Past Ecogia Science Meetings (2022-2023)
Past science meeting calendars, abstracts, and slides can be found at the following links:
February - July 2019
September 2019 - July 2020
September 2020 - July 2021
September 2021 - July 2022
Ecogia Science Meetings 2022-2023
Schedule
Meetings are at 14 in the Pavillon meeting room at Ecogia and on Zoom
While cosmological and astrophysical probes suggest that dark matter would make up for 85% of the total matter content of the Universe, the determination of its nature remains one of the greatest challenges of fundamental physics. Assuming the LambdaCDM cosmological model, Weakly Interacting Massive Particles would annihilate into Standard Model particles, yielding gamma-rays, which could be detected by ground-based telescopes. Dwarf spheroidal galaxies represent promising targets for such indirect searches as they are assumed to be highly dark matter dominated with the absence of astrophysical sources nearby. Previous studies have led to upper limits on the annihilation cross-section assuming single exclusive annihilation channels. In this work, we consider a more realistic situation and take into account the complete annihilation pattern within a given particle physics model. This allows us to study the impact on the derived upper limits on the dark matter annihilation cross-section from a full annihilation pattern compared to the case of a single annihilation channel. We use mock data for the Cherenkov Telescope Array simulating the observations of the promising dwarf spheroidal galaxy Sculptor. We show the impact of considering the full annihilation pattern within a simple framework where the Standard Model of particle physics is extended by a singlet scalar. Such a model shows new features in the shape of the predicted upper limit which reaches a value of = 3.8 x 10^-24 cm^-3.s^-1 for a dark matter mass of 1 TeV at 95 % confidence level. We suggest considering the complete particle physics information in order to derive more realistic limits.
Cross-matching data stored on separate files is an everyday activity in the scientific domain. However, sometimes the relation between attributes may not be obvious. The discovery of foreign keys on relational databases is a similar problem. Thus techniques devised for this problem can be adapted. Nonetheless, when the data is numeric and subject to uncertainty, this adaptation is not trivial. This paper firstly introduces the concept of Equally-Distributed Dependencies, which is similar to the Inclusion Dependencies from the relational domain. We describe a correspondence in order to bridge existing ideas. We then propose PresQ: a new algorithm based on the search of maximal quasi-cliques on hyper-graphs to make it more robust to the nature of uncertain numerical data. This algorithm has been tested on seven public datasets, showing promising results both in its capacity to find multidimensional equally-distributed sets of attributes and in run-time.
Since its launch in October 2002, the INTEGRAL mission has provided a nearly continuous stream of telemetry, that, after an on-the-fly processing, provides the end-user with near-real-time data (NRT). Given its maturity, a great amount of archive data is currently available: this allowed us to build a gallery of standard products that enables a user to explore in an easy and quick way INTEGRAL products of different kind. I will present a first implementation of the gallery, its major features, along with the strategy we have put in place for its population.
Observational extra-galactic analyses are increasingly dependent on the support of simulated data sets to test the software used and explore sources of systematic errors. This is particularly true for modern wide-field galaxy surveys, where pipelines need to be developed in advance of data collection and variation in survey conditions can imprint false signals in our data sets in a scale-dependent way. Alongside this growing need is the developing field of simulation-based inference (SBI). Coupling high-performance computing with efficient generation algorithms, SBI circumvents the often ill-posed inverse problems that are so common in astronomy. I will introduce a new software project, SkyPy, that is designed to be used for these two tasks. Inspired by astropy, it is intended to be open and community driven, based on scientific needs. In the talk I will cover the basic galaxies module and population tuning.
In spite of its numerous successes, the LambdaCDM model of cosmology is fundamentally incomplete, in the sense that 95% of the postulated matter-energy content is in an unknown form. Specifically, the LambdaCDM model postulates the existence of an unknown matter component, dubbed dark matter, which outweighs all the normal matter content of galaxies by a factor of 5-6. The gravitational effects of dark matter can be studied exquisitely well by observing the dynamics of the most massive structures in todays Universe - galaxy clusters. In this respect, deep X-ray observations of nearby galaxy clusters play a key role in our understanding of the gravitational field of collapsed halos. Indeed, galaxy clusters are filled with a hot, tenuous plasma - the intracluster medium (ICM) - which contains the vast majority of their baryons and shines predominantly in X-rays. The pressure exerted by the hot gas equilibrates the gravitational force, such that the total enclosed mass can be derived point-by-point from the thermodynamic properties of the ICM. I will described what can be learned from the gravitational field of galaxy clusters on the properties of the postulated dark matter, with an emphasis on several recent studies focusing on the thermodynamic properties of 12 massive, nearby systems. I will show how such observations can be used to constrain the self-interaction cross section of dark matter and how the measured gravitational field sets constraints on modified gravity theories. Finally, I will describe what can be done to improve the accuracy of our measurements, with a focus on weak gravitational lensing and X-ray micro-calorimeters.
Symbiotic X-ray binaries are systems hosting a neutron star accreting form the wind of a late type companion. These are rare objects and so far only a handful of them are known. One of the most puzzling aspects of the symbiotic X-ray binaries is the possibility that they contain strongly magnetized neutron stars. These are expected to be evolutionary much younger compared to their evolved companions and could thus be formed through the (yet poorly known) accretion induced collapse of a white dwarf. In this paper, we perform a broad-band X-ray and soft -ray spectroscopy of two known symbiotic binaries, Sct X1 and 4U 1700+24, looking for the presence of cyclotron scattering features that could confirm the presence of strongly magnetized NSs. We also report about our long-term monitoring of the last discovered symbiotic X-ray binary IGR J173292731 performed with Swift/XRT. The monitoring revealed that, as predicted, in 2017 this object became a persistent and variable source, showing X-ray flares lasting for a few days and intriguing obscuration events that are interpreted in the context of clumpy wind accretion.
2022-12-05 00:00:00 TBD
The apparent fluence of GRB221009A was an order of magnitude larger than the next brightest extragalactic burst. Even if its intrinsic luminosity may be comparable to that of the other intense GRBs, its unusually nearby location allows us to scrutinize a powerful ultra-relativistic jet in unprecedented detail. I will review what is known so far about the available observations, and their impact.
2022-12-19 00:00:00 TBD
2022-12-26 00:00:00 Holidays
2023-01-02 00:00:00 Holidays
2023-01-09 00:00:00 Holidays
I will present the first and preliminary outcomes of a project to characterized the energy-dependent emission of magnetized X-ray binaries folded at their spin frequency, the so-called pulse profiles. We collected all the observations performed on this class of sources with the NuSTAR observatory, apply a consistent reduction pipeline and investigate recurrent features. At first, we focused on the pulsed fraction and find that there are local reduction of this quantity in correspondence of line-like features in the energy spectrum, namely iron fluorescence and cyclotron resonance scattering features. We also find a general increasing trend of the pulsed fraction with energy and a change of slope around 10--20 keV.
Recently, several gamma-ray bursts (GRBs) have been detected in a new energy window of the sub-TeV very-high-energy (VHE) gamma-ray energy range by ground-based experiments such as MAGIC, H.E.S.S., and LHASSO. The new information in this energy range provides additional insights into unknown aspects of GRBs. VHE emission from at least some GRBs is consistent with synchrotron self-Compton emission inside the shock between relativistic ejecta and ambient medium, however, we need more statistics to further constrain emission mechanisms. In this talk, I summarize the current understanding of the TeV-emitting GRBs including GRB 201216C, which is the most distant source in the VHE energy range. I also mention the prospect of expected results from future experiments.
Current and upcoming weak lensing surveys require accurate estimation of the PSF for precise measurements of galaxy shapes. In the case of a diffraction-limited telescope like Euclid, the PSF is wavelength dependent, therefore we need accurate knowledge of each galaxys SED. Even in a field as rich in multi-band data as COSMOS, the SEDs lack wavelength coverage, especially at the red end of the spectrum. This might lead to biases in estimates of cosmological parameters. In order to prevent it, we need to enrich the wavelength sampling and thereby obtain more accurate SEDs.
In this talk we will explore various methods for flux reconstruction, distinguishing between those that are physics-driven, like template fitting, from those that are purely data-driven. In the latter, known data points are interpolated through regression techniques such as Gaussian Processes, Random Forest and K-Nearest Neighbours. Despite the bias on simulated fluxes being less than 1% in both approaches, accuracy decreases when working with more complex simulations and real data. We will provide a summary of the current findings and discuss possible methods for improvement.
The upcoming wide-field depth surveys like Euclid will detect a large
number of new AGN. Accurate templates of the AGN spectral energy
distribution (SED) will be fundamental for their identification, for
the redshift determination, and for studying their physical
properties. Currently, AGN templates are derived (i) empirically from
observations or (ii) from theoretical models. Empirical templates
provide a simple parametrization, but may be not representative of all
AGN. Theoretical models better describe the diverse AGN emissions, but
they may be difficult to constrain due to the large number of
parameters.
In this talk I will present a phenomenological approach to model the
SED of type1 QSOs at UV/optical/NIR wavelengths, with the aim to
reproduce the observed variety of spectra using a small number of
physical parameters. At UV/optical I will show that most of spectra of
SDSS quasars can be well fitted by the Polletta+07 QSO template if
internal reddening and host galaxy contribution are taken into
account. The model is extended to NIR wavelengths by including thermal
emission from hot dust. I will discuss the relevance of the model and
I will conclude with a comparison between observed and modelled colors
of SDSS quasars.
Astronomical polarimetry, as a new observational window among others (timing, spectroscopy, imaging, etc.), constrains directly the magnetic field configurations and emission geometries of X-/- ray sources, and is thought to be a unique diagnostics for the theoretical modeling of them. In this talk, I will briefly introduce you to current polarization measurements of a few types of sources in the eras of both POLAR/POLAR-2 and IXPE, and their physical implications.
For the upcoming dark energy survey project, Euclid will scan 15,000 deg2 of the sky and cover wavelengths from visible to infrared. This will include about 10 billion sources, of which 1 billion will be used for weak lensing measurement. Euclid aims to achieve 1% precision in the measurement of w, a parameter related to dark energy. In order to achieve this ambitious goal, the precision of photometric redshift, especially the photometric redshift tomographic bins, plays a pivotal role in the Euclid project. In this talk, I will introduce a novel method for calibrating photometric redshifts. This method could be used in other astrophysics research areas, such as galaxy clustering and object classification.
Outreach part:
I am a public science video content creator. I make science videos for the general public. If anyone of you would like to share your research work, I am very happy to discuss with you later. Here is a video I made with our colleagues (Nicolas and Hancheng) taking about the Gamma ray detector they made https://youtu.be/gFRi4jtds5M. For the Euclid members, if you would like to share something, I am able to release your content not only to my own video channel but to the Euclid official video channel and Euclid internal Newsletter. Please drop me an email if you are interested.
The cosmic X-ray background (CXB) is produced by the emission of unresolved active galactic nuclei (AGN), thus providing key information about the properties of the primary and reprocessed emission components of the AGN population. Equally important, studies of individual sources provide more constraints on the properties of AGN, such as their luminosity and obscuration. Until now, these constraints have not been self-consistently addressed fully, i.e. linking absorption and reflection. Here we perform numerical simulations with our ray-tracing code, RefleX, which allows the self-consistent modelling of the X-ray emission of AGN with flexible circumnuclear geometries. Using the RefleX-simulated emission of an AGN population, we attempt to simultaneously reproduce the CXB and other constraints obtained in the X-rays, e.g. the Nh distribution and obscured fraction of observed AGN. We use an intrinsic X-ray luminosity function and construct gradually more complex, physically-motivated, geometrical models. We examine how well each model can match all observational constraints, and finally, derive the fraction of Compton-thick (logNh/cm-2>24) sources.
The Intracluster medium (ICM) is one of the best archives to consult when we want to retrieve information about the past and recent history of clusters of galaxies. All those processes that can affect the dynamical state of clusters are expected to leave traces in the ICM distribution, both in the form of variations of integrated quantities and local edges and discontinuities. I will focus on the detection and analysis of these features in theCHEX-MATE sample. This large, unbiased, signal-to-noise limited sample iscomposed of 118 objects and is built to become the reference for clusters in the local volume and in the high mass regime. The complete and homogeneous X-ray exposures of these systems gave us the opportunity to perform, for the first time, a uniform characterisation of the X-ray morphology of a real cluster population. I will present the X-ray cluster properties highlighted by our analysis and their link to the cluster's dynamical state.
Recent measurements of the matter density of the Universe with several techniques have shown that the clumpiness parameter S8, which is related to the normalization of the primordial matter power spectrum, is different at late epochs compared to the value determined in the CMB data. This problem is usually referred to as the S8 tension and, if confirmed, it may be indicative of new physics. The tension can be investigated by measuring the abundance of massive galaxy clusters, which traces the high-mass end of the halo mass function and is thus highly sensitive to the local matter density. We use a catalogue of galaxy clusters discovered in the XMM-XXL survey to constrain the halo mass function and compare it with our baseline cosmological model. To this end, we construct a Bayesian fitting pipeline to determine the temperature and the luminosity of the detected systems and, in turn, we use the recovered cluster parameters to infer their total mass. We then apply a likelihood-free modeling technique to relate the measured cluster counts to the cosmological parameters and compare the fitted value of S8 with the CMB expectation.
JetSeT is an open-source C/Python framework to reproduce radiative and accelerative processes acting in relativistic jets, and galactic objects (with/without jet), allowing to fit the numerical models to the observed data. I started to work on this project in 2000, during my graduation thesis, and with time it evolved into a full framework.
1) I will give an overview of the philosophy and architecture of the framework, with a focus on reproducibility, and documentation.
2) I will show some live demonstrations with jupyter notebooks.
3) I will describe some of the scientific results I obtained using JetSeT, in particular regarding stochastic acceleration, and multi-wavelength variability of blazars and microquasars
The Cold Dark Matter (CDM) model of cosmology makes clear predictions on the internal structure of dark matter halos. Specifically, the density profiles of gravitationally-bound structures should look remarkably similar across a wide range of halo masses, from dwarf galaxies to the most massive galaxy clusters. Comparison between the observed dark matter halo shapes and CDM predictions can thus tell us about the nature of dark matter and possible modifications to the theory of gravity. It is thus crucial to determine the most accurate dark matter profiles we possibly can. In order to do so we will use multi-wavelengthobservations of some of the most massive galaxy clusters in the Universe to determine their mass distribution. This will be achieved by exploiting jointly the weak gravitational lensing signal and the properties of the hot intracluster gas determined from X-ray and SZ observations.
Due to Gaia's way of acquiring observations and the subsequent calibration steps, so-called scan-angle dependent signals can propagate in the derived photometry, astrometry and radial velocity signals. These non-source intrinsic signals can by themselves lead to detection of spurious periods as they show up at specific locations in the periodogram. We present the Gaia Data Release 3 paper (https://arxiv.org/pdf/2212.11971.pdf) discussing the origins, detection statistics and simulation results regarding these signals and discuss how to treat them in the future.
2023-04-10 00:00:00 Holidays
2023-04-17 00:00:00 Holidays
2023-04-24 00:00:00 TBD
2023-05-01 00:00:00 Holidays
Since their discoveries in 1967 by the Vela satellites, GRBs are still considered as some of the most violent events in the universe. The energy released during a few seconds is equivalent to the one produced by a Sun like star during its entire life. They are thought to be the result of the merger of two neutron stars or the collapse of a massive star into a black hole.
Dedicated space based GRB detectors like BATSE, Swift or POLAR studied them to better understand this phenomenon. To do so, it is critical to localize the signal source accurately, which was until now done by comparing the detector response to simulations, which is a relatively slow and computationally high demanding task.
In a few years from now the POLAR-2 observatory, a dedicated GRB Compton polarimeter, will be launched to the brand-new China Space Station (CSS).
The CSS has a GPU onboard, which makes it possible and advantageous to run Deep Learning model on it. In this work, we explore the possibility to infer GRB localization and spectral parameters with deep learning models.
Using POLAR simulations and data, a feasibility experiment was performed to implement this method on the next generation GRB polarimeter: POLAR-2. We see that the precision achieved using this method exceeds that of traditional localization methods, while the computational time is dramatically reduced. This makes the produced method of high interest to be used in the future.
Supermassive black holes (SMBH) of 10-10 Solar masses are found in thecenters of all galaxies. When fed by the surrounding gas and dust, they become active galactic nuclei (AGN), characterized by intenseultraviolet and X-ray emission resulting from the accretion of matter onto the SMBH, that may exceed the total emission from their host galaxies. In addition, AGN expel a lot of matter in the form of winds that may contribute to the stopping of star formation, and thus may play a role in the evolution of galaxies. To understand this role, it is essential to understand the structure of the surrounding matter, as it determines the main properties of AGN. X-rays are a fundamental piece of the puzzle, as they can pierce through matter, but nevertheless bear the imprint of matter with them. In this work, we will use high-resolution observations of one very absorbed AGN (NGC 4945) with the satellite Chandra that have shown evidence for extended X-ray emission. Using simulations, we will try to reproduce the Chandra energy-resolved images of these objects, and try to understand what constraints they place on the spatial distribution of matter. The simulations will be performed using a unique simulation tool, RefleX, which has been developed by S. Paltani for such studies.
Reaching microarcseconds resolutions in the optical band will allow us to directly image the structure of accretion discs around supermassive black holes (SMBH) in active galactic nuclei (AGN). The size and the structure of such disks have imprints of information about the SMBH's mass, spin, gas feeding rate and multi-wavelength variability of the AGN. Milliarcseconds resolution is reachable in radio, using the phase interferometry technique with very long baselines, while practically impossible in visible light due to much shorter wavelengths of the recorded photons. Intensity interferometry is a technique that originates from experiments of Hanbury Brown & Twiss in the 1950s. Instead of measuring the phase of light waves like traditional interferometry, intensity interferometry, as the name suggests, focuses on light intensity. Correlating fluctuations in the intensity observed by spatially separated detectors allows one to extract information about the observed object.In pursuit of developing a new instrument to be used for intensity interferometry to reach microarcseconds resolution, we started by building a lab setup to test state-of-the-art single-photon avalanche diode (SPAD) photo-detectors and correlators capable of pico-seconds sampling. Such a setup was used to observe individual photons from a small bright source simulating a star. In this talk, I will focus on the lab setup, hardware details, but also discuss the physical prerequisites for intensity interferometry and possible astrophysical applications of this technique.
2023-05-29 00:00:00 Holidays
The recent detection of Carinae in the TeV energy band confirms that wind-wind collision systems are able to accelerate particles up to relativistic energies. A detailed analysis of the - absorption within the huge ultraviolet photon field of the stars becomes now necessary to properly interpret the very-high-energy radiation. We estimated the - optical depth along the orbit of the binary system, assuming the two most probable orientations. We compared the results obtained with the approximated point-like star solution with those one obtained via the full complete treatment. We gradually increased the complexity of the model, estimating the probability of interaction of the UV photons from the primary star with TeV rays emitted from a point-like region, then from an extended single surface, and finally from an extended double surface. The same has then been repeated considering also the thermal photons coming from the secondary star. The simulation predicted a different modulation of the optical depth along the entire Carinae orbit, according to the different models and the different orientations, as well as a rapid variation, on a daily timescale, of the - absorption around periastron. We compared the results of the simulations with the data obtained by the Fermi-LAT satellite and the H.E.S.S. Cherenkov telescope array. The low statistic collected for short orbital intervals and the large systematic uncertainties from the current Cherenkov measurements do not allow at the moment to disentangle among the different proposed models, but likely exclude one of the two possible orientation. The higher performances of the Cherenkov Telescope Array (CTA) under construction will surely do it, constraining also the location where high-energy rays are produced, the radius and temperature of both stars, and the magnetic field. CTA future observations will be fundamental to measure the maximum energy that particle can achieve in colliding-wind binary systems.
Hercules X-1 (Her X-1 / HZ Her) is one of the most well-studied X-ray binary pulsars, comprising a 1.5 M neutron star (NS) and a 2.2 M A/F companion star. Her X-1 has a spin of 1.24 s and an orbital period of 1.7 d. It also exhibits a superorbital precession of the accretion disc of 35 d, resulting in the transition between three different luminosity states. In addition to these timing variabilities, Her X-1 also shows rich spectral features, including soft black bodies, thermal bremsstrahlung, iron lines, and a broad excess of 1-9 keV. Notably, Her X-1 is the first source found with a cyclotron absorption line (Ecyc), which is around 30 to 40 keV and linked to the magnetic field on the NS surface. Recently, the Imaging X-ray Polarimetry Explorer (IXPE) observed Her X-1 with a total exposure of ~470 ks, providing powerful polarimetric results to support the models explaining the superorbital variability with the precession of the accretion disk and the neutron star crust. In this talk, we will present our recent work on reanalyzing Her X-1 polarization with IXPE, and discuss some identical and new features compared to papers published by the IXPE collaboration.
2023-06-19 00:00:00 TBD
2023-06-26 00:00:00 Dimitra Gerolymatou ** nan
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