Context. The isolated neutron star (INS) 2XMM J104608.7-594306 is one of the only two to be discovered through their thermal emission since the ROSAT era. Possibly a remnant of a former generation of ...massive stars in the Carina nebula, the exact nature of the source is unclear, and it might be unique amongst the several classes of Galactic INSs. Aims. In a first dedicated XMM-Newton observation of the source, we found intriguing evidence of a very fast spin period of P ~ 18.6 ms at the 4σ confidence level. Moreover, spectral features in absorption have also been identified. We re-observed 2XMM J104608.7-594306 with XMM-Newton to better characterise the spectral energy distribution of the source, confirm the candidate spin period, and possibly constrain the pulsar spin-down. Methods. We used the two XMM-Newton observations of 2XMM J104608.7-594306 to perform detailed timing and spectral X-ray analysis. Both the spin-down rate and the energy of the spectral features provide estimates on the neutron star magnetic field, which are crucial for investigating the evolutionary state of the neutron star. Results. Statistically acceptable spectral fits and meaningful physical parameters for the source are only obtained when the residuals at energies 0.55 keV and 1.35 keV are taken into account by the spectral modelling. While the former can result from the inhomogeneous temperature distribution on the surface of the neutron star or can be related to a local overabundance of oxygen in the Carina nebula, the one at 1.35 keV is only satisfactorily accounted for by invoking a line in absorption. In this case, the best-fit neutron star atmosphere models constrain the hydrogen column density, the effective temperature, and the luminosity of the source within NH = (2.5−3.3) × 1021 cm-2, Teff = (6−10) × 105 K, and LX = (1.1−7.4) × 1032 erg s-1. The implied distance is consistent with a location in (or in front of) the Carina nebula, and radiation radii are compatible with emission originating on most of the surface. Non-thermal X-ray emission is ruled out at levels above 0.5% (3σ) of the source luminosity. Unfortunately, the second XMM-Newton observation proved inconclusive in terms of confirming (discarding) the fast candidate spin, providing an upper limit on the pulsed fraction of the source that is very close to the limiting sensitivity for detecting the modulation found previously. Conclusions. In the absence of an unambiguous period determination and an estimate of the magnetic field, the nature of the source remains open to interpretation. Its likely association with the Carina cluster and its overall spectral properties (only shared by a handful of other peculiar INSs) disfavour a standard evolutionary path or one in which the source was previously recycled by accretion in a binary system. The star 2XMM J104608.7-594306 may be similar to Calvera (1RXS J141256.0+792204), a neutron star for which the scenario of an evolved anti-magnetar has been discussed. A better age estimate and deeper radio and γ-ray limits are required to further constrain the evolutionary state of the neutron star.
We present the last chapter of a spectroscopy program aimed at deriving the redshift or a lower limit to the redshift of BL Lac objects using medium-resolution spectroscopy. Here we report new ...spectra for 33 BL Lac object candidates obtained in 2008-2009, confirming the BL Lac nature of 25 sources and obtaining new redshifts for 5 objects. These new observations are combined with our previous data in order to construct a homogeneous sample of ~70 BL Lac objects with high-quality spectroscopy. All these spectra can be accessed at the Web site http://www.oapd.inaf.it/zbllac/. The average spectrum, beaming properties of the full sample, discussion of intervening systems, and future perspectives are addressed.
Context. Blazars are the most luminous and variable active galactic nuclei (AGNs). They are thus excellent probes of accretion and emission processes close to the central engine. Aims. We concentrate ...here on PKS 1510–089 (z = 0.36), a blazar belonging to the flat-spectrum radio quasar subclass, an extremely powerful gamma-ray source and one of the brightest in the Fermi-LAT catalog. We aim to study the complex variability of this blazar’s bright multiwavelength spectrum, to identify the physical parameters responsible for the variations and the timescales of possible recurrence and quasi-periodicity at high energies. Methods. The blazar PKS 1510–089 was observed twice in hard X-rays with the IBIS instrument onboard INTEGRAL during the flares of Jan. 2009 and Jan. 2010, and simultaneously with Swift and the Nordic Optical Telescope (NOT), in addition to the constant Fermi monitoring. We also measured the optical polarization in several bands on 18 Jan. 2010 at the NOT.Using these and archival data we constructed historical light curves at gamma-to-radio wavelengths covering nearly 20 yr and applied tests of fractional and correlated variability. We assembled spectral energy distributions (SEDs) based on these data and compared them with those at two previous epochs, by applying a model based on synchrotron and inverse Compton radiation from blazars. Results. The modeling of the SEDs suggests that the physical quantities that undergo the largest variations are the total power injected into the emitting region and the random Lorentz factor of the electron distribution cooling break, that are higher in the higher gamma-ray states. This suggests a correlation of the injected power with enhanced activity of the acceleration mechanism. The cooling likely takes place at a distance of ~1000 Schwarzschild radii(~0.03 pc) from the central engine – a distance muchsmaller than the broad line region (BLR) radius.The emission at a few hundred GeV can be reproduced with inverse Compton scattering of highly relativistic electrons off far-infrared photons if these are located much farther than the BLR, that is, around 0.2 pc from the AGN, presumably in a dusty torus. We determine a luminosity of the thermal component due to the inner accretion disk of Ld ≃ 5.9 × 1045 erg s-1, a BLR luminosity of LBLR ≃ 5.3 × 1044 erg s-1, and a mass of the central black hole of MBH ≃ 3 × 108 M⊙.The fractional variability as a function of wavelength follows the trend expected if X- and gamma-rays are produced by the same electrons as radio and optical photons, respectively.Discrete correlation function (DCF) analysis between the long-term Steward observatory optical V-band and gamma-ray Fermi-LAT light curves yields a good correlation with no measurable delay. Marginal correlation where X-ray photons lag both optical and gamma-ray ones by time lags between 50 and 300 days is found with the DCF.Our time analysis of the RXTE PCA and Fermi-LAT light curves reveals no obvious (quasi-)periodicities, at least up to the maximum timescale (a few years) probed by the light curves, which are severely affected by red noise.
We investigate the optical spectral properties of the blazar PKS 1222+216 during a period of approximately three years. While the continuum is highly variable i.e. from λL
λ(5100 Å) ∼ 3.5 × 1045 erg ...s−1 up to ∼15.0 × 1045 erg s−1 the broad line emission is practically constant. This supports a scenario in which the broad line region is not affected by jet continuum variations. We thus infer the thermal component of the continuum from the line luminosity and show that it is comparable with the continuum level observed during the phases of minimum optical activity. The mass of the black hole is estimated through the virial method from the full width at half-maximum of Mg ii, Hβ and Hα broad lines and from the thermal continuum luminosity. This yields a consistent black hole mass value of ∼6 × 108 M⊙.
Freezing of Gait (FOG) is one of the most disturbing and least understood symptom in advanced stage of Parkinson's disease (PD). The contribution of the underlying pathological process and the ...antiparkinsonian treatment to the development of FOG are controversial.
To study the relationships between clinical features of PD and therapeutic modalities in patients with advanced PD and FOG.
Consecutive patients with 5 years or more of PD symptoms (n = 172) (99 men) with mean age at symptoms onset of 58.3 +/- 13.2 years and mean symptoms duration of 11.8 +/- 5.6 years were studied. Clinical data were collected during the last office visit through physical examination, detailed history, review of patients' charts, and other documents. A patient was considered as "freezer" if he/she reported recent experience that the legs got stuck to the ground while trying to walk. The presence of dyskinesia, early morning dystonia or significant postural reflex abnormalities were assessed through history and neurological examination. Duration of treatment with antiparkinsonian drugs was calculated from history charts. Chi square and t test were used to compare the patients with and without FOG. Logistic regression was used for the comparison of association between the presence of FOG (dependent variable) disease duration and disease stage (explanatory variables) and duration of treatment with anti-parkinsonian drugs.
The study population consisted of 45 patients at Hoehn and Yahr (H&Y) stage 2.5 (26%), 104 patients at stage 3 (60.5%), and 23 patients at H&Y stages 4-5 (13.5%). Ninety one patients (53%) reported FOG at the time of the study. Severity of the disease expressed by H&Y stage at "off" was a significant contributing factor for FOG with a significant trend (z = 4.38, p < 0.0001), as was longer duration of levodopa treatment, and confirmed by FOG using the multivariate logistic regression (p = 0.01 and p = 0.004, respectively). Using a univariate model, longer duration of treatment with dopamine agonists contribute to the appearance of FOG (p = 0.07) while longer duration of amantadine treatment decreased the appearance of FOG (p = 0.09). There was a significant association between FOG and the presence of dyskinesia (p < 0.002), early morning foot dystonia (p < 0.003) and significant postural instability (p < 0.0005).
FOG is a common symptom in advanced PD. It is mainly related to disease progression and levodopa treatment.
The ultraviolet (UV) spectra of 16 blazars (〈z〉≃ 1) from the archives of the Hubble Space Telescope Faint Object Spectrograph have been analysed in order to study in a systematic way the properties ...of their broad UV emission lines. We find that the luminosities of the most prominent and intense lines, Lyα and C ivλ1549, are similar to those of normal radio-loud quasars at comparable redshifts. However, the equivalent widths of blazar lines are significantly smaller than those of radio-loud quasars. Therefore, while the intrinsic broad-line region luminosity of blazars appears to be indistinguishable from that of radio-loud quasars, their continuum must be comparatively higher, most probably due to relativistic beaming. We have combined the UV luminosities of the debeamed continuum with the emitting gas velocity to derive estimates of the masses of the central supermassive black holes. The size of the broad-line region was computed in two ways: (1) via an empirical relationship between UV continuum luminosity and broad-line region size, and (2) through the external photon density required by blazar models to reproduce the inverse Compton components observed at γ-rays. The second method yields significantly different results from the first method, suggesting that it provides only a very rough estimate or a lower limit on the size of the broad-line region. We find that the average mass of the central black holes in blazars is ∼2.8 × 108 M⊙, with a large dispersion, comparable to those computed for other radio-loud active galactic nuclei.
Aims. We consider isolated compact remnants (ICoRs), i.e. neutrons stars and black holes that do not reside in binary systems and therefore cannot be detected as X-ray binaries. ICoRs may represent ... ~5 percent of the stellar mass budget of the Galaxy, but they are very hard to detect. Here we explore the possibility of using microlensing to identify ICoRs. Methods. In a previous paper we described a simulation of neutron star evolution in phase space in the Galaxy, taking into account the distribution of the progenitors and the kick at formation. Here we first reconsider the evolution and distribution of neutron stars and black holes with an added a bulge component. From the new distributions we calculate the microlensing optical depth, event rate and distribution of event time scales, comparing and contrasting the case of ICoRs and “normal stars”. Results. We find that the contribution of remnants to optical depth is slightly lower than without kinematics, owing to the evaporation from the Galaxy. On the other hand, the relative contribution to the rate of events is a factor ~5 higher. In all, ~6−7 percent of the events are likely related to ICoRs. In particular, ~30−40 percent of the events with duration >100 days are possibly related to black holes. Conclusions. It seems therefore that microlensing observations are a suitable tool to probe the population of Galactic ICoRs.
Aims. We attempt to determine the spectroscopic redshifts of bright BL Lac objects, which have proven difficult to measure. Methods. We use the spectra acquired using the newly available spectrograph ...X-Shooter at the European Southern Observatory Very Large Telescope, which combines high resolution with a large wavelength range, to obtain ultraviolet to near-infrared spectra of BL Lacs. Results. Our observations of PKS 0048-097 detect three emission lines, which permit us to derive a redshift z = 0.635. Moreover, we discover a Mg II absorption system at z = 0.154 that is associated with a foreground spiral galaxy a 50 kpc of projected distance. Conclusions. The measured redshift allows us to discuss the optical beaming factor and the absorption of the high energy spectrum by the extragalactic background light.
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