NuSTAR J095551+6940.8: a highly magnetised neutron star with super-Eddington mass accretion

The identification of the Ultraluminous X-ray source (ULX) X-2 in M82 as an accreting pulsar has shed new light on the nature of a subset of ULXs, while rising new questions on the nature of the super-Eddington accretion. Here, by numerically solving the torque equation of the accreting pulsar within the framework of the magnetically threaded-disk scenario, we show that three classes of solutions, corresponding to different values of the magnetic field, are mathematically allowed. We argue that the highest magnetic field one, corresponding to B $\sim 10^{13}$ G, is favoured based on physical considerations and the observed properties of the source. In particular, that is the only solution which can account for the observed variations in $\dot{P}$ (over four time intervals) without requiring major changes in $\dot{M}$, which would be at odds with the approximately constant X-ray emission of the source during the same time. For this solution, we find that the source can only accomodate a moderate amount of beaming, 0.5 $\lesssim b < 1$. Last, we show that the upper limit on the luminosity, L$_X < 2.5 \times 10^{38}$ erg s$^{-1}$ from archival observations, is consistent with a highly-magnetized neutron star being in the propeller phase at that time.Comment: 8 pages, 3 figures, accepted for publication on MNRA

Ionospheric Plasma Response to the Anomalous Minimum of the Solar Cycle 23/24: Modeling and Comparison with IRI-2012

The work inspects the ionospheric plasma response to the last minimum of solar activity (minimum 23/24, years 2008-2009), which was extremely low and prolonged. Characterized by unprecedented features in space era, the last minimum represents then a unique natural window to study the ionospheric plasma behaviors in such extreme conditions. The work is organized in two main parts. The first one focuses on the analysis of the relationships between the parameter foF2 and five widely used solar activity indices: F10.7, Lym-α, MgII, R and EUV0.1-50. Using the long and continuous dataset of the mid-latitude station of Rome (41.8°N, 12.8°E, Italy) and applying a 1-year running mean to both foF2 and solar indices, it is found that a second order polynomial fit represents the best choice to describe the relationships (foF2 vs Index) and that the index MgII is the best one to describe and forecast the variations of foF2. The application of these outcomes to the European regional model SIRM produced an improvement of the corresponding performances. The second part investigates the differences between the last solar minimum and the previous ones, and evaluates the performances of the IRI-2012 model for the parameters NmF2 and hmF2, using data from four ionosondes: Rome, Gibilmanna (37.9°N, 14°E, Italy), Tucumán (26.9°N, 294.6°E, Argentina) and São José dos Campos (23.1ºS, 314.5ºE, Brazil). The inter-minima analysis reveals a decrease for both NmF2 and hmF2 for the last minimum with respect to the previous ones, with more pronounced decreases at low latitudes. The comparison between ionosonde data and IRI outputs shows that: (1) the model does not worsen its performances for the last minimum; (2) it works better at mid latitudes than at low latitudes; (3) it slightly overestimates (~10%) hmF2 at both latitudes

Magnetar central engines in gamma-ray busts follow the universal relation of accreting magnetic stars

Gamma-ray bursts (GRBs), both long and short, are explosive events whose inner engine is generally expected to be a black hole or a highly magnetic neutron star (magnetar) accreting high density matter. Recognizing the nature of GRB central engines, and in particular the formation of neutron stars (NSs), is of high astrophysical significance. A possible signature of NSs in GRBs is the presence of a plateau in the early X-ray afterglow. Here we carefully select a subset of long and short GRBs with a clear plateau, and look for an additional NS signature in their prompt emission, namely a transition between accretion and propeller in analogy with accreting, magnetic compact objects in other astrophysical sources. We estimate from the prompt emission the minimum accretion luminosity below which the propeller mechanism sets in, and the NS magnetic field and spin period from the plateau. We demonstrate that these three quantities obey the same universal relation in GRBs as in other accreting compact objects switching from accretion to propeller. This relation provides also an estimate of the radiative efficiency of GRBs, which we find to be several times lower than radiatively efficient accretion in X-ray binaries and in agreement with theoretical expectations. These results provide additional support to the idea that at least some GRBs are powered by magnetars surrounded by an accretion disc.Comment: 15 pages, 5 figures, accepted for publication in The Astrophysical Journal Letter

Are all Gamma Ray Bursts like GRB 980425, GRB 030329 and GRB 031203?

We study the probability that three GRBs (980425, 030329, 031203) are found within z=0.17, given the luminosity functions consistent with the log N-log S relationship for classical cosmological bursts (i.e., those observed by BATSE). We show that, in order for the probability of these three low-z events to be non-negligible (thus making it more likely that they belong to the same class of the classical cosmological bursts), the bursts' luminosity function must be a broken powerlaw. By reasoning in analogy with beamed AGNs, we show that observations are consistent with the expectations if GRB 980425 and GRB 031203 are indeed normal bursts seen sideways. Within this model, no bright burst within z=0.17 should be observed by a HETE--like instrument within the next \sim 20 yr.Comment: 9 pages, 1 figure. Accepted for publication in ApJ

Young Crab-like pulsars and luminous X-ray sources in starbursts and optically dull galaxies

Recent Chandra observations of nearby galaxies have revealed a number of ultraluminous X-ray sources (ULXs) with super-Eddington luminosities, away from the central regions of non-active galaxies. The nature of these sources is still debated. We argue that a fraction of them could be young, Crab-like pulsars, the X-ray luminosity of which is powered by rotation. We use the pulsar birth parameters estimated from radio pulsar data to compute the steady-state pulsar X-ray luminosity distribution as a function of the star formation rate (SFR) in the galaxy. We find that ~10% of optically dull galaxies are expected to have a source with L_x >~ 10^{39} erg/s, while starbursts galaxies should each have several of these sources. We estimate that the X-ray luminosity of a few percents of galaxies is dominated by a single bright pulsar with L_x >~10^{39} erg/s, roughly independently of its SFR. We discuss observational diagnostics that can help distinguish the young pulsar population in ULXs.Comment: 17 pages, 4 figures, accepted to Ap

Experimental Evaluation of Metallic Coating on Polymer by Cold Spray

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GRAVITATIONAL WAVES FROM MASSIVE MAGNETARS FORMED IN BINARY NEUTRON STAR MERGERS

Binary neutron star (NS) mergers are among the most promising sources of gravitational waves (GWs), as well as candidate progenitors for short gamma-ray bursts (SGRBs). Depending on the total initial mass of the system and the NS equation of state (EOS), the post-merger phase can be characterized by a prompt collapse to a black hole or by the formation of a supramassive NS, or even a stable NS. In the latter cases of post-merger NS (PMNS) formation, magnetic field amplification during the merger will produce a magnetar and induce a mass quadrupole moment in the newly formed NS. If the timescale for orthogonalization of the magnetic symmetry axis with the spin axis is smaller than the spindown time, the NS will radiate its spin down energy primarily via GWs. Here we study this scenario for the various outcomes of NS formation: we generalize the set of equilibrium states for a twisted torus magnetic configuration to include solutions that, for the same external dipolar field, carry a larger magnetic energy reservoir; we hence compute the magnetic ellipticity for such configurations, and the corresponding strength of the expected GW signal as a function of the relative magnitude of the dipolar and toroidal field components. The relative number of GW detections from PMNSs and from binary NSs is a very strong function of the NS EOS, being higher (~1%) for the stiffest EOSs and negligibly small for the softest ones. For intermediate-stiffness EOSs, such as the n = 4/7 polytrope recently used by Giacomazzo and Perna or the GM1 used by Lasky et al., the relative fraction is ~0.3%; correspondingly, we estimate a GW detection rate from stable PMNSs of ~0.1-1 yr-1 with advanced detectors, and of ~100-1000 yr-1 with detectors of third generation such as the Einstein Telescope. Measurement of such GW signals would provide constraints on the NS EOS and, in connection with an SGRB, on the nature of the binary progenitors giving rise to these events

Comunidad de paseriformes nidificantes de la Península Valdés (Patagonia, Argentina)

The Valdes Peninsula is a high-natural value area, located on the east coast of Argentine Patagonia. The aim of the reported research was to analyze the community of breeding passerine birds of the inland areas, with the purpose to identify the species that characterize each community, determining the main environmental typologies frequented, in order to study the relationships between bird richness and abundance, and environmental structure. During the breeding season 2011, 107 point counts were performed. 869 birds belonging to 23 passerine species were contacted and analyzed through a cluster analysis using the Indicator Value method. Results revealed the existence of two different communities: one that essentially refers to the grassy steppe where the characteristic species are Shortbilled Pipit (Anthus furcatus) and Common Miner (Geositta cunicularia), and the other one, which occupies the shrub-steppe consisting of more characteristic species, starting from the Rufous-collared Sparrow (Zonotrichia capensis), the most widespread species. These results update previous results on the community of passerines living in the study area and provide some useful insights for management purposes.La Península de Valdes es un area de gran riqueza natural, localizada en la costa Este de la Pa- tagonia Argentina. El propósito de este trabajo fue analizar la comunidad de aves Passeriformes de las areas internas de la región, con el proposito de identificar las especies que caracterizan cada comuni- dad, determinando las principales tipologias ambientales frecuentadas, para poder estudiar las rela- ciones entre la riqueza y abundancia de aves y la estructura del ambiente. Se realizaron 107 puntos de conteo durante la temporada reproductiva de 2011, en donde se detectaron 869 aves pertenecientes a 23 especies de Passeriformes. Para los análisis se usó el método de agrupamiento por el método del Indicator Value. Los resultados evidencian la existencia de dos diferentes comunidades: una asociada exclusivamente a la estepa herbácea y caracterizada por las especies Cachirla uña corta (Anthus furca- tus) y Minero común (Geositta cunicularia); mientras que la otra, asociada a la estepa arbustiva, es car- acterizada por diferentes especies típicas, como el Chingolo (Zonotrichia capensis), que es la especie de mayor distribución. Estos resultados constituyen una actualización al conocimiento de la fauna de la Península de Valdés, los cuales pueden ser útiles para el manejo y conservación de la avifauna de la región.Fil: Pruscini, Fabio. Università Di Urbino; ItaliaFil: Morelli, Federico. Università Di Urbino; ItaliaFil: Sisti, Davide. Università Di Urbino; ItaliaFil: Perna, Paolo. Universita Degli Di Camerino. Scuola Di Scienze Ambientale; ItaliaFil: Catorci, Andrea. Universita Degli Di Camerino. Scuola Di Scienze Ambientale; ItaliaFil: Bertellotti, Nestor Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Rocchi, Marco Bruno Luigi. Università Di Urbino; ItaliaFil: Santolini, Ricardo. Università Di Urbino; Itali