1,872 research outputs found
A transient ultraviolet outflow in the short-period X-ray binary UW CrB
This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5–26555. These observations are associated with program(s) 12039.Accreting low mass X-ray binaries (LMXBs) are capable of launching powerful outflows such as accretion disc winds. In disc winds, vast amounts of material can be carried away, potentially greatly impacting the binary and its environment. Previous studies have uncovered signatures of disc winds in the X-ray, optical, near-infrared, and recently even the UV band, predominantly in LMXBs with large discs (Porb ≥ 20 hrs). Here, we present the discovery of transient UV outflow features in UW CrB, a high-inclination (i ≥ 77○) neutron star LMXB with an orbital period of only Porb ≈ 111 min. We present P-Cygni profiles identified for Si iv 1400Å and tentatively for N v 1240Å in one 15 min exposure, which is the only exposure covering orbital phase φ ≈ 0.7 − 0.8, with a velocity of ≈1500 km s−1. We show that due to the presence of black body emission from the neutron star surface and/or boundary layer, a thermal disc wind can be driven despite the short Porb, but explore alternative scenarios as well. The discovery that thermal disc winds may occur in NS-LMXBs with Porb as small as ≈111 min, and can potentially be transient on time scales as short as ≈15 min, warrants further observational and theoretical work.PostprintPeer reviewe
Influence of a Concurrent Exercise Training Intervention during Pregnancy on Maternal and Arterial and Venous Cord Serum Cytokines: The GESTAFIT Project
The aim of the present study was to analyze the influence of a supervised concurrent exercise-training program, from the 17th gestational week until delivery, on cytokines in maternal (at 17th and 35th gestational week, and at delivery) and arterial and venous cord serum. Fifty-eight Caucasian pregnant women (age: 33.5 +/- 4.7 years old, body mass index: 23.6 +/- 4.1kg/m(2)) from the GESTAFIT Project (exercise (n = 37) and control (n = 21) groups) participated in this quasi-experimental study (per-protocol basis). The exercise group followed a 60-min 3 days/week concurrent (aerobic-resistance) exercise-training from the 17th gestational week to delivery. Maternal and arterial and venous cord serum cytokines (fractalkine, interleukin (IL)-1 beta, IL-6, IL-8, IL-10, interferon (IFN)-gamma, and tumor necrosis factor (TNF)-alpha) were assessed using Luminex xMAP technology. In maternal serum (after adjusting for the baseline values of cytokines), the exercise group decreased TNF-alpha (from baseline to 35th week, p = 0.02), and increased less IL-1 beta (from baseline to delivery, p = 0.03) concentrations than controls. When adjusting for other potential confounders, these differences became non-significant. In cord blood, the exercise group showed reduced arterial IL-6 and venous TNF-alpha (p = 0.03 and p = 0.001, respectively) and higher concentrations of arterial IL-1 beta (p = 0.03) compared to controls. The application of concurrent exercise-training programs could be a strategy to modulate immune responses in pregnant women and their fetuses. However, future research is needed to better understand the origin and clearance of these cytokines, their role in the maternal-placental-fetus crosstalk, and the influence of exercise interventions on them
Burst-induced spin variations in the accreting magnetic white dwarf PBC J0801.2–4625
PBC J0801.2–4625 is an intermediate polar with a primary spin frequency of 66.08 d−1 and an unknown orbital period. The long-term All Sky Automated Survey for Supernovae (ASAS-SN) light curve of this system reveals four bursts, all of which have similar peak amplitudes (∼2 mag) and durations (∼2 d). In this work, we primarily study the timing properties of this system’s 2019 February burst, which was simultaneously observed by both ASAS-SN and the Transiting Exoplanet Survey Satellite (TESS). Pre-burst, a frequency of 4.064 ± 0.002 d−1(5.906 ± 0.003 h period), likely attributed to the binary orbit, is identified in addition to previous measurements for the white dwarf’s spin. During the burst, however, we find a spin frequency of 68.35 ± 0.28 d−1. Post-burst, the spin returns to its pre-brust value but with a factor 1.82 ± 0.05 larger amplitude. The burst profile is double-peaked, and we estimate its energy to be 3.3 × 1039 erg. We conclude that the burst appears most consistent with thermonuclear runaway (i.e. a 'micronova'), and suggest that the spin variations may be an analogue to burst oscillations (i.e. 'micronova oscillations'). However, we also note that the above findings could be explained by a dwarf nova outburst. With the available data, we are unable to distinguish between these two scenarios
Variability and evolution of the optical polarization of a sample of gamma-ray blazars
We present a polarization variability analysis of a sample of 26 -ray
blazars monitored by the Steward Observatory between 2008 and 2018 in the
optical band. We investigate the properties and long-term variability of their
optical polarization, searching for differences between blazar types. We
observe that BL Lac objects are typically less polarized and less variable than
flat spectrum radio quasars (FSRQs). Moreover, BL Lacs display a distribution
of their polarization angle typically oriented in a preferential direction,
contrary to the rather random distribution of FSRQs. For the latter blazar
type, as well as those sources showing a bright stellar emission, we take into
account the depolarizing effect introduced by the broad line region and the
host galaxy on the measured polarization degree. In this sample we also observe
that BL Lacs present an uncorrelated evolution of the flux and the
polarization. Contrary, FSRQs show a correlation before the depolarization
correction, that is lost however after considering this effect. In addition, we
study the behaviour of the polarization angle, searching for angle rotations in
its long-term evolution. We derive that the FSRQs studied here show rotations
more frequently than BL Lac objects by a factor 1.5. During these periods
we also observe a systematic decrease of the polarization fraction, as well as
a marginal flux increase, not significant however to connect rotations with
optical flares. We interpret these results within the extended shock-in-jet
scenario, able to explain the overall features observed here for the
polarization of the blazar sample.Comment: Accepted for publication in MNRA
GRB 021004: Tomography of a gamma-ray burst progenitor and its host galaxy
We analyse the distribution of matter around the progenitor star of gamma-ray
burst GRB 021004 as well as the properties of its host galaxy with
high-resolution echelle as well as near-infrared spectroscopy. Observations
were taken by the 8.2m Very Large Telescope with the Ultraviolet and Visual
Echelle spectrograph (UVES) and the Infrared Spectrometer And Array Camera
(ISAAC) between 10 and 14 hours after the onset of the event. We report the
first detection of emission lines from a GRB host galaxy in the near-infrared,
detecting H-alpha and the [O III] doublet. These allow an independent
measurement of the systemic redshift (z = 2.3304 +/- 0.0005) which is not
contaminated by absorption as the Ly-alpha line is, and the deduction of
properties of the host galaxy. From the visual echelle spectroscopy, we find
several absorption line groups spanning a range of about 3,000 km/s in velocity
relative to the redshift of the host galaxy. The absorption profiles are very
complex with both velocity-broadened components extending over several 100 km/s
and narrow lines with velocity widths of only 20 km/s. By analogy with QSO
absorption line studies, the relative velocities,widths, and degrees of
ionization of the lines ("line-locking", "ionization--velocity correlation")
show that the progenitor had both an extremely strong radiation field and
several distinct mass loss phases (winds). These results are consistent with
GRB progenitors being massive stars, such as Luminous Blue Variables (LBVs) or
Wolf--Rayet stars, providing a detailed picture of the spatial and velocity
structure of the GRB progenitor star at the time of explosion. The host galaxy
is a prolific star-forming galaxy with a SFR of about 40 solar masses per year.Comment: 11 pages, 5 figures. Accepted for publication in Astronomy and
Astrophysics
Disentangling the nature of the prototype radio weak BL Lac: Contemporaneous multifrequency observations of WISE J141046.00 + 740511.2
Context. The gamma-ray emitting source WISE J141046.00+740511.2 has been
associated with a Fermi-LAT detection by crossmatching with Swift/XRT data. It
has shown all the canonical observational characteristics of a BL Lac source,
including a power-law, featureless optical spectrum. However, it was only
recently detected at radio frequencies and its radio flux is significantly low.
Aims. Given that a radio detection is fundamental to associate lower-energy
counterparts to Fermi-LAT sources, we aim to unambiguously classify this source
by performing a multiwavelength analysis based on contemporaneous data.
Methods. By using multifrequency observations at the Jansky Very Large Array,
Giant Metrewave Radio Telescope, Gran Telescopio Canarias, Gemini, William
Herschel Telescope and Liverpool observatories, together with Fermi-LAT and
Swift data, we carried out two kinds of analyses. On one hand, we studied
several known parameters that account for the radio loudness or weakness
characterization and their application to blazars (in general) and to our
source (in particular). And, on the other hand, we built and analyzed the
observed spectral energy distribution (SED) of this source to try to explain
its peculiar characteristics. Results. The multiwavelength analysis indicates
that WISE J141046.00+740511.2 is a blazar of the high-frequency peaked (HBL)
type that emits highly polarized light and that is likely located at a low
redshift. In addition, the one-zone model parameters that best fit its SED are
those of an extreme HBL (EHBL); this blazar type has been extensively predicted
in theory to be lacking in the radio emission that is otherwise typical of
canonical gamma-ray blazars. Conclusions. We confirm that WISE
J141046.00+740511.2 is indeed a highly polarized BL Lac of the HBL type.
Further studies will be conducted to explain the atypical low radio flux
detected for this source.Comment: accepted for publication in A&A, in pres
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