22 research outputs found
X-ray analysis of the accreting supermassive black hole in the radio galaxy PKS 2251+11
We investigate the dichotomy between jetted and non-jetted Active Galactic
Nuclei (AGNs), focusing on the fundamental differences of these two classes in
the accretion physics onto the central supermassive black hole (SMBH). Our aim
is to study and constrain the structure, kinematics and physical state of the
nuclear environment in the Broad Line Radio Galaxy (BLRG) PKS 2251+11. The high
X-ray luminosity and the relative proximity make such AGN an ideal candidate
for a detailed analysis of the accretion regions in radio galaxies. We
performed a spectral and timing analysis of a 64 ks observation of PKS
2251+11 in the X-ray band with XMM-Newton. We modeled the spectrum considering
an absorbed power law superimposed to a reflection component. We performed a
time-resolved spectral analysis to search for variability of the X-ray flux and
of the individual spectral components. We found that the power law has a photon
index , absorbed by an ionized partial covering medium with
a column density cm, a ionization
parameter erg s cm and a covering factor
. Considering a density of the absorber typical of the Broad Line
Region (BLR), its distance from the central SMBH is of the order of
pc. An Fe K emission line is found at 6.4 keV, whose intensity shows
variability on time scales of hours. We derived that the reflecting material is
located at a distance , where is the Schwarzschild
radius. Concerning the X-ray properties, we found that PKS 2251+11 does not
differ significantly from the non-jetted AGNs, confirming the validity of the
unified model in describing the inner regions around the central SMBH, but the
lack of information regarding the state of the very innermost disk and SMBH
spin still leave unconstrained the origin of the jet
The impact of non-target events in synthetic soundscapes for sound event detection
International audienceDetection and Classification Acoustic Scene and Events Challenge 2021 Task 4 uses a heterogeneous dataset that includes both recorded and synthetic soundscapes. Until recently only target sound events were considered when synthesizing the soundscapes. However, recorded soundscapes often contain a substantial amount of non-target events that may affect the performance. In this paper, we focus on the impact of these non-target events in the synthetic soundscapes. Firstly, we investigate to what extent using non-target events alternatively during the training or validation phase (or none of them) helps the system to correctly detect target events. Secondly, we analyze to what extend adjusting the signal-to-noise ratio between target and non-target events at training improves the sound event detection performance. The results show that using both target and non-target events for only one of the phases (validation or training) helps the system to properly detect sound events, outperforming the baseline (which uses non-target events in both phases). The paper also reports the results of a preliminary study on evaluating the system on clips that contain only non-target events. This opens questions for future work on non-target subset and acoustic similarity between target and non-target events which might confuse the system
Neutrino search from {\gamma}-ray bursts during the prompt and X-ray afterglow phases using 10 years of IceCube public data
Neutrino emission from gamma-ray bursts (GRBs) has been sought for a long
time, and stringent limits on the most accredited GRB emission models have been
obtained from IceCube. Multi-wavelength GRB observations of the last decades
improved our knowledge of the GRB emission parameters, such as the Lorentz
factor and the luminosity, which can vary from one GRB to another by several
orders of magnitude. Empirical correlations among such parameters have been
identified during the prompt phase, with direct implications on GRB models. In
this work, we use the PSLab open-access code, developed for IceCube data
analyses, to search for individual neutrino emission from the prompt and
afterglow phases of selected GRBs, and for stacking emission from the ensemble
of such GRBs. For the afterglow phase, we focus in particular on GRBs with
X-ray flares and plateaus. While past stacking searches assumed the same GRB
fluence at Earth, we present a stacking scheme based on physically motivated
GRB weights. Moreover, we conceive a new methodology for the prompt phase that
uses the empirical correlations to infer the GRB luminosity and Lorentz factor,
when redshift measurements are not available. We do not observe any significant
neutrino excess. Hence, we set constraints on the GRB neutrino fluxes and on
relevant GRB parameters, including the magnetic field in the jet. Notably, the
baryon loading is found to be <10 for typical GRB prompts, thus disfavoring a
baryonic-dominated origin of the GRB ejecta.Comment: Submitted for publication to A&A. Comments are welcom
Combined X-ray and optical analysis to probe the origin of the plateau emission in -ray bursts afterglows
A large fraction of gamma-ray bursts (GRBs) shows a plateau phase during the
X-ray afterglow emission, whose physical origin is still debated. In this work
we define a sample of 30 GRBs with simultaneous X-ray and optical data during
and after the plateau phase. Through a time-resolved spectral analysis of the
X-ray plateaus, we test the consistency of the unabsorbed optical fluxes with
those obtained via X-ray-to-optical spectral extrapolation by assuming a
synchrotron spectrum. Combining X-ray with optical data, we find that 63%
(19/30) GRBs are compatible with a single synchrotron spectrum thus suggesting
that both the optical and X-ray radiations are produced from a single emitting
region. For these GRBs we derive the temporal evolution of the break frequency
and we compare it with the expectations predicted by several models. For 11/30
GRBs the optical emission is above the predicted range of values extrapolated
from the X-rays in at least one temporal bin of the light curve. These GRBs may
not be explained with a single zone emission, indicating the necessity of
invoking two cooperating processes in order to explain the broad band spectral
behaviour during X-ray plateaus. We discuss our findings in the framework of
different scenarios invoked to explain the plateau feature, including the
energy injection from a spinning-down magnetar and the high latitude emission
from a structured jet.Comment: submitted to A&
Perspectives for multi-messenger astronomy with the next generation of gravitational-wave detectors and high-energy satellites
The Einstein Telescope (ET) is going to bring a revolution for the future of
multi-messenger astrophysics. In order to detect the counterparts of binary
neutron star (BNS) mergers at high redshift, the high-energy observations will
play a crucial role. Here, we explore the perspectives of ET, as single
observatory and in a network of gravitational-wave (GW) detectors, operating in
synergy with future -ray and X-ray satellites. We predict the
high-energy emission of BNS mergers and its detectability in a theoretical
framework which is able to reproduce the properties of the current sample of
observed short GRBs (SGRB). We estimate the joint GW and high-energy detection
rate for both the prompt and afterglow emissions, testing several combinations
of instruments and observational strategies. We find that the vast majority of
SGRBs detected in -rays will have a detectable GW counterpart; the
joint detection efficiency approaches considering a network of third
generation GW observatories. The probability of identifying the electromagnetic
counterpart of BNS mergers is significantly enhanced if the sky localisation
provided by GW instruments is observed by wide field X-ray monitors. We
emphasize that the role of the future X-ray observatories will be very crucial
for the detection of the fainter emission outside the jet core, which will
allow us to probe the yet unexplored population of low-luminosity SGRBs in the
nearby Universe, as well as to unveil the nature of the jet structure and the
connections with the progenitor properties.Comment: Submitted to the journa
Detecting VHE prompt emission from binary neutron-star mergers: ET and CTA synergies
The current generation of very-high-energy ray (VHE; E above 30 GeV)
detectors (MAGIC and H.E.S.S.) have recently demonstrated the ability to detect
the afterglow emission of GRBs. However, the GRB prompt emission, typically
observed in the 10 keV-10 MeV band, has so far remained undetected at higher
energies. Here, we investigate the perspectives of multi-messenger observations
to detect the prompt emission of short GRBs in VHE. Considering binary neutron
star mergers as progenitors of short GRBs, we evaluate the joint detection
efficiency of the Cherenkov Telescope Array (CTA) observing in synergy with the
third generation of gravitational wave detectors, such as the Einstein
Telescope (ET) and Cosmic Explorer (CE). In particular, we evaluate the
expected capabilities to detect and localize gravitational wave events in the
inspiral phase and to provide an early warning alert able to drive the VHE
search. We compute the amount of possible joint detections by considering
several observational strategies, and demonstrate that the sensitivities of CTA
make the detection of the VHE emission possible even if it is several orders
fainter than the one observed at 10 keV-10 MeV. We discuss the results in terms
of possible scenarios of production of VHE photons from binary neutron star
mergers by considering GRB prompt and afterglow emissions
Spectral index-flux relation for investigating the origins of steep decay in -ray bursts
-ray bursts (GRBs) are short-lived transients releasing a large
amount of energy ( erg) in the keV-MeV energy range. GRBs are
thought to originate from internal dissipation of the energy carried by
ultra-relativistic jets launched by the remnant of a massive star's death or a
compact binary coalescence. While thousands of GRBs have been observed over the
last thirty years, we still have an incomplete understanding of where and how
the radiation is generated in the jet. Here we show a relation between the
spectral index and the flux found by investigating the X-ray tails of bright
GRB pulses via time-resolved spectral analysis. This relation is incompatible
with the long standing scenario which invokes the delayed arrival of photons
from high-latitude parts of the jet. While the alternative scenarios cannot be
firmly excluded, the adiabatic cooling of the emitting particles is the most
plausible explanation for the discovered relation, suggesting a
proton-synchrotron origin of the GRB emission.Comment: Published in Nature Communication
Spectral index-flux relation for investigating the origins of steep decay in Îł-ray bursts
Îł-ray bursts (GRBs) are short-lived transients releasing a large amount of energy (10 â 10 erg) in the keV-MeV energy range. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive starâs death or a compact binary coalescence. While thousands of GRBs have been observed over the last thirty years, we still have an incomplete understanding of where and how the radiation is generated in the jet. Here we show a relation between the spectral index and the flux found by investigating the X-ray tails of bright GRB pulses via time-resolved spectral analysis. This relation is incompatible with the long standing scenario which invokes the delayed arrival of photons from high-latitude parts of the jet. While the alternative scenarios cannot be firmly excluded, the adiabatic cooling of the emitting particles is the most plausible explanation for the discovered relation, suggesting a proton-synchrotron origin of the GRB emission.The research leading to these results has received funding from the European Unionâs Horizon 2020 Programme under the AHEAD2020 project (Grant agreement n. 871158). G. Ghir. acknowledges the support from the ASI-Nustar Grant (1.05.04.95). M.B., P.D., and G.G. acknowledge support from PRIN-MIUR 2017 (Grant 20179ZF5KS). G.O. acknowledges financial contribution from the agreement ASI-INAF n.2017-14-H.0. S.A. acknowledges the PRIN-INAF âTowards the SKA and CTA era: discovery, localization, and physics of transient sourcesâ and the ERC Consolidator Grant âMAGNESIAâ (nr. 817661). M.G.B. and P.D. acknowledge ASI Grant I/004/11/3. O.S.S. acknowledges the INAF-Prin 2017 (1.05.01.88.06) and the Italian Ministry for University and Research Grant âFIGAROâ (1.05.06.13) for support. G.O. and S.R. are thankful to INAFâOsservatorio Astronomico di Brera for kind hospitality during the completion of this work. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester
Lunar Gravitational-Wave Antenna
Monitoring of vibrational eigenmodes of an elastic body excited by
gravitational waves was one of the first concepts proposed for the detection of
gravitational waves. At laboratory scale, these experiments became known as
resonant-bar detectors first developed by Joseph Weber in the 1960s. Due to the
dimensions of these bars, the targeted signal frequencies were in the kHz
range. Weber also pointed out that monitoring of vibrations of Earth or Moon
could reveal gravitational waves in the mHz band. His Lunar Surface Gravimeter
experiment deployed on the Moon by the Apollo 17 crew had a technical failure
rendering the data useless. In this article, we revisit the idea and propose a
Lunar Gravitational-Wave Antenna (LGWA). We find that LGWA could become an
important partner observatory for joint observations with the space-borne,
laser-interferometric detector LISA, and at the same time contribute an
independent science case due to LGWA's unique features. Technical challenges
need to be overcome for the deployment of the experiment, and development of
inertial vibration sensor technology lays out a future path for this exciting
detector concept.Comment: 29 pages, 17 figure
Science with the Einstein Telescope: a comparison of different designs
The Einstein Telescope (ET), the European project for a third-generation
gravitational-wave detector, has a reference configuration based on a
triangular shape consisting of three nested detectors with 10 km arms, where in
each arm there is a `xylophone' configuration made of an interferometer tuned
toward high frequencies, and an interferometer tuned toward low frequencies and
working at cryogenic temperature. Here, we examine the scientific perspectives
under possible variations of this reference design. We perform a detailed
evaluation of the science case for a single triangular geometry observatory,
and we compare it with the results obtained for a network of two L-shaped
detectors (either parallel or misaligned) located in Europe, considering
different choices of arm-length for both the triangle and the 2L geometries. We
also study how the science output changes in the absence of the low-frequency
instrument, both for the triangle and the 2L configurations. We examine a broad
class of simple `metrics' that quantify the science output, related to compact
binary coalescences, multi-messenger astronomy and stochastic backgrounds, and
we then examine the impact of different detector designs on a more specific set
of scientific objectives.Comment: 197 pages, 72 figure