Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>A Zevatron is an accelerator scheme envisaged to accelerate particles to ZeV energies (1 ZeV = 10<jats:sup>21</jats:sup> eV). Schemes, most notably the internal shock model, have been proposed to explain the acceleration of ultra-high-energy cosmic-ray particles that have been sporadically detected reaching Earth since 1962. Here, the cyclotron auto-resonance acceleration (CARA) mechanism is tailored and used to demonstrate the possible acceleration of particles ejected as a result of violent astrophysical processes such as the merger of a binary system or a supernova explosion. Such events result in emission of highly energetic particles and ultra-intense beamed radiation. In the simultaneous presence of a super-strong magnetic field, the condition for cyclotron auto-resonance may be met. Thus CARA can act like a <jats:italic>booster</jats:italic> for particles pre-accelerated inside their progenitor by shock waves, possibly among other means. As examples, it is shown that nuclei of hydrogen, helium, and iron-56, may reach ZeV energies by CARA, under which conditions the particles, while gyrating around the lines of an ultra-strong magnetic field, also surf on the waves of a super-intense radiation field. When radiation-reaction is taken into account, it is shown that the ZeV energy gained by a particle can fall off by less than an order of -magnitude if the resonance condition is missed by roughly less than 20%.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The nature of fast radio bursts (FRBs) is currently unknown. Repeating FRBs offer better observation opportunities than nonrepeating FRBs because their simultaneous multiwavelength counterparts might be identified. The magnetar flare model of FRBs is one of the most promising models that predict high-energy emission in addition to radio burst emission. To investigate such a possibility, we have searched for simultaneous and quasi-simultaneous short-term hard X-ray bursts in all Swift/BAT event mode data, which covered the periods when FRB detections were reported in the repeating FRB 121102, by making use of BAT’s arcminute-level spatial resolution and wide field of view. We did not find any significant hard X-ray bursts that occurred simultaneously with those radio bursts. We also investigated potential short X-ray bursts that occurred quasi-simultaneously with those radio bursts (occurrence time differs in the range from hundreds of seconds to thousands of seconds) and concluded that even the best candidates are consistent with background fluctuations. Therefore, our investigation concluded that there were no hard X-ray bursts detectable with Swift/BAT that occurred simultaneously or quasi-simultaneously with those FRBs in the repeating FRB 121102.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Microlensing not only allows for extra magnification lightcurves on top of the intrinsic ones but also shifts them in time domain, causing the actual time delays between images of strongly lensed active galactic nucleus to change on the ∼day(s) light-crossing timescale of the emission region. The microlensing-induced time delays would bias strong lens time-delay cosmography if unaccounted for. However, due to the uncertainties of the disk size and the disk model, the impact is hard to accurately estimate. In this work, we study how to reduce the bias with a designed observation strategy based on a standard disk model. We find that long time monitoring of the images could alleviate the impact since it averages the microlensing time-lag maps due to the peculiar motion of the source relative to the lens galaxy. In addition, images in bluer bands correspond to smaller disk sizes and therefore benefit time-delay measurements as well. We conduct a simulation based on a PG 1115+080-like lensed quasar. The results show that the time-delay dispersions caused by microlensing can be reduced by  ∼40% with 20 yr lightcurves, while <jats:italic>u</jats:italic> band relative to <jats:italic>r</jats:italic> band reduces  ∼75% of the dispersions. Nevertheless, such an effect cannot be totally eliminated in any cases. Further studies are still needed to appropriately incorporate this effect into inferences of an accurate Hubble constant.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Precise masses and radii have been reported by Murphy et al. for the components of the THOR 42 binary. Murphy et al. provide evidence that, in their opinion, supports an earlier suggestion by Bell et al. that THOR 42 is a member of the 32 Ori moving group, which, according to Bell et al., has an age of about 24 Myr. From the positions of the THOR 2 components in the mass–radius diagram (MRD), Murphy et al. derive ages of 22–26 Myr using standard (nonmagnetic) models. However, they also find that these models cannot simultaneously reproduce the observed masses, radii, effective temperatures, and luminosities of the assumed coeval components. Their Hertzsprung–Russell diagram (HRD) ages are found to be 2–4 times younger than the MRD ages, and the masses determined from the HRD are found to be ∼50% smaller than the dynamical masses. Here, we attempt to replicate the precise global properties of THOR 24 by applying a model of magnetoconvection. We find that MRD isochrones and HRD isochrones lead to consistent ages provided that the surface magnetic fields have strengths of 300–400 G. However, the ages that our models yield for THOR 24 are in the vicinity of 40 Myr. If this age estimate is correct, it could call into question the membership of THOR 42 in the 32 Ori moving group.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze the ultraviolet (UV) and X-ray data of NGC 1275 obtained with Swift/UV/Optical Telescope (UVOT), X-ray Telescope (XRT), Burst Alert Telescope (BAT) and Fermi Large Area Telescope over about 10 yr to investigate the origin of the nuclear emission from NGC 1275. We confirm that the UV and soft/hard X-ray fluxes gradually increased along with the GeV gamma rays. At times, short-term variations in the UV or soft X-ray spectral regions showed rapid variations correlated with the GeV gamma rays. However there was no significant correlation between the UV and soft X-rays. The UV spectrum had a narrow spectral shape that could be represented by single-temperature blackbody radiation. These results could possibly indicate that the long-term variability of UV and X-ray emissions is caused by the jet, while the emissions from the accretion disk contribute to the UV and X-ray bands to some extent.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a study of strong intervening absorption systems in the near-IR spectra of 31 luminous quasars at <jats:italic>z</jats:italic> &gt; 5.7. The quasar spectra were obtained with Gemini GNIRS that provide continuous wavelength coverage from ∼0.9 to ∼2.5 <jats:italic>μ</jats:italic>m. We detect 32 strong Mg <jats:sc>ii</jats:sc>  doublet absorbers with rest-frame equivalent width <jats:italic>W</jats:italic> <jats:sub> <jats:italic>r</jats:italic> </jats:sub>(<jats:italic>λ</jats:italic>2796) &gt; 1.0 Å at 2.2 &lt; <jats:italic>z</jats:italic> &lt; 6.0. Each Mg <jats:sc>ii</jats:sc>  absorber is confirmed by at least two associated Fe <jats:sc>ii</jats:sc> absorption lines in the rest-frame wavelength range of ∼1600–2600 Å. We find that the comoving line density (<jats:italic>dN</jats:italic>/<jats:italic>dX</jats:italic>) of the strong Fe <jats:sc>ii</jats:sc>-bearing Mg <jats:sc>ii</jats:sc>  absorbers decreases toward higher redshift at <jats:italic>z</jats:italic> &gt; 3, consistent with previous studies. Compared with strong Mg <jats:sc>ii</jats:sc>  absorbers detected in damped Ly<jats:italic>α</jats:italic> systems at 2 &lt; <jats:italic>z</jats:italic> &lt; 4, our absorbers are potentially less saturated and show much larger rest-frame velocity widths. This suggests that the gas traced by our absorbers are potentially affected by galactic superwinds. We analyze the Hubble Space Telescope near-IR images of the quasars and identify possible associated galaxies for our strong absorbers. There are a maximum of two galaxy candidates found within 5″ radius of each absorber. The median F105W-band magnitude of these galaxy candidates is 24.8 mag, which is fainter than the <jats:italic>L</jats:italic>* galaxy luminosity at <jats:italic>z</jats:italic> ∼  4. By using our observed <jats:italic>dN</jats:italic>/<jats:italic>dX</jats:italic> of strong Mg <jats:sc>ii</jats:sc> absorbers and galaxy candidates median luminosity, we suggest that at high redshift, strong Mg <jats:sc>ii</jats:sc> absorbers tend to have a more disturbed environment but smaller halo size than that at <jats:italic>z</jats:italic> &lt; 1.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Relativistic shocks propagating into a medium with low magnetization are generated and sustained by small-scale but very strong magnetic field turbulence. This so-called “microturbulence” modifies the typical shock acceleration process, and in particular that of electrons. In this work we perform Monte Carlo (MC) simulations of electrons encountering shocks with microturbulent fields. The simulations cover a three-dimensional parameter space in shock speed, acceleration efficiency, and peak magnetic field strength. From these, a Markov Chain Monte Carlo (MCMC) method was employed to estimate the maximum electron momentum from the MC-simulated electron spectra. Having estimated this quantity at many points well-distributed over an astrophysically relevant parameter space, an MCMC method was again used to estimate the parameters of an empirical formula that computes the maximum momentum of a Fermi-accelerated electron population anywhere in this parameter space. The maximum energy is well-approximated as a broken power law in shock speed, with the break occurring when the shock decelerates to the point where electrons can begin to escape upstream from the shock.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It is now clear that a significant population of accreting black holes are undetected by commonly employed optical, mid-infrared color, X-ray, and radio selection methods as a result of obscuration or contamination of the emission from the nuclear region caused by star formation in the host galaxy. These elusive active galactic nuclei (AGNs) are an important component of the AGN population. They are often found in mergers, where significant black hole growth likely takes place, and in the lowest-mass galaxies or galaxies that lack classical bulges, a demographic that places important constraints on models of supermassive black hole seed formation and merger-free models of AGN fueling. In this work, we demonstrate the power of the James Webb Space Telescope (JWST) in uncovering and characterizing these elusive AGNs. We present an integrated modeling approach in which both the line and emergent continuum are predicted from gas exposed to the ionizing radiation from a young starburst and an AGN, focusing specifically on the spectral diagnostics available through JWST, and provide predictions on the detectability of key diagnostic lines by the near- and mid-infrared spectrometers, assuming typical conditions for the gas. We demonstrate the crucial need for JWST in uncovering low-level accretion activity even in nearby galaxies and out to redshifts of ≈1–3, depending on the ionization parameter, and gas phase metallicity. We present a redshift-dependent selection strategy that can be used to identify promising elusive AGN candidates for future follow-up study. The full suite of simulations is available online, where users can select specific parameters and retrieve the predicted continuum and infrared line luminosities from our models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The shape of the heliosphere is thought to resemble a long, comet tail, however, recently it has been suggested that the heliosphere is tailless with a two-lobe structure. The latter study was done with a three-dimensional (3D) magnetohydrodynamic code, which treats the ionized and neutral hydrogen atoms as fluids. Previous studies that described the neutrals kinetically claim that this removes the two-lobe structure of the heliosphere. In this work, we use the newly developed Solar-wind with Hydrogen Ion Exchange and Large-scale Dynamics (SHIELD) model. SHIELD is a self-consistent kinetic-MHD model of the outer heliosphere that couples the MHD solution for a single plasma fluid from the BATS-R-US MHD code to the kinetic solution for neutral hydrogen atoms solved by the Adaptive Mesh Particle Simulator, a 3D, direct simulation Monte Carlo model that solves the Boltzmann equation. We use the same boundary conditions as our previous simulations using multi-fluid neutrals to test whether the two-lobe structure of the heliotail is removed with a kinetic treatment of the neutrals. Our results show that despite the large difference in the neutral hydrogen solutions, the two-lobe structure remains. These results are contrary to previous kinetic-MHD models. One such model maintains a perfectly ideal heliopause and does not allow for communication between the solar wind and interstellar medium. This indicates that magnetic reconnection or instabilities downtail play a role for the formation of the two-lobe structure.</jats:p>