Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We present a search for gravitational waves from merging binary neutron stars (BNSs) which have non-negligible eccentricity as they enter the Laser Interferometer Gravitational Wave Observatory (LIGO) observing band. We use the public Advanced LIGO data which covers the period from 2015 through 2017 and contains ∼164 days of LIGO–Hanford and LIGO–Livingston coincident observing time. The search was conducted using matched-filtering using the PyCBC toolkit. We find no significant BNS candidates beyond GW170817, which has previously been reported by searches for binaries in circular orbits. We place a 90% upper limit of ∼1700 mergers Gpc<jats:sup>−3</jats:sup> yr<jats:sup>−1</jats:sup> for eccentricities ≲0.43 at a dominant-mode gravitational-wave frequency of 10 Hz. The absence of a detection with these data is consistent with theoretical predictions of eccentric BNS merger rates. Using our measured rate we estimate the sensitive volume of future gravitational-wave detectors and compare this to theoretical rate predictions. We find that, in the absence of a prior detection, the rate limits set by six months of Cosmic Explorer observations would constrain all current plausible models of eccentric BNS formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on the observations of gamma-ray burst (GRB) 190114C by the <jats:italic>Fermi Gamma-ray Space Telescope</jats:italic> and the <jats:italic>Neil Gehrels Swift Observatory</jats:italic>. The prompt gamma-ray emission was detected by the <jats:italic>Fermi</jats:italic> GRB Monitor (GBM), the <jats:italic>Fermi</jats:italic> Large Area Telescope (LAT), and the <jats:italic>Swift</jats:italic> Burst Alert Telescope (BAT) and the long-lived afterglow emission was subsequently observed by the GBM, LAT, <jats:italic>Swift</jats:italic> X-ray Telescope (XRT), and <jats:italic>Swift</jats:italic> UV Optical Telescope. The early-time observations reveal multiple emission components that evolve independently, with a delayed power-law component that exhibits significant spectral attenuation above 40 MeV in the first few seconds of the burst. This power-law component transitions to a harder spectrum that is consistent with the afterglow emission observed by the XRT at later times. This afterglow component is clearly identifiable in the GBM and BAT light curves as a slowly fading emission component on which the rest of the prompt emission is superimposed. As a result, we are able to observe the transition from internal-shock- to external-shock-dominated emission. We find that the temporal and spectral evolution of the broadband afterglow emission can be well modeled as synchrotron emission from a forward shock propagating into a wind-like circumstellar environment. We estimate the initial bulk Lorentz factor using the observed high-energy spectral cutoff. Considering the onset of the afterglow component, we constrain the deceleration radius at which this forward shock begins to radiate in order to estimate the maximum synchrotron energy as a function of time. We find that even in the LAT energy range, there exist high-energy photons that are in tension with the theoretical maximum energy that can be achieved through synchrotron emission from a shock. These violations of the maximum synchrotron energy are further compounded by the detection of very high-energy (VHE) emission above 300 GeV by MAGIC concurrent with our observations. We conclude that the observations of VHE photons from GRB 190114C necessitates either an additional emission mechanism at very high energies that is hidden in the synchrotron component in the LAT energy range, an acceleration mechanism that imparts energy to the particles at a rate that is faster than the electron synchrotron energy-loss rate, or revisions of the fundamental assumptions used in estimating the maximum photon energy attainable through the synchrotron process.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The detailed magnetic field structure of the starless dense core CB81 (L1774, Pipe 42) in the Pipe Nebula was determined based on near-infrared polarimetric observations of background stars to measure dichroically polarized light produced by magnetically aligned dust grains in the core. The magnetic fields pervading CB81 were mapped using 147 stars and axisymmetrically distorted hourglass-like fields were identified. On the basis of simple 2D and 3D magnetic field modeling, the magnetic inclination angles in the plane-of-sky and line-of-sight directions were determined to be 4° ± 8° and 20° ± 20°, respectively. The total magnetic field strength of CB81 was found to be 7.2 ± 2.3 <jats:italic>μ</jats:italic>G. Taking into account the effects of thermal/turbulent pressure and magnetic fields, the critical mass of CB81 was calculated to be <jats:italic>M</jats:italic> <jats:sub>cr</jats:sub> = 4.03 ± 0.40 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, which is close to the observed core mass of <jats:italic>M</jats:italic> <jats:sub>core</jats:sub> = 3.37 ± 0.51 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. We thus conclude that CB81 is in a condition close to the critical state. In addition, a spatial offset of 92″ was found between the center of the magnetic field geometry and the dust extinction distribution; this offset structure could not have been produced by self-gravity. The data also indicate a linear relationship between polarization and extinction up to <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> ∼ 30 mag going toward the core center. This result confirms that near-infrared polarization can accurately trace the overall magnetic field structure of the core.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Low-frequency (quasi-)monochromatic electromagnetic waves near the ion-cyclotron frequency always exhibit both left-hand (LH) and right-hand (RH) polarization in solar-terrestrial spacecraft observations. However, due to the Doppler frequency shift resulting from the bulk flow of charged particles, the nature of these waves in the plasma frame is still unclear. This paper proposes a useful method to directly identify the nature of the observed waves. Using three wave parameters including polarization, direction of the parallel Poynting flux, and correlation between perpendicular magnetic field and perpendicular ion/electron velocity, we could discriminate the wave mode (Alfvén/ion-cyclotron wave or fast-magnetosonic/whistler wave) and its propagation direction (along or against the magnetic field) in the plasma frame. Using <jats:italic>Magnetospheric Multiscale</jats:italic> spacecraft measurements, we analyze two wave events containing both LH- and RH-polarized low-frequency electromagnetic waves in the Earth’s magnetosheath, and find that these waves correspond to counter-propagating Alfvén/ion-cyclotron waves in the plasma frame. Our method is helpful for studying low-frequency electromagnetic waves detected by satellites that have particle measurements with an adequate temporal resolution.</jats:p>