31 research outputs found
Polarization Measurements of Arecibo-Sky Pulsars: Faraday Rotations and Emission-Beam Analyses
We present Faraday Rotation Measure (RM) values derived at L- and P-band as
well as some 60 Stokes-parameter profiles, both determined from our
longstanding Arecibo dual-frequency pulsar polarimetry programs. Many of the RM
measurements were carried out toward the inner Galaxy and the Anticenter on
pulsars with no previous determination, while others are re-measurements
intended to confirm or improve the accuracy of existing values.
Stokes-parameter profiles are displayed for the 58 pulsars for which no
meaningful Stokes profile at lower frequency is available and four without a
high frequency pair. This is a population that includes many distant pulsars in
the inner Galaxy. A number of these polarized pulse profiles exhibit clear
interstellar-scattering tails; nonetheless, we have attempted to interpret the
associated emission-beam structures and to provide morphological
classifications and geometrical models where possible
Author Correction: A consensus-based transparency checklist.
An amendment to this paper has been published and can be accessed via a link at the top of the paper
Comprehensive Bayesian analysis of FRB-like bursts from SGR 1935+2154 observed by CHIME/FRB
The bright millisecond-duration radio burst from the Galactic magnetar SGR
1935+2154 in 2020 April was a landmark event, demonstrating that at least some
fast radio burst (FRB) sources could be magnetars. The two-component burst was
temporally coincident with peaks observed within a contemporaneous short X-ray
burst envelope, marking the first instance where FRB-like bursts were observed
to coincide with X-ray counterparts. In this study, we detail five new radio
burst detections from SGR 1935+2154, observed by the CHIME/FRB instrument
between October 2020 and December 2022. We develop a fast and efficient
Bayesian inference pipeline that incorporates state-of-the-art Markov chain
Monte Carlo techniques and use it to model the intensity data of these bursts
under a flexible burst model. We revisit the 2020 April burst and corroborate
that both the radio sub-components lead the corresponding peaks in their
high-energy counterparts. For a burst observed in 2022 October, we find that
our estimated radio pulse arrival time is contemporaneous with a short X-ray
burst detected by GECAM and HEBS, and Konus-Wind and is consistent with the
arrival time of a radio burst detected by GBT. We present flux and fluence
estimates for all five bursts, employing an improved estimator for bursts
detected in the side-lobes. We also present upper limits on radio emission for
X-ray emission sources which were within CHIME/FRB's field-of-view at trigger
time. Finally, we present our exposure and sensitivity analysis and estimate
the Poisson rate for FRB-like events from SGR 1935+2154 to be
events/day above a fluence of
during the interval from 28 August 2018 to 1 December 2022, although we note
this was measured during a time of great X-ray activity from the source.Comment: 22 pages, 6 figures, 4 tables. To be submitted to Ap
Multiwavelength Constraints on the Origin of a Nearby Repeating Fast Radio Burst Source in a Globular Cluster
Since fast radio bursts (FRBs) were discovered, their precise origins have
remained a mystery. Multiwavelength observations of nearby FRB sources provide
one of the best ways to make rapid progress in our understanding of the
enigmatic FRB phenomenon. We present results from a sensitive, broadband
multiwavelength X-ray and radio observational campaign of FRB 20200120E, the
closest known extragalactic repeating FRB source. At a distance of 3.63 Mpc,
FRB 20200120E resides in an exceptional location, within a ~10 Gyr-old globular
cluster in the M81 galactic system. We place deep limits on both the persistent
X-ray luminosity and prompt X-ray emission at the time of radio bursts from FRB
20200120E, which we use to constrain possible progenitors for the source. We
compare our results to various classes of X-ray sources and transients. In
particular, we find that FRB 20200120E is unlikely to be associated with:
ultraluminous X-ray bursts (ULXBs), similar to those observed from objects of
unknown origin in other extragalactic globular clusters; giant flares, like
those observed from Galactic and extragalactic magnetars; or most intermediate
flares and very bright short X-ray bursts, similar to those seen from magnetars
in the Milky Way. We show that FRB 20200120E is also unlikely to be powered by
a persistent or transient ultraluminous X-ray (ULX) source or a young,
extragalactic pulsar embedded in a Crab-like nebula. We also provide new
constraints on the compatibility of FRB 20200120E with accretion-based FRB
models involving X-ray binaries and models that require a synchrotron maser
process from relativistic shocks to generate FRB emission. These results
highlight the power that multiwavelength observations of nearby FRBs can
provide for discriminating between potential FRB progenitor models.Comment: 58 pages, 10 figures, 7 tables, submitte
A fast radio burst localized at detection to a galactic disk using very long baseline interferometry
Fast radio bursts (FRBs) are millisecond-duration, luminous radio transients
of extragalactic origin. These events have been used to trace the baryonic
structure of the Universe using their dispersion measure (DM) assuming that the
contribution from host galaxies can be reliably estimated. However,
contributions from the immediate environment of an FRB may dominate the
observed DM, thus making redshift estimates challenging without a robust host
galaxy association. Furthermore, while at least one Galactic burst has been
associated with a magnetar, other localized FRBs argue against magnetars as the
sole progenitor model. Precise localization within the host galaxy can
discriminate between progenitor models, a major goal of the field. Until now,
localizations on this spatial scale have only been carried out in follow-up
observations of repeating sources. Here we demonstrate the localization of FRB
20210603A with very long baseline interferometry (VLBI) on two baselines, using
data collected only at the time of detection. We localize the burst to SDSS
J004105.82+211331.9, an edge-on galaxy at , and detect recent
star formation in the kiloparsec-scale vicinity of the burst. The edge-on
inclination of the host galaxy allows for a unique comparison between the line
of sight towards the FRB and lines of sight towards known Galactic pulsars. The
DM, Faraday rotation measure (RM), and scattering suggest a progenitor
coincident with the host galactic plane, strengthening the link between the
environment of FRB 20210603A and the disk of its host galaxy. Single-pulse VLBI
localizations of FRBs to within their host galaxies, following the one
presented here, will further constrain the origins and host environments of
one-off FRBs.Comment: 40 pages, 13 figures, submitted. Fixed typo in abstrac
Cigarette Smoke Affects Keratinocytes SRB1 Expression and Localization via H2O2 Production and HNE Protein Adducts Formation
Scavenger Receptor B1 (SR-B1), also known as HDL receptor, is involved in cellular cholesterol uptake. Stratum corneum (SC), the outermost layer of the skin, is composed of more than 25% cholesterol. Several reports support the view that alteration of SC lipid composition may be the cause of impaired barrier function which gives rise to several skin diseases. For this reason the regulation of the genes involved in cholesterol uptake is of extreme significance for skin health. Being the first shield against external insults, the skin is exposed to several noxious substances and among these is cigarette smoke (CS), which has been recently associated with various skin pathologies. In this study we first have shown the presence of SR-B1 in murine and human skin tissue and then by using immunoblotting, immunoprecipitation, RT-PCR, and confocal microscopy we have demonstrated the translocation and the subsequent lost of SR-B1 in human keratinocytes (cell culture model) after CS exposure is driven by hydrogen peroxide (H2O2) that derives not only from the CS gas phase but mainly from the activation of cellular NADPH oxidase (NOX). This effect was reversed when the cells were pretreated with NOX inhibitors or catalase. Furthermore, CS caused the formation of SR-B1-aldheydes adducts (acrolein and 4-hydroxy-2-nonenal) and the increase of its ubiquitination, which could be one of the causes of SR-B1 loss. In conclusion, exposure to CS, through the production of H2O2, induced post-translational modifications of SR-B1 with the consequence lost of the receptor and this may contribute to the skin physiology alteration as a consequence of the variation of cholesterol uptake
CHIME/FRB Discovery of 25 Repeating Fast Radio Burst Sources
We present the discovery of 25 new repeating fast radio burst (FRB) sources
found among CHIME/FRB events detected between 2019 September 30 and 2021 May 1.
The sources were found using a new clustering algorithm that looks for multiple
events co-located on the sky having similar dispersion measures (DMs). The new
repeaters have DMs ranging from 220 pc cm to 1700 pc
cm, and include sources having exhibited as few as two bursts to as many
as twelve. We report a statistically significant difference in both the DM and
extragalactic DM (eDM) distributions between repeating and apparently
nonrepeating sources, with repeaters having lower mean DM and eDM, and we
discuss the implications. We find no clear bimodality between the repetition
rates of repeaters and upper limits on repetition from apparently nonrepeating
sources after correcting for sensitivity and exposure effects, although some
active repeating sources stand out as anomalous. We measure the repeater
fraction and find that it tends to an equilibrium of % over
our exposure thus far. We also report on 14 more sources which are promising
repeating FRB candidates and which merit follow-up observations for
confirmation.Comment: Submitted to ApJ. Comments are welcome and follow-up observations are
encouraged
Sub-second periodicity in a fast radio burst
Fast radio bursts (FRBs) are millisecond-duration flashes of radio waves that
are visible at distances of billions of light-years. The nature of their
progenitors and their emission mechanism remain open astrophysical questions.
Here we report the detection of the multi-component FRB 20191221A and the
identification of a periodic separation of 216.8(1) ms between its components
with a significance of 6.5 sigmas. The long (~3 s) duration and nine or more
components forming the pulse profile make this source an outlier in the FRB
population. Such short periodicity provides strong evidence for a neutron-star
origin of the event. Moreover, our detection favours emission arising from the
neutron-star magnetosphere, as opposed to emission regions located further away
from the star, as predicted by some models.Comment: Updated to conform to the accepted versio
A consensus-based transparency checklist
We present a consensus-based checklist to improve and document the transparency of research reports in social and behavioural research. An accompanying online application allows users to complete the form and generate a report that they can submit with their manuscript or post to a public repository