43 research outputs found
A deep XMM-Newton serendipitous survey of a middle-latitude area
The radio quiet neutron star 1E1207.4-5209 has been the target of a 260 ks
XMM-Newton observation, which yielded, as a by product, an harvest of about 200
serendipitous X-ray sources above a limiting flux of 2E-15 erg/cm2/s, in the
0.3-8 keV energy range. In view of the intermediate latitude of our field (b~10
deg), it comes as no surprise that the logN-logS distribution of our
serendipitous sources is different from those measured either in the Galactic
Plane or at high galactic latitudes. Here we shall concentrate on the analysis
of the brightest sources in our sample, which unveiled a previously unknown
Seyfert-2 galaxy.Comment: 8 pages, 7 figures, 2 tables. Accepted for publication by Astronomy &
Astrophysic
Development of machine learning models to prognosticate chronic shunt-dependent hydrocephalus after aneurysmal subarachnoid hemorrhage
Background: Shunt-dependent hydrocephalus significantly complicates subarachnoid hemorrhage (SAH), and reliable prognosis methods have been sought in recent years to reduce morbidity and costs associated with delayed treatment or neglected onset. Machine learning (ML) defines modern data analysis techniques allowing accurate subject-based risk stratifications. We aimed at developing and testing different ML models to predict shunt-dependent hydrocephalus after aneurysmal SAH. Methods: We consulted electronic records of patients with aneurysmal SAH treated at our institution between January 2013 and March 2019. We selected variables for the models according to the results of the previous works on this topic. We trained and tested four ML algorithms on three datasets: one containing binary variables, one considering variables associated with shunt-dependency after an explorative analysis, and one including all variables. For each model, we calculated AUROC, specificity, sensitivity, accuracy, PPV, and also, on the validation set, the NPV and the Matthews correlation coefficient (ϕ). Results: Three hundred eighty-six patients were included. Fifty patients (12.9%) developed shunt-dependency after a mean follow-up of 19.7 (± 12.6) months. Complete information was retrieved for 32 variables, used to train the models. The best models were selected based on the performances on the validation set and were achieved with a distributed random forest model considering 21 variables, with a ϕ = 0.59, AUC = 0.88; sensitivity and specificity of 0.73 (C.I.: 0.39–0.94) and 0.92 (C.I.: 0.84–0.97), respectively; PPV = 0.59 (0.38–0.77); and NPV = 0.96 (0.90–0.98). Accuracy was 0.90 (0.82–0.95). Conclusions: Machine learning prognostic models allow accurate predictions with a large number of variables and a more subject-oriented prognosis. We identified a single best distributed random forest model, with an excellent prognostic capacity (ϕ = 0.58), which could be especially helpful in identifying low-risk patients for shunt-dependency
Black hole masses and the Fundamental Plane of BL Lac objects
We report on measurements of the stellar velocity dispersion (sigma) from the
optical spectra of the host galaxies of four BL Lac objects. Together with our
earlier results on seven BL Lac objects (Falomo et al. 2002), and with the
previously derived photometrical and structural properties, these data are used
to construct the Fundamental Plane (FP) of the BL Lac hosts. We find that the
BL Lacs follow the same FP as low redshift radio galaxies and inactive luminous
ellipticals, in agreement with similar results presented by Barth et al.
(2003). This indicates that the photometrical, structural and kinematical
properties of the host galaxies of BL Lacs are indistinguishable from those of
inactive massive ellipticals. Using the correlation between black hole mass
(M_BH) and sigma in nearby elliptical galaxies, we derive the masses of the
central black hole in BL Lacs. These masses, in the range of 6 x 10^7 to 9 x
10^8 M_o, are consistent with the values derived from the bulge luminosity and
appear to be linearly correlated with the mass of the galaxies (M_BH} ~0.001 x
M_bulge).Comment: ApJ, accepted, 17 page
Spectroscopy of BL Lac Objects: new redshifts and mis-identified sources
We are carrying out a program of high signal to noise optical spectroscopy of
BL Lacs with unknown or tentative redshift. Here we report some preliminary
results. New redshifts are measured for PKS0754+100 (z=0.266) and 1ES0715-259
(z=0.464) . From lineless spectra of PG1553+113 and PKS1722+119 we set a lower
limit of z>0.3 for both sources. In two cases (UM493 and 1620+103) stellar
spectra indicate a wrong classification.Comment: 4 pages; Conference proceeding "High Energy Blazar Astronomy", Tuorla
Observatory, Finland, 17-21 June 2002; to be published in the PASP conference
serie
The HELLAS2XMM survey: IV. Optical identifications and the evolution of the accretion luminosity in the Universe
We present results from the photometric and spectroscopic identification of
122 X-ray sources recently discovered by XMM-Newton in the 2-10 keV band (the
HELLAS2XMM 1dF sample). Their flux cover the range 8E-15-4E-13 cgs and the
total area surveyed is 0.9 deg2. About 20% of the hard X-ray selected sources
have an X-ray to optical flux ratio (X/O) ten times or more higher than that of
optically selected AGN. Unlike the faint sources found in the ultra-deep
Chandra and XMM-Newton surveys, which reach X-ray (and optical) fluxes more
than one order of magnitude lower than the HELLAS2XMM survey sources, many of
the extreme X/O sources in our sample have R<=25 and are therefore accessible
to optical spectroscopy. We report the identification of 13 sources with
X/O>10: 8 are narrow line QSO (i.e. QSO2), four are broad line QSO. We use a
combined sample of 317 hard X-ray selected sources (HELLAS2XMM 1dF, CDFN 1Msec,
SSA13 and Lockman Hole flux limited samples), 221 with measured z, to evaluate
the cosmological evolution of the hard X-ray source's number and luminosity
densities. Looking backward in time, the low luminosity sources (logL(2-10keV)
= 43-44 erg/s) increase in number at a rate different than the high luminosity
sources (logL(2-10keV)>44.5 erg/s), reaching a maximum around z=1 and then
levelling off beyond z=2. This translates into an accretion driven luminosity
density which is dominated by sources with logL(2-10keV) < 44.5 erg/s up to at
least z=1, while the contribution of the same sources and of those with
logL(2-10keV)>44.5 erg/s appear to be comparable between z=2 and 4.Comment: v2, minor changes, A&A in pres