Explore the vast range of titles available.

Preserving species within protected areas (PAs) does not guarantee adequate levels of protection if not coupled with conservation of functional connectivity for a target species. We propose an analytical framework to assess the effectiveness of PAs in preserving habitat and functional connectivity for mobile vertebrates. We implemented it in central Italy by using as a case study a bat species (common noctule, Nyctalus noctula) to: (i) determine suitable areas by means of Species Distribution Models (SDMs); (ii) identify potential commuting corridors through a functional connectivity analysis; (iii) develop a new tool to rank corridors according to their functional irreplaceability; (iv) implement a gap analysis on both suitable areas and functional corridors; and (v) propose management recommendations for the conservation of N. noctula. The SDM output and a set of proxies of commuting routes were used to build a resistance layer for the connectivity analysis. The resulting functional corridors were ranked according to their isolation (distance to other corridors and to suitable areas) to obtain an irreplaceability index, with isolated corridors scoring high values. The PA effectiveness assessed by overlapping the PA map with the SDM and the ranked functional corridors highlighted that PAs cover just a small portion of suitable sites (20.3%) and functional corridors for the species (20.8%). The irreplaceability index allowed us to identify those areas inside and outside the PAs that critical for persistence of the species in question require immediate protection regimes. The approach we present could be easily extended to other taxa and offers sound insight on how to promote the conservation at landscape scale.

Supergiant Fast X-ray Transients (SFXT) are High Mass X-ray Binaries displaying X-ray outbursts reaching peak luminosities of 10\\(^{38}\\) erg/s and spend most of their life in more quiescent states with luminosities as low as 10\\(^{32}\\)-10\\(^{33}\\) erg/s. The main goal of our comprehensive and uniform analysis of the SFXT Swift triggers is to provide tools to predict whether a transient which has no known X-ray counterpart may be an SFXT candidate. These tools can be exploited for the development of future missions exploring the variable X-ray sky through large FoV instruments. We examined all available data on outbursts of SFXTs that triggered the Swift/BAT collected between 2005-08-30 and 2014-12-31, in particular those for which broad-band data, including the Swift/XRT ones, are also available. We processed all BAT and XRT data uniformly with the Swift Burst Analyser to produce spectral evolution dependent flux light curves for each outburst. The BAT data allowed us to infer useful diagnostics to set SFXT triggers apart from the general GRB population, showing that SFXTs give rise uniquely to image triggers and are simultaneously very long, faint, and `soft' hard-X-ray transients. The BAT data alone can discriminate very well the SFXTs from other fast transients such as anomalous X-ray pulsars and soft gamma repeaters. However, to distinguish SFXTs from, for instance, accreting millisecond X-ray pulsars and jetted tidal disruption events, the XRT data collected around the time of the BAT triggers are decisive. The XRT observations of 35/52 SFXT BAT triggers show that in the soft X-ray energy band, SFXTs display a decay in flux from the peak of the outburst of at least 3 orders of magnitude within a day and rarely undergo large re-brightening episodes, favouring in most cases a rapid decay down to the quiescent level within 3-5 days (at most). [Abridged]

X-ray spectroscopy is a powerful technique for the analysis of the energy distribution of X-rays from astrophysical sources. It allows for the study of the properties, composition, and physical processes taking place at the site of emission. X-ray spectral analysis methods are diverse, as they often need to be tailored to the specific type of instrument used to collect the data. In addition, these methods advance together with the improvement of the technology of the telescopes and detectors. Here, we present a compact overview of the common procedures currently employed in this field. We describe the fundamental data structure and the essential auxiliary information required for conducting spectral analysis and we explore some of the most relevant aspects related to statistical and computational challenges in X-ray spectroscopy. Furthermore, we outline some practical scenarios in the context of data reduction, modeling and fitting of spectra, and spectral simulations.

Based on almost 20 years of data collected by the high-resolution spectrometer SPI on board the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) we present constraints on a decaying dark matter particle undergoing a decay into two bodies, at least one of which is a photon, manifesting itself via a narrow line-like spectral feature. Our ON-OFF type analysis of the Milky Way observations allowed us to constrain the lifetime to be \\(\\gtrsim 10^{20}-10^{21}\\) yrs for DM particles with masses \\(40\\,\\text{keV}\\,<\\,M_{\\text{DM}}\\,<\\,14\\,\\text{MeV}\\). Within this mass range our analysis also reveals 32 line-like features detected at \\(\\geq 3\\sigma\\) significance, 29 of which coincide with known instrumental and astrophysical lines. In particular, we report on the detection of the electron-positron annihilation (511 keV) and \\(^{26}\\)Al (1809 keV) lines with spatial profiles consistent with previous results in the literature. For the particular case of the sterile neutrino DM we report the limits on the mixing angle as a function of sterile neutrino mass. We discuss the dominant impact of systematic uncertainties connected to the strongly time-variable INTEGRAL/SPI instrumental background as well as the ones connected to the uncertainties of MW DM density profile measurements on the derived results.

We present in this paper a first step toward a semi-analytical treatment of the accretion process in wind-fed neutron star supergiant X-ray binaries with eccentric orbits. We consider the case of a spherically symmetric wind for the supergiant star and a simplified model for the accretion onto the compact object. A self-consistent calculation of the photoionization of the stellar wind by the X-rays from the accreting neutron star is included. This effect is convolved with the modulation of the mass accretion rate induced by the eccentric orbit to obtain the expected X-ray luminosity of a system along the orbit. As part of our results, we first show that the bi-modality of low and high X-ray luminosity solutions for supergiant X-ray binaries reported in previous papers is likely to result from the effect of the neutron star approaching first and then moving away from the companion (without coexisting simultaneously). We propose that episodes of strong wind photoionization can give rise to off-states of the sources. Our calculations are applied to the case of a few classical supergiant X-ray binary systems with known eccentricities (Vela X-1, 4U 1907+09, GX 301-2) and to the case of the only supergiant fast X-ray transient with a confirmed eccentric orbit, IGR J08408-4503. The results are compared with observational findings on these sources. We also discuss the next steps needed to expand the calculations toward a more comprehensive treatment in future publications.

Classical novae are known to demonstrate a supersoft X-ray source (SSS) state following outbursts, which is associated with residual thermonuclear burning on the white dwarf (WD) surface. During its all-sky survey (eRASS1), the eROSITA telescope onboard the Spectrum-Roentgen-Gamma observatory discovered a bright new SSS, whose position is consistent with the known classical nova AT 2018bej in the Large Magellanic Cloud. There were two eROSITA spectra obtained during eRASS1 and eRASS2 monitoring epochs and one XMM-Newton grating spectrum close to the eRASS1 epoch. We aim to describe the eROSITA and XMM-Newton spectra of AT 2018bej with our local thermodynamic equilibrium (LTE) atmosphere models. We focused on the evolution of the hot WD properties between the eRASS1 and eRASS2 epochs, especially on the change of the carbon abundance. A grid of LTE model atmosphere spectra were calculated for different values of the effective temperature (from \\(T_{\\rm eff}= 525\\) to \\(700\\,\\rm kK\\)), surface gravity (six values) and chemical composition with five different values of carbon and nitrogen abundances. Both eRASS1 and XMM \\(0.3-0.6\\) keV spectral analyses yield a temperature of the WD of \\(T_{\\rm eff}{\\sim}\\,600\\, \\rm kK\\) and a WD radius of \\(8000-8700\\,\\rm km\\). Simultaneous fitting of the eROSITA spectra for two epochs (eRASS1 and eRASS2) with a common WD mass parameter demonstrates a decrease in \\(T_{\\rm eff}\\) accompanied by an increase in the WD radius and a decrease in the carbon abundance. However, these changes are marginal and coincide within errors. The derived WD mass is estimated to be \\(1.05-1.15\\, M_\\odot\\). We traced a minor evolution of the source on a half-year timescale accompanied by a decrease in carbon abundance and concluded that LTE model atmospheres can be used to analyse the available X-ray spectra of classical novae during their SSS stage.

3A 1954+319 has been classified for a long time as a symbiotic X-ray binary, hosting a slowly rotating neutron star and an aged M red giant. Recently, this classification has been revised thanks to the discovery that the donor star is an M supergiant. This makes 3A 1954+319 a rare type of high mass X-ray binary consisting of a neutron star and a red supergiant donor. In this paper, we analyse two archival and still unpublished XMM-Newton and NuSTAR observations of the source. We perform a detailed hardness ratio-resolved spectral analysis to search for spectral variability that could help investigating the structures of the inhomogeneous M supergiant wind from which the neutron star is accreting. We discuss our results in the context of wind-fed supergiant X-ray binaries and show that the newest findings on 3A 1954+319 reinforce the hypothesis that the neutron star in this system is endowed with a magnetar-like magnetic field strength (\\(\\gtrsim10^{14}\\) G).

IGR J17407-2808 is an enigmatic and poorly studied X-ray binary that was recently observed quasi-simultaneously with NuSTAR and XMM-Newton. In this paper we report the results of this observational campaign. During the first 60 ks of observation, the source was caught in a relatively low emission state, characterised by a modest variability and an average flux of ~8.3E-13 erg/cm^2/s (4-60 keV). Afterwards, IGR J17407-2808 entered a significantly more active emission state that persisted for the remaining ~40 ks of the NuSTAR observation. During this state, IGR J17407-2808 displayed several fast X-ray flares, featuring durations of ~1-100 s and profiles with either single or multiple peaks. The source flux in the flaring state reached values as high as 2E-9 erg/cm^2/s (4-60 keV), leading to a measured dynamic range during the NuSTAR and XMM-Newton campaign of >~ 10^3. We also analysed available archival photometric near-infrared data of IGR J17407-2808 to improve the constraints available so far on the the nature of the donor star hosted in this system. Our analysis shows that the donor star can be either a rare K or M-type sub-subgiant or an K type main sequence star, or sub-giant star. Our findings support the classification of IGR J17407-2808 as a low-mass X-ray binary. We discuss the source X-ray behaviour as recorded by NuSTAR and XMM-Newton in view of this revised classification.

The masses of white dwarfs (WDs) in intermediate polars (IPs) can be determined from the shape of their hard X-ray spectra. Here we study the importance of all possible systematic uncertainties in this X-ray spectroscopy method, including finite radii and rotation of magnetospheres, finite accretion column height and accretion-flow inclination relative to the WD surface. We also investigate the importance of accretion-heated envelopes on WD surfaces in IPs which are increasing WD radii. Their presence changes the commonly used mass-radius relation for cold white dwarfs. As a first approximation we use thick (\\(10^{-4}M_\\odot\\)) hydrogen envelope models with a surface temperature of 30 kK. We present a new model grid of hard X-ray spectra of high-luminous IPs computed among other things with using a new mass-radius relation. This grid is used for fitting Swift/BAT spectra of 47 IPs. The average WD mass in this sample is 0.82 \\(M_\\odot\\) and coincides with the average WD mass in cataclysmic variables obtained by optical methods. This means that the calculated hard X-ray spectra and the assumptions made that the magnetospheric radii in IPs are close to the corotation radii, and the relative heights of the accretion columns are small are basically correct, because most IPs have high luminosities. But this universal grid (as well as previous universal grids) cannot give correct results for the low-luminous IPs with probably relatively tall accretion columns on the WD surfaces. Such IPs have to be investigated with individual accretion column models.

A0538-66 is a Be/X-ray binary (Be/XRB) hosting a 69 ms pulsar. It emitted bright X-ray outbursts with peak luminosity up to \\(\\sim 10^{39}\\) erg/s during the first years after its discovery in 1977. Since then, it was always seen in quiescence or during outbursts with \\(L_x \\lesssim 4 \\times 10^{37}\\) erg/s. In 2018 we carried out XMM-Newton observations of A0538-66 during three consecutive orbits when the pulsar was close to periastron. In the first two observations we discovered a remarkable variability, with flares of typical durations between \\(\\sim\\)2-50 s and peak luminosities up to \\(\\sim 4\\times 10^{38}\\) erg/s (0.2-10 keV). Between the flares the luminosity was \\(\\sim 2\\times 10^{35}\\) erg/s. The flares were absent in the third observation, during which A0538-66 had a steady luminosity of \\(2\\times 10^{34}\\) erg/s. In all observations, the X-ray spectra consist of a softer component, well described by an absorbed power law with photon index \\(\\Gamma_1\\approx 2-4\\) and \\(N_H\\approx 10^{21}\\) cm\\(^{-2}\\), plus a harder power-law component (\\(\\Gamma_2\\approx 0-0.5\\)) dominating above \\(\\sim\\)2 keV. The softer component shows larger flux variations than the harder one, and a moderate hardening correlated with the luminosity. The fast flaring activity seen in these observations was never observed before in A0538-66, nor, to our best knowledge, in other Be/XRBs. We explore the possibility that during our observations the source was accreting in a regime of nearly spherically symmetric inflow. In this case, an atmosphere can form around the neutron star magnetosphere and the observed variability can be explained by transitions between the accretion and supersonic propeller regimes.