Downsizing of supermassive black holes from the SDSS quasar survey (II). Extension to z~4 (2009)
Labita, Marzia, Decarli, Roberto, Treves, Aldo, Falomo, Renato
Starting from the quasar sample of the Sloan Digital Sky Survey (SDSS) for which the CIV line is observed, we use an analysis scheme to derive the z-dependence of the maximum mass of active black...
Downsizing of supermassive black holes from the SDSS quasar survey (2009)
Labita, Marzia, Decarli, Roberto, Treves, Aldo, Falomo, Renato
Starting from the ~50000 quasars of the Sloan Digital Sky Survey for which MgII line width and 3000 A monochromatic flux are available, we aim to study the dependence of the mass of active black...
Primordial black holes are again on the limelight (2009)
Roncadelli, Marco, Treves, Aldo, Turolla, Roberto
We derive a strong upper bound on the amount of Primordial Black Holes (PBHs) that can still be present in the Universe. Gravitational capture of PBHs by the Milky Way stars during their formation...
Vrijhk Photometry of PKS 0537-441 and PKS 2155-304 in 2006-2008 (2008)
Impiombato, Domenico, Tosti, Gino, Treves, Aldo, Covino, Stefano, Pian, Elena, Ciprini, Stefano
We report the 2006-2008 light curves obtained with the REM telescope in VRIJHK bands for the two BL Lac objects PKS 0537-441 and PKS 2155-304
HST snapshot imaging of BL Lac objects (2007)
Falomo Osservatorio Astronomico, R. Falomo, C. Megan Urry, Riccardo Scarpa, Joseph E. Pesce, Aldo Treves
. Snapshot images of 100 BL Lac objects were obtained with WFPC2 on HST. Sources from various samples, in the redshift range 0.05 to 1.2, were observed and 61 resolved (51 with known z). The high...
C. Megan Urry, Riccardo Scarpa, Tom Broadhurst, Renato Falomo, Jochen Heidt, Aldo Treves, ...
We have carried out an HST snapshot survey of 108 BL Lac objects, at redshifts from z = 0.051 to z 1
C. Megan Urry, Riccardo Scarpa, Mauro Giavalisco, Renato Falomo, Joseph E. Pesce, Aldo Treves
AGN are known to lie in galaxies, and both galaxies and AGN evolve similarly over cosmic time (e.g., Silk and Rees 1998). This suggests a close connection between the nuclear phenomena associated...
Hubble Space Telescope Observations of BL Lacertae Environments. I. The GO Targets (2007)
Joseph E. Pesce, C. Megan Urry, Riccardo Scarpa, Renato Falomo, Aldo Treves
We analyze images of BL Lacertae objects obtained with the Hubble Space Telescope WFPC2 and the F814W filter. The nine objects cover a redshift range of 0.19 to 0.997. The relatively deep images are...
Multiwavelength Observations of the BL Lacertae Object PKS 2155-304 with XMM-Newton (2007)
Zhang, You-Hong, Bai, J.M., Zhang, S.N., Treves, Aldo, Maraschi, L., Celotti, Annalisa
The optical-UV and X-ray instruments on-board XMM-Ndewton provide an excellent opportunity to perform simultaneous observations of violently variable objects over a broad wavelength range. The UV and...
The NIR to UV continuum of radio loud vs. radio quiet quasars (2007)
Labita, Marzia, Treves, Aldo, Falomo, Renato
Starting from a sample of SDSS quasars appearing also in the 2MASS survey, we study the continuum properties of about 1000 objects observed in 8 bands, from NIR to UV. We construct the mean spectral...
On the distance of PG 1553+11. A lineless BL Lac object active in the TeV band (2007)
Treves, Aldo, Falomo, Renato, Uslenghi, Michela
Context: The redshift of PG 1553+11, a bright BL Lac object (V~14), is still unknown. It has been recently observed in the TeV band, a fact that offers an upper limit for the redshift z
The BH mass of nearby QSOs: a comparison of the bulge luminosity and virial methods (2006)
Labita, Marzia, Treves, Aldo, Falomo, Renato, Uslenghi, Michela
We report on the analysis of the photometric and spectroscopic properties of a sample of 29 low redshift (z
Pian, Elena, Falomo, Renato, Treves, Aldo
The ultraviolet (UV) spectra of 16 blazars ( ~1) from the archives of the Hubble Space Telescope Faint Object Spectrograph have been analyzed in order to study in a systematic way the properties...
Bondi Accretion and the Problem of the Missing Isolated Neutron Stars (2003)
Perna, Rosalba, Narayan, Ramesh, Rybicki, George, Stella, Luigi, Treves, Aldo
A large number of neutron stars (NSs), ~10^9, populate the Galaxy, but only a tiny fraction of them is observable during the short radio pulsar lifetime. The majority of these isolated NSs, too cold...
Host galaxies and black hole masses of low and high luminosity radio loud active nuclei (2003)
Falomo, Renato, Carangelo, Nicoletta, Treves, Aldo
We investigate the host galaxy luminosities of BL Lac Objects (BLLs) and Radio Loud Quasars (RLQs) at z
The black hole mass of BL Lacs from stellar velocity dispersion of the host galaxy (2001)
Falomo, Renato, Kotilainen, Jari, Treves, Aldo
We present the first results from our on-going program to estimate black hole masses [M(BH)] of nearby BL Lac objects. The estimates are based on stellar velocity dispersion (sigma) of the BL Lac...
Near-infrared imaging of the host galaxies of three radio-loud quasars at z = 1.5 (2000)
Falomo, Renato, Kotilainen, Jari, Treves, Aldo
We present high spatial resolution near-infrared H-band (1.65 microns) images, taken with ISAAC on UT1 of ESO VLT, of three radio-loud quasars at z = 1.5, as a pilot study for imaging of a larger...
Tommasi, Leonardo, Diaz, Ruben, Palazzi, Eliana, Pian, Elena, Poretti, Ennio, Scaltriti, Franco, ...
The polarized and total flux of the BL Lac object PKS 2155-304 were monitored intensively and simultaneously in the optical UBVRI bands with the Turin photopolarimeter at the CASLEO 2.15 m telescope...
Ultra-strong Elelctric Fields and Vacuum Breakdown: Search for an Astrophysical Scenario (2000)
Treves, Aldo, Turolla, Roberto, Popov, S. B.
In some models of $\gamma$-ray bursts super-strong electric fields ($E\sim 10^{14} {\rm statvolt cm}^{-1}$) have been surmized. Such large fields may provide copious pair production through vacuum...
Isolated Neutron Stars: Accretors and Coolers (1999)
Treves, Aldo, Turolla, Roberto, Zane, Silvia, Colpi, Monica
As many as $10^9$ neutron stars populate the Galaxy, but only $\approx 10^3$ are directly observed as pulsars or as accreting sources in X-ray binaries. In principle also the accretion of the...
Scarpa, Riccardo, Urry, C. Megan, Falomo, Renato, Pesce, Joseph E., Treves, Aldo
We report on a large HST imaging survey of BL Lac objects, at spatial resolution ~10 times better than previous ground-based surveys. We focus on data reduction and analysis, describing the...
The HST Survey of BL Lacertae Objects. II. Host Galaxies (1999)
Urry, C. Megan, Scarpa, Riccardo, O'Dowd, Matthew, Falomo, Renato, Pesce, Joseph E., Treves, Aldo
We have used the HST WFPC2 camera to survey 132 BL Lac objects comprising seven complete radio-, X-ray-, and optically-selected samples. We obtained useful images for 110 targets spanning the...
HST snapshot imaging of BL Lac objects (1998)
Falomo, R., Urry, C. Megan, Scarpa, Riccardo, Pesce, Joseph E., Treves, Aldo
Snapshot images of about 100 BL Lac objects were obtained with WFPC2 on HST. Sources from various samples, in the redshift range 0.05 to 1.2, were observed and 61 resolved (51 with known z). The high...
Falomo, Renato, Maraschi, Laura, Pian, Elena, Treves, Aldo
The contribution of an astrophysics group based in Milan to the science with the IUE satellite during its almost 20 years lifetime has focussed on high energy sources, of both galactic (LMXRB, HMXRB,...
BeppoSAX Observations of the BL Lac Object Mkn 501 in an Intermediate State (1998)
Pian, Elena, Palazzi, Eliana, Chiappetti, Lucio, Maraschi, Laura, Tavecchio, Fabrizio, Ghisellini, Gabriele, ...
The BL Lac object Mkn 501 was observed with the BeppoSAX satellite at three epochs in April-May 1998, simultaneously with the Whipple and HEGRA Cherenkov telescopes. The X-ray spectrum is well...
HST Observations of the Host Galaxies of BL Lacertae Objects (1998)
Urry, C. Megan, Falomo, Renato, Scarpa, Riccardo, Pesce, Joseph E., Treves, Aldo, Giavalisco, Mauro
Six BL Lac objects from the complete 1 Jy radio-selected sample of 34 objects were observed in Cycle 5 with the HST WFPC2 camera to an equivalent limiting flux of mu_I~26 mag/arcsec^2. Here we report...
BeppoSAX Observations of Unprecedented Synchrotron Activity in the BL Lac Object Mkn 501 (1997)
Pian, Elena, Vacanti, Giuseppe, Tagliaferri, Gianpiero, Ghisellini, Gabriele, Maraschi, Laura, Treves, Aldo, ...
The BL Lac object Mkn 501, one of the only three extragalactic sources (with Mkn 421 and 1ES 2344+514) so far detected at TeV energies, was observed with the BeppoSAX satellite on 7, 11, and 16 April...
Pian, Elena, Urry, C. Megan, Treves, Aldo, Maraschi, Laura, Penton, Steve, Shull, J. Michael, ...
PKS 2155-304, the brightest BL Lac object in the ultraviolet sky, was monitored with the IUE satellite at ~1 hour time-resolution for ten nearly uninterrupted days in May 1994. The campaign, which...
Old Isolated Accreting Neutron Stars: The Diffuse X--ray Emission From The Galactic Center (1996)
Zane, Silvia, Turolla, Roberto, Treves, Aldo
The contribution of weakly--magnetized ($B\sim 10^9$ G) neutron stars accreting the interstellar medium to the diffuse X--ray emission observed in the Galactic Center is investigated. It is shown...
Zane, Silvia, Zampieri, Luca, Turolla, Roberto, Treves, Aldo
Old isolated accreting neutron stars may show up among unidentified soft X--ray sources detected by the ROSAT All Sky Survey. We argue that the chances of identification are greater for ONSs located...
Zane, Silvia, Turolla, Roberto, Zampieri, Luca, Colpi, Monica, Treves, Aldo
The issue of the observability of Old Isolated Neutron Stars (ONSs) accreting from the interstellar gas, is reconsidered using the spectra presented in Zampieri {\it et al.\/} (1995). In particular,...
On the electrodynamics of a magnetized rotating accretor (1995)
Treves, Aldo, Szuszkiewicz, Ewa
We consider the current flow in an accreting rotating neutron star (X-ray pulsator) and propose that the active magnetosphere is limited by the Alfv\`en surface. Formulae for the luminosity and...
On the electrodynamics of a magnetized rotating accretor (1995)
Treves, Aldo, Szuszkiewicz, Ewa
We consider the current flow in an accreting rotating neutron star (X-ray pulsator) and propose that the active magnetosphere is limited by the Alfv`en surface. Formulae for the luminosity and torque...
Zane, Silvia, Turolla, Roberto, Zampieri, Luca, Colpi, Monica, Treves, Aldo
The issue of the observability of Old Isolated Neutron Stars (ONSs) accreting from the interstellar gas, is reconsidered using the spectra presented in Zampieri {\it et al.\/} (1995). In particular,...
X--Ray Spectra from Neutron Stars Accreting at Low Rates (1994)
Zampieri, Luca, Turolla, Roberto, Zane, Silvia, Treves, Aldo
The spectral properties of X--ray radiation produced in a static atmosphere around a neutron star accreting at very low rates are investigated. Previous results by Alme \& Wilson (1973) are extended...
Spherical Accretion onto Neutron Stars Revisited: Are Hot Solutions Possible ? (1994)
Turolla, Roberto, Zampieri, Luca, Colpi, Monica, Treves, Aldo
Stationary, spherical accretion onto an unmagnetized neutron star is here reconsidered on the wake of the seminal paper by Zel'dovich \& Shakura (1969). It is found that new ``hot'' solutions may...
Dynamically Comptonized Spectra from Near Critical Accretion onto Neutron Stars (1993)
Zampieri, Luca, Turolla, Roberto, Treves, Aldo
We investigate the effects of dynamical Comptonization on the emergent radiation spectrum produced by near critical accretion onto a neutron star. The flow dynamics and the transfer of radiation are...