|
|
październik/october 2016 |
|
2016-10-07 |
|
mgr MARIUSZ TARNOPOLSKI |
OA UJ |
ZN OA 1432 |
Analysis of gamma-ray burst duration distribution using mixtures of skewed distributions
Two classes of gamma-ray bursts (GRBs) have
been confidently identified thus far. A third, intermediate in duration
class, was suggested to be present in previous catalogues, such as BATSE
and Swift, based on statistical tests regarding a mixture of two or three
lognormal distributions of T90. However, this might possibly not be an
adequate model. Mixtures of standard normal, skew-normal, sinh-arcsinh and
alpha-skew-normal distributions are fitted using a maximum likelihood
method. The preferred model is chosen based on the Akaike information
criterion. It is found that mixtures of two skew-normal or two
sinh-arcsinh distributions are more likely to describe the observed
duration (T90) distribution of Fermi than a mixture of three standard
Gaussians, and that mixtures of two sinh-arcsinh or two skew-normal
distributions are models competing with the conventional three-Gaussian in
the case of BATSE and Swift. Based on statistical reasoning, it is shown
that other phenomenological models may describe the observed Fermi, BATSE,
and Swift duration distributions at least as well as a mixture of standard
normal distributions, and hence the existence of a third (intermediate in
duration) class of GRBs in Fermi data is rejected.
|
2016-10-14 |
|
dr ARTI GOYAL |
OA UJ |
ZN OA 1433 |
Multi-frequency variability study of blazars from decades to minutes
The power spectral densities (PSDs) of
blazar light curves, P(f) = A f-β, where A is the normalization
and β is the slope, indicate that the variability is generated by
the underlying stochastic processes which is of colored noise type
(i.e., β ≃ 1-3). Study of power-law slopes, normalization or
characteristic timescales (if any), in the PSD is important for
constraining the physics of emission and energy dissipation processes in
the blazar jets. We present the results of PSD analysis of 4 blazars at
GeV (Fermi-LAT), X-ray (Swift-XRT and RXTE), optical
(R-band) and radio (GHz band from UMRAO and OVRO programmes) frequencies
covering few decades to minutes timescales. The novelty of this study is
that at optical frequency, by combining long-term (historical optical
light curves) and densely sampled intra-night lightcurves, the PSD
characterisitics are investigated for temporal frequencies ranging over 7
orders of magnitude. Our main results are : (1) nature of processes
generating flux variability at optical/radio frequencies is different from
those at GeV freqeuncies (β ∼ 2 and 1, respectively); this could
imply, that γ-ray variability, unlike the Synchrotron
(radio-to-optical) one, is generated by superposition of two stochastic
processes with different relaxation timescales, (2) the main driver behind
the optical variability is same on years, months, days, and hours
timescales (β ∼ 2), which argues against the scenario where
different drivers behind the long-term flux changes and intra-night flux
changes are considered, such as internal shocks due to the jet bulk
velocity fluctuation (long-term flux changes) versus small-scale magnetic
reconnection events taking place at the jet base (intra-night flux
changes). Implications of these results are discussed in the context of
blazar emission models.
|
2016-10-21 |
|
prof. DAVID VALLS-GABAUD |
Observatoire de Paris-Meudon, France
Churchill College, Cambridge, UK |
ZN OA 1434 |
The MESSIER orbiter: lifting the veil on the ultra-low surface brightness universe
The S-class MESSIER satellite has been designed to explore the
extremely low surface brightness universe at UV and optical wavelengths.
The two driving science cases target the mildly- and highly non-linear
regimes of structure formation to test two key predictions of the LCDM
scenario: (1) the detection of the putative large number of galaxy
satellites, and (2) the identification of the filaments of the cosmic web.
The satellite will drift scan the entire sky in 6 bands covering the
200-1000 nm wavelength range to reach the unprecedented surface brightness
levels of 34 mag/arcsec2 in the optical and 37 mag/arcsec2 in the
UV. Many important secondary science cases will result as free by-products
and will be discussed in some detail, such as the luminosity function of
galaxies, the contribution and role of intracluster light, the
cosmological background radiation at UV and optical wavelengths, the
molecular hydrogen content of galaxies at z=0.25, time domain studies of
supernovae, GRBs and tidal disruption events, the chemical enrichment of
the interstellar medium through mass loss of red giant stars and the
accurate measure of the BAO scale at z=0.7 with over 30 million galaxies
detected in Lyman-alpha at this redshift. It will provide the astronomical
community the first space-based reference UV-optical photometric catalogue
of the entire sky, and synergies with GAIA, EUCLID and WFIRST will also be
discussed. Technical issues will likewise be addressed for possible
improvements on the current design.
|
2016-10-28 |
|
prof. JACQUES DELABROUILLE |
Laboratoire Astroparticule & Cosmologie,
Université Paris Diderot, France |
ZN OA 1435 |
The future of the CMB: from temperature to polarization
The ESA Planck space mission has fully exploited the
cosmological information available in Cosmic Microwave Background
temperature anisotropies. A standard cosmological model has emerged. Our
Universe, however, remains a mystery. What are the invisible matter and
energy that seem to constitute 96% of our universe? Did the Universe truly
begin with an superluminal expansion that stretched quantum fluctuations
to cosmological scales to generate the initial perturbations that
eventually gave raise to galaxies, stars, and ultimately ourselves? In
this talk, I will review the theoretical motivations for digging even
further in the CMB, and in particular to accurately measure the properties
of CMB polarization with a future Cosmic Origins Explorer space mission,
to probe physics ranging from the absolute mass of all neutrino species to
grand unification physics at an energy scale thousand billion times bigger
than that of the LHC.
|
|
|
listopad/november 2016 |
|
2016-11-04 |
|
dr OLEH KOBZAR |
Institute of Nuclear Physics PAN, Poland |
ZN OA 1436 |
Search of the Ultra High Energy Cosmic Rays from Virgo A
Virgo A (M87) is the second closest to the Milky Way active galaxy.
According to existing estimations it can be a prominent source of ultra
high energy cosmic rays (UHECR). However not many events have been
registered in the sky region near Virgo A, possibly due to the magnetic
field influence. In the present work we carried out the simulation of
UHECR motion from Virgo A taking into account their deflections in
galactic (GMF) as well as extragalactic (EGMF) magnetic fields according
to the latest models. The maps of expected UHECR arrival directions have
been obtained as a result. We also check the UHECR events from recent sets
of data (AUGER, Telescope Array etc.) for possibility of their origination
in this AGN.
|
seminarium nadzwyczajne: wtorek, godzina 15:00 / Tuesday at 3:00 p.m. |
2016-11-08 |
|
Prof. INEKE DE MOORTEL |
University of St Andrews, Scotland UK |
|
Transverse Velocity Perturbations in Solar Coronal Loops
In this talk, I will give an overview of transverse, propagating velocity
perturbations observed in solar coronal loops. These ubiquitous
perturbations are observed to contain substantial amounts of energy and
undergo strong damping as they propagate. Using both numerical and
analytical modelling, we demonstrate that these can be understood in terms
of coupling of different wave modes in the inhomogeneous boundaries of the
loops: we perform 3D numerical simulations of footpoint-driven transverse
waves propagating in a coronal plasma with a cylindrical density
structure. Mode coupling in the inhomogeneous boundary layers of the loops
leads to the coupling of the transversal (kink) mode to the azimuthal
(Alfven) mode, observed as the decay of the transverse kink oscillations.
In addition, recent analysis of CoMP (Coronal Multi-channel Polarimeter)
Doppler shift observations of a large, off-limb, trans-equatorial loops
system show that Fourier power at the apex appears to be higher in the
high-frequency part of the spectrum than expected from theoretical models.
We suggest that this excess high-frequency FFT power could be tentative
evidence for the onset of a cascade of the low-to-mid frequency waves into
(Alfvenic) turbulence, potentially contributing to heating of the loops.
|
2016-11-18 |
|
mgr JUSTYNA ŚREDZIŃSKA |
CAMK Warszawa, Poland |
ZN OA 1437 |
Mg II line in intermediate redshift quasars, and its connections with dark energy
The Universe day after day give us more discoveries and even more
surprises. Current astronomical observations indicate that the Universe
consists in only 5% of the well-known matter, but in 95% of invisible
and not understood substances: dark matter and dark energy. This last
component is most difficult to understand. Dark energy acts in the
opposite way to gravitational attraction: it causes the acceleration of
the universal expansion. This conclusion is extremely peculiar. Precise
and independent measurement methods of this effect are necessary to
understand the nature of dark energy. Quasars are very luminous centres of
active galaxies, which are observed from very large distances (wide range
of redshift) and it turned out they are ideal candidates for this purpose.
They are not standard candles, but their use is based on the determination
of the absolute luminosity for each of them. This can be achieved by
measuring the time delay between the variable nuclear continuum and the
emission lines, as confirmed by the delay measurement of the Hβ line
done for nearby AGNs. The time delays in quasars are of the order of a few
years, so the project requires sparse monitoring over an extended period
of time. We monitor quasars at redshift z=1, which requires using the MgII
line, and such monitoring has never been done before. The observations
performed so far with SALT showed that we achieve the requested accuracy
(below 2%) of the MgII measurement to determine its variability, and the
simulations indicate that the program can provide accuracy of 0.06-0.32
mag in the distance modulus for each single quasar.
|
2016-11-25 |
|
dr GOPAL BHATTA |
OA UJ |
ZN OA 1438 |
Constraining Jet Structures in the blazars S5 0716+714 and OJ 287 using exceptionally dense optical observations
Blazars exhibit variability in diverse timescales ranging from a few
minutes up to a few decades. Variability studies, therefore, offer
important insight into the various physical mechanisms occurring in both
the jets and the disks. Here we present the summary of our studies
involving exceptionally dense optical observations of blazar S5 0716+714
and OJ 287. 0716+714 was monitored in multi-frequency photo-polarimetric
bands during Whole Earth Blazar Telescope (WEBT) observation campaigns.
The results of the analyses show that the source often displays fast
variability with an amplitude as large as 0.3 mag within a few hours, as
well as color variability on similar time scales often characterized by
``bluer-when-brighter'' trend. Similarly, the correlation between
variability in flux and polarization appears to depend upon the
configuration of the optical polarization angle relative to the positional
angle of the innermost radio core of the jet. Other fascinating
observations include a sudden and temporary disappearance in the observed
variability lasting for ∼ 6 h. In addition, the modeling of individual
microflares strongly suggests that the phenomenon of microvariability can
be best explained by convolved emission from compact emission sites
distributed stochastically in the turbulent jet. Besides, analysis of some
of the well resolved micro-flares exhibiting high degrees of polarization
points towards a complex magnetic geometry pervading the jet with the
possible presence of small-scale regions of highly ordered and enhanced
magnetic field. In another study, we detected a year like QPO in the long
term optical light curve of the blazar OJ 287. The result is discussed in
the contexts of various processes occurring in the disk and the jets.
|
|
|
grudzień/december 2016 |
|
2016-12-02 |
|
prof. JERZY MACHALSKI |
OA UJ |
ZN OA 1439 |
Dynamical Analysis of FRII-Type Radio Sources: Statistical Correlations between the model parameters in the large sample of sources
The FRII-type radio sources are characterised by the evident superluminal
shocks at the extremities of their extended linear structure. These shocks
originate from an interference of powerful jets (emanating from an AGN)
with the external gaseous environment surrounding a galaxy comprising that
AGN. A number of physical parameters characterising such radio structure,
e.g. its age, the jet power, the ambient density, can be determined by the
fit of the analytical model of the structure to its observational data
(the size, volume, luminosities and spectrum) using the DYNAGE algorithm
of Machalski et al. (2007). The statistical correlations between selected
model parameters in the more or less homogeneous sample of 260 radio
sources will be presented. Due to the fact that a direct correlation
between any two parameters may arise or be contaminated by their
correlations with the third (or the third and fourth) ones - the Spearman
"partial rank correlation coefficient" test is used to determine which
correlation is the strongest. A particular attention will be directed onto
the correlation of the initial energy distribution of relativistic
particles at the shock front with the jet power, external density, and
redshift.
|
2016-12-09 |
|
prof. MAREK SIKORA |
N. Copernicus Astronomical Center PAN Warszawa, Poland |
ZN OA 1440 |
Broad-emission-line radio galaxies provide challenges to jet production
theories
Accretion onto supermassive black holes located in broad-emission-line radio
galaxies (BLRGs) is predicted by theory to proceed via geometrically very thin
accretion disks, which makes them most challenging objects regarding their
ability to produce powerful jets. As recent numerical simulations indicate,
even the magnetically-arrested-disk (MAD) scenario is not able to reproduce the
jet power observed in these objects - those are measured to approach and
sometimes even exceed the accretion luminosities. Possible origins of this
discrepancy are discussed.
|
2016-12-16 |
|
dr hab. JACEK NIEMIEC |
Institute of Nuclear Physics PAN, Poland |
ZN OA 1441 |
The IBEX ribbon and the pickup ion scattering in the outer heliosheath
The nearly circular band of an increased energetic neutral atom emission
discovered the IBEX satellite can be naturally explained by the effect
of charge exchange of secondary pickup ions gyrating around magnetic field
lines in the outer heliosheath and the interstellar space beyond. This
scenario requires that the distribution of the pickup ions remained stable
against scattering on the waves they have generated on time scales much
longer than required for the charge exchange. In my talk I will present
the results of our recent studies of the stability of the pickup ion
ring-like distributions and also a more realistic distributions obtained
from modeling of atomic hydrogen in the heliosphere. The studies have been
performed using theoretical analysis and numerical tools - hybrid kinetic
and fully kinetic Particle-In-Cell simulations. The results will be
discussed in the context of IBEX observations of the ribbon and the recent
Voyager 1 in-situ measurements of the magnetic field fluctuations in the
outer heliosheath.
|
2016-12-23 |
|
|
|
|
przerwa świąteczna / Holiday break |
2016-12-30 |
|
|
|
|
przerwa świąteczna / Holiday break |
|
|
styczeń/january 2017 |
|
2017-01-06 |
|
|
|
|
Święto Trzech Króli / Holiday break |
2017-01-13 |
|
dr DOROTA KOZIEŁ-WIERZBOWSKA |
OA UJ |
ZN OA 1442 |
Host galaxies of radio-loud and radio-quiet AGNs
Active galactic nuclei (AGNs) are known
to cover an extremely broad range of radio luminosities and the spread of
their radio-loudness is very large at any value of the Eddington ratio.
This implies very diverse jet production efficiencies which can result
from the spread of the black hole spins and magnetic fluxes. Magnetic
fluxes can be developed stochastically in the innermost zones of accretion
discs, or can be advected to the central regions prior to the AGN phase.
In the latter case one might expect systematic differences between the
properties of galaxies hosting radio-loud (RL) and radio-quiet (RQ) AGNs.
In the former case the differences should be negligible for objects having
the same Eddington ratio. To study the problem we decided to conduct a
comparison study of host galaxy properties of RL and RQ AGNs. In this
study we selected AGNs from SDSS spectroscopic catalogues. These AGNs were
divided into RL and RQ based on the Best & Heckman (2012) catalogue. To
compare RL and RQ galaxies that have the same AGN parameters we used
pair-matching technique, and matched galaxies in black hole mass,
Eddington ratio and redshift. We compared several properties of the host
galaxies in these two groups of objects like galaxy mass, colour,
concentration index, star-formation rate, line widths, morphological type
and interaction signatures. Here, I will present the results of this
comparison.
|
2017-01-20 |
|
dr JULIAN SITAREK |
Wydział Fizyki i Informatyki Stosowanej,
Uniwersytet Łódzki, Łódź |
ZN OA 1443 |
Observations of blazar variability with the MAGIC telescopes
I will present the selected, recent results of observations of flares
from blazars performed with the MAGIC telescopes.
In particular I will discuss the strong flare from a distant flat
spectrum radio quasar PKS1441+25.
I will show the first detection of a VHE gamma ray emission from a
gravitationally lensed blazar B0218+357.
I will also discuss the multiwavelength observations of flat spectrum
radio quasar PKS1510-089 during the first detection of VHE gamma ray
variability from this object.
|
2017-01-27 |
|
mgr ARTEM BOHDAN |
Instytut Fizyki Jądrowej PAN, Kraków |
ZN OA 1444 |
Turbulent magnetic reconnection and particle acceleration at
nonrelativistic shocks of young supernova remnants
Particle heating and acceleration, and the effects of spontaneous turbulent
magnetic reconnection at high Mach number perpendicular nonrelativistic
collisionless shocks for parameters that are applicable to conditions at
young supernova remnants are studied with two-dimensional fully kinetic
Particle-In-Cell (PIC) simulations. These unprecedented high-resolution
large-scale simulations sample a representative portion of the shock surface
to fully account for time-dependent effects of the cyclic shock reformation.
The physics of strong shocks is governed by ion reflection that leads to the
formation of magnetic filaments in the shock ramp, resulting from
Weibel-type instabilities, and to electrostatic Buneman modes in the shock
foot. Merging magnetic filaments can also trigger spontaneous turbulent
magnetic reconnection in the shock transition. We discuss the nonlinear
shock structure and particle energization processes with the emphasis on the
dynamics of electron heating and pre-acceleration needed for their injection
into diffusive shock acceleration. On this line we study physical and
numerical parameter space to find conditions providing the most efficient
acceleration. The importance of turbulent magnetic reconnection processes is
scrutinized. Relevance of our results to the physics of fully
three-dimensional systems is discussed.
|
|
|
luty/february 2017 |
|
2017-02-03 |
|
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|
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Przerwa egzaminacyjna / Egzam break |
2017-02-10 |
|
dr GRAŻYNA STASIŃSKA
dr NATALIA VALE ASARI |
Observatoire de Paris - Univ. Paris Diderot, France
Universidade Federal de Santa Catarina, Brasil |
ZN OA 1445 |
BOND: Bayesian Oxygen and Nitrogen abundance Determinations
The abundances of chemical elements other than hydrogen and helium in a
galaxy are the fossil record of its star formation history. Empirical
relations such as mass-metallicity relation are thus seen as guides for
studies on the history and chemical evolution of galaxies. Those relations
usually rely on nebular metallicities measured with strong-line methods,
which assume that HII regions are a one- (or at most two-) parameter family
where the oxygen abundance is the driving quantity. Nature is however much
more complex than that, and metallicities from strong lines may be strongly
biased. We have developed the method BOND (Bayesian Oxygen and Nitrogen
abundance Determinations) to simultaneously derive oxygen and nitrogen
abundances in giant HII regions by comparing strong and semi-strong observed
emission lines to a carefully-defined, finely-meshed grid of photoionization
models. Our code and results are public and available at
http://bond.ufsc.br
|
2017-02-17 |
|
|
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|
Przerwa semestralna / Semester break |
2017-02-24 |
|
mgr MAŁGORZATA SIUDEK |
Centrum Fizyki Teoretycznej PAN, Warszawa |
ZN OA 1446 |
Formation and evolution of stellar population based on the red passive galaxies observed up to z ∼ 1
We would like to present the studies over the evolution and the star
formation history of passive galaxies observed by the VIMOS Public
Extragalactic Redshift Survey (VIPERS). We compare the 4000A break
(D4000n) and the Hδ Lick index (HδA) measured on VIPERS
stacked spectra with a grid of synthetic spectra to constrain the star
formation epochs of these galaxies. Assuming a single burst formation, we
find that high-mass passive galaxies formed their stars at zform
∼ 2, while low-mass galaxies formed their main stellar population more
recently, at zform ∼ 1. The consistency of these results,
obtained using two independent estimator of the formation redshift (D4000
and HδA), further strengthens a scenario in which star formation
proceeds from higher- to lower-mass systems as time passes, i. e. what has
become known as the 'downsizing' picture.
|
|
|
marzec/march 2017 |
|
2017-03-03 |
|
dr hab. ŁUKASZ STAWARZ |
OA UJ |
ZN OA 1447 |
On the electron acceleration at Saturns bow shock observed with Cassini
A leading explanation for the origin of Galactic cosmic rays is
acceleration at strong shock waves in the collisionless plasma surrounding
young supernova remnants. Evidence for this is provided by multiwavelength
non-thermal emission thought to be associated with ultrarelativistic
electrons at these shocks. However, the dependence of the electron
acceleration process on the orientation of the upstream magnetic field
with respect to the local normal to the shock front
(quasi-parallel/quasi-perpendicular), as well as on the shock Mach number,
is still being debated. Data taken by the Cassini spacecraft at Saturns
bow shock has revealed many examples of electron acceleration under
quasi-perpendicular conditions, but also the first example of electron
acceleration at a quasi-parallel shock up to at least MeV energies. Here
we present those data surveyed in a systematic way, and make in particular
the first detailed comparison between the electron energy spectra
resulting in differing upstream magnetic field regimes. We discuss whether
the acceleration is consistent with diffusive shock acceleration theory in
each case, and comment on a role of energy-dependent interaction between
the electrons and short, large-amplitude magnetic structures present in
the upstream of high-Mach number quasi-parallel shocks.
|
2017-03-10 |
|
dr PATRYK MACH |
Instytut Fizyki UJ |
ZN OA 1448 |
Massive disks around black holes
I will give a brief introduction to the basic theory of selfgravitating
rotating fluids both in Newtonian gravity and in General Relativity (GR).
I will recall some basic results concerning the solutions representing
selfgravitating disks (toroids) around point masses (in Newtonian theory)
and black holes (in GR). I will then review recent results concerning
general-relativistic Keplerian disks and the estimates of their masses and
the angular momentum.
|
seminarium nadzwyczajne: środa, godzina 14:00 / Wednesday, at 2:00 p.m. |
2017-03-15 |
|
prof. RALF-JUERGEN DETTMAR |
Ruhr-Univeristaet Bochum, Germany |
|
A fresh look on cosmic rays and magnetic fields in disk galaxies |
2017-03-17 |
|
dr hab. GRAŻYNA SIEMIENIEC-OZIĘBŁO |
OA UJ |
ZN OA 1449 |
Gamma-ray emission from galaxy cluster outskirts versus radio relics
Galaxy cluster peripheries provide important information on the nature of
ICM/IGM linkage. After commenting why cluster outskirts are particularly
interesting and why they are extensively studied, we consider potential
future observations in the gamma-ray domain at cluster edges involving the
radio relic phenomenon. We postulate here that a merger shock together
with a longliving accretion shock form the so-called double shock
structure, which provides for larger efficiencies both in injection and CR
acceleration. Therefore the multifrequency nonthermal emission i.e. gamma,
and hard X should also be expected in the location of radio relic. We
focus on the spectral signature of gamma radiation that should be evident
in the energy range of Fermi--LAT, i.e. ≥ 10-2 GeV and the CTA
energy range ∼ 102 GeV. As an example, we carried out analyses
of two types of non-thermal diffuse radio emission: the radio relic of
A 2256 and the radio halo of Coma cluster. We suggest that in both cases
the expected spatially correlated gamma-ray spectrum should have a
characteristic structure that depends on the strength of the local
magnetic field. The revealed spectral dependence on the magnetic field
would allow us to relate the future spectral observations, in particular
the position of the gamma-ray signature, to the value of the magnetic
field in the border area between galaxy clusters and their connecting
filaments.
|
Odwołane / Cancelled |
2017-03-24 |
|
prof. dr hab. TOMASZ BULIK |
Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Warszawa |
|
On the origin of merging binary black holes
The detection of merging binary black holes by LIGO leads to the
question of
where do they originate from. Several scenarios have been proposed: evolution
of binaries in the filed, stellar evolution in globular clusters, and
population III binaries. I will review the models and their consequence. I will
discuss possible ways to distinguish between them with the use of various
observations.
|
2017-03-24 |
|
mgr ALEKSANDER KUREK |
OA UJ |
ZN OA 1450 |
Usability of parametric light amplification (OPA) for high angular resolution astronomical imaging
High angular resolution imaging is crucial for many applications in modern
astronomy and astrophysics. The fundamental diffraction limit constrains
the resolving power of both ground- based and spaceborne telescopes. The
recent idea of a Quantum Telescope based on the Optical Parametric
Amplification (OPA) is aimed at bypassing this limit for imaging of
extended sources by an order of magnitude or more.
I present an updated scheme of such a device and a more accurate model of
signal amplification. According to the results based on this model, OPA is
more efficient in localizing a point source than classical optics.
However, the usability of OPA in astronomy becomes questionable.
Additionally, I discuss the perspectives of OPA in astronomy and other
fields requiring distant target imaging.
Another bottleneck of imaging of most distant galaxies is the inhomogenity
of the Space itself. This is one of the reasons why the morphology of the
most distant galaxies is still mostly unknown. I discuss the possibility
of mitigation of the image blur caused by such inhomogenity.
|
2017-03-31 |
|
dr hab. MAGDALENA KUNERT-BAJRASZEWSKA |
Uniwersytet Mikołaja Kopernika w Toruniu, Toruń |
ZN OA 1451 |
What have we learned so far about young radio sources?
Despite the intensive studies of the evolution of radio-loud AGNs we still
don't know many details of this process. We already know that not all
radio-loud AGNs follow the same evolutionary path. There are more of them and
not all tracks finally lead to the development of large-scale radio structure.
Possibly part of the young and small radio objects will never be able to grow
up and become a large-scale radio sources. Thus we predict that they will
appear as transients, the short-lived objects. The Caltech- NRAO Stripe 82
Survey (CNSS), a multi-epoch radio transient survey carried out recently with
the Jansky VLA, has facilitated an unbiased study of such objects for the first
time. The total number of 12 new radio transients have been discovered and they
are the subject of our presentation. These objects did not occur previously in
any catalog of radio sources until a sudden outburst of their AGN activity
recorded by CNSS monitoring. This discovery gives us not only a possibility of
investigation of the population of short-lived objects but also an unique
opportunity to study fast-evolving young jets. Moreover, according to the
preliminary calculations, the new sources have been radio-quiet so far. Thus,
the recorded radio transient phenomenon is not only the moment of the birth of
the radio source, but also the moment of transition from radio-quiet to the
radio-loud state. I will present the new interesting conclusions on the
evolution of radio-loud AGNs found by our group based on the previous studies
and new discoveries.
|
|
|
kwiecień/april 2017 |
|
2017-04-07 |
|
dr AGATA KARSKA |
Centrum Astronomii UMK, Toruń |
ZN OA 1452 |
Sunbathing around protostars - new insights from Herschel
Stars form in dense molecular clouds, where gas and dust are well-shielded
from the interstellar UV radiation. Nonetheless, UV photons can be produced
in situ in the surroundings of young protostars: either by the accretion of
material onto the disk or its partial ejection in the powerful jets. Recent
observations with the Herschel Space Telescope reveal that even relatively
small UV fields dramatically alter the chemical composition of the gaseous
envelopes. In my talk, I will show the main results from Space Telescope
Herschel related to feedback from low-mass protostars. In particular, I will
demonstrate that standard models of shocks do not agree with observations
unless their irradiation by UV photons is included.
|
2017-04-14 |
|
|
|
|
Wielki Piątek / Holiday break |
2017-04-21 |
|
dr KOSMAS GAZEAS |
National and Kapodistrian University of Athens, Greece |
ZN OA 1453 |
Contact Binaries Towards Merging - (CoBiToM Project)
Contact binaries are the most frequently observed type of variable eclipsing
star systems. They are small, cool, lightweight, and belong to the old stellar
population group. They follow certain empirical relationships, which closely
correlate physical parameters with each other, following Roche geometry. As a
result, contact binaries provide an excellent test for stellar evolution, and
specifically stellar merging scenarios. A consortium of observing campaigns
have cataloged thousands of contact binaries, leading to statistical studies of
many of their properties. As a corollary of such campaigns, many contact
binaries have been found exhibiting extraordinary behavior, requiring follow up
observations to study their peculiarities in detail. For example, a doubly
eclipsing quadruple system consisting of a contact binary and a detached
binary, offering a highly constrained gravitationally bound system. This is an
excellent candidate to test orbital and evolutionary theories of star systems.
CoBiToM is a new observing project, which was initiated at the University of
Athens in 2012, in order to investigate the possible lower limit for the
orbital period of binary star systems before coalescence, as a prediction from
stellar evolution prior to merging.
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2017-04-28 |
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prof. MASAHIRO HOSHINO |
Department of Earth and Planetary Science, The University of Tokyo,
Japan |
ZN OA 1454 |
Particle acceleration and reconnection in collisionless accretion disks
Nonthermal particles are ubiquitous in astrophysical plasmas, and explosive
phenomena such as pulsar wind nebula, gamma ray bursts, and solar flares have
demonstrated evidence for the production of high-energy particles. Yet the
rapid magnetic energy dissipation and particle acceleration remains to be
unresolved. While a great variety of acceleration processes are occurring in
those astrophysical settings, magnetic reconnection is known to be one of major
mechanisms of generating nonthermal high energy particles and of dissipating
magnetic field energy. In my talk, I quickly review the basic physics of
particle acceleration in magnetic reconnection, and then I argue about particle
acceleration and angular momentum transport in collisionless accretion disks
around massive black holes, by paying special attention to the role of
reconnection. I discuss that the efficient particle acceleration and enhanced
angular momentum transport can be realized by some kinetic effects of
reconnection.
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maj/may 2017 |
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2017-05-05 |
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dr SZYMON SIKORA |
OA UJ |
ZN OA 1455 |
An example of an inhomogeneous cosmological model; the problem of the averaging in cosmology
In this talk I present the topic of the inhomogeneities averaging in cosmology. I
explain why this
task is so complicated and describe the two important approaches: the Green-Wald
scheme and the Buchert framework.
In recent years there was an interesting dispute between these two viewpoints,
concerning the role
of the inhomogeneities in the estimation of the amount of the "dark energy".
I show the simple cosmological model which approximates the periodically distributed
dust overdensities on the Einstein-de Sitter background.
The model construction enables application of the Green-Wald averaging scheme and
the Buchert averaging technique simultaneously.
On basis of this model I comment on the impact of the inhomogeneities on the
luminocity distance observable.
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2017-05-12 |
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dr MICHAŁ DRAHUS |
OA UJ |
ZN OA 1456 |
Asteroid disruptions today
Disruptions of asteroids are often viewed as ancient events leading to the
formation of asteroid families and pairs, binary and multiple systems, and
discrete dust bands within the Zodiacal cloud. But thanks to the
remarkable progress in solar system science over the last decade, we can
now directly observe asteroidal disruptions occurring before our eyes.
Various lines of evidence suggest that the disruption can be a consequence
of a rapid rotation resulting from a long-term spin-up, or a result of a
hypervelocity collision with another minor object. Up until recently the
two mechanisms were difficult to distinguish because of the unknown
rotation rates of the disrupting small asteroids, but this has changed
after our team investigated the recently disrupted asteroid P/2012 F5.
Using the Keck II telescope atop Mauna Kea we discovered several fragments
of the object and obtained the highly anticipated measurement of the
rotation rate, which turns out to be the fastest known among active
asteroids and is fast enough to support the rotational disruption
scenario. Further observations with the Hubble Space Telescope have
revealed that the system is in fact the first ultra-young asteroid family
identified to date, and given its likely formation via rotational
disruption, it can also be the first known asteroid family of
non-collisional origin.
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Odwołane / Cancelled |
2017-05-19 |
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dr SABRINA CASANOVA |
Instytut Fizyki Jądrowej PAN |
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2017-05-26 |
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prof. DAVID L. BLOCK |
University of the Witwatersrand, Johannesburg, South Africa |
ZN OA 1457 |
Priorities in Scientific Discovery - Stigler's Law of Eponymy
Stigler's Law of Eponymy states that no scientific discovery is named
after the actual discoverer. This seminar highlights several examples
within the realms of galaxy morphology and cosmology. The seminar will
commence by focusing on a paper entitled "Un univers homogène de masse
constante et de rayon croissant, rendant compte de la vitesse radiale des
nebuleuses extra-galactiques" ("A homogeneous universe of constant mass
and increasing radius accounting for the radial velocity of extra-galactic
nebulae"). It is perhaps not widely known in undergraduate astronomy
texts that Lemaître, although a master in relativity, had also spent the
years 1924-25 at the Harvard College Observatory, and had a profound
insight into aspects of observational astronomy, such as the effective
temperatures of stars, trigonometric parallaxes, moving-cluster
parallaxes, absolute bolometric magnitudes, dwarf branch stars and giant
branch stars. Two years prior to the appearance of Hubble (1929),
Lemaître (1927) derived a linear relationship between the radial
velocities of galaxies and their distances. He then proceeded to use the
radial velocities of 42 extragalactic nebulae tabulated by Strömberg
(1925), to derive a value for the rate of expansion of the Universe of
625 km s-1 Mpcs-1. In view of the title of the paper by
Lemaître, should Lemaître perhaps not be credited with the discovery
(in 1927) of an expanding Universe? We then delve into other fascinating
examples -- in galaxy morphology -- where the original discoverer has, for
a variety of possible reasons, been eclipsed, in accordance with Stigler's
Law of Eponymy.
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czerwiec/june 2017 |
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2017-06-02 |
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mgr MARIUSZ TARNOPOLSKI |
OA UJ |
ZN OA 1458 |
Nonlinear time series analysis of Hyperion's lightcurves
Hyperion is a satellite of Saturn that was predicted to remain in a
chaotic rotational state. This was confirmed to some extent by Voyager 2
and Cassini series of images and some ground-based photometric
observations. The aim of this article is to explore conditions for
potential observations to meet in order to estimate a maximal Lyapunov
Exponent (mLE), which being positive is an indicator of chaos and allows
to characterise it quantitatively. Lightcurves existing in literature as
well as numerical simulations are examined using standard tools of theory
of chaos. It is found that existing datasets are too short and
undersampled to detect a positive mLE, although its presence is not
rejected. Analysis of simulated lightcurves leads to an assertion that
observations from one site should be performed over a year-long period to
detect a positive mLE, if present, in a reliable way. Another approach
would be to use 2-3 telescopes spread over the world to have observations
distributed more uniformly.
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2017-06-09 |
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dr KAROL SEWERYN |
Centrum Badan Kosmicznych Polskiej Akademii Nauk, Warszawa |
ZN OA 1459 |
The new prototype of sampling device driven by rotary hammering actions
Sample return space missions are one of the possible options to extend our
knowledge about extra-terrestrial materials, processes occurring on
surface and subsurface level, as well as interactions between regolith and
technology. Collection of surface or subsurface material from such bodies
is a key technical process that needs to be performed to achieve the goals
of such missions. Although in terrestrial environment the sampling process
is relatively easy, smart solutions are needed for near zero gravity,
unknown and remotely accessible space environment. In this presentation
the concept of a new type of sampling device, called PACKMOON, dedicated
for low gravity bodies space environment, is presented. The principle of
operation of the PACKMOON device is based on two key elements: insertion
of the spherical jaws (casing) into regolith by rotary hammering actions
and minimization of interaction with the lander by taking advantage of
doubling mechanical subsystems, which operate in the same angular
direction but in opposite sense. As a result a significant improvement of
effectiveness in comparison to previous CBK penetrometers were achived.
Numerical simulations validated by experimental results allow to optimize
the device and developed final prototype. As a result, the PACKMOON device
is a reliable mechatronic system that effectively uses power to sample
relatively hard material (up to 5-7 MPa) with minimum interaction with the
lander. In addition, both thermal and mechanical interaction with the
sample is relatively small, and in that sense the sample is more valuable
for further scientific investigations. This issue is a key driver for
planned sample return missions such as ESA Phootprint mission to Phobos or
Roskosmos Luna missions to the Moon.
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2017-06-16 |
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piątek po Święcie Bożego Ciała / Holiday break |
2017-06-23 |
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dr HELEN JERMAK |
Liverpool John Moores University, Liverpool, UK |
ZN OA 1460 |
Photopolarimetric Monitoring of OJ287 using the Liverpool Telescope
I will present the Liverpool Telescope and its instrument suite, focussing
on the polarimeters. The RINGO polarimeters continue to be used to conduct
long-term monitoring of gamma-ray bright blazars. I will present results
from the RINGO2 and DIPOL polarimetric study of blazars and discuss
further analysis being carried out using multicolour RINGO3 data. In
particular I will speak about the data taken for OJ287, the binary
supermassive black hole blazar. I will also present the design of the new
fully-optimised polarimeter, MOPTOP, which will allow rapid, multicolour,
polarimetric observations with greater sensitivity than RINGO2 and RINGO3.
This polarimeter is designed for use on the current 2 metre Liverpool
Telescope, but will be adapted for use on the future Liverpool Telescope 2;
4 metre, fully robotic and autonomous facility that will be co-located
with the Liverpool Telescope on La Palma.
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seminarium nadzwyczajne: godzina 14:00 / at 2:00 p.m. |
2017-06-23 |
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dr GREGORY GREEN |
KIPAC, Stanford University, USA |
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3D Dust Mapping with Pan-STARRS 1
Dust is a critical foreground for many areas of astronomy, extinguishing
and reddening sources in the ultraviolet, optical and near-infrared
regions of the spectrum, and contaminating our view of the cosmic
microwave background in the far-infrared. Dust also traces the
interstellar medium, and is therefore itself an interesting probe of Milky
Way structure. Maps of interstellar dust therefore find wide application
in astronomy. Up until recently, most such maps have been two-dimensional
in nature, tracing the column density of dust with angle on the sky.
However, in order to correct observations of sources embedded in the Milky
Way, or to study dust clouds within the Galaxy, a three-dimensional map
that traces dust density with distance is desirable. I present a
three-dimensional map of interstellar dust reddening, covering the
northernmost three-quarters of the sky out to a distance of several
kiloparsecs, based on optical and near-infrared stellar photometry from
Pan-STARRS 1 and 2MASS. The map is probabilistic, yielding the uncertainty
in dust reddening along each line of sight. It has an angular resolution
ranging from 3.4' to 13.7', and a distance resolution of ∼ 25%. The
map reveals detailed structure within the Milky Way, from filaments to
large cloud complexes. Out of the plane of the Galaxy, where we can see
through the entire dust column, we find good agreement with previous
two-dimensional dust maps. In the plane of the Galaxy, our map gives
distances to dust clouds which are consistent with known literature
distances. In order to extend the map further into the Southern
Hemisphere, I have completed an optical/near-infrared survey of the
Galactic plane south of a declination of -30 degrees, using the Dark
Energy Camera on the 4m Blanco telescope on Cerro Tololo. In the near
future, the addition of Gaia parallaxes and spectrophotometry will help us
to refine the distances in our map.
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seminarium nadzwyczajne: wtorek, godzina 14:00 / Tuesday at 2:00 p.m. |
2017-06-27 |
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dr YOSUKE MATSUMOTO |
Department of Physics, Chiba University, Japan |
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High-performance computing for exploring electron accelerations at astrophysical shock waves
Collisionless shock waves provide us great opportunities to explore
nonlinear dynamics in strongly inhomogeneous plasmas. Dynamics therein
result in excitation of various types of electrostatic and electromagnetic
waves and associated plasma heating and acceleration. Extreme
circumstances encountered in such situations can be realized in
astrophysical phenomena, such as supernova remnant (SNR) shocks where the
plasma kinetic energy overwhelms other magnetic and plasma internal
energies. SNR shocks have been thought to be a generator of cosmic rays,
and exploring nonlinear dynamics in extreme circumstances therefore
clarifies how charged particles are accelerated to relativistic energies
out of the thermal counterpart. We present results from ab initio
particle-in-cell (PIC) simulations of strong shock waves by the help of
state-of-the-art supercomputer systems. We found different types of
electron acceleration mechanisms: A shock surfing acceleration via
interactions with coherent electrostatic waves in the upstream region, and
a stochastic acceleration by turbulent magnetic fields. These were found
to be very effective in multi-dimensional shock structures.
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2017-06-30 |
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dr TAKANOBU AMANO |
The University of Tokyo, Japan |
ZN OA 1461 |
In-situ signatures of whistler-electron interactions in the Earth's bow shock and the implication for the electron injection
The acceleration of nonthermal particles is one of the most important
problems in space physics and astrophysics. The standard first-order Fermi
mechanism needs a seed population. It must be provided by some microscopic
plasma processes occurring in the collisionless shock transition layer,
which is known as the injection problem. Recently, NASA's MMS spacecraft
with its unprecedented temporal resolution revealed the electron scale
dynamics in the shock for the first time. I will discuss how the observed
signatures fit into proposed theories of electron acceleration that may
ultimately lead to the injection. Similarities and dissimilarities between
the observations and fully kinetic particle-in-cell simulation results
will also be discussed.
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lipiec/july 2017 |
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seminarium nadzwyczajne: godzina 12:00 / at 12:00 a.m. |
2017-07-07 |
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prof. WILLIAM FORMAN |
Harvard-Smithsonian Center for Astrophysics, USA |
ZN OA 1462 |
Supermassive Black Holes at Work: "Fossil Records" of Outbursts from Supermassive Black Holes and the Effects of Outbursts on the Evolution of Gas Rich Galaxies, Groups, and Galaxy Clusters
Supermassive black holes (SMBHs) play key roles in galaxy and cluster
evolution. This is most clearly seen in the "fossil record" that is
imprinted in the gas rich atmospheres of early type galaxies, groups, and
clusters by powerful SMBH outbursts. I will discuss the outburst history
of M87 as chronicled in its radio and X-ray images and the implications of
these outbursts for heating gas rich environments. In addition to
discussing the outburst around M87, I will review the results of a galaxy
survey that shows the effects of SMBH feedback on early type galaxies and
which suggests that, at very early epochs, SMBH outbursts have truncated
star formation and altered the "normal" evolution of the stellar
component of galaxy bulges. I conclude by describing a future X-ray
mission, X-ray Surveyor, with sub-arcsecond angular resolution, that would
allow us to study the evolution of SMBHs and hot, X-ray emitting
atmospheres from high redshifts to the present.
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seminarium nadzwyczajne: godzina 12:00 / at 12:00 a.m. |
2017-07-14 |
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dr ADAM ZADROŻNY |
Narodowe Centrum Badań Jądrowych, Warszawa, Poland |
ZN OA 1463 |
Searching for optical counterparts to gravitational waves registered in LIGO-Virgo detectors network
In 2015, gravitational waves were directly detected for the first time in
LIGO detectors. This have openned new possibilities in observations of
universe. Very interesting is a possibility to jointly observe an event in
eletromagnetic and gravitational waves. For this purpose LSC-Virgo
consortium along with astronomical partners have EM Follow-up project. The
project aim is search for optical counterparts to events registered in
LIGO-Virgo detector network. Such observations, if successful could help
verify theoretical models of phenomena like for example: short GRB or
supernova core collapse.
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sierpień/august 2017 |
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wrzesień/september 2017 |
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2017-09-22 |
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prof. ALOK CHANDRA GUPTA |
Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, India |
ZN OA 1464 |
Multi-wavelength Variability and QPOs in Blazars
Blazar is a subclass of radio loud AGN which show flux variation in the
complete EM spectrum on diverse timescales ranging from as short as a few
tens of minutes and as long as several years. The blazar emission is
predominantly non-thermal.
In the present talk, I will discuss some of interesting recent results
published by my group based on multi-wavelength ground and space based data.
We have detected flux variation in blazars on diverse time scales,
cross-correlated multi-wavelength flux and spectral variabilities. We have
also detected quasi-periodic oscillations (QPOs) in time series data of
blazars in optical and X-ray bands. I will also briefly describe which are
dominant AGN standard models which can explain our findings.
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