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.
On the cool gaseous haloes of quasars Farina, E. P; Falomo, R; Decarli, R ...
Monthly notices of the Royal Astronomical Society,
02/2013, Letnik:
429, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present the optical spectroscopy of projected quasar (QSO) pairs in order to investigate the Mg ii and C iv absorption features imprinted on the spectrum of the background object by the gaseous ...halo surrounding the foreground QSO. We have observed 13 projected pairs in the redshift range 0.7 z
F 2.2, spanning projected separations between 60 and 120 kpc. In the spectra of the background QSOs, we have identified Mg ii intervening absorption systems associated with the foreground QSOs in seven out of 10 pairs, and one absorption system out of three is found for C iv. The distribution of the equivalent width (EW) as a function of the impact parameter shows that, unlike the case of normal galaxies, some strong absorption systems (EWr > 1 Å) are also present beyond a projected radius of ∼70 kpc. If we take into account the mass of the galaxies as an additional parameter that influences the extent of the gaseous haloes, the distribution of the absorptions connected to the QSOs is consistent with that of galaxies. In the spectra of the foreground QSOs, we do not detect any Mg ii absorption lines originated by the gas surrounding the QSO itself, but in two cases, these features are present for C iv. A comparison between the absorption features observed in the transverse direction and those along the line of sight allows us to comment on the distribution of the absorbing gas and on the emission properties of the QSOs.
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.
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.
Aims. The detection of old neutron stars and stellar mass black holes in isolation is one of the most sought after goals of compact object astrophysics. Microlensing surveys may help in achieving ...this aim because the lensing mechanism is independent of the emission properties of the lens. Several black hole candidates have indeed been detected by means of microlensing observations have been reported in the literature. The identification of counterparts, especially in the X-rays, would be a strong argument in favor of the compact nature of these lenses. Methods. We perform a cross-correlation between the catalogs of microlensing events produced by the OGLE, MACHO, and MOA teams, and those of X-rays sources from the data acquired by the XMM-Newton and Chandra satellites. On the basis of our previous work, we select only microlensing events with durations longer than one hundred days, which should contain a large fraction of lenses as compact objects. Our matching criterion takes into account the positional coincidence on the sky. Results. We find a single match between a microlensing event, OGLE-2004-BLG-081 (tE ~ 103 days), and the X-ray source 2XMM J180540.5-273427. The angular separation is ~0.5 arcsec, i.e. well within the 90% error box of the X-ray source. The hardness ratios reported in the 2XMM catalog imply that it has a hard spectrum with a peak between 2 keV and 4.5 keV or it has a softer but highly absorbed spectrum. Moreover, the microlensing event is not fully constrained, and other authors propose a possible association of the source star with either a flaring cataclysmic variable or a RS Canum Venaticorum-like star. Conclusions. The very small angular separation (within uncertainties) is a strong indicator that 2XMM J180540.5-273427 is the X-ray counterpart of the OGLE event. However, the uncertainties in the nature of both the lensed system and the lens itself challenge the interpretation of 2XMM J180540.5-273427 as the first confirmed isolated black hole identified so far. In any case, it verifies the diagnostic capacity of microlensing surveys and open the pathway for further identifications of black hole or neutron star candidates.
PDF
![[123I]-FP/CIT SPECT imaging...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0885-3185/small "[123I]-FP/CIT SPECT imaging for distinguishing drug-induced parkinsonism from Parkinson's disease")
