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After 15 yr, in late 2018, the magnetar XTE J1810−197 underwent a second recorded X-ray outburst event and reactivated as a radio pulsar. We initiated an X-ray monitoring campaign to follow the timing and spectral evolution of the magnetar as its flux decays using Swift, XMM–Newton, NuSTAR , and NICER observations. During the year-long campaign, the magnetar reproduced similar behaviour to that found for the first outburst, with a factor of 2 change in its spin-down rate from ∼7.2 × 10−12 to ∼1.5 × 10−11 s s−1 after two months. Unique to this outburst, we confirm the peculiar energy-dependent phase shift of the pulse profile. Following the initial outburst, the spectrum of XTE J1810−197 is well modelled by multiple blackbody components corresponding to a pair of non-concentric, hot thermal caps surrounded by a cooler one, superposed to the colder star surface. We model the energy-dependent pulse profile to constrain the viewing and surface emission geometry and find that the overall geometry of XTE J1810−197 has likely evolved relative to that found for the 2003 event. [ABSTRACT FROM AUTHOR]

After two major outbursts in 2006 and 2011, on 2017 May 16 the magnetar CXOU J164710.2−455216, hosted within the massive star cluster Westerlund I, emitted a short (∼20 ms) burst, which marked the onset of a new active phase. We started a long-term monitoring campaign with Swift (45 observations), Chandra (five observations), and NuSTAR (four observations) from the activation until 2018 April. During the campaign, Swift Burst Alert Telescope (BAT) registered the occurrence of multiple bursts, accompanied by two other enhancements of the X-ray persistent flux. The long time span covered by our observations allowed us to study the spectral and the timing evolution of the source. After ∼11 months since the 2017 May outburst onset, the observed flux was ∼15 times higher than its historical minimum level and a factor of ∼3 higher than the level reached after the 2006 outburst. This suggests that the crust has not fully relaxed to the quiescent level, or that the source quiescent level has changed following the multiple outburst activities in the past 10 yr or so. This is another case of multiple outbursts from the same source on a yearly time-scale, a somehow recently discovered behaviour in magnetars. [ABSTRACT FROM AUTHOR]

We report on a new NuSTAR observation and on the ongoing Swift X-Ray Telescope monitoring campaign of the peculiar source 1E 161348–5055, located at the centre of the supernova remnant RCW 103, which is recovering from its last outburst in 2016 June. The X-ray spectrum at the epoch of the NuSTAR observation can be described by either two absorbed blackbodies ( $kT_{\rm BB_1}$  ∼ 0.5 keV, $kT_{\rm BB_2}$  ∼ 1.2 keV) or an absorbed blackbody plus a power law ( $kT_{\rm BB_1}$  ∼ 0.6 keV, Γ ∼ 3.9). The observed flux was ∼9 × 10−12 erg s−1 cm−2, ∼3 times lower than what observed at the outburst onset, but about one order of magnitude higher than the historical quiescent level. A periodic modulation was detected at the known 6.67 h periodicity. The spectral decomposition and evolution along the outburst decay are consistent with 1E 161348–5055 being a magnetar, the slowest ever detected. [ABSTRACT FROM AUTHOR]

Population synthesis studies constitute a powerful method to reconstruct the birth distribution of periods and magnetic fields of the pulsar population. When this method is applied to populations in different wavelengths, it can break the degeneracy in the inferred properties of initial distributions that arises from single-band studies. In this context, we extend previous works to include X-ray thermal emitting pulsars within the same evolutionary model as radiopulsars. We find that the cumulative distribution of the number of X-ray pulsars can be well reproduced by several models that, simultaneously, reproduce the characteristics of the radiopulsar distribution. However, even considering the most favourable magneto-thermal evolution models with fast field decay, lognormal distributions of the initial magnetic field overpredict the number of visible sources with periods longer than 12 s. We then show that the problem can be solved with different distributions of magnetic field, such as a truncated lognormal distribution, or a binormal distribution with two distinct populations.We use the observational lack of isolated neutron stars (NSs) with spin periods P > 12 s to establish an upper limit to the fraction of magnetars born with B > 1015 G (less than 1 per cent). As future detections keep increasing the magnetar and high-B pulsar statistics, our approach can be used to establish a severe constraint on the maximum magnetic field at birth of NSs. [ABSTRACT FROM AUTHOR]

We perform a detailed modelling of the post-outburst surface emission of the low magnetic field magnetar SGR 0418+5729. The dipolar magnetic field of this source, B=6×1012 G estimated from its spin-down rate, is in the observed range of magnetic fields for normal pulsars. The source is further characterized by a high pulse fraction and a single-peak profile. Using synthetic temperature distribution profiles, and fully accounting for the general-relativistic effects of light deflection and gravitational redshift, we generate synthetic X-ray spectra and pulse profiles that we fit to the observations. We find that asymmetric and symmetric surface temperature distributions can reproduce equally well the observed pulse profiles and spectra of SGR 0418. None the less, the modelling allows us to place constraints on the system geometry (i.e. the angles ψ and ξ that the rotation axis makes with the line of sight and the dipolar axis, respectively), as well as on the spot size and temperature contrast on the neutron star surface. After performing an analysis iterating between the pulse profile and spectra, as done in similar previous works, we further employed, for the first time in this context, a Markov-Chain Monte Carlo approach to extract constraints on the model parameters from the pulse profiles and spectra, simultaneously. We find that, to reproduce the observed spectrum and flux modulation: (a) the angles must be restricted to 65° ≲ ψ + ξ ≲ 125° or 235° ≲ ψ + ξ ≲ 295°; (b) the temperature contrast between the poles and the equator must be at least a factor of ~6, and (c) the size of the hottest region ranges between 0.2 and 0.7 km (including uncertainties on the source distance). Lastly, we interpret our findings within the context of internal and external heating models. [ABSTRACT FROM AUTHOR]

In 2013 April a new magnetar, SGR 1745-2900, was discovered as it entered an outburst, at only 2.4 arcsec angular distance from the supermassive black hole at the centre of the Milky Way, Sagittarius A*. SGR 1745-2900 has a surface dipolar magnetic field of ~2 x 1014 G, and it is the neutron star closest to a black hole ever observed. The new source was detected both in the radio and X-ray bands, with a peak X-ray luminosity LX ~ 5 x 1035 erg s-1. Here we report on the long-term Chandra (25 observations) and XMM-Newton (eight observations) X-ray monitoring campaign of SGR 1745-2900 from the onset of the outburst in 2013 April until 2014 September. This unprecedented data set allows us to refine the timing properties of the source, as well as to study the outburst spectral evolution as a function of time and rotational phase. Our timing analysis confirms the increase in the spin period derivative by a factor of ~2 around 2013 June, and reveals that a further increase occurred between 2013 October 30 and 2014 February 21. We find that the period derivative changed from 6.6 × 10-12 to 3.3 × 10-11 s s-1 in 1.5 yr. On the other hand, this magnetar shows a slow flux decay compared to other magnetars and a rather inefficient surface cooling. In particular, starquake-induced crustal cooling models alone have difficulty in explaining the high luminosity of the source for the first ~200 d of its outburst, and additional heating of the star surface from currents flowing in a twisted magnetic bundle is probably playing an important role in the outburst evolution. [ABSTRACT FROM AUTHOR]

The magnetic field strength at birth is arguably one of the most important properties to determine the evolutionary path of a neutron star. Objects with very high fields, collectively known as magnetars, are characterized by high X-ray quiescent luminosities, occurrence of outbursts, and, for some of them, sporadic giant flares. While the magnetic field strength is believed to drive their collective behaviour, however, the diversity of their properties, and, especially, the observation of magnetar-like bursts from 'low-field' pulsars, has been a theoretical puzzle. In this review, we discuss results of long-term simulations following the coupled evolution of the X-ray luminosity and the timing properties for a large, homogeneous sample of X-ray emitting isolated neutron stars, accounting for a range of initial magnetic field strengths, envelope compositions, and neutron star masses. In addition, by following the evolution of magnetic stresses within the neutron star crust, we can also relate the observed magnetar phenomenology to the physical properties of neutron stars, and in particular to their age and magnetic field strength and topology. The dichotomy of 'high-B' field pulsars versus magnetars is naturally explained, and occasional outbursts from old, low B-field neutron stars are predicted. We conclude by speculating on the fate of old magnetars, and by presenting observational diagnostics of the neutron star crustal field topology. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We present the detection of persistent soft X-ray radiation with ${L}_{x}\sim {10}^{41}$–1042 erg s–1 at the location of the extremely luminous, double-humped transient ASASSN-15lh as revealed by Chandra and Swift. We interpret this finding in the context of observations from our multiwavelength campaign, which revealed the presence of weak narrow nebular emission features from the host-galaxy nucleus and clear differences with respect to superluminous supernova optical spectra. Significant UV flux variability on short timescales detected at the time of the rebrightening disfavors the shock interaction scenario as the source of energy powering the long-lived UV emission, while deep radio limits exclude the presence of relativistic jets propagating into a low-density environment. We propose a model where the extreme luminosity and double-peaked temporal structure of ASASSN-15lh is powered by a central source of ionizing radiation that produces a sudden change in the ejecta opacity at later times. As a result, UV radiation can more easily escape, producing the second bump in the light curve. We discuss different interpretations for the intrinsic nature of the ionizing source. We conclude that, if the X-ray source is physically associated with the optical–UV transient, then ASASSN-15lh most likely represents the tidal disruption of a main-sequence star by the most massive spinning black hole detected to date. In this case, ASASSN-15lh and similar events discovered in the future would constitute the most direct probes of very massive, dormant, spinning, supermassive black holes in galaxies. Future monitoring of the X-rays may allow us to distinguish between the supernova hypothesis and the hypothesis of a tidal disruption event., Astronomy

We present a long-term study of the 2011 outburst of the magnetar Swift J1834.9−0846 carried out using new Chandra observations, as well as all the available Swift, RXTE and XMM–Newton data. The last observation was performed on 2011 November 12, about 100 d after the onset of the bursting activity that had led to the discovery of the source on 2011 August 7. This long time-span enabled us to refine the rotational ephemeris and observe a downturn in the decay of the X-ray flux. Assuming a broken power law for the long-term light curve, the break was at ∼46 d after the outburst onset, when the decay index changed from α ∼ 0.4 to ∼4.5. The flux decreased by a factor of ∼2 in the first ∼50 d and then by a factor of ∼40 until 2011 November (overall, by a factor of ∼70 in ∼100 d). At the same time, the spectrum, which was well described by an absorbed blackbody all along the outburst, softened, the temperature dropping from ∼1 to ∼0.6 keV. Diffuse X-ray emission extending up to 20 arcsec from the source was clearly detected in all Chandra observations. Its spatial and spectral properties, as well as its time evolution, are consistent with a dust-scattering halo due to a single cloud located at a distance of ≈200 pc from Swift J1834.9−0846, which should be in turn located at a distance of ∼5 kpc. Considering the time delay of the scattered photons, the same dust cloud might also be responsible for the more extended emission detected in XMM–Newton data taken in 2011 September. We searched for the radio signature of Swift J1834.9−0846 at radio frequencies using the Green Bank Radio Telescope and in archival data collected at Parkes from 1998 to 2003. No evidence for radio emission was found, down to a flux density of 0.05 mJy (at 2 GHz) during the outburst and ∼0.2–0.3 mJy (at 1.4 GHz) in the older data. [ABSTRACT FROM AUTHOR]

ABSTRACT Fallback discs around neutron stars (NSs) are believed to be an expected outcome of supernova explosions. Here we investigate the consequences of such a common outcome for the timing and spectral properties of the associated NS population, using Monte Carlo population synthesis models. We find that the long-term torque exerted by the fallback disc can substantially influence the late-time period distribution, but with quantitative differences which depend on whether the initial spin distribution is dominated by slow or fast pulsars. For the latter, a single-peaked initial spin distribution becomes bimodal at later times. Timing ages tend to underestimate the real age of older pulsars, and overestimate the age of younger ones. Braking indices cluster in the range 1.5 ≲ n≲ 3 for slow-born pulsars, and −0.5 ≲ n≲ 5 for fast-born pulsars, with the younger objects found predominantly below n≲ 3. Large values of n, while not common, are possible, and associated with torque transitions in the NS+disc system. The 0.1-10 keV thermal luminosity of the NS+disc system is found to be generally dominated by the disc emission at early times, yr, but this declines faster than the thermal surface emission of the NS. Depending on the initial parameters, there can be occasional periods in which some NSs switch from the propeller to the accretion phase, increasing their luminosity up to the Eddington limit for ∼103-104 years. [ABSTRACT FROM AUTHOR]

ABSTRACT The return to the quiescent state of the anomalous X-ray pulsar (AXP) XTE J1810−197 following its 2003 outburst represents a unique opportunity to probe the surface emission properties of a magnetar. The quiescent emission of XTE J1810−197 is composed of two thermal components, one arising from the whole star surface and the other from a small warm spot on it. By modelling the magnitude and shape of the pulse profile in narrow spectral bands, we have been able to constrain the physical characteristics and geometrical parameters of the system: the two angles that the line of sight and the spin axis make with respect to the warm spot axis (ψ and ξ respectively), the angular size of the spot and the overall surface temperature distribution. Our modelling accounts for the general relativistic effects of gravitational redshift and light bending near the stellar surface, and allows for local anisotropic emission. We found that the surface temperature distribution on the neutron star is consistent with the expectations of a dipole magnetic field configuration; the local radiation requires a pencil-beamed emission pattern, suggesting the presence of a magnetized atmosphere. For a typical value of the radius, R= 13 km, the viewing parameters (symmetric for an interchange between ψ and ξ) range from ψ=ξ= 38° to (ψ, ξ)=(52°, 29°). These angles are consistent with those obtained by modelling the AXP in outburst, with uncertainty contours reduced by a factor of 2.5. [ABSTRACT FROM AUTHOR]

We report on the detailed study of the 2008 October outburst from the anomalous X-ray pulsar 1E 5408 discovered through the Swift/Burst Alert Telescope (BAT) detection of soft gamma-ray repeater like short X-ray bursts on 2008 October 3. The Swift/X-ray Telescope (XRT) started observing the source after less than 100 s since the BAT trigger, when the flux ( in the 2-10 keV range) was >50 times higher than its quiescent level. Swift monitored the outbursting activity of 1E 5408 on a daily basis for approximately three weeks. This strategy allowed us to find a phase-coherent solution for the source pulsations after the burst, which, besides P and , requires a positive term (spin-down increase). The time evolution of the pulse shape is complex and variable, with the pulsed fraction increasing from 20 to 50 per cent within the Swift observational window. The XRT spectra can be fitted well by means of a single component, either a power law (PL) or a blackbody. During the very initial phases of the outburst the spectrum is hard, with a PL photon index (or ), which steepens to (or ) within one day from the BAT trigger, though the two components are likely present simultaneously during the first-day spectra. An INTEGRAL observation carried out five days after the trigger provided an upper limit of to the emission of 1E 5408 in the 18-60 keV band. [ABSTRACT FROM AUTHOR]

We report on submillimetre bolometer observations of the isolated neutron star RX J1856.5−3754 using the Large Apex Bolometer Camera bolometer array on the Atacama Pathfinder Experiment telescope. No cold dust continuum emission peak at the position of RX J1856.5−3754 was detected. The 3σ flux density upper limit of 5 mJy translates into a cold dust mass limit of a few earth masses. We use the new submillimetre limit, together with a previously obtained H-band limit, to constrain the presence of a gaseous, circumpulsar disc. Adopting a simple irradiated disc model, we obtain a mass accretion limit of and a maximum outer disc radius of . By examining the projected proper motion of RX J1856.5−3754, we speculate about a possible encounter of the neutron star with a dense fragment of the CrA molecular cloud a few thousand years ago. [ABSTRACT FROM AUTHOR]

We report here on the outburst onset and evolution of the new soft gamma-ray repeater SGR 0501+4516. We monitored the new SGR with XMM–Newton starting on 2008 August 23, 1 day after the source became burst active, and continuing with four more observations in the following month, with the last one on 2008 September 30. Combining the data with the Swift X-ray telescope ( Swift–XRT) and Suzaku data, we modelled the outburst decay over a 3-month period, and we found that the source flux decreased exponentially with a time-scale of . In the first XMM–Newton observation, a large number of short X-ray bursts were observed, the rate of which decayed drastically in the following observations. We found large changes in the spectral and timing behaviour of the source during the first month of the outburst decay, with softening emission as the flux decayed, and the non-thermal soft X-ray spectral component fading faster than the thermal one. Almost simultaneously to our second and fourth XMM–Newton observations (on 2008 August 29 and September 2), we observed the source in the hard X-ray range with INTEGRAL, which clearly detected the source up to ∼100 keV in the first pointing, while giving only upper limits during the second pointing, discovering a variable hard X-ray component fading in less than 10 days after the bursting activation. We performed a phase-coherent X-ray timing analysis over about 160 days starting with the burst activation and found evidence of a strong second derivative period component [ ]. Thanks to the phase connection, we were able to study the phase-resolved spectral evolution of SGR 0501+4516 in great detail. We also report on the ROSAT quiescent source data, taken back in 1992 when the source exhibits a flux ∼80 times lower than that measured during the outburst, and a rather soft, thermal spectrum. [ABSTRACT FROM AUTHOR]

We report on two new XMM–Newton observations of the anomalous X-ray pulsar (AXP) 4U 0142+614 performed in 2004 March and July, collecting the most accurate spectrum for this source. Furthermore, we analyse two short archival observations performed in 2002 February and 2003 January in order to study the long-term behaviour of this AXP. 4U 0142+614 appears to be relatively steady in flux between 2002 and 2004, and the phase-averaged spectrum does not show any significant variability between the four epochs. We derive the deepest upper limits to date on the presence of lines in 4U 0142+614 spectrum as a function of energy: equivalent width in the 1–3 keV energy range <4 and <8 eV for narrow and broad lines, respectively. A remarkable energy dependence in both the pulse profile and the pulsed fraction is detected, and consequently pulse–phase spectroscopy shows spectral variability as a function of phase. By making use of XMM–Newton and INTEGRAL data, we successfully model the 1–250 keV spectrum of 4U 0142+614 with three models, namely the canonical absorbed blackbody plus two power laws, a resonant cyclotron scattering model plus one power-law and two log-parabolic functions. [ABSTRACT FROM AUTHOR]

We compute the probability that intermediate mass black holes (IMBHs) capture companions due to dynamical interactions and become accreting sources, and explore the possibility that the accreting IMBHs would appear as ultraluminous X-ray sources (ULXs). We focus on IMBHs originating from low-metallicity Population III stars. Two channels of IMBH formation are considered: from primordial haloes in the framework of hierarchical clustering, and from non-mixed, zero-metallicity primeval gas in galactic discs. IMBHs can form binary systems due to tidal captures of single stars and exchange interactions with existing binary systems in galactic discs. We find that neither formation mechanism of the accreting IMBH binary is able to provide enough sources to explain the observed population of ULXs. Even at sub-ULX luminosity, the total number of accreting IMBHs with with dynamically captured companions is found to be <0.01 per galaxy. [ABSTRACT FROM AUTHOR]

The unusual Plio-Pleistocene arcid Ambrogia mytiloides (Brocchi, 1814) has a large, elongate, smooth and streamlined shell. On the basis of these characters and the occurrence of moderate shell torsion, the mode of life of this species was formerly thought to be semi-infaunal endobyssate, obliquely oriented like the twisted arcid Trisidos . The discovery of shells in life position suggests that this species lived in a subvertical position. Rather than a recliner, this arcid was then a sticker, whose stability was provided by the byssus, which also was used to aid the bivalve in burrowing, and by its large size. The morphology of juvenile valves, smaller than 4 mm, suggests an epibyssate mode of life in its early growth stages. Ambrogia represents a remarkable pathway in the secondary return of arcids to soft bottoms: with this genus, they reached their deepest burrowing level. However, this strategy was not very successful, probably because of evolutionary constraints on the Arcoida. [ABSTRACT FROM AUTHOR]

ABSTRACT Rapid, hyper-Eddington accretion is likely to power the central engines of gamma-ray bursts (GRBs). In the extreme conditions of densities and temperatures the accreting torus is cooled by neutrino emission rather than by radiation. Another important cooling mechanism is the advection of energy into the central black hole. We compute the time evolution of a neutrino-dominated disc that proceeds during the burst and investigate the changes in its density and temperature. The discrimination between short and long bursts is made on the basis of the different rates of material inflow to the outer parts of the disc, thus favouring the binary merger scenario for the short GRBs and the collapsar scenario for the long GRBs. Within the context of the collapsar model, we also study the evolution of the photon luminosity of the remnant disc up to times of ∼1 d, and we discuss its implications for the production of emission lines in GRB spectra. [ABSTRACT FROM AUTHOR]

We investigate through dedicated numerical simulations the evolution of the soft X-ray absorption properties of a cloud surrounding a gamma-ray burst source. We show that the absorption properties of the material are strongly modified by the ionization induced by the intense burst flux. We derive the temporal evolution of the measured column density as a function of the density and size of the absorbing medium. Even if their statistical significance is not extremely compelling, we find that the detection in several bursts of variable absorption during the gamma-ray phase can be accounted for if these bursts are associated to overdense regions in molecular clouds with properties similar to those of star formation globules. We fit our model variable column density to the data of GRB 980329 and GRB 780506, showing that with this method the size, density and density distribution of the material surrounding a burst can be measured. [ABSTRACT FROM AUTHOR]

Most of the baryons in the low-redshift Universe reside in a warm/hot component which is difficult to detect with standard absorption/emission-line techniques. We propose to use quasar refractive scintillation as a useful, complementary probe for such ionized, intergalactic gas. In particular, an application to the case of the intracluster medium is presented. We show that clusters located at z≈0.02 should produce a source rms intensity fluctuation at 50–100 GHz of several tens of per cent and on time-scales ranging from days to months, depending on the projected location of the source on the foreground cluster. However, in order to produce such a signal, the source needs to be very compact. This effect, if observed, can be used as an independent test of the baryonic mass fraction in clusters. [ABSTRACT FROM AUTHOR]

Gallerista, organizzatrice e curatrice di mostre, Romana Loda è stata un personaggio chiave nella diffusione dell'arte delle donne in Italia negli anni Settanta: l'articolo si propone di riconsiderare il suo ruolo, concentrandosi sulle esposizioni al femminile da lei organizzate tra il 1974 e il 1978. Rileggere l'attività di Loda consente di affrontare alcuni nodi essenziali del dibattito critico sul femminismo e sull'arte delle donne, in particolare la presa di coscienza e la denuncia delle disparità tra i sessi, le difficoltà delle artiste nell'accesso agli spazi espositivi e nel rapporto con le istituzioni, e, soprattutto, il ruolo controverso delle cosiddette mostre "ghetto".

Objective: A common SVT is the Test of Memory Malingering (TOMM). Clinicians have recently begun using an abbreviated version of the TOMM; however, to date, no research has specifically looked at children with ADHD. Our hypothesis is that children with ADHD who pass TOMM1 also pass Trial2. Method: Data were collected on 144 children (boys = 66%, girls = 34%; age range 6–18) who were referred due to academic and behavioral problems. All children were diagnosed with ADHD. No children were involved in litigation, custody disputes, or recent accidents or had intellectual disability or brain injuries. Participants completed a neuropsychological evaluation and data was analyzed via SPSS. Analyses included frequencies, SN, SP, PPV, and NPV. Results: Mean FSIQ was 88.7 (15.9). On TOMM1, 40% (n = 58) of the sample scored below the established cutoff. Of those who scored above the TOMM Trial2 cutoff on Trial1, 100% (n = 86) went on to meet/exceed the cut score for Trial2. TOMM Trial1 scores were significantly positively correlated with TOMM Trial2 scores (r = .631, p = .000). For TOMM1, optimal results were >40 (SN = 90%, SP = 92%, NPV = 99%). Conclusion(s): Growing data support a high likelihood of passing Trail2, if Trial1 was passed. Our results indicate that a score < 40 on Trial1 is suggestive of poor effort and a high likely to fail the TOMM in children with ADHD. If a passing score is achieved during Trial1, 99% of cases also passed Trial2. Only administering Trial1 to determine effort could be time and diagnostically efficient. [ABSTRACT FROM AUTHOR]