Wednesday Colloquium


"The CTA site search"

Tomasz Bulik (Astronomical Observatory, Warsaw University)

I will describe the detailes of the CTA site search and the current site choice process.


"Probing the Cosmic X-ray and MeV Gamma-ray Background Radiation through the Anisotropy"

Yoshiyuki Inoue ( 井上 芳幸) (KIPAC / SLAC / Stanford)

The origin of the cosmic hard X-ray and MeV gamma-ray background is not fully understood. It is expected that Seyferts including Compton thick population may explain the cosmic hard X-ray background. At MeV energy range, Seyferts having non-thermal electrons in coronae above accretion disks or MeV blazars may explain the background radiation. I will discuss that future measurements of the angular power spectra of anisotropy of the cosmic X-ray and MeV gamma-ray backgrounds will be key to deciphering these backgrounds and the evolution of active galactic nuclei.


"What makes the jet production efficiency in AGN so diverse"

Marek Sikora (NCAC, Warsaw)

Magnetic fluxes required to power jets in radio-loud quasars are significantly greater than those that can develop in standard accretion disks. The required levels of those fields are achievable only by the accumulation process, which proceeds via advection of magnetic fields by the accreting matter. Eventually, this leads to the formation of a magnetosphere around the black hole and the innermost portions of the accretion flow. Since such an advection is expected not to work efficiently in geometrically thin disks, we suggest that such an accumulation of magnetic flux occurs via hot, quasi-spherical accretion. Without this pre-phase, the cold accretion events would result in radio quiet (or at most, moderately radio-loud) quasars.


"Could IMBH be formed in a globular cluster?"

Mirosław Giersz (NCAC, Warsaw)

I will discuss a new scenario for intermediate mass black hole (IMBH) formation in dense stellar clusters. The new scenario does not need any special conditions. In this scenario IMBH is formed as a result of dynamical interactions of a hard binary, containing a stellar mass black hole (BH), with other stars and binaries. The mass of the BH constantly increases due to mergers with incoming stars and mass transfer from companions. I will discuss the necessary conditions to initiate the process of IMBH formation and dependence of the rate of IMBH mass increase on the global cluster properties.


"Mysterious long-period variables"

Igor Soszyński (Astronomical Observatory, Warsaw University)

Pulsating red giants are probably the least understood of all variable stars. I will discuss two unresolved issues concerning long-period variables: which modes of pulsation are associated to different period-luminosity relations and what is the origin of the phenomenon of long secondary periods observed in one third of semiregular variables? I will present new observational results that may be important to solve both problems.