties derived from modeling of blazar radiation spectra depend on geometry of broad-emission-line region and on dust distribution in molecular torus. Realization of the project will require certain modifications in a BLAZAR code which is available in NCAC and is assigned to compute multi-band electromagnetic spectra in blazars.

 

 

Subject: Observational astrophysics with a global network of robotic telescopes

Advisor: Prof. Maciej Konacki (maciej@ncac.torun.pl)

 

Thanks to the funding from the European Research Council ("Ideas" funding scheme, 1.5 mln Euro), FNP (FOCUS grant), MNiSW (supporting grant) and NCN (research grant) totaling over 2.5 million Euro, we are establishing a network of robotic telescopes (four 0.5-m telescopes - Australia, South Africa and Argentina). Project web page: Project Solaris. We are looking for a grad student who would enhance our group. Preference will be given to an astronomer with programming or technical skills. However, anyone is encouraged to apply.

 

 

Subject: Spectroscopic study of symbiotic binary systems

Advisor: Prof. Joanna Mikołajewska (mikolaj@camk.edu.pl)

Co-Advisor: Dr Cezary Gałan (cgalan@camk.edu.pl)

 

Symbiotic stars are long-period interacting binaries composed of evolved red giant and a hot luminous companion ionizing a circumbinary nebula. The aims of this project are detailed spectroscopic analysis of symbiotic binaries in Milky Way and the Magellanic Clouds based on already obtained spectra in the optical (including SALT, VLT) and near infrared (4m KPNO, IRTF) as well as possible new observations (especially using ESO telescopes and SALT). In particular, the project will include determination of chemical abundances, rotational velocities, and the binary component masses.

 

 

Subject: Finding thousands symbiotic stars 

Advisor: Prof. Joanna Mikołajewska (mikolaj@camk.edu.pl)

 

A key goal of this project (realised in collaboration with prof. M. Shara from AMNH) is to survey a significant fraction of the Galactic halo, and the nearby spiral galaxies M31 and M33, for symbiotic binary stars using very large imaging and catalogue databases. We expect to identify over a thousand symbiotic star candidates; a large, representative sample of will be confirmed by follow up spectroscopy. The obtained results will allow us to better assess the likelihood that symbiotic stars give rise to type Ia supernovae; to constrain the lifetimes, populations and galactic environments of symbiotic stars; and to constrain evolutionary links with closely related types of binary stars.

 

 

Subject: The Penrose process

Advisor: Prof. Marek Abramowicz (marek.abramowicz@physics.gu.se)

 

In the classic Penrose process, a particle with energy E0 > 0 comes into the black hole ''ergosphere'', where negative energy states are possible, and decays into two particles. One of them, with negative energy E1 < 0, drops directly into the black hole, and another one with energy E2 = E0 - E1 > E0 flies out. This implies a positive energy gain ∆E = E2 - E0 > 0 at ''infinity''. There are well known reasons that make this process astrophysically uninteresting. In the decay 0 → 1 + 2, the decay products must move with a relative velocity v > c/2 to assure that E2 < 0 and therefore ∆E  > 0. In recent years, modifications of the Penrose process have been discussed. They may lead to a greater efficiency ∆E/E0 and to a greater degree of astrophysical realism. They involve multiple collisions rather than a decay. (1) I am working on this project at the Copernicus Center together with Dr Michał Bejger. We collaborate with professor Tsvi Piran of the Hebrew University in Jerusalem. There is still much to be done. This is a project for a theorist, a need for numerical calculations will be very small. (2) At the Copernicus Center we are also investigating, in collaboration with the group of professor Ramesh Narayan of Harvard, an electromagnetical version of the Penrose process (the Blandford-Znajek mechanism, magnetically arrested disks, etc.). Student interested in these aspects of the project should be already strong in numerical calculations, or willing to quickly learn numerical methods. (3) The third aspect of the project is an application of (2) to the theory of relativistic jets. As a doctoral project, initial choices (1), (2), (1)+(2), or (2)+(3) may be considered (they may be later changed).

 

 

Subject: Stability of transonic, magnetized accretion onto black holes

Advisor: Prof. Marek Abramowicz (marek.abramowicz@physics.gu.se)

 

Last year we have started at the Copernicus Center a pioneering research project on the magnetohydrodynamical stability of inner parts of accretion disks, very near black holes. The student will work on a well defined sub-project in a wider context of our team research. Our team is strong and dynamic and right now includes me, professor Włodek Kluźniak and three students. We are collaborating with dr Jiři Horák from Prague and dr Paola Rebusco of MIT. The candidate should be strong in mathematics. No pre-knowledge of general relativity is required.

 

 

Subject: Numerical and analytic studies of QPOs

Advisor: Prof. Marek Abramowicz (marek.abramowicz@physics.gu.se)

 

High frequency (in the kilo-Hertz range) quasi-periodic oscillations (HFQPO) appear in the X-ray variability of several accreting low-mass binaries. In the black hole sources, pairs of HFQPO with commensurate frequency ratios, most often 3:2, were detected. There are strong reasons to think that they represent a resonance in accretion disks oscillations. However, despite a lot of serious efforts by several researchers, analytic studies did not explain which modes of accretion disk oscillations are coupled in the 3:2 resonance or how the resonance is excited. The 3:2 resonance has never been seen in any numerical simulations of accretion, hydrodynamical or MHD. The QPO phenomenon is certainly one of the most intriguing unsolved problems in the accretion disk theory. The research project will concentrate on new mathematical approaches that may enable analytic and numerical methods to grasp on the HFQPOs. The student should be mathematically strong and be able to solve analytic problems (partial differential equations, perturbation theory, Fourier analysis) as well as having programming skills. The student will spend some time at Harvard University, as we are collaborating closely with Professor Ramesh Narayan and Dr Aleksander Sądowski there.

 

 

Subject: Neutron stars - observational constraints on dense matter theory

Advisor: Dr hab. Leszek Zdunik (email: jlz@camk.edu.pl)

 

Neutron stars, observed as radio pulsars, X-ray bursters, X-ray pulsars, and magnetars, are cosmic laboratories for studying properties of matter under extreme astrophysical conditions. The goal of the project is to confront recent observations of neutron stars properties (mass of the neutron star, fast rotation, cooling) with theories describing these processes. The project involves the study of the properties of the crust of neutron stars using methods of theoretical physics, and performing numerical simulations of the crust structure and dynamics. The crust plays very important role in neutron star evolution and dynamics and its properties are crucial for neutron star cooling and surface temperature. Another subject is the study of spin-up of a neutron star by accretion, including  the impact of the properties of superdense matter on the rotational evolution. The problems listed above should be solved for a broad range of possible models of dense matter.

 

 

Subject: Jets in microquasars

Advisor: Prof. Andrzej Zdziarski (aaz@camk.edu.pl

 

Accretion in stellar binary systems containing a black hole or a neutron star is often accompanied by ejection of matter, forming symmetric twin jets. The jets radiate most of the radio emission of those systems, and contribute to emission at higher energies, from infrared to gamma rays. So far, the level of the contribution at energies above the radio range remains poorly determined. Also, the current theoretical understanding of these jets remains rudimentary, in contrast to a much more detailed understanding of jets in active galactic nuclei. The project will consist of theoretical modeling of jets in binary systems, and applying the results to observational data from the radio to gamma ray range.

 

 

Subject: Gravitational wave data analysis and the physics of neutron stars

Advisor: Dr hab. Michał Bejger (bejger@camk.edu.pl)

 

In June 2015 interferometric gravitational wave detectors of the Advanced LIGO project will start observations with the best sensitivity up to date. In the next few years Advanced LIGO (USA) and Advanced Virgo (France, Italy, Hungary, Netherlands and Poland) allow, for the first time in history, direct detection of gravitational waves from astrophysical sources from the local vicinity of the Galaxy - the reach for merging binary neutron star systems ≈ 200 Mpc - opening in this way a new observational window to the Universe: gravitational astronomy.

The topic of the PhD study is the design and implementation of data analysis algorithms for gravitational wave detectors (in collaboration with the Polish Polgraw group, member of the LIGO-Virgo community), development of computational methods using massive parallelization in large clusters' and the grid environment (MPI and hardware acceleration with GPUs), and construction of realistic theoretical models of neutron stars, to compare the with current and future observations (like LOFT and Athena+) in order to put constrains on the very dense matter equation of state (in collaboration with CAMK neutron star group).

 

 

Subject: Polarization of X-rays in illuminated accretion disk atmospheres

Advisor: Dr. hab. Agata Różańska (agata@camk.edu.pl)

 

The goal of this PhD is numerical modeling of an accretion disk spectra in active galactic nuclei and X-ray binaries. Since many years scientists are trying to build X-ray polarimeter, and we need models to work with data. The PhD student will include Sotkes equations on polarisation into advanced numerical code on radiative transfer with relativistic Compton scattering. The work will by mostly numerical resulting in proper treatment of absorption Compton scattering and polarisation, all angular dependent. There is a great importance to tread all effects together in illuminated accretion disks where w see hot, quit dense comptonized  medium. We plan to compare our models with observations.

 

 

Subject: Hot coranae above accretions disks

Advisor: Dr. hab. Agata Różańska (agata@camk.edu.pl)

 

The goal of this PhD is to create the global model of hot coronae above accretion disks. Up to now there is a debate about geometry and physical conditions of the observed hot plasma from those objects. Its temperature rises up to 200 keV. We do not understand how such coronae interact with colder accretion disks. Existing models, which are compare to the data always assume the geometry of those regions.

We propose to build the model of hot corona taking into account radiative interaction and mass exchange between different phases, i.e. disk evaporation. Our models will be time dependent, so we would be able to trace the formation of corona. Recently, observers reported that they have determined the size of corona in two objects. Therefore, our work will be at once compared to observations from X-ray satellites.

 

 

Subject: Brightest meteors in Polish Fireball Network data

Advisor: Dr hab. Arkadiusz Olech (olech@camk.edu.pl)

 

The PhD student will analyze the database of Polish Fireball Network and search for the brightest meteors. Their basic parameters and orbits will be analyzed in order to find new asteroidal meteor showers and to estimate the probability of collision of such bodies with the Earth and satellites.

 

 

Subject: Analysis and theoretical interpretation of ground and space-based Cepheid observations

Advisor: Prof. Paweł Moskalik (pam@camk.edu.pl)

Co-Advisor: Dr Radosław Smolec (smolec@camk.edu.pl)

 

Cepheids are among the most important variable stars in astrophysics. They are not only excellent distance indicators but also serve as a testbed for stellar pulsation and evolution theories. Still, some of the phenomena in Cepheid pulsation are not well understood (e.g. excitation of non-radial modes, long-term modulation of pulsation - the Blazhko effect). The goal of the project is to perform analysis and theoretical interpretation of Cepheid pulsation. Ground-based observations (OGLE, MACHO, ASAS) and space observations from the BRITE satellites will be used. So far only for one Cepheid extensive space-based photometry is available. With the precise multi-band observations with the polish BRITE satellites we can expect very interesting and important new results.

The student will search for multiperiodic pulsation in both radial and non-radial modes, for possible period-doubling effect and for modulation of pulsation. Next, these phenomena will be modeled with the help of existing pulsation codes and stellar evolution codes (Warsaw codes and publicly available MESA code).

Experience in numerical programming is important and welcome for the project. The student will learn techniques of time-series analysis and will learn the theories of stellar structure and evolution, also in practice, through computation of stellar models.