Browsing by Department "Direzione Scientifica"

Kepler-20 is a solar-type star (V = 12.5) hosting a compact system of five transiting planets, all packed within the orbital distance of Mercury in our own solar system. A transition from rocky to gaseous planets with a planetary transition radius of ∼1.6 R_E has recently been proposed by several articles in the literature. Kepler-20b (R_p ∼ 1.9 R_E) has a size beyond this transition radius; however, previous mass measurements were not sufficiently precise to allow definite conclusions to be drawn regarding its composition. We present new mass measurements of three of the planets in the Kepler-20 system that are facilitated by 104 radial velocity measurements from the HARPS-N spectrograph and 30 archival Keck/HIRES observations, as well as an updated photometric analysis of the Kepler data and an asteroseismic analysis of the host star (M_star = 0.948+/- 0.051 M☉ and R_star = 0.964+/- 0.018 R☉). Kepler-20b is a 1.868_(-0.034)^(+0.066) R_E planet in a 3.7 day period with a mass of 9.70_(-1.44)^(+1.41) M_E, resulting in a mean density of 8.2_(-1.3)^(+1.5) g/cm^3, indicating a rocky composition with an iron-to-silicate ratio consistent with that of the Earth. This makes Kepler-20b the most massive planet with a rocky composition found to date. Furthermore, we report the discovery of an additional non-transiting planet with a minimum mass of 19.96_(-3.61)^(+3.08) M_E and an orbital period of ∼34 days in the gap between Kepler-20f (P ∼ 11 days) and Kepler-20d (P ∼ 78 days). -- Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofísica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

During the month of 2009 December, the blazar 3C 454.3 became the brightest gamma-ray source in the sky, reaching a peak flux F 2000 × 10 -8 photons cm-2 s-1 for E > 100 MeV. Starting in 2009 November intensive multifrequency campaigns monitored the 3C 454 gamma-ray outburst. Here, we report on the results of a two-month campaign involving AGILE, INTEGRAL, Swift/XRT, Swift/BAT, and Rossi XTE for the high-energy observations and Swift/UVOT, KANATA, Goddard Robotic Telescope, and REM for the near-IR/optical/UV data. GASP/WEBT provided radio and additional optical data. We detected a long-term active emission phase lasting 1 month at all wavelengths: in the gamma-ray band, peak emission was reached on 2009 December 2-3. Remarkably, this gamma-ray super-flare was not accompanied by correspondingly intense emission in the optical/UV band that reached a level substantially lower than the previous observations in 2007-2008. The lack of strong simultaneous optical brightening during the super-flare and the determination of the broadband spectral evolution severely constrain the theoretical modeling. We find that the pre- and post-flare broadband behavior can be explained by a one-zone model involving synchrotron self-Compton plus external Compton emission from an accretion disk and a broad-line region. However, the spectra of the 2009 December 2-3 super-flare and of the secondary peak emission on 2009 December 9 cannot be satisfactorily modeled by a simple one-zone model. An additional particle component is most likely active during these states. © 2010. The American Astronomical Society. All rights reserved.

Fast radio bursts (FRBs) are millisecond-duration, bright (approximately Jy) extragalactic bursts, whose production mechanism is still unclear¹. Recently, two repeating FRBs were found to have a physically associated persistent radio source of non-thermal origin^2,3. These two FRBs have unusually large Faraday rotation measure values^2,3, probably tracing a dense magneto-ionic medium, consistent with synchrotron radiation originating from a nebula surrounding the FRB source^4–8. Recent theoretical arguments predict that, if the observed Faraday rotation measure mostly arises from the persistent radio source region, there should be a simple relation between the persistent radio source luminosity and the rotation measure itself^7,9. Here we report the detection of a third, less luminous persistent radio source associated with the repeating FRB source FRB 20201124A at a distance of 413 Mpc, substantially expanding the predicted relation into the low luminosity–low Faraday rotation measure regime (<1,000 rad m^‑2). At lower values of the Faraday rotation measure, the expected radio luminosity falls below the limit-of-detection threshold for present-day radio telescopes. These findings support the idea that the persistent radio sources observed so far are generated by a nebula in the FRB environment and that FRBs with low Faraday rotation measure may not show a persistent radio source because of a weaker magneto-ionic medium. This is generally consistent with models invoking a young magnetar as the central engine of the FRB, in which the surrounding ionized nebula—or the interacting shock in a binary system—powers the persistent radio source.

Fast radio bursts (FRBs) are millisecond-duration, bright (approximately Jy) extragalactic bursts, whose production mechanism is still unclear¹. Recently, two repeating FRBs were found to have a physically associated persistent radio source of non-thermal origin^2,3. These two FRBs have unusually large Faraday rotation measure values^2,3, probably tracing a dense magneto-ionic medium, consistent with synchrotron radiation originating from a nebula surrounding the FRB source^4–8. Recent theoretical arguments predict that, if the observed Faraday rotation measure mostly arises from the persistent radio source region, there should be a simple relation between the persistent radio source luminosity and the rotation measure itself^7,9. Here we report the detection of a third, less luminous persistent radio source associated with the repeating FRB source FRB 20201124A at a distance of 413 Mpc, substantially expanding the predicted relation into the low luminosity–low Faraday rotation measure regime (<1,000 rad m^‑2). At lower values of the Faraday rotation measure, the expected radio luminosity falls below the limit-of-detection threshold for present-day radio telescopes. These findings support the idea that the persistent radio sources observed so far are generated by a nebula in the FRB environment and that FRBs with low Faraday rotation measure may not show a persistent radio source because of a weaker magneto-ionic medium. This is generally consistent with models invoking a young magnetar as the central engine of the FRB, in which the surrounding ionized nebula—or the interacting shock in a binary system—powers the persistent radio source.

Fast radio bursts (FRBs) are millisecond-duration, bright (approximately Jy) extragalactic bursts, whose production mechanism is still unclear¹. Recently, two repeating FRBs were found to have a physically associated persistent radio source of non-thermal origin^2,3. These two FRBs have unusually large Faraday rotation measure values^2,3, probably tracing a dense magneto-ionic medium, consistent with synchrotron radiation originating from a nebula surrounding the FRB source^4–8. Recent theoretical arguments predict that, if the observed Faraday rotation measure mostly arises from the persistent radio source region, there should be a simple relation between the persistent radio source luminosity and the rotation measure itself^7,9. Here we report the detection of a third, less luminous persistent radio source associated with the repeating FRB source FRB 20201124A at a distance of 413 Mpc, substantially expanding the predicted relation into the low luminosity–low Faraday rotation measure regime (<1,000 rad m^‑2). At lower values of the Faraday rotation measure, the expected radio luminosity falls below the limit-of-detection threshold for present-day radio telescopes. These findings support the idea that the persistent radio sources observed so far are generated by a nebula in the FRB environment and that FRBs with low Faraday rotation measure may not show a persistent radio source because of a weaker magneto-ionic medium. This is generally consistent with models invoking a young magnetar as the central engine of the FRB, in which the surrounding ionized nebula—or the interacting shock in a binary system—powers the persistent radio source.

Fast radio bursts (FRBs) are millisecond-duration, bright (approximately Jy) extragalactic bursts, whose production mechanism is still unclear¹. Recently, two repeating FRBs were found to have a physically associated persistent radio source of non-thermal origin^2,3. These two FRBs have unusually large Faraday rotation measure values^2,3, probably tracing a dense magneto-ionic medium, consistent with synchrotron radiation originating from a nebula surrounding the FRB source^4–8. Recent theoretical arguments predict that, if the observed Faraday rotation measure mostly arises from the persistent radio source region, there should be a simple relation between the persistent radio source luminosity and the rotation measure itself^7,9. Here we report the detection of a third, less luminous persistent radio source associated with the repeating FRB source FRB 20201124A at a distance of 413 Mpc, substantially expanding the predicted relation into the low luminosity–low Faraday rotation measure regime (<1,000 rad m^‑2). At lower values of the Faraday rotation measure, the expected radio luminosity falls below the limit-of-detection threshold for present-day radio telescopes. These findings support the idea that the persistent radio sources observed so far are generated by a nebula in the FRB environment and that FRBs with low Faraday rotation measure may not show a persistent radio source because of a weaker magneto-ionic medium. This is generally consistent with models invoking a young magnetar as the central engine of the FRB, in which the surrounding ionized nebula—or the interacting shock in a binary system—powers the persistent radio source.

Fast radio bursts (FRBs) are millisecond-duration, bright (approximately Jy) extragalactic bursts, whose production mechanism is still unclear¹. Recently, two repeating FRBs were found to have a physically associated persistent radio source of non-thermal origin^2,3. These two FRBs have unusually large Faraday rotation measure values^2,3, probably tracing a dense magneto-ionic medium, consistent with synchrotron radiation originating from a nebula surrounding the FRB source^4–8. Recent theoretical arguments predict that, if the observed Faraday rotation measure mostly arises from the persistent radio source region, there should be a simple relation between the persistent radio source luminosity and the rotation measure itself^7,9. Here we report the detection of a third, less luminous persistent radio source associated with the repeating FRB source FRB 20201124A at a distance of 413 Mpc, substantially expanding the predicted relation into the low luminosity–low Faraday rotation measure regime (<1,000 rad m^‑2). At lower values of the Faraday rotation measure, the expected radio luminosity falls below the limit-of-detection threshold for present-day radio telescopes. These findings support the idea that the persistent radio sources observed so far are generated by a nebula in the FRB environment and that FRBs with low Faraday rotation measure may not show a persistent radio source because of a weaker magneto-ionic medium. This is generally consistent with models invoking a young magnetar as the central engine of the FRB, in which the surrounding ionized nebula—or the interacting shock in a binary system—powers the persistent radio source.

We present deep near-infrared J, {K}_{{s}} photometry of the old, metal-poor Galactic globular cluster M15 obtained with images collected with the LUCI1 and PISCES cameras available at the Large Binocular Telescope (LBT). We show how the use of First Light Adaptive Optics (FLAO) system coupled with the PISCES camera allows us to improve the limiting magnitude by ̃2 mag in {K}_{{s}}. By analyzing archival Hubble Space Telescope data, we demonstrate that the quality of the LBT/PISCES color-magnitude diagram is fully comparable with analogous space-based data. The smaller field of view is balanced by the shorter exposure time required to reach a similar photometric limit. We investigated the absolute age of M15 by means of two methods: (i) by determining the age from the position of the main-sequence turnoff (MSTO), and (ii) by the magnitude difference between the MSTO and the well-defined knee detected along the faint portion of the MS. We derive consistent values of the absolute age of M15, that is, 12.9 ± 2.6 Gyr and 13.3 ± 1.1 Gyr, respectively.

Observations were carried out using the Large Binocular Telescope at Mount Graham, AZ. The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are the University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; the Ohio State University; and the Research Corporation, on behalf of the University of Notre Dame, University of Minnesota, and University of Virginia.

We present the confirmation of a small, moderately irradiated (F = 155 ± 7 F _⊕) Neptune with a substantial gas envelope in a P = 11.8728787 ± 0.0000085 day orbit about a quiet, Sun-like G0V star Kepler-1655. Based on our analysis of the Kepler light curve, we determined Kepler-1655b’s radius to be 2.213 ± 0.082 R _⊕. We acquired 95 high-resolution spectra with Telescopio Nazionale Galileo/HARPS-N, enabling us to characterize the host star and determine an accurate mass for Kepler-1655b of 5.0{+/- }_2.8^3.1 {M}_\oplus via Gaussian-process regression. Our mass determination excludes an Earth-like composition with 98% confidence. Kepler-1655b falls on the upper edge of the evaporation valley, in the relatively sparsely occupied transition region between rocky and gas-rich planets. It is therefore part of a population of planets that we should actively seek to characterize further.

This paper describes the active optics system of the VLT Survey Telescope, the 2.6-m survey telescope designed for visible wavelengths of the European Southern Observatory at Cerro Paranal, in the Atacama desert. The telescope is characterized by a wide field of view (1.42 deg diameter), leading to tighter active optics than in conventional telescopes, in particular for the alignment requirements. We discuss the effects of typical error sources on the image quality and present the specific solutions adopted for wavefront sensing and correction of the aberrations, which are based on the shaping of a monolithic primary mirror and the positioning of the secondary in five degrees of freedom.

The VST telescope is equipped with an Atmospheric Dispersion Corrector to counterbalance the spectral dispersion introduced by the atmosphere. The well known effect of atmospheric refraction is the bending of incoming light due to variable atmospheric density along the light path. This effect depends on the tangent of the zenith angle and also varies with altitude, humidity and wavelength. Since the magnitude of refraction depends on the wavelength, the resulting effect is not only a deviation of the light beam from its original direction but also a spectral dispersion of the beam. This effect can be corrected by introducing a dispersing element in the instrument. In the VST case the device that compensates for this effect is based on a set of four prisms in two cemented doublet pairs. The system provides an adjustable counter dispersion by counter-rotating the two pairs of prisms. The counter-rotating angle depends on the atmospheric dispersion, which is computed with an atmospheric model using both environmental data (temperature, pressure, humidity) and the telescope position. Two different approaches have been compared for the computations to cross-check the results. The electromechanical system has been assembled, tested and debugged prior to the shipping to Chile. This paper describes the atmospheric models used in the VST case and the most recent phases of work.

GRB 190114C represents a breakthrough for the physics of gamma-ray bursts (GRBs), being the first GRB with delayed emission above 300 GeV, as reported by MAGIC. We present in this paper the sub-MeV/MeV data of the prompt and early afterglow emissions of GRB 190114C, as detected by AGILE and Konus-Wind, in the 20 keV-100 MeV energy range. The first stages of the burst exhibit multiple emission components, associated with an interesting spectral evolution. The first 2 s of the prompt emission can be described by a single "Band-like" spectral component. The successive 4 s show the presence of an additional high-energy spectral component, which quickly evolves into a "hard-flat" component of the νF_ν spectrum, extending up to 10-100 MeV and likely produced by inverse Compton radiation, whose onset and evolution are clearly shown in our data. After this phase, the νF_ν spectrum evolves into a "V shape," showing the persistence and spectral hardening of the additional high-energy component in substantial agreement with Fermi and Swift results. We also analyze the first ∼200 s of the early afterglow that show a reflaring episode near T₀ + 15 s. We identify a new, so-far-unnoticed flux temporal break near T₀ + 100 s, which is detected in hard X-rays by both Konus-Wind and INTEGRAL/SPI-ACS. We find this break incompatible with the commonly assumed adiabatic evolution of a fireball in a constant-density medium. We interpret this break as a consequence of radiative evolution of the early afterglow from a fireball expanding in a wind-like circumburst medium.

We study the capability of the AGILE gamma ray space mission in detecting magnetospheric particles (mostly electrons) in the energy range 10-100 MeV. Our measurements focus on the inner magnetic shells with L ≲ 1.2 in the magnetic equator. The instrument characteristics and a quasi-equatorial orbit of ∼500 km altitude make it possible to address several important properties of the particle populations in the inner magnetosphere. We review the on board trigger logic and study the acceptance of the AGILE instrument for particle detection. We find that the AGILE effective geometric factor (acceptance) is R≃50 cm2 sr for particle energies in the range 10-100 MeV. Particle event reconstruction allows to determine the particle pitch angle with the local magnetic field with good accuracy. We obtain the pitch angle distributions for both the AGILE "pointing" phase (July 2007 to October 2009) and the "spinning" phase (November 2009 to present). In spinning mode, the whole range (0-180 degrees) is accessible every 7 min. We find a pitch angle distribution of the "dumbbell" type with a prominent depression near α = 90° which is typical of wave-particle resonant scattering and precipitation in the inner magnetosphere. Most importantly, we show that AGILE is not affected by solar particle precipitation events in the magnetosphere. The satellite trajectory intersects magnetic shells in a quite narrow range (1.0 ≲ L ≲ 1.2); AGILE then has a high exposure to a magnetospheric region potentially rich of interesting phenomena. The large particle acceptance in the 10-100 MeV range, the pitch angle determination capability, the L shell exposure, and the solar-free background make AGILE a unique instrument for measuring steady and transient particle events in the inner magnetosphere.

We report the detection by the AGILE satellite of a rapid gamma-ray flare from the powerful gamma-ray quasar PKS 1510-089, during a pointing centered on the Galactic Center region from 1 March to 30 March 2008. This source has been continuosly monitored in the radio-to-optical bands by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT). Moreover, the gamma-ray flaring episode triggered three ToO observations by the Swift satellite in three consecutive days, starting from 20 March 2008. In the period 1-16 March 2008, AGILE detected gamma-ray emission from PKS 1510-089 at a significance level of 6.2-sigma with an average flux over the entire period of (84 +/- 17) x 10^{-8} photons cm^{-2} s^{-1} for photon energies above 100 MeV. After a predefined satellite re-pointing, between 17 and 21 March 2008, AGILE detected the source at a significance level of 7.3-sigma, with an average flux (E > 100 MeV) of (134 +/- 29) x 10^{-8} photons cm^{-2} s^{-1} and a peak level of (281 +/- 68) x 10^{-8} photons cm^{-2} s^{-1} with daily integration. During the observing period January-April 2008, the source also showed an intense and variable optical activity, with several flaring episodes and a significant increase of the flux was observed at millimetric frequencies. Moreover, in the X-ray band the Swift/XRT observations seem to show an harder-when-brighter behaviour of the source spectrum. The spectral energy distribution of mid-March 2008 is modelled with a homogeneous one-zone synchrotron self Compton emission plus contributions from inverse Compton scattering of external photons from both the accretion disc and the broad line region. Indeed, some features in the optical-UV spectrum seem to indicate the presence of Seyfert-like components, such as the little blue bump and the big blue bump.

We report on the extreme gamma-ray activity from the FSRQ PKS 1510-089 observed by AGILE in March 2009. In the same period a radio-to-optical monitoring of the source was provided by the GASP-WEBT and REM. Moreover, several Swift ToO observations were triggered, adding important information on the source behaviour from optical/UV to hard X-rays. We paid particular attention to the calibration of the Swift/UVOT data to make it suitable to the blazars spectra. Simultaneous observations from radio to gamma rays allowed us to study in detail the correlation among the emission variability at different frequencies and to investigate the mechanisms at work. In the period 9-30 March 2009, AGILE detected an average gamma-ray flux of (311+/-21)x10^-8 ph cm^-2 s^-1 for E>100 MeV, and a peak level of (702+/-131)x10^-8 ph cm^-2 s^-1 on daily integration. The gamma-ray activity occurred during a period of increasing activity from near-IR to UV, with a flaring episode detected on 26-27 March 2009, suggesting that a single mechanism is responsible for the flux enhancement observed from near-IR to UV. By contrast, Swift/XRT observations seem to show no clear correlation of the X-ray fluxes with the optical and gamma-ray ones. However, the X-ray observations show a harder photon index (1.3-1.6) with respect to most FSRQs and a hint of harder-when-brighter behaviour, indicating the possible presence of a second emission component at soft X-ray energies. Moreover, the broad band spectrum from radio-to-UV confirmed the evidence of thermal features in the optical/UV spectrum of PKS 1510-089 also during high gamma-ray state. On the other hand, during 25-26 March 2009 a flat spectrum in the optical/UV energy band was observed, suggesting an important contribution of the synchrotron emission in this part of the spectrum during the brightest gamma-ray flare, therefore a significant shift of the synchrotron peak.

The origin of cosmic neutrinos is still largely unknown. Using data obtained by the gamma-ray imager on board the Astro-rivelatore Gamma a Immagini Leggero (AGILE) satellite, we systematically searched for transient gamma-ray sources above 100 MeV that are temporally and spatially coincident with 10 recent high-energy neutrino IceCube events. We found three AGILE candidate sources that can be considered possible counterparts to neutrino events. Detecting three gamma-ray/neutrino associations out of 10 IceCube events is shown to be unlikely due to a chance coincidence. One of the sources is related to the BL Lac source TXS 0506+056. For the other two AGILE gamma-ray sources there are no obvious known counterparts, and both Galactic and extragalactic origin should be considered.

We report the results of an extensive search through the AGILE data for a gamma-ray counterpart to the LIGO gravitational-wave (GW) event GW150914. Currently in spinning mode, AGILE has the potential of cover 80% of the sky with its gamma-ray instrument, more than 100 times a day. It turns out that AGILE came within a minute of the event time of observing the accessible GW150914 localization region. Interestingly, the gamma-ray detector exposed ∼65% of this region during the 100 s time intervals centered at -100 and +300 s from the event time. We determine a 2σ flux upper limit in the band 50 MeV-10 GeV, UL = 1.9 × 10^-8 erg cm^-2 s^-1, obtained ∼300 s after the event. The timing of this measurement is the fastest ever obtained for GW150914, and significantly constrains the electromagnetic emission of a possible high-energy counterpart. We also carried out a search for a gamma-ray precursor and delayed emission over five timescales ranging from minutes to days: in particular, we obtained an optimal exposure during the interval -150/-30 s. In all these observations, we do not detect a significant signal associated with GW150914. We do not reveal the weak transient source reported by Fermi-GBM 0.4 s after the event time. However, even though a gamma-ray counterpart of the GW150914 event was not detected, the prospects for future AGILE observations of GW sources are decidedly promising.