28 research outputs found
Relativistic models of magnetars: structure and deformations
We find numerical solutions of the coupled system of Einstein-Maxwell's
equations with a linear approach, in which the magnetic field acts as a
perturbation of a spherical neutron star. In our study, magnetic fields having
both poloidal and toroidal components are considered, and higher order
multipoles are also included. We evaluate the deformations induced by different
field configurations, paying special attention to those for which the star has
a prolate shape. We also explore the dependence of the stellar deformation on
the particular choice of the equation of state and on the mass of the star. Our
results show that, for neutron stars with mass M = 1.4 Msun and surface
magnetic fields of the order of 10^15 G, a quadrupole ellipticity of the order
of 10^(-6) - 10^(-5) should be expected. Low mass neutron stars are in
principle subject to larger deformations (quadrupole ellipticities up to
10^(-3) in the most extreme case). The effect of quadrupolar magnetic fields is
comparable to that of dipolar components. A magnetic field permeating the whole
star is normally needed to obtain negative quadrupole ellipticities, while
fields confined to the crust typically produce positive quadrupole
ellipticities.Comment: 25 pages, 9 figures, submitted to MNRA
Validation of satellite OPEMW precipitation product with ground-based weather radar and rain gauge networks
Abstract. The Precipitation Estimation at Microwave Frequencies (PEMW) algorithm was developed at the Institute of Methodologies for Environmental Analysis of the National Research Council of Italy (IMAA-CNR) for inferring surface rain intensity (sri) from satellite passive microwave observations in the range from 89 to 190 GHz. The operational version of PEMW (OPEMW) has been running continuously at IMAA-CNR for two years. The OPEMW sri estimates, together with other precipitation products, are used as input to an operational hydrological model for flood alert forecast. This paper presents the validation of OPEMW against simultaneous ground-based observations from a network of 20 weather radar systems and a network of more than 3000 rain gauges distributed over the Italian Peninsula and main islands. The validation effort uses a data set covering one year (July 2011–June 2012). The effort evaluates dichotomous and continuous scores for the assessment of rain detection and quantitative estimate, respectively, investigating both spatial and temporal features. The analysis demonstrates 98% accuracy in correctly identifying rainy and non-rainy areas; it also quantifies the increased ability (with respect to random chance) to detect rainy and non-rainy areas (0.42–0.45 Heidke skill score) or rainy areas only (0.27–0.29 equitable threat score). Performances are better than average during summer, fall, and spring, while worse than average in the winter season. The spatial–temporal analysis does not show seasonal dependence except over the Alps and northern Apennines during winter. A binned analysis in the 0–15 mm h−1 range suggests that OPEMW tends to slightly overestimate sri values below 6–7 mm h−1 and underestimate sri above those values. With respect to rain gauges (weather radars), the correlation coefficient is larger than 0.8 (0.9). The monthly mean difference and standard deviation remain within ±1 and 2 mm h−1 with respect to rain gauges (respectively −2–0 and 4 mm h−1 with respect to weather radars)
Relativistic models of magnetars: the twisted-torus magnetic field configuration
We find general relativistic solutions of equilibrium magnetic field
configurations in magnetars, extending previous results of Colaiuda et al.
(2008). Our method is based on the solution of the relativistic Grad-Shafranov
equation, to which Maxwell's equations can be reduced in some limit. We obtain
equilibrium solutions with the toroidal magnetic field component confined into
a finite region inside the star, and the poloidal component extending to the
exterior. These so-called twisted-torus configurations have been found to be
the final outcome of dynamical simulations in the framework of Newtonian
gravity, and appear to be more stable than other configurations. The solutions
include higher order multipoles, which are coupled to the dominant dipolar
field. We use arguments of minimal energy to constrain the ratio of the
toroidal to the poloidal field.Comment: 13 pages, 12 figures. Minor changes to match the version published on
MNRA
Structure and deformations of strongly magnetized neutron stars with twisted torus configurations
We construct general relativistic models of stationary, strongly magnetized
neutron stars. The magnetic field configuration, obtained by solving the
relativistic Grad-Shafranov equation, is a generalization of the twisted torus
model recently proposed in the literature; the stellar deformations induced by
the magnetic field are computed by solving the perturbed Einstein's equations;
stellar matter is modeled using realistic equations of state. We find that in
these configurations the poloidal field dominates over the toroidal field and
that, if the magnetic field is sufficiently strong during the first phases of
the stellar life, it can produce large deformations.Comment: 10 pages, 5 figures. Minor changes to match the version published on
MNRA
A meteorological–hydrological regional ensemble forecast for an early-warning system over small Apennine catchments in Central Italy
Abstract. The weather forecasts for precipitation have considerably improved in recent years thanks to the increase of computational power.
This allows for the use of both a higher spatial resolution and the parameterization schemes specifically developed for representing sub-grid scale physical processes at high resolution. However, precipitation estimation is still affected by errors that can impact the response of hydrological models. To the aim of improving the hydrological forecast and the characterization of related uncertainties, a regional-scale meteorological–hydrological ensemble is presented. The uncertainties in the precipitation forecast and how they propagate in the hydrological model are also investigated. A meteorological–hydrological offline coupled ensemble is built to forecast events in a complex-orography terrain where catchments of different sizes are present. The Best Discharge-based Drainage (BDD; both deterministic and probabilistic) index, is defined with the aim of forecasting hydrological-stress conditions and related uncertainty.
In this context, the meteorological–hydrological ensemble forecast is implemented and tested for a severe hydrological event which occurred over Central Italy on 15 November 2017, when a flood hit the Abruzzo region with precipitation reaching 200 mm (24 h)−1 and producing damages with a high impact on social and economic activities. The newly developed meteorological–hydrological ensemble is compared with a high-resolution deterministic forecast and with the observations (rain gauges and radar data) over the same area. The receiver operating characteristic (ROC) statistical indicator shows how skilful the ensemble precipitation forecast is with respect to both rain-gauge- and radar-retrieved precipitation. Moreover, both the deterministic and probabilistic configurations of the BDD index are compared with the alert map issued by Civil Protection Department for the event showing a very good agreement.
Finally, the meteorological–hydrological ensemble allows for an estimation of both the predictability of the event a few days in advance and the uncertainty of the flood. Although the modelling framework is implemented on the basins of the Abruzzo region, it is portable and applicable to other areas
Bayesian timing analysis of giant flare of SGR 1806-20 by RXTE PCA
By detecting high frequency quasi-periodic oscillations (QPOs) and estimating
frequencies of them during the decaying tail of giant flares from Soft
Gamma-ray Repeaters (SGRs) useful constraints for the equation of state (EoS)
of superdense matter may be obtained via comparison with theoretical
predictions of eigenfrequencies. We used the data collected by the Rossi X-Ray
Timing Explorer (RXTE/XTE) Proportional Counter Array (PCA) of a giant flare of
SGR 1806-20 on 2004 Dec 27 and applied a Bayesian periodicity detection method
(Gregory & Loredo, 1992) for the search of oscillations of transient nature. In
addition to the already detected frequencies, we found a few new frequencies
(f_{QPOs} ~ 16.9, 21.4, 36.4, 59.0, 116.3 Hz) of oscillations predicted by
Colaiuda et al. (2009) based on the APR_{14} EoS (Akmal et al., 1998) for SGR
1806-20.Comment: 5 pages, 7 figures, A&A accepte
Overview of the first HyMeX Special Observation Period over Italy: observations and model results
Abstract. The Special Observation Period (SOP1), part of the HyMeX campaign (Hydrological cycle in the Mediterranean Experiments, 5 September–6 November 2012), was dedicated to heavy precipitation events and flash floods in the western Mediterranean, and three Italian hydro-meteorological monitoring sites were identified: Liguria–Tuscany, northeastern Italy and central Italy. The extraordinary deployment of advanced instrumentation, including instrumented aircrafts, and the use of several different operational weather forecast models, including hydrological models and marine models, allowed an unprecedented monitoring and analysis of high-impact weather events around the Italian hydro-meteorological sites. This activity has seen strong collaboration between the Italian scientific and operational communities. In this paper an overview of the Italian organization during SOP1 is provided, and selected Intensive Observation Periods (IOPs) are described. A significant event for each Italian target area is chosen for this analysis: IOP2 (12–13 September 2012) in northeastern Italy, IOP13 (15–16 October 2012) in central Italy and IOP19 (3–5 November 2012) in Liguria and Tuscany. For each IOP the meteorological characteristics, together with special observations and weather forecasts, are analyzed with the aim of highlighting strengths and weaknesses of the forecast modeling systems, including the hydrological impacts. The usefulness of having different weather forecast operational chains characterized by different numerical weather prediction models and/or different model set up or initial conditions is finally shown for one of the events (IOP19)
Sviluppo di strumenti tecnologici predittivi sanitario/meteo-ambientali per potenziare l’efficienza e la sostenibilità degli impianti di molluschicoltura: avvio del progetto FORESHELL
FORESHELL project is funded by the FLAG Costa Blu trough 2014-20 EMFF program of the Abruzzo Region. It is carrying out a pilot initiative to develop sanitary/weather-environmental predictive technological tools to enhance the efficiency and sustainability of the mussel farm in the Giulianova Maritime District. The hydrographic basins of the rivers close to the farm, Vibrata and Salinello, are constantly monitored trough the hydrological model (CHyM), to forecast occurrences of discharge peaks at the river mouth. Moreover, a specific sampling programme is established before and after severe weather events to determine the concentration of E. coli in freshwater at the river mouths and in mussels/seawater at the farming area. Until September 2021, there were 4 meteorological events that did not cause a peak discharge at the river mouth. Results did not show a significant increase of E. coli in the mussels. At the same time, the environmental parameters such as sea water temperature, salinity, chlorophyll a, sea currents and wave motion are acquired by the satellites and in situ probe. The web application for data visualisation is under construction, as well as the early warning signalling to the farmer. Furthermore, the growth of mussels is constantly monitored with biometric controls. In conclusion, the implementation of all phases of the FORESHELL project are progressing according to the timeline in order to develop innovative tools useful for the management of mussel farming area
Gravitational waves from single neutron stars: an advanced detector era survey
With the doors beginning to swing open on the new gravitational wave
astronomy, this review provides an up-to-date survey of the most important
physical mechanisms that could lead to emission of potentially detectable
gravitational radiation from isolated and accreting neutron stars. In
particular we discuss the gravitational wave-driven instability and
asteroseismology formalism of the f- and r-modes, the different ways that a
neutron star could form and sustain a non-axisymmetric quadrupolar "mountain"
deformation, the excitation of oscillations during magnetar flares and the
possible gravitational wave signature of pulsar glitches. We focus on progress
made in the recent years in each topic, make a fresh assessment of the
gravitational wave detectability of each mechanism and, finally, highlight key
problems and desiderata for future work.Comment: 39 pages, 12 figures, 2 tables. Chapter of the book "Physics and
Astrophysics of Neutron Stars", NewCompStar COST Action 1304. Minor
corrections to match published versio
Strongly magnetized pulsars: explosive events and evolution
Well before the radio discovery of pulsars offered the first observational
confirmation for their existence (Hewish et al., 1968), it had been suggested
that neutron stars might be endowed with very strong magnetic fields of
-G (Hoyle et al., 1964; Pacini, 1967). It is because of their
magnetic fields that these otherwise small ed inert, cooling dead stars emit
radio pulses and shine in various part of the electromagnetic spectrum. But the
presence of a strong magnetic field has more subtle and sometimes dramatic
consequences: In the last decades of observations indeed, evidence mounted that
it is likely the magnetic field that makes of an isolated neutron star what it
is among the different observational manifestations in which they come. The
contribution of the magnetic field to the energy budget of the neutron star can
be comparable or even exceed the available kinetic energy. The most magnetised
neutron stars in particular, the magnetars, exhibit an amazing assortment of
explosive events, underlining the importance of their magnetic field in their
lives. In this chapter we review the recent observational and theoretical
achievements, which not only confirmed the importance of the magnetic field in
the evolution of neutron stars, but also provide a promising unification scheme
for the different observational manifestations in which they appear. We focus
on the role of their magnetic field as an energy source behind their persistent
emission, but also its critical role in explosive events.Comment: Review commissioned for publication in the White Book of
"NewCompStar" European COST Action MP1304, 43 pages, 8 figure