Abstracts YERAC 2018


Abstracts for the YERAC2018 (4-6 September)

There are 32 participants who submitted an abstract.

Name Title
Abstract
Cruces, Marilyn Title: Follow-up of FAST pulsar discoveries
Abstract:
Pulsars are fundamental tools for astronomy and physics. Every
single new pulsar has the potential to provide an outstanding laboratory for a wide variety of physics, ranging from a better understanding of the stellar evolution to testing theories of gravity and placing limits on the equation-of-state. The most stable pulsars, who’s precision approaches that of atomic clocks, are our only window into the extremely low-frequency (< 10?8 Hz) gravitational waves expected from supermassive black hole binaries, which are not detectable by LIGO or LISA (Zoltan et. al 2017).

With the aim of finding the most exciting pulsars (e.g. a pulsar-black-hole binary), the Chinese Academy of Science (CAS), the MPI für Radioastronomie (MPIfR) and the Australia Telescope National Facility (ATNF) have started a major pulsar survey using the giant “Five-hundred-meter Spherical-dish Telescope" (FAST), the world’s biggest radio-telescope. Since first light in September 2016, FAST has been undergoing commissioning observations. Already at this early stage, the pulsar survey is producing exciting science by finding new pulsars, demonstrating FAST’s unprecedented sensitivity. The survey using FAST is one of the first science projects at the telescope. It makes use of the drift-scan mode and a wide-band receiver covering from 270
MHz to 1.6 GHz to search for pulsars and radio-transients. The follow-up observations of the promising candidates are carried by the 100m Effelsberg and 64m Parkes radio-telescopes given their the excellent pointing precision, positional and frequency agility.

Up to date, around two dozens of candidates have been confirmed and followed-up by Effelsberg and Parkes. Highlight of the discoveries are millisecond pulsars and binary systems.
Dutkowska, Katarzyna Title: Infrared and 22 GHz water emission associated with a Sun-like protostar
Abstract:
Water plays an important role in the cooling process of the gas in low-mass, solar-type protostars (Karska et al. 2013). Far-infrared emission of water is associated with jets / outflows and can be used to determine the shock type, its velocity, and the pre-shock density of the medium. Water maser emission at 22 GHz is also linked to regions with active jets and abundant high-density gas (e.g. Furuya et al. 2001). Here, we report a strongly variable water maser at 22 GHz towards L1448 IRS 2 detected with Toru? 32 m radiotelescope. The source shows a strong variability both in the line strength and the profile features. Comparison of the radio and infrared observations can provide useful tools in understanding of the processes linked to this kind of sources.

References:
Karska, A., Herczeg, G. J., van Dishoeck, E. F., et al. A&A ,552, A141 (2013)
Furuya T et al., ApJ, 559, pp. L143-L147 (2001)
Tobin et al., ApJ, 818, pp. 36 (2016)
Gan, Hyoyin Title: Exploring subtle artefacts in data calibration of LOFAR
Abstract:
LOFAR (Low Frequency ARray) is a new generation radio interferometer covering the unexplored low-frequency range from 10 to 240 MHz. Among its key science projects, LOFAR-EoR (Epoch of Reionisation) is set to detect the spectral fluctuations of the redshifted neutral hydrogen (HI) 21-cm signal. Because most radio sources in the sky do not show circular polarisation, the thermal noise in an observation can be estimated by the Stokes V parameter. However, the observed data from LOFAR showed higher noise levels than those expected from the Stokes V parameter. Possible sources of this can be the incompleteness of the sky model, ionospheric effects and gain calibration etc. In this project, we focus on artefacts of gain calibration on noise levels. The correlation between properties of gain solutions (i.e. averages, variances) and the Stokes I and V ratio of HI power spectra is investigated using statistical methods.
Gourdji, Kelly Title: Low-frequency radio follow-up of gravitational wave merger events with LOFAR
Abstract:
On 17 August 2017, gravitational waves (GWs) from a binary neutron star inspiral (GW170817) were detected for the first time, by the Advanced LIGO and Advanced VIRGO GW detectors. A short gamma-ray burst was independently detected 1.7 s later, definitively launching the multimessenger era of astronomy. This triggered an observing campaign of unprecedented scale that covered the full electromagnetic spectrum. Ongoing monitoring of the radio emission in particular, which traces the high-velocity ejecta from the merger, has proven to be instrumental in discriminating between models of the merger event. Here, I outline the LOFAR HBA (high-band) rapid response and follow-up strategy of compact merger events such as GW170817, in particular making use of the telescope’s very large instantaneous field of view. I will present initial LOFAR results from gravitational wave events. I also show how deep 145-MHz images obtained from the follow-up observations can facilitate some of the deepest low-frequency searches for transients to date.
Haniewicz, Henryk Title: PSR J1829+2456: A double neutron star system with measured masses
Abstract:
PSR J1829+2456 is a recycled pulsar in a double neutron star system with an orbital period of 28 hr. After its discovery in 2003, follow-up timing was only conducted until 2008, resulting in individual mass limits. New data has been acquired with the PUPPI coherent dedispersion backend at the Arecibo telescope at L-band and 430 MHz.
Thanks to much improved data quality, timing analysis has allowed us to measure the Einstein delay to within 10%, and for the first time revealed a significant Shapiro delay signal. As a result, the masses of the system have been determined to high precision. In this talk, I will describe our analysis, including new RFI excision methods, and results showcasing what they may imply about the evolution of this system.
Hanson, Joe Title: Investigating Cosmic Magnetism with Machine Learning
Abstract:
Research into cosmic magnetism still lacks answers to some key questions, but the Faraday effect offers a unique astrophysical probe to investigate the most distant and largest-scale magnetic fields in the universe. Polarimetric observations of Faraday Rotation from upcoming radio telescopes such as the SKA and MeerKAT will be able to provide new insights into these open questions in cosmic magnetism, but only if new methods are developed which allow astronomers to make these insights. Tackling these issues is a significant big data problem in astronomy.

My interdisciplinary research investigates the use of machine learning to find solutions which will allow astronomers to be better equipped for making the most of the new possibilities these telescopes will bring. My research also considers the complications inherent with the data, e.g. the need for accuracy in a difficult classification, and the problems of multi-class imbalances in the dataset.
Irabor, Tonye Title: A radio selected sample of planetary nebulae
Abstract:
A new radio-selected sample of PNe from the CORNISH survey is presented. The CORNISH is a radio continuum survey of the inner Galactic plane covering Galactic longitude, 10^0 < l < 65^0, and latitude, |b| < 1^0, with a resolution of 1.5” and sensitivity better than 0.4 mJy/beam. The radio regime, being unbiased by dust extinction, allows for a more complete sample selection, especially towards the Galactic mid-plane. Here, we explore the use of visual inspection, multi-wavelength diagnostic plots and analysis to verify and classify the candidate PNe. We find 90 new PNe, of which 12 are newly discovered and 78 are newly classified as PNe. A further 47 previously suspected PNe are confirmed as such from the analysis presented here and 24 known PNe are detected. Eight sources are classified as possible PNe or other source types. Our sample includes a young sub-sample, with physical diameters < 0.12 pc, brightness temperatures (> 1000 K) and located closer than 7 kpc. Such a radio-selected sample, unaffected by extinction, will be particularly useful to compare with population synthesis models and should contribute to the understanding of the formation and evolution of PNe.
Kazantsev, Andrey Title: Giant radio pulses from pulsars: observation and investigation.
Abstract:
Generation of Giant Radio Pulses (GRP) is one of the most intriguing phenomenon in the modern pulsar physics. GRPs was defined first as strong individual pulses which peak flux density was tens, hundreds or even thousand times stronger than that of the average pulse. There are known two “classic” millisecond period pulsars emitting pulses which exhibit extremely short (nanoseconds) and strong (MJy) pulses with power-low distribution in amplitude. The rest of known pulsars referred as pulsars with GRPs have pulses that are not so strong and short, but nevertheless they clearly differs from regular pulses in amplitude and duration, and their power-low distribution is typical for GRPs, when the log-normal is typical for regular pulses. The subset of these GRP generating objects consists of pulsars with second period, magnetic fields on light cylinder ~1 – 100 Gs, observed mostly on frequency <= 100 MHz. This subset of GRP generating pulsars is the object of our investigations.
Since 2012 we have carrying out observations of more than 70 second period pulsars of the Northern Hemisphere at 111 MHz frequency, using the Large Phased Array (LPI) radio telescope of the Pushchino Radio Astronomy Observatory. Our main goals were to find out new pulsars with GRPs and to monitor earlier known pulsars with GRPs. We discovered for the first time GRPs from two isolated second period pulsars, and we detected several possible candidates, which exhibit regularly strong anomalous pulses with complex distribution in pulses' amplitudes. We analyzed also distributions of regular pulses from several well-known ordinary pulsars, and we found out that sometimes they differ from the simple log-normal model.
Kravtsov, Ihor Title: THE NORTHERN SKY SURVEY IN ORDER TO FIND SPORADIC RADIO EMISSION SOURCES IN DECAMETER WAVE RANGE
Abstract:
The world’s largest decameter UTR-2 radio telescope has recently accomplished a full survey of the Northern sky in order to find sporadic radio emission sources. As a result, about 100 TB of observational data were obtained and completely processed. A special test was carried out which showed the inability to generate pulses, such as those found, by ionospheric scintillations. For the avoidance of a large number of interference among the signals, a threshold level of SNR (8 RMS) was introduced which significantly exceeds the level of all signals that we consider to be interference and ionospheric scintillations. There were 380 signals of cosmic origin. Distributions of these signals’ dispersion measures, galactic latitudes, SNRs and times of appearance were built. Signals arrival times’ distribution (during the observational session) is quite uniform. DMs’ distribution is similar to the simulated DMs’ distribution of known pulsars, which will be observable by the SKA radio telescope in future. SNRs’ distribution is similar to the distribution of the anomalously intense pulses of known pulsars by energy. Signals’ distribution by galactic latitude also has much in common with the one of close known pulsars (DM < 30 pc/cm3 and P > 0.2 s).
In present work we estimate the number of sporadic radio emission sources, which are potentially available for the low-frequency observation and compare their number with the obtained results.
Thus, analysis of the detected signals, analysis of the signals’ parameters distributions and their comparison with the similar distributions for known sources show that the signals found have a cosmic origin and are generated, most likely, by different types of neutron stars.
Kumari, Anshu Title: Multiwavelength Observations of Coronal Mass Ejection and associated High Frequency Type II Burst
Abstract:
Corona, the outermost region of the Sun, is believed to be present from a heliocentric distance of ~1.01 R? (where R? is the radius of the solar photosphere) to more than 1 AU. Being a highly tenuous plasma medium, it harbours large scale structures, as multi-frequency observations reveal, such as coronal helmet streamers (white-light), coronal holes (X-ray and EUV), and coronal condensations (radio) etc. It is recognized to exhibit incessant and inhomogeneous outward flow of plasma material, named solar wind, and to exemplify intermittent injection of huge mass of coronal material (Coronal Mass Ejections (CMEs)), in to the interplanetary medium, and therefore the region appears to be highly dynamic.
We present the detailed studies of one of such high CMEs and its radio signature as a radio transient, a high frequency type II radio burst (440 –30 MHz) that occurred in the solar corona on 2015 November 4. The drift rate of the burst was unusually high (? 2 MHz/s). Our analysis shows that the estimated speed of the magneto- hydrodynamic shock driving the burst is not constant. The peak speed and acceleration are very large, 2450 km/s and 17 km/s, respectively. There is spatio-temporal good correlation between the type II burst and the associated coronal mass ejection (CME) in the white-light and extreme-ultraviolet images. The time profile of the shock speed from radio observations and the light curve of the associated soft X-ray profile obtained with ATSROSAT/SSM are well matched with a correlation coefficient of ? 86 %. These results provide clinching evidence that the CMEs are responsible for radio transients (type II) originating close to the Sun.
Liu, Xiaojin Title: High-precision pulsar timing and the motion of the pulsar in our Galaxy
Abstract:
Pulsar timing has provided a useful tool to probe a broad series of interesting topics, such pulsar dynamics, interstellar medium and detecting gravitational waves. With the coming online of the next generation of radio telescopes, e.g. FAST, MeerKat and the future SKA, higher timing precision will be achieved and some once unnoticed effects may become detectable. In this talk, I will focus on the timing impacts due to the motion of the pulsar in our Galaxy. I will discuss a new method to detect the pulsar radial velocity by using pulsar timing.
Locatelli, Nicola Title: Assessing the magnetic cosmic web nearby galaxy cluster Abell 2744
Abstract:
Magnetic Fields are observed across a very large range of scales, from planetary size, to galaxies, up to galaxy clusters. Interesting physics of the early Universe may have left its signature on magnetic fields in rarefied environments, such as cluster outskirts, cosmological filaments and voids. At these very large scales however, their magnitude and origin is still debated. Observing ~Mpc large-scale structures (LSS) is made challenging by their relatively cold and diluted plasma conditions. However, significant energy content is expected in non-thermal component, yielding radio emission. Moreover, large scale magnetic fields can be detected through the Faraday Rotation effect they induce on the polarised emission from background sources. This gives hope for a detection of LSS magnetic fields, thanks also to new promising radio facilities (JVLA, LOFAR, ASKAP, MeerKat) and techniques (Rotation Measure Synthesis) which has become available since a few years.
In this context I review the observational techniques and earliest preliminary results in my efforts to detect the tip of the iceberg of the magnetized cosmic web, in particular through the analysis of Faraday Rotation in cluster Abell 2744, which is the first one in which evidence of intracluster filaments has been reported by XMM-Newton analysis.
Mazumdar, Parichay Title: LASMA (13CO, J= 3-2) Survey of the Milky Way
Abstract:
Surveys of the Milky Way are fundamental tools to obtain reliable constraints for the gas distribution for the models that aim to simulate our Galaxy's spiral arms and bar potentials. While continuum surveys (e.g.- GLIMPSE, Hi-GAL, ATLASGAL, MIPSGAL) trace the dense ISM and recent star forming activity going on in the Milky Way; spectroscopic follow-ups (e.g. GRS, HOPS, CHIMPS, COHRS, SEDIGISM) reveal the kinematics (radial velocities and kinematic distances) of the molecular clouds and clumps detected in the continuum surveys. They also constraint their dynamical state in addition to gas excitation, chemical abundances and turbulence. With advancements in technology we are able to observe the Galaxy with much higher angular resolution than the past revealing cloud sub-structures as well as providing us with a more detailed view on the large-scale structure of the molecular gas. In this talk I will present the on-going LASMA survey of the inner Milky Way in 12/13CO (J=3-2) performed with the Atacama Pathfinder EXperiment (APEX) telescope in Chile and the early science from the data collected so far.
Mhaskey, Mukul Title: Extragalactic radio sources with sharply inverted spectrum at metre wavelengths
Abstract:
Many previous studies have shown that there is a direct connection between AGN evolution and the nature of compact objects like Gigahertz spectrum (GPS)/ Compact steep spectrum (CSS) sources. These objects display a concave radio-spectrum, resultant of radiation absorption at low frequencies (sub GHz). These objects are believed to be either young AGNS or normal AGNs surrounded by lot of ambient gas. The spectrum of these sources are determined by the nature of absorption by this ambient gas specifically at the low frequency part of the radio-spectrum. In this context, two different evolutionary pictures are discussed in literature. Mainly two absorption mechanisms are popular, the synchrotron self absorption and free-free absorption. A clear understanding of which will help in constraining the evolutionary phases of the AGNs.

In an attempt to understand the nature of low frequency absorption mechanisms in these compact/ young AGNs, we initiated a targeted search for ‘Extremely Inverted Spectrum Extragalactic Radio Sources’ (EISERS) characterized by an integrated radio spectrum which turns over, attaining a slope alpha that exceeds alpha_critical = +2.5. This critical value is important as it represents the theoretical limit which can be achieved for an (even perfectly homogeneous) source of incoherent synchrotron radiation arising from a power-law energy distribution of relativistic charged particles, which is the basic mechanism widely believed to be responsible for the radio continuum emission from active galactic nuclei, known as synchrotron self absorption (SSA) limit.

Discovery of rare radio galaxies with alpha > +2.5 may then call for some non-standard explanation for the observed radio emission. One possibility is the free-free absorption (FFA) due to clouds/screen of thermal plasma that causes the sharp inversion of the integrated radio spectrum.
Molet, Jordan Title: Molecular complexity in the star forming region W43-MM1
Abstract:
The "mini-starburst" region associated to W43-MM1 includes a number of massive pre-stellar and proto-stellar cores candidates (e.g. Motte et al. 2018 and Nony et al. in prep.). It is an important sample of molecular cores at various evolutionary stages and moreover, it may contain the most massive cold core known in the whole Galaxy.

We used high spatial resolution data from ALMA Cycle 2 and Cycle 3 and a spectral survey obtained at the IRAM 30m telescope. I will introduce the technique I developed to substract automatically the continuum in large regions of molecular emission in order to study weak emission lines. Then I will present the current state of our comparison of the molecular composition of the cores in W43-MM1, in particular the distribution of complex molecules.
Mthembu , Nhlakanipho, Kwazi Title: Calibrating HERA-19 with a Galactic Centre Observation
Abstract:
We present sky calibration and imaging using HERA-19. We exploit the fact that the Galactic Center transits through the main beam of the telescope. The Galactic Center provides a bright source which, we show, can be approximated as a point source sufficiently well to derive initial delays and antenna gains. The Hydrogen Epoch of Reionization Array (HERA; http://reionization.org) is a low frequency (50?250 MHz), 350-dish radio interferometer currently under construction at the SKA site in the Karoo. Its main goal is to observe the evolution of the 21-cm line emitted by the intergalactic medium (IGM)in the 6 < z < 12 range, therefore providing a complete characterization of cosmic reionization. The first 19 dishes were deployed at the end of 2015. The full HERA instrument will be a 350-element interferometer (320 in a dense core + 30 outriggers) 14-m parabolic dishes observing from 50 to 250 MHz [1].
Murthy, Suma Title: Feedback from low luminosity radio AGNs: A case study of B2 0258+35
Abstract:
The interplay between nuclear activity and the interstellar medium of galaxies plays an important role in their evolution: the gas accreting onto the dormant supermassive black hole turns it into an active galactic nucleus (AGN) and the ensuing activity is believed to starve the host galaxy of the fuel needed to form stars. The contribution of radio-loud AGNs to this feedback effect is yet to be well understood, more so that of low luminosity radio AGNs. These make up a significant fraction of the radio-loud AGN population, but are generally believed to be too weak to cause any significant impact. I will present the case of one such radio AGN B2 0258+35. Here, a combination of HI absorption, CO emission, continuum studies, and numerical simulations indicate that low power radio activity, under favourable circumstances, can not only disturb gas locally but also result in the formation of large scale radio structures. This thereby highlights the potential importance of low luminosity radio AGNs in the context of feedback.
Mutie, Isaac Title: Fuelling star-formation and accretion in Galaxies - tracing dense, molecular gas.
Abstract:

Much of the star-formation underway in local galaxies resides in dust and gas rich galaxies with high levels of optical obscuration. These galaxies, often dubbed Starbursts, exhibit high rates of star-formation and are responsible for a large fraction of the massive stars formed in the local Universe.

Within each of these star-forming galaxies, dense regions of gas and dust form massive stars, which quickly evolve to produce significant populations of supernovae and supernova remnants. These stellar end-points can then be used to probe the on-going star-formation rate, supernovae astrophysics and the ISM environment.

However critical questions remain regarding the environment where this heightened star-formation occurs, and the effects on the gas in galaxies of the on-going star-formation and accretion processes. The project will utilize new state of-the-art observations with radio interferometers including e-MERLIN and the JVLA to observe the fuel of these star-formation and accretion activities seen in galaxies.

These new radio observations include faint dense molecular gas tracers, such as OH, HCN, HCO+, as well as the neutral hydrogen and provide a high angular resolution view of the dense gas in nearby active galaxies (both starbursts and Active Galactic Nuclei). Using these observations this project will investigate the dense gas properties of the central regions of these sources. This will be combined with deep radio continuum observations of these sources charting the star-formation and accretion processes themselves, and thus the project will allow an obscuration free view of both the causes (fuel - dense gas) and consequences of star-formation and
accretion within galaxies.
Obonyo, Willice Title: A search for non-thermal radio emission from jets of massive young stellar objects
Abstract:
Massive young stellar objects are known to be associated with jets, the majority of which may be magnetically or radiatively driven. We report a search for non-thermal radio emission, associated with magnetised jets from a sample of 15 MYSOs. We computed and compared their 1.5 GHz?6 GHz spectral indices (?_LC) with 6 GHz?44 GHz (?_CQ) and found that ?_LC is lower than ?_CQ in most cases, suggesting the presence of non-thermal radiation at 1.5 GHz or that there may be a contribution from dust emission at 44 GHz. About 70% of the sources show evidence for non-thermal emission with 30% showing clear non-thermal lobes. All the central cores of the sources are thermal with corresponding mass-loss rates that lie in the range?1.4±2.2×10^?7 to 7.3±4.1×10^?6 Myr^?1. Given the presence of non-thermal lobes in some of the sources and a hint of non-thermal emission from spectral indices, it seems that the majority of MYSOs drive magneto-hydrodynamic jets. Two of the sources have spectra that resemble those of optically thick HII regions and were interpreted as young MYSOs with radiative hydrodynamic jets. Also noted is that some of the sources show evidence of binarity and variability.
Olivares, Valeria Title: ALMA observations of cold molecular gas in Brightest Cluster of Galaxies
Abstract:
The core of galaxy clusters are very dynamic environments and host some of the most energetic AGN known in the local universe. Therefore we used CO(1-0) or/and CO(2-1) and/or CO(3-2) ALMA observations to map the dynamics and morphology of the extended molecular filamentary structures located around the central 1 arc minute of 12 galaxy clusters. We found that the velocity dispersion of the molecular filaments are significantly below the escape speed from the central galaxy and so these clouds should rain back towards the galaxy center to fuel the AGN.

The ALMA observations show that extended filaments of molecular gas are located along the peripheries of the radio bubbles, showing ordered molecular gas flows around. This suggest that the molecular clouds have been lifted directly by the radio bubbles or formed via thermal instabilities induced in low entropy gas lifted in the updraft of the bubbles.

Furthermore we used MUSE observations to map the ionized nebular components of the filamentary structures surrounding the core of the galaxy clusters. Its warm ionized and cold molecular components are both cospatial and comoving, consistent with the hypothesis that the optical nebula traces the warm envelopes of many cold molecular clouds that drift in the turbulent velocity field of the hot X-ray atmosphere.
Parker, Raeesa Title: Categorising protoplanetary disc asymmetries observed with ALMA
Abstract:
Observations with the Atacama Large Millimetre and Submillimetre Array (ALMA) have revealed a wide range of structure in protoplanetary discs. ALMA have observed discs surrounding young stellar objects in various stages of evolution; from Class 1 objects featuring circumstellar envelopes, outflows and a protoplanetary disc to Class 3 objects featuring only a debris disc with large regions devoid of gas and dust.

The wide range of structure in the protoplanetary discs include rings, famously seen in HL Tau; cavities, seen in LKCa15; and dust pile ups, observed surrounding the Herbig Ae star HD142527.

It is thought that the protoplanetary disc rings are formed as a protoplanet accretes gas and dust from the surrounding disc. However, the rings seen in HL Tau could not have been formed by a planet due to the young age of the system. This conclusion has raised a number of questions in regards to the different mechanisms that form asymmetries in protoplanetary discs. These formation mechanisms include: gravitational instabilities, dust settling and rapid pebble growth around condensation fronts.

We have explored the ALMA archive in search of protoplanetary discs that have a range of asymmetries. We have accumulated over 40 discs at various evolutionary stages featuring either dust traps, protoplanetary rings or large cavities.

Radial intensity profiles as well as surface density profiles have been calculated for each disc. Various parameters for each system have been found in the Literature including stellar mass, stellar temperature and system age. We have ordered the systems according to their ages in order to produce a classification model for the evolution of protoplanetary discs.

We plan to run radiative transfer simulations to model the various protoplanetary discs we have found. This will also be done in an attempt to distinguish between the various formation mechanisms of asymmetries in protoplanetary discs.
Popkov, Aleksandr Title: Relation between broad-band radio spectra and parsec-scale structure of extragalactic radio sources
Abstract:
We have conducted a joint analysis of total broad-band radio spectra and VLBI measurements for the complete sample of 502 extragalactic radio sources with declination >+75 degrees and flux density > 0.2 Jy selected from the NVSS catalogue at 1.4 GHz. The data of our VLBA Northern Polar Cap Survey were collected at 13 and 3.6 cm. We supplemented them by instantaneous 2-22 GHz continuum spectra obtained at RATAN-600. Properties of the structure at parsec scales, such as detections, core size, compactness, brightness and spectral index, were correlated against the form of integrated spectra (flat, steep, peaked, etc.). It allows us to analyze the fraction and properties of archetypal blazars, CSS, and GPS targets within the whole population of active galactic nuclei and make predictions of a fraction of detections expected for future blind VLBI surveys.
Rico, Fernando Title: Witnessing the early stages of the formation of Super Star Clusters in the nucleus of NGC253
Abstract:
Starburst galaxies efficiently convert large amounts of gas and dust into stars in their nuclei in very short time scales, 10^7 - 19^8 years. A large fraction of the star formation is believed to occur in Super Star Clusters (SSC). SSCs are compact, with sizes of ~1pc, massive (~10^5 Msun) and young (from few to 100 Myears).
Understanding the formation and evolution of SSCs is crucial to determine the conditions leading to the emergence of the starburst and also to
evaluate the effect of their associated radiative and kinematic (superwinds) feedback on the evolution of Galaxies. In the Galaxy, the earliest phase (< 10^5 years) of massive star formation in clusters (protoclusters) is commonly recognised as very compact (0.02 - 0.1 pc), hot (200-300 K), and dense condensations (~10^7 cm^-3), known as Hot Cores - HCs. We have used 0.2" ALMA images of the HC3N vibrational excited emission (HC3N*) to reveal the Super-Hot Core (SHC) phase
associated to Super Star Clusters (SSCs) in the nearby starburst galaxy NGC253. HC3N* emission is a direct probe of unobscured
mid-IR emission since it is radiatively pumped by the dust heated by the protostars. The detected 6 unresolved SHCs with
temperatures >230 K and high densities are tracing the proto-SSC phase just before massive stars ionise their surroundings. We
estimate that proto-SSCs account for more than 1/3 of the total luminosity of the galaxy. However, our estimates are still very rough
and better resolution and sensitivity are required to make robust estimates of the luminosities.
Ryan, Aoife Maria Title: IMAGING THE SOLAR CORONA DURING THE MARCH 2015 SOLAR ECLIPSE AT LOW FREQUENCIES USING LOFAR
Abstract:
Abstract
The solar corona is a highly-structured plasma which reaches temperatures of more than ~2MK. At low radio frequencies (? 400 MHz), scattering and refraction of electromagnetic waves are thought to broaden sources to several arcminutes. Previous observations (Gary et al., 1987 & Kathiravan et al., 2011) have found evidence for spatial scales of less than 1 arcminute, however these remain unconfirmed. Here, we investigate these small spatial scales by using the LOw Frequency ARray (LOFAR) to image the corona during a solar eclipse >80% totality, on 20 March 2015. The Sun was imaged using the High Band Antennae of 23 of LOFAR’s core stations giving a maximum baseline of approx. 3.5km. We present an initial analysis detailing interferometric imaging of the radio corona using multi-frequency synthesis techniques.

Co-authors:
Aoife M. Ryan1,2, Peter T. Gallagher1 , Michiel A. Brentjens3, Eoin P. Carley1, Diana E. Morosan4,1, Pietro Zucca3, Christian Vocks5, Max Gueret1.

1Trinity College Dublin, Ireland.
2Astrotec Holding B.V., the Netherlands.
3ASTRON, the Netherlands.
4University of Helsinki, Helsinki, Finland.
5Leibniz-Institut für Astrophysik, Potsdam, Germany.
Sanchis, Enrique Title: Modeling Circumstellar disk observations for effective radii determination
Abstract:
In this work we determine the effective radii of dusty planet forming disks in Lupus, from ALMA observations at 890um. Our sample spans from disks around young solar mass analogues down to substellar objects.
We use an efficient visibilities fitting package (GALARIO, Tazzari et al 2018) to model each disk with various brightness profiles (Nuker profile, Broken powerlaw, and power law with exponential cut-off) and derive the effective emission radius for each disk. For each circumstellar disk we fit in the uv-plane its observational data with each model. We compare the results of these models with previous analysis based on fitting a radiative transfer models to each disk, using the two-layer approximation model. The advantages of our approach is that it does not make assumptions on the physical structure of the disk, which is instead required for the radiation transfer. Additional tests are carried out to determine the quality of the fit using the different brightness profiles and the physical model.
Shevchuk, Mykola Title: Comparative analysis of the solar decameter spikes and striae
Abstract:
Solar fine structured bursts, stria and spikes, have been known since the beginning of 60th. These bursts are observed in the wide frequency band from GHz to some MHz during high solar activity. Independently from the frequency range spikes and striae reveal short durations and narrow bandwidths. However, there is one essential difference between them - while spikes are randomly located on a dynamic spectrum, striae are grouped into the chains drifting from high towards low frequencies forming Type IIIb bursts.
Up to nowadays spikes and striae in the decameter range have not been studied well because of the lack of the observational data in the relatively wide frequency band with sufficient temporal and frequency resolutions. After equipment of the UTR-2 radio telescope with the new receiver DSP-Z a possibility to observe and analyze different solar radio bursts in continuous frequency band 8 - 32 MHz with high temporal (100 ms) and frequency (4 kHz) resolutions appeared.
Detailed analysis of the decameter spikes and striae observed on 14 June 2012 showed that at certain frequency they have close values of the durations and bandwidths. For example, at frequency 25 MHz spikes and striae average durations are 0,65 s and 0,62 s, and bandwidths are 50 kHz and 53 kHz respectively. We also found that spikes and striae durations decrease and bandwidth increase with the frequency.
We conclude that both spikes and striae durations are determined by the temperature of the ambient coronal plasma and bandwidth by the magnetic field in the place of bursts generation based on the obtained results and in the frames of plasma emission mechanism.
We also come to conclusion that decameter spikes and striae most probably the same type of bursts, however, the question concerning their location on the dynamic spectrum still remains open and needs further study.
Steinbergs, Janis Title: First VLBI maser observations in Irbene - Torun baseline
Abstract:

Janis Steinbergs, Vladislavs Bezrukovs, Ivars Shmelds, Karina Skirmante, Artis Aberfelds, M?rcis Bleiders, Art?rs Orbid?ns, Marcin Gawro?ski, Roman Feiler

Ventspils International Radio Astronomy Centre (VIRAC, Latvia) operates with two radio telescopes RT-16 and RT-32 accordingly with 16 and 32 m fully steerable Cassegrain type antennas. The main receiving systems of both telescopes are cryogenic receivers with 4.5 – 8.8 GHz frequency range, additionally radio telescope RT-32 is equipped with L band receiver. On the both antennas data registration units are suitable for interferometric observations. VIRAC also has a high performance computer cluster with installed SFXC software correlator developed at JIVE.
The Department of Radio Astronomy of Nicolaus Copernicus University in Torun, Poland, operates 32 m radio telescope, which also works in similar bands – L, K, C and M and regularly participates in the VLBI observations.
Since March 2018 there were conducted three VLBI observations. On the 3rd observation data correlation returned first fringes on baseline Irbene – Torun, where observation was prepared by VIRAC staff from scheduling to data processing on VIRAC HPC using JIVE SFXC correlator. In this VLBI observation there were used setup like the EVN Network Monitoring Experiments (NME): 2 polarization, 16 channels 8 MHZ bandwidth. As targets sources were selected 2 strong calibrators with extended emission (3C84, 3C123) and one strong OH maser source (W3OH).
Results of VLBI test observations on baseline Irbene – Torun are discussed. Overview of VIRAC current level in the software developments related to the VLBI data processing is also given. And brief talk about possible scientific use of interferometric maser observation with baseline Irbene – Torun is presented.
Talebpour Sheshvan, Nasrin Title: Study of the Directivity of Compact Interplanetary Radio Type IV Bursts
Abstract:
Recently, we have analyzed interplanetary type IV radio bursts at decameter-hectometer (DH) wavelengths to find out their source origin and to explain their observed directivity. The events occurred in 2011-2012 when STEREO A, STEREO B, and Wind spacecraft were located approximately 90 degrees apart from each other, providing a 3D view of the Sun. In some of the events, we have observed metric type IV radio bursts in the low corona, from a direction where the DH type IV emission was not
detectable in their higher location. Our studies include data analysis of the different eruptive phenomena, and we have compared and listed the characteristics of white-light and extreme ultraviolet (EUV) observations of flares, EUV waves, and coronal mass ejections (CMEs)
with the radio data. We found out that strong and compact type IV radio bursts are observed when EUV waves propagate globally across the whole visible disk and are associated with halo-type, fast CMEs. The Potential Field Source Surface (PFSS) models provide us with a good approximation of the structure and evolution of the magnetic field. The combined data and modeling give us a better understanding of the particle acceleration mechanisms, as the emission in type IV bursts can
contain both plasma and synchrotron emission. We suggest that one possibility for the directivity effects in these events may be absorption. The absorption - or suppression of emission - would be caused by the higher density plasma located at the radio type II burst shock fronts.
We found that the type II bursts were most probably created by shock-streamer interactions as streamers were present in each of the analyzed events and they were located at the flanks of the CMEs. Therefore, in this study, we discuss the different interpretations by using the confirmed conditions for the observed directivity.
Tang, Hongming Title: Convolutional Neural Network for Giant Radio Galaxy (GRG) Identification
Abstract:
GRGs historically have been poorly detected due to a combination of poor surface brightness sensitivity, the field of view limits and a tendency to build telescopes at higher frequencies due to technical limitations. In radio galaxy evolution models, GRGs are thought to represent the end of the evolutionary process. They are also believed to serve as a probe of the low-density IGM. Building a statistically meaningful sample of GRGs, therefore, is essential. My Ph.D. project initially looked at machine learning based object in radio survey data (e.g., FIRST, NVSS) using convolutional neural networks (CNN). Later, this object detection will be combined with multi-wavelength analysis to better identify giants (> 1 Mpc) radio galaxies.
Timirkeeva, Maria Title: Radio pulsars with expected gamma-ray radiation and gamma-ray pulsars as pulsating radio emitters
Abstract:
The discovery of pulsars in the XX century is one of the most significant results of modern astrophysics and radio astronomy. Pulsars are unique astrophysical laboratories with super-strong magnetic fields and densities of order of nuclear ones, created by nature to solve a wide range of physical and astrophysical problems. At present, more than 2500 pulsars are included in the ATNF online-catalog. They radiate in the radio range usually, but the space telescope Fermi with LAT have detected over 117 new gamma-ray pulsars. It was shown by Malov and Timirkeeva (ASP Conference Series, Vol. 510, P. 498, 2017) that radio pulsars detected as pulsed gamma-ray sources, are characterized by high magnetic fields at the light cylinder, two or three orders of magnitude larger than values for quiet radio pulsars. Moreover, losses of rotational energy for these objects are also three orders of magnitude higher than the values for the bulk of radio pulsars. Earlier, we found a correlation between the gamma-ray and radio luminosities (Malov and Timirkeeva, arXiv:1712.06990, 2017). The high values of the losses of rotational energy and magnetic field at the light cylinder are the main criteria for search for new pulsed sources. A common table contains radio pulsars, whose gamma-ray radiation has not been detected yet, but it is possible. On the other hand, there are sources in the catalog of gamma-ray pulsars, which are not known as radio pulsars. Some of them have a large gamma-ray luminosity and, in accordance with the obtained correlation, we can expect radio emission from them. We proposed the program to search for these pulsars by the most sensitive in the world at meter range (111 MHz) BSA telescope (Pushchino Radio Astronomical Observatory) with an effective area of 45,000 m^2 and the sensitivity of 100 mJy.
Traianou, Thalia Title: Resolving the Innermost Jet Region of Radio Quasars 3C454.3 and TXS 2013+370
Abstract:
Blazars are among the most powerful and variable known astrophysical objects. The very long baseline interferometry (VLBI) technique provides the opportunity to directly look deep into the heart of these compact objects and probe the physical processes that occur in close vicinity to the central engine. In this talk, we will present new results from (1) a kinematic and polarization study of the quasar 3C454.3, and (2) a case study of the gamma-ray flaring events which occurred in the compact blazar TXS 2013+370 during the period 2003-2017. The latter allows us to give an estimation of the high energy emission location.
Vyas, Charitarth Title: Fuel for the Milky Way star formation: Tracing the high Galactic latitude molecular clouds
Abstract:
To form stars persistently along Gyrs, it is widely accepted that the Milky Way Galaxy accretes pristine gas (G-dwarf problem) from its environment. Various accretion channels are proposed in the literature. One of them, the Galactic fountains e.g. are thought to intermix disk and halo gas, replenishing the disk with the required sub-solar metallicity gas.

In this talk, I will present a study we have conducted towards two proto-typical high Galactic latitude clouds, Draco and Spider to understand this channel. The radial velocities of these clouds imply that they are approaching the Galactic disk and eventually could fuel the star formation in future. We focus on the two most important tracers of the interstellar medium - dust, and gas - in this project. Multi-wavelength single dish and radio interferometric studies supplement our analyzes. It allows identifying compact cold gas condensations already forming molecular hydrogen out of the gaseous phase. Estimating dust temperature, V_lsr, volume density, surface mass density, linear size, and other relevant physical parameters allow constraining the current physical conditions of this high altitude clouds. I will also talk about our very recent Pico-Veleta CO observations disclosing the content of CO-dark gas in these clouds.

 

 

 

E-mail: yerac2018@jive.eu