83 research outputs found
Searching for Gamma-Ray counterparts to Gravitational Waves from merging binary neutron stars with the Cherenkov Telescope Array
The merger of binary neutron star (BNS) systems are predicted to be
progenitors of short gamma-ray bursts (GRBs); the definitive probe of this
association came with the recent detection of gravitational waves (GWs) from a
BNS merger by Advanced LIGO and Advanced Virgo (GW170817), in coincidence with
the short GRB 170817A observed by Fermi-GBM and INTEGRAL. Short GRBs are also
expected to emit very-high energy (VHE, > 100 GeV) photons and VHE
electromagnetic (EM) upper limits have been set with observations performed by
ground-based gamma-ray detectors and during the intense EM follow-up campaign
associated with GW170817/GRB 170817A. In the next years, the searches for VHE
EM counterparts will become more effective thanks to the Cherenkov Telescope
Array (CTA): this instrument will be fundamental for the EM follow-up of
transient GW events at VHE, owing to its unprecedented sensitivity, rapid
response (few tens of seconds) and capability to monitor large sky areas via
survey-mode operation. We present a comprehensive study on the prospects for
joint GW and VHE EM observations of merging BNSs with Advanced LIGO, Advanced
Virgo and CTA, based on detailed simulations of the multi-messenger emission
and detection. We propose a new observational strategy optimized on the prior
assumptions about the EM emission. The method can be further generalized to
include other electromagnetic emission models. According to this study CTA will
cover most of the region of the GW skymap for the intermediate and most
energetic on-axis GRBs associated to the GW event. We estimate the expected
joint GW and VHE EM detection rates and we found this rate goes from 0.08 up to
0.5 events per year for the most energetic EM sources.Comment: 26 pages, 8 figures. Submitted to JCA
The discovery of gravitational waves: a gentle fight against noise
The recent direct observation of gravitational waves coming from collisions between black holes is the fulfillment of a dream started more than sixty years ago with the pioneering experiments of J. Weber. This has been possible by reaching with interferometric detectors an unprecedented sensitivity, which requires the reduction of several technical and fundamental noise sources, thermal and quantum in particular. I discuss some of these, with some emphasis on quantum noise. I also briefly discuss the first detection results and their impact on fundamental physics, commenting about future perspectives and challenges
Prospects for joint observations of gravitational waves and gamma rays from merging neutron star binaries
The detection of the events GW150914 and GW151226, both consistent with the
merger of a binary black hole system (BBH), opened the era of gravitational
wave (GW) astronomy. Besides BBHs, the most promising GW sources are the
coalescences of binary systems formed by two neutron stars or a neutron star
and a black hole. These mergers are thought to be connected with short Gamma
Ray Bursts (GRBs), therefore combined observations of GW and electromagnetic
(EM) signals could definitively probe this association. We present a detailed
study on the expectations for joint GW and high-energy EM observations of
coalescences of binary systems of neutron stars with Advanced Virgo and LIGO
and with the \emph{Fermi} gamma-ray telescope. To this scope, we designed a
dedicated Montecarlo simulation pipeline for the multimessenger emission and
detection by GW and gamma-ray instruments, considering the evolution of the GW
detector sensitivities. We show that the expected rate of joint detection is
low during the Advanced Virgo and Advanced LIGO 2016-2017 run; however, as the
interferometers approach their final design sensitivities, the rate will
increase by a factor of ten. Future joint observations will help to
constrain the association between short GRBs and binary systems and to solve
the puzzle of the progenitors of GWs. Comparison of the joint detection rate
with the ones predicted in this paper will help to constrain the geometry of
the GRB jet.Comment: 24 pages, 4 figure
New Seismic Attenuation System (SAS) for the Advanced LIGO Configurations (LIGO2)
A new passive seismic attenuation system is being developed to replace the current passive attenuation stacks in LIGO 2, it is expected to drive the seismic contribution to the interferometer noise below any other noise source. The SAS will be effective completely starting at about 5 Hz, well inside the (uncompensated) gravity gradient noise wall
Prospects for Stochastic Background Searches Using Virgo and LSC Interferometers
We consider the question of cross-correlation measurements using Virgo and
the LSC Interferometers (LIGO Livingston, LIGO Hanford, and GEO600) to search
for a stochastic gravitational-wave background. We find that inclusion of Virgo
into the network will substantially improve the sensitivity to correlations
above 200 Hz if all detectors are operating at their design sensitivity. This
is illustrated using a simulated isotropic stochastic background signal,
generated with an astrophysically-motivated spectrum, injected into 24 hours of
simulated noise for the LIGO and Virgo interferometers.Comment: 11 pages, uses IOP style files, submitted to CQG for GWDAW11
proceedings; revised in response to referee comment
Improved detection statistics for non Gaussian gravitational wave stochastic backgrounds
In a recent paper we described a novel approach to the detection and
parameter estimation of a non-Gaussian stochastic background of gravitational
waves. In this work we propose an improved version of the detection procedure,
preserving robustness against imperfect noise knowledge at no cost of detection
performance: in the previous approach, the solution proposed to ensure
robustness reduced the performances of the detection statistics, which in some
cases (namely, mild non-Gaussianity) could be outperformed by Gaussian ones
established in literature. We show, through a simple toy model, that the new
detection statistic performs better than the previous one (and than the
Gaussian statistic) everywhere in the parameter space. It approaches the
optimal Neyman-Pearson statistics monotonically with increasing non-Gaussianity
and/or number of detectors. In this study we discuss in detail its efficiency.
This is a second, important step towards the implementation of a
nearly--optimal detection procedure for a realistic non-Gaussian stochastic
background. We discuss the relevance of results obtained in the context of the
toy model used, and their importance for understanding a more realistic
scenario.Comment: 12 pages, 5 figures (published on 23 June 2023
Detecting non-Gaussian gravitational wave backgrounds: a unified framework
We describe a novel approach to the detection and parameter estimation of a
non\textendash Gaussian stochastic background of gravitational waves. The
method is based on the determination of relevant statistical parameters using
importance sampling. We show that it is possible to improve the Gaussian
detection statistics, by simulating realizations of the expected signal for a
given model. While computationally expensive, our method improves the detection
performance, leveraging the prior knowledge on the expected signal, and can be
used in a natural way to extract physical information about the background. We
present the basic principles of our approach, characterize the detection
statistic performances in a simplified context and discuss possible
applications to the detection of some astrophysical foregrounds. We argue that
the proposed approach, complementarily to the ones available in literature
might be used to detect suitable astrophysical foregrounds by currently
operating and future gravitational wave detectors.Comment: 12 Pages, 4 Figures, Supplemental material (published on 24 March
2023
The b -> s gamma decay revisited
In this work we compute the leading logarithmic corrections to the b -> s
gamma decay in a dimensional scheme which does not require any definition of
the gamma5 matrix. The scheme does not exhibit unconsistencies and it is
therefore a viable alternative to the t'Hooft Veltman scheme, particularly in
view of the next-to-leading computation. We confirm the recent results of
Ciuchini et al.Comment: 11 pages RevTeX + 2 EPSF figures, report IFUP-TH 2/94, HUTP-93/A038.
PostScript file or hardcopy available from the authors upon reques
HIV-2 infection in a migrant from Gambia: the history of the disease combined with phylogenetic analysis revealed the real source of infection
Human immunodeficiency virus type 2 (HIV-2) infection prevalence is increasing in some European countries. The increasing migratory flow from countries where HIV-2 is endemic has facilitated the spread of the virus into Europe and other regions. We describe a case of HIV-2 infection in a migrant individual in the Asylum Seeker Centre (ASC) in Italy. The patient's virus was sequenced, and found to be a typical HIV-2 genotype A virus. Bayesian evolutionary analysis revealed that the HIV-2 sequence from migrant dated back to 1986 in a subcluster including sequences from Guinea Bissau. This was coherent with the migrant history who lived in Guinea Bissau from his birth until 1998 when he was 13 years old. Monitoring for HIV-2 infection in migrants from western Africa is necessary using adequate molecular tools to improve the diagnosis and understand the real origin of infection
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