Ecogia Science Meetings
Past Ecogia Science Meetings (2021-2022)
Past science meeting calendars, abstracts, and slides can be found at the following links:
Ecogia Science Meetings 2021-2022
Schedule
Meetings are at 14 in the Pavillon meeting room at Ecogia and on Zoom
2021-09-13 Skipped
2021-09-20 Skipped
2021-09-27 Dominique Eckert ** The gravitational field of X-COP galaxy clusters
The LambdaCDM model of cosmology makes clear predictions on the shape of collapsed halos in the Universe. The radial mass density profiles should follow a universal form across a wide range of halo masses and redshifts. Deviations from the predicted universal profile, if any, would provide us clues on fundamental properties of dark matter particles (e.g. self-interaction cross section, warm dark matter mass) and on any modification of the laws of gravity on large scales. Under the hydrostatic equilibrium assumption, precise constraints on the shape of galaxy cluster mass profiles can be obtained from a joint analysis of X-ray and Sunyaev Zel'dovich data. I will discuss how this technique can be used to determine the shape of the mass profiles across a wide radial range in the XMM Cluster Outskirts Project (X-COP). The resulting profiles will then be used to set new constraints on the dark matter self-interaction cross section and on possible modifications of the laws of gravity.
2021-10-04 Satoshi Fukami ** Very-high-energy gamma-ray emission from gamma-ray bursts
Gamma-ray bursts (GRBs) are the most luminous phenomena in the Universe that emit electromagnetic radiation.Although more than 50 years have passed since the discovery, fundamental aspects such as the mechanism of their relativistic jet formation are still under debate.The multiwavelength emission after the main burst is called afterglow, which is known to have temporal and spectral features predicted by a simple model of synchrotron emission with several parameters concerning the jets and their ambient medium. However, since the parameters vary widely and are sometimes not defined well, there are no strong constraints on the jet parameters.Thanks to the recent advance of Imaging Atmospheric Cherenkov Telescopes and the improved observation strategy, very-high-energy (VHE) gamma-ray emission above 50 GeV has been detected from a few GRBs since 2018. The emission mechanism of these GRBs in the VHE range turned out to be a new component since the accepted synchrotron emission cannot reach the VHE range due to the cooling of relativistic electrons.In this presentation, I will overview the analysis results of GRBs recently detected at the VHE range. Then I will describe new insights on the physical parameters obtained by the new emission component.
2021-10-11 Celine Armand ** Combined dark matter searches towards dwarf spheroidal galaxies with Fermi-LAT, HAWC, H.E.S.S., MAGIC, and VERITAS
Cosmological and astrophysical observations suggest that 85% of the total matter of the Universe is made of Dark Matter (DM). However, its nature remains one of the most challenging and fundamental open questions of particle physics. Assuming particle DM, this exotic form of matter cannot consist of Standard Model (SM) particles. Many models have been developed to attempt unraveling the nature of DM such as Weakly Interacting Massive Particles (WIMPs), the most favored particle candidates. WIMP annihilations and decay could produce SM particles which in turn hadronize and decay to give SM secondaries such as high energy rays. In the framework of indirect DM search, observations of promising targets are used to search for signatures of DM annihilation. Among these, the dwarf spheroidal galaxies (dSphs) are commonly favored owing to their expected high DM content and negligible astrophysical background. In this work, we present the very first combination of 20 dSph observations, performed by the Fermi-LAT, HAWC, H.E.S.S., MAGIC, and VERITAS collaborations in order to maximize the sensitivity of DM searches and improve the current results. We use a joint maximum likelihood approach combining each experiments individual analysis to derive more constraining upper limits on the WIMP DM self-annihilation cross-section as a function of DM particle mass. We present new DM constraints over the widest mass range ever reported, extending from 5 GeV to 100 TeV thanks to the combination of these five different -ray instruments.
2021-10-18 Stephane Paltani ** RefleX 3.0 and beyond
RefleX is a generic X-ray photon tracing code that implements mostphysical processes in cold matter irradiated by a source of X-rays.RefleX has been primarily designed to model X-ray emission of AGN, butit can be used for any X-ray source where surrounding cold matter ispresent. Matter is distributed in a number of independent user-specifiedbuilding blocks, so that the geometrical distribution and composition ofmatter can be practically arbitrary, so that RefleX can generaterealistic X-ray spectra of these objects, as well as images. Since thefirst release of RefleX, a number of improvements have been implemented.RefleX 3.0 is now ready and will be released as soon as the accompanyingpaper is submitted. I will present the new functionalities that havebeen implemented since the original version, and show some recentresults obtained with RefleX. Finally, I will describe ideas for Reflex 4.0.
2021-10-25 Holidays
2021-11-01 Will Hartley ** The Spectral Energy Distributions of Faint Galaxies
The Euclid mission will survey more than 1 billion galaxies in order to characterise the impact of Dark Energy on the expansion history of the Universe though weak lensing cosmic shear. In order to make best use of the photons that reach the telescope from each galaxy, and maximise measurement signal-to-noise, the passband that will be used for shape measurement is very broad. Being a relatively small space-based telescope, the Euclid PSF through this passband is wavelength dependent, and we must therefore know the spectral energy distribution (SED) of each galaxy that enters the analysis. I will discuss some of the challenges and early work we are doing in trying to make these estimates and solve what could become our most difficult challenge in the Geneva OU-PHZ group.
2021-11-08 Volodymyr Savchenko ** Knowledge Graphs
Knowledge Graphs offer a form of modeling, representation, and communication of diverse data. They consist of collections of connected entities, constrained and driven to evolve by specially designed rules. They may be also seen as collection of logical propositions with an ontology and inference rules.Knowledge Graphs were proposed early on by authors of the world wide web as an open standard to improve on the web's structure. At that time, this initiative did not gain sufficient traction, but some private developments leveraged similar technology to develop revolutionary business insights which aided them in achieving market dominance. In the last few years, developments and exploitation of open linked knowledge graphs has re-energized, owing to evolution of underlying technologies and increasing need of FAIR knowledge stewardship.Knowledge graphs (or their elements) are becoming somewhat widely used, only at UNIGE multiple groups in different departments adopted them as principal data knowledge representation tool. We have also adopted elements of Knowledge Graphs in many of our scientific and supporting activities. Our common project with Swiss Data Science Center at EPFL focuses on leveraging the knowledge graph developed by SDSC. We use knowledge graphs (coordinated with more widely known databases) where we face the challenge of storing and communicating diverse, complex, and interconnected data: in the database of reproducible cross-calibration workflows, in communicating multi-messenger transient events, and in INTEGRAL quick look analysis activities. I find that this approach is valuable for creating, communicating, and effectively exploiting more clear representation of our idea of what we know.
2021-11-15 Marc Audard ** The Square Kilometer Array Observatory
The SKAO will be the worlds largest radio telescope, with eventually over a square kilometre (one million square metres) of collecting area.It will eventually use thousands of dishes and up to a million low-frequency antennas that will enable astronomers to monitor the sky inunprecedented detail and survey the entire sky much faster than any system currently in existence. It will also have the ability to image hugeareas of sky in parallel a feat which no survey telescope has ever achieved on this scale with this level of sensitivity. With a range of otherlarge telescopes in the optical and infra-red being built and launched into space over the coming decades, the SKA will perfectly augment,complement and lead the way in scientific discovery. Switzerland has recently become a member of SKAO through its leading house, EPFL,and should become next year a full member until 2030. I will present the main technical and scientific capabilities of SKAO and will showthe interests and activities in the different partners in Switzerland.
2021-11-22 Skipped
2021-11-29 Guillaume Desprez ** Photometric redshifts
Photometric redshifts (photo-zs) are an important tool on which are based large extragalactic and cosmological studies. Surveys like DES or HSC-SSP, and soon Euclid and LSST have to measure accurately photo-zs for millions/billions of sources to reach their science goals. The requirements on the photo-z quality set for the success of the Euclid mission are tight and provide a difficult challenge for the photo-z team. I will present my work on the different project I participated on during my PhD as part of the Euclid photo-z team. I will talk about the Euclid photo-z challenge, the exploration of the limits of the Euclid photometry and my work on the validation of the Euclid template fitting software : Phosphoros
2021-12-06 Roland Walter ** Resolving Accretion Disks with Quantum Optics
--
2021-12-13 Philipp Schuler ** Scaling intensity interferometry to higher frequencies with Xilinx RFSOC.
In continuation of Roland Walters talk about Quantum optics, I will present my Masters project to implement the correlation logic used in intensity interferometry onto a high-speed FPGA (Xilinx RFSoC). The goal of this project is to be able to do correlations between multiple sources on dedicated high speed hardware to allow for quicker calculations to increase sampling frequency and/or input channels.
2021-12-20 Fiona Hubert Martrou ** Rotating shutter design for the EQUATOR instrument
I will present the process I followed, from the technical choices to the tests of the prototype, while passing by the work done on the CATIA software.
2021-12-27 Holidays
2022-01-03 Holidays
2022-01-10 Holidays
2022-01-17 Holidays
2022-01-24 Skipped
2022-01-31 Nicolas Produit ** Practical calculation of correlations
Philipp Schuler did his EPFL diploma work in Electrical engineering in our group.He implemented fast real time calculation of correlation using our HTG acquisition card.I will explain the exact calculation and the challenges and show someresults about performances and noise scaling.
2022-02-07 Andrea Tramacere ** Radio-gamma ray response in blazars as a signature of adiabatic blob expansion: a self-consistent approach
Multiwavelength light curves in long-term campaigns have shown that, for several blazars, the radio emission occurs with a significant delay w.r.t. to gamma ray band, with timescales ranging from weeks to years. Such observational evidence has been a matter of debate for years and usually is interpreted as a signature of the gamma ray emission originating upstream in the jet, with the emitting region becoming radio transparent at larger scales. In this paper, we show, by means of self-consistent numerical modelling, that the adiabatic expansion of relativistic blob can explain these delays. We use the JetSeT framework to reproduce the numerical modelling of the radiative/accelerative processes, reproducing the temporal evolution, from the initial flaring activity, and the subsequent expansion. We follow the spectral evolution and the light curves, investigating the relations among the observed parameters, rise, time, and decay time, identifying the link with the physical parameters. We find that, when adiabatic expansion is active, lags due to the shift of the synchrotron frequency occur, with an offset equal to the distance in time between the flaring onset and the beginning of the expansion, whilst the rising and decaying timescales depend on the velocity of the expansion and on time required to the source to exhibit a synchrotron self-absorption frequency. We derive an inter-band response function, and we investigate the effects of the competitions between radiative and adiabatic cooling timescales on the response. We apply the response function to long-term radio and gamma ray light curves of Mrk 421, Mrk 501 and 3C 273, finding a satisfactory agreement on the log-term behaviour, and we use a Monte Carlo Markov Chain approach, to estimate some physical relevant parameters. We discuss the applications to polarization measurements, and to jets collimation profile kinematics.
2022-02-14 Devina Misra ** Formation of Ultraluminous X-ray binaries
Observations of anomalous sources help in our understanding of stellar and binary evolution. Ultraluminous X-ray sources (ULXs) are bright X-ray binaries that exceed the Eddington limit of stellar-mass black holes (10^39 erg/s). X-ray pulses show that some of them even have accreting neutron stars (pulsating ULXs). The Eddington limit of the neutron stars (10^38 erg/s) makes pulsating ULXs very difficult to explain by classical accretion physics. There are many ideas proposed to explain these sources. Using POSYDON, a new framework that combines the computational benefits of rapid binary populations synthesis codes and the detailed calculations of stellar/binary evolution codes, we generate multiple populations of X-ray binaries and study their evolution. We get the observed luminosities of the binaries in the X-rat binary phase from grids of detailed simulations and compare them to HMXB observations.
2022-02-21 Holidays
2022-02-28 Holidays
2022-03-07 Xing Zapei ** ON THE FORMATION OF BLACK HOLE NEUTRON STAR BINARY
The two black hole neutron star (BHNS) merger events GW200105 and GW200115 provide us with new constraints on the evolution and formation physics of BHNS systems. In this work, we perform a binary population synthesis (BPS) study on the BHNS mergers with the novel BPS code POSYDON, which incorporates extensive detailed stellar and binary evolution grids. with detailed evolution of both binary components, we display the evolutionary paths of individual BHNSs from different formation channels. We present the result from our simulation and explore the effect of variations in the common envelope evolution and supernova explosion. We find that at solar metallicity, the majority of merging BHNSs have a BH mass less than 15M and a chirp mass less than 4.5 M. We estimate the local merger rate density of BHNSs is in the range 30.52121.08 Gpc^3 yr^1.
2022-03-14 Hangcheng Li ** Measuring the Cosmic X-ray Background accurately
The Cosmic X-ray Background (CXB) dominate the X-ray fluxes over the sky, as it is believed to be a superposition of numerous discrete sources, which are primarily Active Galactic Nuclei (AGNs). The CXB intensity therefore offers an unique probe to study the AGN population. Limited by background modeling and (cross) calibration issues, the uncertainty of the CXB measurements remain currently an order of 20 per cent on its normalization. In this context, a dedicated CXB detector is needed to measure the CXB accurately. We present here the concept, simulated performances and science goals of the EQUATOR CXB detector, which is mainly consist of an array of collimated spectrometers with a rotating shutter on top of the aperture. With two years operation in space, such a detector could measure the CXB with ~1 per cent uncertainty in 10-100 keV energy range, and thus gain us knowledge of the accretion power in the Universe.
2022-03-21 Carlo Ferrigno ** Exploring wind accretion in HMXB with XMM-Newton and Swift/XRT
Wind-fed supergiant X-ray binaries are precious laboratories not only to study accretion under extreme gravity and magnetic field conditions, but also to probe still highly debated properties of massive star winds. These includes the so-called clumps, originating from the inherent instability of line driven winds, and larger structures as the corotating interaction regions.We will illustrate our results on on-going monitoring campaigns performed with XMM-Newton and Swift/XRT that started back in 2007 and that evenly sample the X-ray emission of supergiant X-ray binaries over several orbital cycles. By employing standardized techniques, we probe the presence of large scale structures in the medium surrounding the compact objects. These can be associated either to corotating interaction regions or to accretion/photoionization wakes, as well as tidal streams.
2022-04-04 Marco Tucci ** Validating the Euclid Photometric Redshift pipeline through the Scientific Challenge 8
One of the main goal of the Euclid mission is to understand the nature of dark energy by determining its equation of state. A sensitive probe of dark energy is the weak gravitational lensing. To perform weak lensing analysis Euclid will measure the photometric redshift of ~1 billion of galaxies. In the presentation I will describe the Euclid photo-z (PHZ) pipeline, developed by the team at Ecogia and aimed to produce photometric redshifts, emphasizing the challenges that the pipeline has to deal with.As the launch date is approaching, the Euclid Consortium organized a test campaign, the Scientific Challenge 8, to test and validate the full Euclid pipeline. The PHZ pipeline was involved in this campaign. I will show the main results, focusing on the performance of the photometric redshift computation with respect to Euclid requirements.
2022-04-11 Jakub Jurysek ** Full LST-1 data reconstruction with the use of convolutional neural networks
The Cherenkov Telescope Array (CTA) will be the world's largest and the most sensitive ground-based gamma-ray observatory in the energy range from a few tens of GeV to tens of TeV. To achieve the best performance in such a wide range of primary gamma-ray photon energies, the whole array will consist of Imaging Atmospheric Cherenkov Telescopes of three different sizes. The Large-Sized Telescopes (LSTs) are designed to be the most sensitive in the low-energy band of CTA. The LST-1 prototype, currently in the commissioning phase, was inaugurated in October 2018 in La Palma (Spain) and it is the first of the four largest CTA telescopes, that will be built in the northern site of CTA.The Random Forest method is currently employed in the reconstruction of the first data from the LST-1. This method, however, requires extensive preprocessing that includes signal integration and image parametrization, leading to the loss of information contained in the shower images. We will present a full-image reconstruction method using Inception deep convolutional neural network (CNN) applied on non-parametrized shower images.
2022-04-18 Holidays
2022-04-25 Skipped
2022-05-02 Federica Tarsitano ** Galaxy morphology and cosmological predictions for wide-field surveys analyses
Current and upcoming cosmological wide-field surveys use hundreds of millions of galaxy images to investigate the nature of dark matter, dark energy and large scale gravity. Their measurements lead to thriving research in the fields of Astrophysics and Cosmology. The large number of images they generate is an unprecedented source of information to study the cosmic evolution of galaxies with enhanced statistical power. In particular, they provide information about the shape and the internal structure of galaxies. In order to extract it from such large data sets researchers need to develop and optimize dedicated and automated algorithms. Those surveys have also opened the era of Precision Cosmology, where measurements need to be interpreted with theoretical predictions which are equally precise. Thus we need numerical frameworks able to predict cosmological quantities accurately and fast. These two applications, the morphological classification of galaxies, which are tracers of the evolution of the Universe, and the study of the prop- erties of the Universe as a whole, complement each other and are the two main topics of this talk.First, I will present the structural and morphological catalogue for first year dataset of the Dark Energy Survey, and its application in a collaborative work to study the properties of NGC 4993, the host Galaxy of the gravitational wave event detected in August 2017. I will proceed exploring a novel approach to classify galaxy images, combining isophotal fitting and ML algorithms. Finally, I will present PyCosmo, a Python-based framework providing accurate theoretical predictions for cosmological observables.
2022-05-09 Skipped
2022-05-16 Berry Holl ** Scan-angle dependent signals in Gaia
The ESA Gaia mission is observing over a billion sources up to magnitude ~21 during its (currently extended) mission of perhaps up till 10 years, re-observing each source on average about 70-140 times.Observations made by the rotating spacecraft are mainly along the direction of rotation, also called along-scan. Even though Gaia has Hubble-like resolution, binaries and the compact centres of galaxies are frequently at spatial scales comparable to the diffraction limit and pixel size of the instrument, causing (partially) unresolved images to be recorded. The image parameter determination procedure (that estimates flux, centroid, and background levels) is generally matching the recorded images against single-star PSF and LSF profiles and thus can produce biassed estimations. These biases are dependent on the difference of the position angle (i.e. the line connecting two stars, or the long axis of a galaxy) and the angle of the scanning direction of the satellite. Due to the changing scan direction angles of the satellite for each observation, the observation biases can introduce artificial signals. Due to the temporal and geometric pattern of the scanning law, this can translate in the spurious detection of periodicity in the Gaia photometric/astrometric and radial velocity data, as well as other derived parameters like parallax. In this talk we will highlight several aspects of this problem, which will be discussed in more detail in an upcoming DR3 DPAC publication.
2022-05-23 Vitali Sliasur ** Multi-wavelength variability of blazars: radio-gamma ray response
The study of long-term multi-wavelength variability properties in blazar jet has the potential to shed light on the particle acceleration and emission mechanisms. Blazars' jets emit non-thermal Doppler-boosted radiation across the electromagnetic spectrum from radio to gamma rays. The spectral energy distribution of these sources has a characteristic broad two-hump structure. One hump, typically peaking in IR-optical-UV, is associated with the synchrotron emission from relativistic electrons. The other hump typically peaks in gamma rays, with leptonic (Inverse Compton) or/and hadronic emission processes. A distinctive feature of the emission is that the radiation of different wavelengths has a different relative lag. Using multi-wavelength long-term data for bright blazars Mrk 421, Mrk 501 and 3C 273, we investigate the correlations and find the delays between the light curves. We employ an adiabatic relativistic blob expansion model to explain the delay between the radio and the gamma-ray emission. We identify the main physical drivers of the delay and derive the response function, which can be used to reproduce the delayed radio flare as a response to the -ray flares. We find that the observed long-term emission variability timescales are generally compliant with the ones expected from the leptonic scenario.
2022-05-30 Matteo Balbo ** --
--
2022-06-06 Holidays
2022-06-13 Lorenzo Rimoldini ** --
--
2022-06-20 Nami Mowlavi ** --
--
| Title | Filename | Size |
|---|---|---|
| Science-Meeting-Presentations | Science-Meeting-Presentations |