I will briefly discuss how the first image of a black hole was obtained by the EHT collaboration. In particular, I will describe the theoretical aspects that have allowed us to model the dynamics of the plasma accreting onto the black hole and how such dynamics was used to generate synthetic black-hole images. I will also illustrate how the comparison between the theoretical images and the observation has allowed us to deduce the presence of a black hole in M87 and to extract information about its properties. Finally, I will describe the lessons we have learned about strong-field gravity and alternatives to black holes.
Cosmology with galaxy clusters: impact of theoretical and observational systematic uncertainties1h
Galaxy clusters are a powerful cosmological probe, being able to track the evolution of large scale structure in the latest Universe. The theoretical modelling for the cosmological analysis of galaxy clusters is based on three main ingredients: the scaling relation between cluster observable and cluster mass (the mass-observable relation), the mass and redshift distribution of clusters (described by the halo mass function) and the description of the cluster detection and selection process (modelled through the selection function). In this talk I will show how different assumptions for these ingredients can impact the accuracy and precision of cosmological constraints inferred from galaxy clusters.
I will discuss a new analysis of clusters detected in mm wavelengths by the Planck satellite, highlighting the need of an improved description and calibration for the mass-observable relation. I will also show an independent point of view on the mass calibration problem, through a novel, still undergoing, analysis based on the combination of Planck and South Pole Telescope cluster catalogs.
I will conclude my talk focusing on how to improve our analysis in view of future surveys, such as the Euclid satellite. In particular, I will show how the calibration of the halo mass function can strongly impact the results on cosmological parameters.
Testing primordial black holes with the gravitational wave background1h
Primordial black holes (PBHs) are becoming increasingly popular as they could constitute a significant fraction of the Cold Dark Matter and be consistent with the population of black holes probed by the LIGO-Virgo-KAGRA network. In this talk, I will highlight the importance of the Stochastic Gravitational Wave Background (SGWB) as a tool to constrain PBHs. On one hand, PBHs formation during the radiation era produces a background whose spectral shape directly records the one of the primordial power spectrum of scalar fluctuations. On the other, the subsequent mergers of unresolvable PBHs binaries form a second background, whose shape also depends on the PBHs merger rate. I will describe the spectral and statistical features to distinguish the two backgrounds and discuss how their observation can be used to place constraints on PBHs scenarios and eventually distinguish PBHs from black holes of astrophysical origin.
link ZOOM: https://infn-it.zoom.us/j/82476243555?pwd=Vlc0T0QrYWk5ajNrWDhraUk5S0Q3Zz09
Matteo Braglia(Instituto de Física Teorica, Universidad Autónoma de Madrid)
Prospects for cosmological and population GRB studies with Konus-Wind20m
Gamma-ray bursts (GRBs) with measured redshifts (z) may provide essential insights into cosmology and GRB population. We present the results of a systematic study of temporal and spectral parameters, as well as energetics of GRBs with known z detected by Konus-Wind (KW). The first part of this work comprises 171 events detected in the triggered mode from 1997 February to 2019 March. The second part includes the bursts detected simultaneously by KW in the waiting mode and by the Swift/BAT (BAT) telescope during the period from 2005 January to the end of 2018. By taking advantage of the high sensitivity of BAT and the wide spectral band of KW, we were able to constrain the peak spectral energies, the broadband energy fluences, and the peak fluxes for the joint KW–BAT sample of 167 weak, relatively soft GRBs. Thus, the whole sample of KW GRBs with known z comprises 338 events, which makes it the largest set of cosmological GRBs studied to date over a broad energy band.
Based on the GRB redshifts, which span the range 0.04 < z < 9.4, we estimate the rest frame isotropic-equivalent energy and peak luminosity. For 46 GRBs with reasonably constrained jet breaks, we provide the collimation-corrected values of the energetics. With the full KW sample, accounting for the instrumental bias, we explore GRB rest-frame properties, including the hardness–intensity correlations, GRB luminosity evolution, luminosity and isotropic-energy functions, and the evolution of the GRB formation rate.
The analysis of a sample of GRBs jointly detected by various instruments allows understanding the systematics in GRB spectral parameters and energetics. We performed spectral cross-comparison of KW, Fermi/GBM (GBM), and BAT gamma-telescopes using simultaneously observed GRBs as calibration sources. For the first time, a systematic cross-calibration of the KW and the GBM spectral data was performed. This study will facilitate the interpretation of the GRB prompt emission data acquired in different experiments.
Anastasia Tsvetkova(Max Planck Institure for extraterrestrial physics, Munich)