28 research outputs found
Deep Synoptic Array Science: Polarimetry of 25 New Fast Radio Bursts Provides Insights into their Origins
We report on a full-polarization analysis of the first 25 as yet
non-repeating FRBs detected at 1.4 GHz by the 110-antenna Deep Synoptic Array
(DSA-110) during commissioning observations. We present details of the data
reduction, calibration, and analysis procedures developed for this novel
instrument. The data have 32 s time resolution and sensitivity to Faraday
rotation measures (RMs) between rad m. RMs are detected for
20 FRBs with magnitudes ranging from rad m. FRBs are
found to have high () linear-polarization fractions. The remaining
FRBs exhibit significant circular polarization (), or are either
partially depolarized () or unpolarized (). We investigate the
mechanism of depolarization, disfavoring stochastic RM variations within a
scattering screen as a dominant cause. Polarization-state and possible RM
variations are observed in the four FRBs with multiple sub-components, but only
one other FRB shows a change in polarization state. We combine the DSA-110
sample with polarimetry of previously published FRBs, and compare the
polarization properties of FRB sub-populations and FRBs with Galactic pulsars.
Although FRBs are typically far more polarized than the average profiles of
Galactic pulsars, and exhibit greater spread in polarization fractions than
pulsar single pulses, we find a remarkable similarity between FRB polarization
fractions and the youngest (characteristic ages yr) pulsars. Our
results support a scenario wherein FRB emission is intrinsically highly
linearly polarized, and where propagation effects within progenitor
magnetospheres can result in conversion to circular polarization and
depolarization. Young pulsar emission and magnetospheric-propagation geometries
may form a useful analogy for the origin of FRB polarization.Comment: 43 pages, 17 figure
Deep Synoptic Array Science: Implications of Faraday Rotation Measures of Localized Fast Radio Bursts
Faraday rotation measures (RMs) of fast radio bursts (FRBs) offer the
prospect of directly measuring extragalactic magnetic fields. We present an
analysis of the RMs of ten as yet non-repeating FRBs detected and localized to
host galaxies by the 110-antenna Deep Synoptic Array (DSA-110). We combine this
sample with published RMs of 15 localized FRBs, nine of which are repeating
sources. For each FRB in the combined sample, we estimate the host-galaxy
dispersion measure (DM) contributions and extragalactic RM. We find compelling
evidence that the extragalactic components of FRB RMs are often dominated by
contributions from the host-galaxy interstellar medium (ISM). Specifically, we
find that both repeating and as yet non-repeating FRBs show a correlation
between the host-DM and host-RM in the rest frame, and we find an
anti-correlation between extragalactic RM (in the observer frame) and redshift
for non-repeaters, as expected if the magnetized plasma is in the host galaxy.
Important exceptions to the ISM origin include a dense, magnetized circum-burst
medium in some repeating FRBs, and the intra-cluster medium (ICM) of host or
intervening galaxy clusters. We find that the estimated ISM magnetic-field
strengths, , are characteristically larger than those inferred from
Galactic radio pulsars. This suggests either increased ISM magnetization in FRB
hosts in comparison with the Milky Way, or that FRBs preferentially reside in
regions of increased magnetic-field strength within their hosts
Deep Synoptic Array science I: discovery of the host galaxy of FRB 20220912A
We report the detection and interferometric localization of the repeating
fast radio burst (FRB) source FRB 20220912A during commissioning observations
with the Deep Synoptic Array (DSA-110). Two bursts were detected from FRB
20220912A, one each on 2022 October 18 and 2022 October 25. The best-fit
position is (R.A. J2000, decl. J2000) = (23:09:04.9, +48:42:25.4), with a 90%
confidence error ellipse of arcsec and arcsec in right ascension
and declination respectively. The two bursts have disparate polarization
properties and temporal profiles. We find a Faraday rotation measure that is
consistent with the low value of rad m reported by CHIME/FRB. The
DSA-110 localization overlaps with the galaxy PSO J347.2702+48.7066 at a
redshift , which we identify as the likely host. PSO
J347.270248.7066 has a stellar mass of approximately ,
modest internal dust extinction, and a star-formation rate likely in excess of
yr. The host-galaxy contribution to the dispersion
measure is likely pc cm. The FRB 20220912A source is
therefore likely viewed along a tenuous plasma column through the host galaxy.Comment: 10 pages, 7 figures, 2 tables, submitted to AAS Journal
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
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
Circulating microRNAs in sera correlate with soluble biomarkers of immune activation but do not predict mortality in ART treated individuals with HIV-1 infection: A case control study
Introduction: The use of anti-retroviral therapy (ART) has dramatically reduced HIV-1 associated morbidity and mortality. However, HIV-1 infected individuals have increased rates of morbidity and mortality compared to the non-HIV-1 infected population and this appears to be related to end-organ diseases collectively referred to as Serious Non-AIDS Events (SNAEs). Circulating miRNAs are reported as promising biomarkers for a number of human disease conditions including those that constitute SNAEs. Our study sought to investigate the potential of selected miRNAs in predicting mortality in HIV-1 infected ART treated individuals. Materials and Methods: A set of miRNAs was chosen based on published associations with human disease conditions that constitute SNAEs. This case: control study compared 126 cases (individuals who died whilst on therapy), and 247 matched controls (individuals who remained alive). Cases and controls were ART treated participants of two pivotal HIV-1 trials. The relative abundance of each miRNA in serum was measured, by RTqPCR. Associations with mortality (all-cause, cardiovascular and malignancy) were assessed by logistic regression analysis. Correlations between miRNAs and CD4+ T cell count, hs-CRP, IL-6 and D-dimer were also assessed. Results: None of the selected miRNAs was associated with all-cause, cardiovascular or malignancy mortality. The levels of three miRNAs (miRs -21, -122 and -200a) correlated with IL-6 while miR-21 also correlated with D-dimer. Additionally, the abundance of miRs -31, -150 and -223, correlated with baseline CD4+ T cell count while the same three miRNAs plus miR- 145 correlated with nadir CD4+ T cell count. Discussion: No associations with mortality were found with any circulating miRNA studied. These results cast doubt onto the effectiveness of circulating miRNA as early predictors of mortality or the major underlying diseases that contribute to mortality in participants treated for HIV-1 infection
Development and Validation of a Risk Score for Chronic Kidney Disease in HIV Infection Using Prospective Cohort Data from the D:A:D Study
Ristola M. on työryhmien DAD Study Grp ; Royal Free Hosp Clin Cohort ; INSIGHT Study Grp ; SMART Study Grp ; ESPRIT Study Grp jäsen.Background Chronic kidney disease (CKD) is a major health issue for HIV-positive individuals, associated with increased morbidity and mortality. Development and implementation of a risk score model for CKD would allow comparison of the risks and benefits of adding potentially nephrotoxic antiretrovirals to a treatment regimen and would identify those at greatest risk of CKD. The aims of this study were to develop a simple, externally validated, and widely applicable long-term risk score model for CKD in HIV-positive individuals that can guide decision making in clinical practice. Methods and Findings A total of 17,954 HIV-positive individuals from the Data Collection on Adverse Events of Anti-HIV Drugs (D:A:D) study with >= 3 estimated glomerular filtration rate (eGFR) values after 1 January 2004 were included. Baseline was defined as the first eGFR > 60 ml/min/1.73 m2 after 1 January 2004; individuals with exposure to tenofovir, atazanavir, atazanavir/ritonavir, lopinavir/ritonavir, other boosted protease inhibitors before baseline were excluded. CKD was defined as confirmed (>3 mo apart) eGFR In the D:A:D study, 641 individuals developed CKD during 103,185 person-years of follow-up (PYFU; incidence 6.2/1,000 PYFU, 95% CI 5.7-6.7; median follow-up 6.1 y, range 0.3-9.1 y). Older age, intravenous drug use, hepatitis C coinfection, lower baseline eGFR, female gender, lower CD4 count nadir, hypertension, diabetes, and cardiovascular disease (CVD) predicted CKD. The adjusted incidence rate ratios of these nine categorical variables were scaled and summed to create the risk score. The median risk score at baseline was -2 (interquartile range -4 to 2). There was a 1: 393 chance of developing CKD in the next 5 y in the low risk group (risk score = 5, 505 events), respectively. Number needed to harm (NNTH) at 5 y when starting unboosted atazanavir or lopinavir/ritonavir among those with a low risk score was 1,702 (95% CI 1,166-3,367); NNTH was 202 (95% CI 159-278) and 21 (95% CI 19-23), respectively, for those with a medium and high risk score. NNTH was 739 (95% CI 506-1462), 88 (95% CI 69-121), and 9 (95% CI 8-10) for those with a low, medium, and high risk score, respectively, starting tenofovir, atazanavir/ritonavir, or another boosted protease inhibitor. The Royal Free Hospital Clinic Cohort included 2,548 individuals, of whom 94 individuals developed CKD (3.7%) during 18,376 PYFU (median follow-up 7.4 y, range 0.3-12.7 y). Of 2,013 individuals included from the SMART/ESPRIT control arms, 32 individuals developed CKD (1.6%) during 8,452 PYFU (median follow-up 4.1 y, range 0.6-8.1 y). External validation showed that the risk score predicted well in these cohorts. Limitations of this study included limited data on race and no information on proteinuria. Conclusions Both traditional and HIV-related risk factors were predictive of CKD. These factors were used to develop a risk score for CKD in HIV infection, externally validated, that has direct clinical relevance for patients and clinicians to weigh the benefits of certain antiretrovirals against the risk of CKD and to identify those at greatest risk of CKD.Peer reviewe