Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We perform a stringent search for precursor emission of short gamma-ray bursts (SGRBs) from the Fermi/GBM data and find 16 precursor events with ≳4.5<jats:italic>σ</jats:italic> significance. We find that the durations of the main SGRB emission (<jats:inline-formula> <jats:tex-math> <?CDATA ${T}_{\mathrm{GRB}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabbfb8ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) and the precursor emission (<jats:inline-formula> <jats:tex-math> <?CDATA ${T}_{\mathrm{pre}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabbfb8ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>), as well as the waiting time (<jats:inline-formula> <jats:tex-math> <?CDATA ${T}_{\mathrm{wt}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabbfb8ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>) in between, are roughly comparable to each other, with <jats:inline-formula> <jats:tex-math> <?CDATA ${T}_{\mathrm{wt}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabbfb8ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> ≈ 2.8 <jats:inline-formula> <jats:tex-math> <?CDATA ${T}_{\mathrm{GRB}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabbfb8ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> <jats:sup>1.2</jats:sup> approximately satisfied for most cases except one significant outlier. We also perform spectral analyses to the precursors and SGRBs, and find that the spectra of precursor emission can be fitted with the blackbody, nonthermal cutoff power law and/or power-law models. We consider several possible models for precursor emission in SGRBs and find that the luminosity and spectral shape may be explained by the the shock breakout or the photospheric radiation of a fireball launched after the merger for thermal precursors, or magnetospheric interaction between two neutron stars prior to the merger for nonthermal precursors. For the fireball photospheric model, a matter-dominated jet is preferred and a constraint on the fireball Lorentz factor can be placed as Γ ∼ 30. For the magnetospheric interaction model, the jet launching mechanism may be constrained. In particular, those events with <jats:inline-formula> <jats:tex-math> <?CDATA ${T}_{\mathrm{wt}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabbfb8ieqn6.gif" xlink:type="simple" /> </jats:inline-formula>/<jats:inline-formula> <jats:tex-math> <?CDATA ${T}_{\mathrm{GRB}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabbfb8ieqn7.gif" xlink:type="simple" /> </jats:inline-formula> ≫ 1 (e.g., GRB191221802) require the formation of a supramassive or stable neutron star after the merger, with the delay time defined by the timescale for an initially baryon-loaded jet to become magnetically dominated and relativistic.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present new energetic neutral atom (ENA) maps from the Ion and Neutral Camera (INCA) instrument on Cassini from the year 2000, prior to Cassini’s encounter with Jupiter. These maps are the first produced for the year 2000 and are the only maps with comprehensive spatial coverage from the peak of solar cycle 23. These ENA maps span the energy range from 5.2 to 55 keV covering the pickup to suprathermal energy range. These maps represent a novel glimpse into the influence of the solar cycle on the structure of the outer heliosphere, specifically on the heliosheath where pickup and suprathermal ions dominate. The observations are consistent with the picture of the heliosheath from previous observations by the Cassini, Interstellar Boundary Explorer (IBEX), and Voyager missions. These maps have some consistent spatial features to maps produced by Cassini during solar cycle 24 such as reduced intensities in the mid-latitude basins. These maps also have distinct spatial features such as enhanced intensities at the poles and reduced intensities at the low-latitude flanks. These maps do not indicate a strong intensity increase in the regions adjacent to the nose and also show an intensity increase in the regions adjacent to the tailward direction.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the discovery of 1.97 ms period gamma-ray pulsations from the 75 minute orbital-period binary pulsar now named PSR J1653−0158. The associated Fermi Large Area Telescope gamma-ray source 4FGL J1653.6−0158 has long been expected to harbor a binary millisecond pulsar. Despite the pulsar-like gamma-ray spectrum and candidate optical/X-ray associations—whose periodic brightness modulations suggested an orbit—no radio pulsations had been found in many searches. The pulsar was discovered by directly searching the gamma-ray data using the GPU-accelerated Einstein@Home distributed volunteer computing system. The multidimensional parameter space was bounded by positional and orbital constraints obtained from the optical counterpart. More sensitive analyses of archival and new radio data using knowledge of the pulsar timing solution yield very stringent upper limits on radio emission. Any radio emission is thus either exceptionally weak, or eclipsed for a large fraction of the time. The pulsar has one of the three lowest inferred surface magnetic-field strengths of any known pulsar with <jats:italic>B</jats:italic> <jats:sub>surf</jats:sub> ≈ 4 × 10<jats:sup>7</jats:sup> G. The resulting mass function, combined with models of the companion star’s optical light curve and spectra, suggests a pulsar mass ≳2 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The companion is lightweight with mass ∼0.01 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, and the orbital period is the shortest known for any rotation-powered binary pulsar. This discovery demonstrates the Fermi Large Area Telescope's potential to discover extreme pulsars that would otherwise remain undetected.</jats:p>