Precision orbital dynamics from interstellar scintillation arcs for PSR J0437-4715

Intensity scintillations of radio pulsars are known to originate from interference between waves scattered by the electron density irregularities of interstellar plasma, often leading to parabolic arcs in the two-dimensional power spectrum of the recorded dynamic spectrum. The degree of arc curvature depends on the distance to the scattering plasma and its transverse velocity with respect to the line-of-sight. We report the observation of annual and orbital variations in the curvature of scintillation arcs over a period of 16 years for the bright millisecond pulsar, PSR J0437-4715. These variations are the signature of the relative transverse motions of the Earth, pulsar, and scattering medium, which we model to obtain precise measurements of parameters of the pulsar's binary orbit and the scattering medium itself. We observe two clear scintillation arcs in most of our $>$5000 observations and we show that they originate from scattering by thin screens located at distances $D_1 = 89.8 \pm 0.4$ pc and $D_2 = 124 \pm 3$ pc from Earth. The best-fit scattering model we derive for the brightest arc yields the pulsar's orbital inclination angle $i = 137.1 \pm 0.3^\circ$, and longitude of ascending node, $\Omega=206.3\pm0.4^\circ$. Using scintillation arcs for precise astrometry and orbital dynamics can be superior to modelling variations in the diffractive scintillation timescale, because the arc curvature is independent of variations in the level of turbulence of interstellar plasma. This technique can be used in combination with pulsar timing to determine the full three-dimensional orbital geometries of binary pulsars, and provides parameters essential for testing theories of gravity and constraining neutron star masses.Comment: 19 pages, 10 figures. Accepted for publication in Ap

Multi-Messenger Gravitational Wave Searches with Pulsar Timing Arrays: Application to 3C66B Using the NANOGrav 11-year Data Set

When galaxies merge, the supermassive black holes in their centers may form binaries and, during the process of merger, emit low-frequency gravitational radiation in the process. In this paper we consider the galaxy 3C66B, which was used as the target of the first multi-messenger search for gravitational waves. Due to the observed periodicities present in the photometric and astrometric data of the source of the source, it has been theorized to contain a supermassive black hole binary. Its apparent 1.05-year orbital period would place the gravitational wave emission directly in the pulsar timing band. Since the first pulsar timing array study of 3C66B, revised models of the source have been published, and timing array sensitivities and techniques have improved dramatically. With these advances, we further constrain the chirp mass of the potential supermassive black hole binary in 3C66B to less than $(1.65\pm0.02) \times 10^9~{M_\odot}$ using data from the NANOGrav 11-year data set. This upper limit provides a factor of 1.6 improvement over previous limits, and a factor of 4.3 over the first search done. Nevertheless, the most recent orbital model for the source is still consistent with our limit from pulsar timing array data. In addition, we are able to quantify the improvement made by the inclusion of source properties gleaned from electromagnetic data to `blind' pulsar timing array searches. With these methods, it is apparent that it is not necessary to obtain exact a priori knowledge of the period of a binary to gain meaningful astrophysical inferences.Comment: 14 pages, 6 figures. Accepted by Ap

Multimessenger Gravitational-wave Searches with Pulsar Timing Arrays:Application to 3C 66B Using the NANOGrav 11-year Data Set

When galaxies merge, the supermassive black holes in their centers may form binaries and emit low-frequency gravitational radiation in the process. In this paper, we consider the galaxy 3C 66B, which was used as the target of the first multimessenger search for gravitational waves. Due to the observed periodicities present in the photometric and astrometric data of the source, it has been theorized to contain a supermassive black hole binary. Its apparent 1.05-year orbital period would place the gravitational-wave emission directly in the pulsar timing band. Since the first pulsar timing array study of 3C 66B, revised models of the source have been published, and timing array sensitivities and techniques have improved dramatically. With these advances, we further constrain the chirp mass of the potential supermassive black hole binary in 3C 66B to less than (1.65 ± 0.02) × 109 M o˙ using data from the NANOGrav 11-year data set. This upper limit provides a factor of 1.6 improvement over previous limits and a factor of 4.3 over the first search done. Nevertheless, the most recent orbital model for the source is still consistent with our limit from pulsar timing array data. In addition, we are able to quantify the improvement made by the inclusion of source properties gleaned from electromagnetic data over "blind"pulsar timing array searches. With these methods, it is apparent that it is not necessary to obtain exact a priori knowledge of the period of a binary to gain meaningful astrophysical inferences

PSR J1024-0719:A Millisecond Pulsar in an Unusual Long-Period Orbit

PSR J1024-0719 is a millisecond pulsar that was long thought to be isolated. However, puzzling results concerning its velocity, distance, and low rotational period derivative have led to a reexamination of its properties. We present updated radio timing observations along with new and archival optical data which show that PSR J1024-0719 is most likely in a long-period (2-20 kyr) binary system with a low-mass (approximate to 0.4 M-circle dot), low-metallicity (Z approximate to -0.9 dex) main-sequence star. Such a system can explain most of the anomalous properties of this pulsar. We suggest that this system formed through a dynamical exchange in a globular cluster that ejected it into a halo orbit, which is consistent with the low observed metallicity for the stellar companion. Further astrometric and radio timing observations such as measurement of the third period derivative could strongly constrain the range of orbital parameters

COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study

Background: The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods: International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results: ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each P < 0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country. Interpretation: This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men

Bizarre Nearby Galaxies from the Sloan Digital Sky Survey

The Sloan Digital Sky Survey (SDSS) has been collecting data for more than 15 years, mapping the sky and revolutionizing our understanding of the structure of the Universe, galaxies beyond the Milky Way, and our own Solar system. By looking at images and spectra of nearby galaxies, we can learn about the evolution and morphology of galaxies in general. In this project, we use the latest data release from SDSS to find rare nearby (z\u3c0.4) galaxies with characteristics similar to low mass, young galaxies in the early universe. Detailed studies of the physical conditions in these galaxies may shed light on the early stages of galaxy formation and evolution. Here we present the preliminary results of this analysis and how our findings compare with galaxies in the early universe

The Never-Ending Story of a Star (Free Astronomy Public Lectures)

Like humans, stars often live their long lives in pairs, called binaries. At the end of their lives, they experience drastic transformations, rather than simply ending, and these transformations greatly affect their companions. In this lecture, I will take you on a journey of the many lives (and spectacular deaths/rebirths) of a massive star with a lighter companion star. The mass of a star, among other factors, determines the path it takes and the changes it experiences, and stars in binaries affect each other greatly. In a quiet stellar neighbourhood, this massive star will peacefully spend millions of years with its companion before undergoing a sudden transformation into one of the most extreme objects in the universe. Billions of years later, a second transformation will occur when the star’s companion quietly reaches the end of its life. However, under the right conditions, the pair’s story will not end there. Presented on Friday 20 September, 2019

ARCC@UWM: The Search for Pulsars

Pulsars are dense, evolved stars, called neutron stars, that rotate with an extremely reliable period and emit an intense beam of radiation that can be seen from Earth in radio frequencies, appearing similar to a lighthouse pulse. This unique signal allows for novel ways to observe the universe, the most exciting of which is the potential to detect previously undiscovered gravitational waves, giving further evidence to Einstein’s theory of relativity. We currently know of over 2000 pulsars, of which around 10% have frequencies of ~500 Hz and are known as millisecond pulsars. However, methods for using pulsars to detect gravitational waves become more sensitive with every additional millisecond pulsar, so active searches for new pulsars are very important. By remotely observing from UWM with two of the world’s largest radio telescopes, the Arecibo telescope in Puerto Rico and the Green Bank telescope in West Virginia, students discover, confirm, and study these incredible neutron stars while collaborating with scientists around the globe

Patient-reported barriers to prenatal diagnosis of congenital heart defects: A mixed-methods study

Objective:To ascertain patient-reported, modifiable barriers to prenatal diagnosis of congenital heart defects (CHDs). Methods:This was a mixed-methods study among caretakers of infants who received congenital heart surgery from 2019 to 2020 in the Chicagoland area. Quantitative variables measuring sociodemographic characteristics and prenatal care utilization, and qualitative data pertaining to patient-reported barriers to prenatal diagnosis were collected from electronic health records and semi-structured phone surveys. Thematic analysis was performed using a convergent parallel approach. Results:In total, 160 caretakers completed the survey, 438 were eligible for survey, and 49 (31%) received prenatal care during the COVID-19 pandemic. When comparing respondents and non-respondents, there was a lower prevalence of maternal Hispanic ethnicity and a higher prevalence of non-English/Spanish-speaking households. Of all respondents, 34% reported an undetected CHD on ultrasound or echocardiogram, while 79% reported at least one barrier to prenatal diagnosis related to social determinants of health. Among those social barriers, the most common were difficulty with appointment scheduling (n = 12, 9.5%), far distance to care/lack of access to transportation (n = 12, 9.5%) and difficulty getting time off work to attend appointments (n = 6, 4.8%). The latter two barriers were correlated. Conclusion:While technical improvements in the detection of CHDs remain an important area of research, it is equally critical to produce evidence for interventions that mitigate barriers to prenatal diagnosis due to social determinants of health