10 research outputs found
A direct localization of a fast radio burst and its host
Fast radio bursts are astronomical radio flashes of unknown physical nature
with durations of milliseconds. Their dispersive arrival times suggest an
extragalactic origin and imply radio luminosities orders of magnitude larger
than any other kind of known short-duration radio transient. Thus far, all FRBs
have been detected with large single-dish telescopes with arcminute
localizations, and attempts to identify their counterparts (source or host
galaxy) have relied on contemporaneous variability of field sources or the
presence of peculiar field stars or galaxies. These attempts have not resulted
in an unambiguous association with a host or multi-wavelength counterpart. Here
we report the sub-arcsecond localization of FRB 121102, the only known
repeating burst source, using high-time-resolution radio interferometric
observations that directly image the bursts themselves. Our precise
localization reveals that FRB 121102 originates within 100 mas of a faint 180
uJy persistent radio source with a continuum spectrum that is consistent with
non-thermal emission, and a faint (25th magnitude) optical counterpart. The
flux density of the persistent radio source varies by tens of percent on day
timescales, and very long baseline radio interferometry yields an angular size
less than 1.7 mas. Our observations are inconsistent with the fast radio burst
having a Galactic origin or its source being located within a prominent
star-forming galaxy. Instead, the source appears to be co-located with a
low-luminosity active galactic nucleus or a previously unknown type of
extragalactic source. [Truncated] If other fast radio bursts have similarly
faint radio and optical counterparts, our findings imply that direct
sub-arcsecond localizations of FRBs may be the only way to provide reliable
associations.Comment: Nature, published online on 4 Jan 2017, DOI: 10.1038/nature2079
Testosterone Levels in Athletes at Rest and Exhaustion: Effects of Calcium Supplementation
Effect of O2 availability on neuroendocrine variables at rest and during exercise: O2 breathing increases plasma prolactin
Sex Hormones Response to Physical Hyperoxic and Hyperbaric Stress in Male Scuba Divers: A Pilot Study
The use of hyperbaric oxygen plays a significant role in many aspects of medicine. However, there are few studies that analyzed the role of hyperbaric oxygen, in addition to physical exercise, on the endocrine profile. The aim of this study was to compare changes in plasma male sex hormones after hyperbaric physical exercise with different hyperbaric oxygen pre-conditionings. We recruited six healthy, well-trained recreational male divers. Concentrations of prolactin (PRL), follicle-stimulating hormone (FSH), luteotrophic hormone (LH), cortisol, 17-β estradiol (E2), and total testosterone (TT) were measured in venous blood immediately after four different study conditions. Exercise increased PRL and hyperbaric oxygen potentiated this effect. Hyperbaria stimulated the E2 reduction and hyperoxia partially inhibited this reduction. Hyperbaria, but not hyperoxia, stimulated the TT reduction. There were no changes in FSH, LH, and cortisol. The increase in PRL likely reflects a stress response after physical exercise, amplified by hyperbaric oxygen. TT reduction may be interpreted as an acute and transient fertility impairment. Age, blood pressure, and BMI were taken into account as covariates for statistical analyses, and they significantly affected the results, in particular TT. These data open new insight into the role of E2 and PRL in male endocrine adaptive responses