Context. The compact radio source Sagittarius A* (Sgr A*) at the centre of our Galaxy harbours a supermassive black hole, whose mass (≈3.7 $\times$ 106 $M_{\odot}$) has been measured from stellar ...orbital motions. Sgr A* is therefore the nearest laboratory where super-massive black hole astrophysics can be tested, and the environment of black holes can be investigated. Since it is not an active galactic nucleus, it also offers the possibility of observing the capture of small objects that may orbit the central black hole. Aims. We study the effects of the strong gravitational field of the black hole on small objects, such as a comet or an asteroid. We also explore the idea that the flares detected in Sgr A* might be produced by the final accretion of single, dense objects with mass of the order of 1020 g, and that their timing is not a characteristic of the sources, but rather of the space-time of the central galactic black hole in which they are moving. Methods. The problem of tidal disruption of small objects by a black hole is studied numerically, using ray-tracing techniques, in a Schwarzschild background. Results. We find that tidal effects are strong enough to melt sufficiently massive, solid objects, and present calculations of the temporal evolution of the light curve of infalling objects as a function of various parameters. Our modelling of tidal disruption suggests that during tidal squeezing, the conditions for synchrotron radiation can be met. We show that the light curve of a flare can be deduced from dynamical properties of geodesic orbits around black holes and that it depends only weakly on the physical properties of the source.
Context. Low-mass satellites, like asteroids and comets, are expected to be present around the black hole at the Galactic center. We consider small bodies orbiting a black hole, and we study the ...evolution of their orbits due to tidal interaction with the black hole. Aims. In this paper we investigate the consequences of the existence of plunging orbits when a black hole is present. We are interested in finding the conditions that exist when capture occurs. Methods. Earlier analysis of the evolution of classical Keplerian orbits was extended to relativistic orbits around a Schwarzschild black hole. Results. The main difference between the Keplerian and black hole cases is in the existence of plunging orbits. Orbital evolution, leading from bound to plunging orbits, goes through a “final” unstable circular orbit. On this orbit, tidal energy is released on a characteristic black hole timescale. Conclusions. This process may be relevant for explaining how small, compact clumps of material can be brought onto plunging orbits, where they may produce individual short duration accretion events. The available energy and the characteristic timescale are consistent with energy released and the timescale typical of Galactic flares.
Background
Grass pollen‐related seasonal allergic rhinoconjunctivitis (SARg) is clinically heterogeneous in severity, comorbidities, and response to treatment. The component‐resolved diagnostics ...disclosed also a high heterogeneity at molecular level. Our study aimed at analyzing the characteristics of the IgE sensitization to Phleum pratense molecules and investigating the diagnostic relevance of such molecules in childhood.
Methods
We examined 1120 children (age 4‐18 years) with SARg. Standardized questionnaires on atopy were acquired through informatics platform (AllergyCARD™). Skin prick tests were performed with pollen extracts. Serum IgE to airborne allergens and eight P. pratense molecules (rPhl p 1, rPhl p 2, rPhl p 4, rPhl p 5b, rPhl p 6, rPhl p 7, rPhl p 11, rPhl p 12) were tested by ImmunoCAP FEIA.
Results
The analysis of IgE responses against eight P. pratense molecules showed 87 profiles. According to the number of molecules recognized by IgE, the more complex profiles were characterized by higher serum total IgE, higher grass‐specific serum IgE, and higher number and degree of sensitization to pollens. The most frequent IgE sensitization profile was the monomolecular Phl p 1. Sensitization to Phl p 7 was a reliable biomarker of asthma, whereas Phl p 12 of oral allergy syndrome. Sensitization to Phl p 7 was associated with a higher severity of SARg, and complex profiles were associated with longer disease duration.
Conclusions
In a large pediatric population, the complexity of IgE sensitization profiles against P. pratense molecules is related to high atopic features although useless for predicting the clinical severity. The detection of serum IgE to Phl p 1, Phl p 7, and Phl p 12 can be used as clinical biomarkers of SARg and comorbidities. Further studies in different areas are required to test the impact of different IgE molecular profiles on AIT response.
Background
Pollen‐food syndrome (PFS) is heterogeneous with regard to triggers, severity, natural history, comorbidities, and response to treatment. Our study aimed to classify different endotypes of ...PFS based on IgE sensitization to panallergens.
Methods
We examined 1271 Italian children (age 4–18 years) with seasonal allergic rhinoconjunctivitis (SAR). Foods triggering PFS were acquired by questionnaire. Skin prick tests were performed with commercial pollen extracts. IgE to panallergens Phl p 12 (profilin), Bet v 1 (PR‐10), and Pru p 3 (nsLTP) were tested by ImmunoCAP FEIA. An unsupervised hierarchical agglomerative clustering method was applied within PFS population.
Results
PFS was observed in 300/1271 children (24%). Cluster analysis identified five PFS endotypes linked to panallergen IgE sensitization: (i) cosensitization to ≥2 panallergens (‘multi‐panallergen PFS’); (ii–iv) sensitization to either profilin, or nsLTP, or PR‐10 (‘mono‐panallergen PFS’); (v) no sensitization to panallergens (‘no‐panallergen PFS’). These endotypes showed peculiar characteristics: (i) ‘multi‐panallergen PFS’: severe disease with frequent allergic comorbidities and multiple offending foods; (ii) ‘profilin PFS’: oral allergy syndrome (OAS) triggered by Cucurbitaceae; (iii) ‘LTP PFS’: living in Southern Italy, OAS triggered by hazelnut and peanut; (iv) ‘PR‐10 PFS’: OAS triggered by Rosaceae; and (v) ‘no‐panallergen PFS’: mild disease and OAS triggered by kiwifruit.
Conclusions
In a Mediterranean country characterized by multiple pollen exposures, PFS is a complex and frequent complication of childhood SAR, with five distinct endotypes marked by peculiar profiles of IgE sensitization to panallergens. Prospective studies in cohorts of patients with PFS are now required to test whether this novel classification may be useful for diagnostic and therapeutic purposes in the clinical practice.
Hexavalent vaccines, protecting against six diseases (diphtheria, tetanus, pertussis DTaP, poliovirus, hepatitis B virus HBV, and Haemophilus influenzae type b Hib, are routinely the standard of care ...in Europe. The use of combined vaccines allows the reduction of number of injections and side effects, the reduction of costs, and the increase in adherence of the family to the vaccination schedule both in terms of the number of doses and timing. The safety profile, efficacy and effectiveness of hexavalent vaccines have been extensively documented in infants and children born at term, and data are accumulating in preterm infants. Hexavalent vaccines are particularly important for preterm infants, who are at increased risk for severe forms of vaccine preventable diseases. However, immunization delay has been commonly reported in this age group. All the three hexavalent vaccines currently marketed in Italy can be used in preterm infants, and recent data confirm that hexavalent vaccines have a similar or lower incidence of adverse events in preterm compared to full-term infants; this is likely due to a weaker immune system response and reduced ability to induce an inflammatory response in preterm infants. Apnoea episodes are the adverse events that can occur in the most severe preterm infants and / or with history of respiratory distress. The risk of apnoea after vaccination seems to be related to a lower gestational age and a lower birth weight, supporting the hypothesis that it represents an unspecific response of the preterm infant to different procedures. High seroprotection rates have been reported in preterm infants vaccinated with hexavalent vaccine. However, a lower gestational age seems to be associated with lower antibody titres against some vaccine antigens (e.g. HBV, Hib, poliovirus serotype 1, and pertussis), regardless of the type of hexavalent vaccine used. Waiting for large effectiveness studies, hexavalent vaccines should be administered in preterm infants according to the same schedule recommended for infants born at term, considering their chronological age and providing an adequate monitoring for cardio-respiratory events in the 48-72 h after vaccination, especially for infants at risk of recurrence of apnoea.
We compute the virial mass (M) of the central black hole and the luminosity-to-mass (L/M) ratio of ≈300 low-z quasars and luminous type 1 Seyfert nuclei. We analyse the following: (1) whether ...radio-quiet and radio-loud objects show systematic differences in terms of M and L/M; (2) the influence of M and L/M on the shape of the Hβ broad component line profile; and (3) the significance of the so-called ‘blue outliers’, i.e. sources showing a significant blueshift of the O iiiλλ4959,5007 lines with respect to the narrow component of Hβ, which is used as an estimator of the quasar reference frame. We show that M and L/M distributions for radio-quiet and radio-loud sources are probably different for samples matched in luminosity and redshift, in the sense that radio-quiet sources have systematically smaller masses and larger L/M. However, the L/M ratio distributions become indistinguishable if 8.5 < log M < 9.5. Line profile comparisons for median spectra computed over narrow ranges of M and L/M indicate that a Lorentz function provides a better fit for higher L/M sources and a double Gaussian for lower L/M values. A second (redshifted) Gaussian component at low L/M appears as a red asymmetry frequently observed in radio-loud and radio-quiet sources with broader (full width at half-maximum ≳4000 km s−1) Hβ broad component profiles. This component becomes stronger in larger mass and lower L/M sources. No specific influence of radio loudness on the Hβ broad component profile is detected, although equivalent widths of Hβ broad component and especially of O iiiλλ4959,5007 are larger for radio-loud sources. We identify five more ‘blue outlier’ sources. Since these sources are, on average, one magnitude brighter than other active galactic nuclei with similar mass, their resulting Eddington ratio is 2–3 times higher. We hint at evolutionary effects that explain some of these results, and reinforce the ‘eigenvector 1’ correlations.
The Crab nebula pulsar was observed in 2009 January and December with a novel very fast optical photon counter, Iqueye, mounted at the ESO 3.5 m New Technology Telescope. Thanks to the exquisite ...quality of the Iqueye data, we computed accurate phase coherent timing solutions for the two observing runs and over the entire year 2009. Our statistical uncertainty on the determination of the phase of the main pulse and the rotational period of the pulsar for short (a few days) time intervals are 1 μs and ∼0.5 ps, respectively. Comparison with the Jodrell Bank radio ephemerides shows that the optical pulse leads the radio one by ∼ 240 μs in January and ∼ 160 μs in December, in agreement with a number of other measurements performed after 1996. A third-order polynomial fit adequately describes the spin-down for the 2009 January plus December optical observations. The phase noise is consistent with being Gaussian distributed with a dispersion σ of 15 μs in most observations, in agreement with theoretical expectations for photon noise-induced phase variability.
What brakes the Crab pulsar? Čadež, A.; Zampieri, L.; Barbieri, C. ...
Astronomy and astrophysics (Berlin),
03/2016, Volume:
587
Journal Article
Peer reviewed
Open access
Context. Optical observations provide convincing evidence that the optical phase of the Crab pulsar follows the radio one closely. Since optical data do not depend on dispersion measure variations, ...they provide a robust and independent confirmation of the radio timing solution. Aims. The aim of this paper is to find a global mathematical description of Crab pulsar’s phase as a function of time for the complete set of published Jodrell Bank radio ephemerides (JBE) in the period 1988−2014. Methods. We apply the mathematical techniques developed for analyzing optical observations to the analysis of JBE. We break the whole period into a series of episodes and express the phase of the pulsar in each episode as the sum of two analytical functions. The first function is the best-fitting local braking index law, and the second function represents small residuals from this law with an amplitude of only a few turns, which rapidly relaxes to the local braking index law. Results. From our analysis, we demonstrate that the power law index undergoes “instantaneous” changes at the time of observed jumps in rotational frequency (glitches). We find that the phase evolution of the Crab pulsar is dominated by a series of constant braking law episodes, with the braking index changing abruptly after each episode in the range of values between 2.1 and 2.6. Deviations from such a regular phase description behave as oscillations triggered by glitches and amount to fewer than 40 turns during the above period, in which the pulsar has made more than 2 × 1010 turns. Conclusions. Our analysis does not favor the explanation that glitches are connected to phenomena occurring in the interior of the pulsar. On the contrary, timing irregularities and changes in slow down rate seem to point to electromagnetic interaction of the pulsar with the surrounding environment.
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