Understanding the structures of relativistic jets in X-ray binaries and the parameters of their binary orbits have traditionally both been challenging problems. I will show that we can take advantage of the fact that the jets extend well outside the binary orbits to help understand both of these, by using the eclipses of the jets by the donor stars in the binaries both to probe the jet structure and also to estimate binary mass ratios and inclination angles. This work is feasible for a few objects already with VLA and ALMA, but will benefit dramatically from the ngVLA for expanding the sample size of objects that can be studied in this manner.
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Most black hole X-ray binaries (BHXBs) spend the majority of their time in a weakly accreting 'quiescent' state, which we define as Eddington ratios Lx/Ledd < 1e-5 (where Lx is the X-ray luminosity). In quiescence, a larger fraction of the radiative power from the accretion flow/jet system tends to be released as jetted synchrotron radio emission, when compared to hard state BHXBs (i.e., 1e-5 < Lx/Ledd < 1e-2). I will discuss radio variability of two different quiescent BHXBs using the VLA, showing radio variations on timescales of minutes through decades. These observations provide new constraints on quiescent jet physics, and also provide empirical limits on variability-induced systematics one should consider when planning coordinated multiwavelength observations of quiescent BHXBs.
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We have performed a series of global 2D isothermal hydrodyanmical simulation of the binary stellar mass black hole (BH) embedded in active galactic nucleus (AGN) accretion disks to study whether the binary can be hardened due to the surrounding gas. For the prograde binary with respect to the disk, we find that the gravitational softening scale for the stellar mass BH could be a crucial parameter for controlling the binary dynamics. We confirm the results from previous simulations that the binary is hardened with time when the softening scale is about half of the initial binary separation. However, the binary BH is outspiraling when the gravitational softening becomes much smaller. Such a conclusion does not sensitively depends on the accretion prescription for the binary we adopt. The outspiraling is mainly due to the domination of the positive gravitational torque from the region very close to the binary. For the outspiraling case, the binary's eccentricity can be significantly excited within a few hundred orbits of the binary's center of mass, which can thus still bring the binary into a small separation transiently. For the retrograde binary, we find that the binary inspirals towards each other for both the large and small softening cases. We further discuss the physical implications of the disk-assisted binary BH mergers observed with the gravitational wave detectors.
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The origin of the cosmic diffuse gamma-ray (CDG) background in the 0.3 - 30 MeV energy range is a mystery that has persisted for over 40 years. The Mini Astrophysical MeV Background Observatory (MAMBO) is a new CubeSat mission under development at Los Alamos National Laboratory, motivated by the fact that, since the MeV CDG is relatively bright, only a small detector is required to make high-quality measurements of it. Indeed, the sensitivity of space-based gamma-ray instruments to the CDG is limited not by size, but by the locally generated instrumental background produced by interactions of energetic particles in spacecraft materials. Comparatively tiny CubeSat platforms provide a uniquely quiet environment relative to previous gamma-ray science missions. The MAMBO mission will provide the best measurements ever made of the MeV CDG spectrum and angular distribution, utilizing two key innovations: 1) low instrumental background on a 12U CubeSat platform; and 2) an innovative shielded spectrometer design that simultaneously measures signal and background. We describe the MAMBO instrument and mission concept in detail, including simulations and laboratory measurements demonstrating the key measurement concept.
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POLARBEAR is a cosmic microwave background (CMB) polarization experiment located in the Atacama desert in Chile. The science goals of the project include a deep search for CMB B-mode polarization created by inflationary gravitational waves, as well as characterization of the CMB B-mode signal from gravitational lensing. POLARBEAR-1 observed from 2012-2017 and made initial measurements of the CMB B-mode signal. POLARBEAR/Simons Array is an expansion to three identical 3-meter telescopes with larger, more sensitive focal planes, and increased frequency coverage, with staged deployment of three new cryogenic receivers known as POLARBEAR-2a, -2b, and -2c. When completed, POLARBEAR/Simons Array will have over 20,000 superconducting transition-edge sensor bolometers, cooled to 300 mK with closed-cycle cryogenics. These detectors are read out with Dfmux frequency-division multiplexing readout, with 40 detectors read out by a series SQUID array, with frequency channels between 1 and 5 MHz defined by an inductor and capacitor in series with each detector. The array will cover 95 GHz, 150 GHz, 220 GHz, and 280 GHz frequency bands, allowing greater control of foregrounds. The PB2-b and later cryogenic readout included small modifications to improve performance, based on the integrated performance in POLARBEAR-2a. We present the characterization of the integrated cryogenic readout system for POLARBEAR-2a and POLARBEAR-2b, and comparison of properties including stray impedances, frequency scatter, and peak stability.
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We present a new algorithm, the A-to-Z solver, which models the antenna aperture illumination pattern (AIP) in terms of Zernike polynomials. We use these aperture models in the AW projection algorithm (Bhatnagar et al., 2013), and we obtained improved results over the existing A-solver methodology (Jagannathan et al., 2018), particularly in polarization.

In order to achieve thermal noise limited imaging with modern radio interferometers such as JVLA, ALMA, MeerKAT, and uGMRT, it is necessary to correct for the instrumental effects of the antenna primary beam (PB) as a function of time, frequency, and polarization. The wideband AW projection algorithm (Bhatnagar et al., 2013) enables those corrections provided an accurate model of the AIP is available.

Our new approach with the A-to-Z solver models the antenna aperture holography directly, accurately capturing the full Jones response of the antenna. This provides us with accurate measurements of off-axis leakage, as opposed to the old A-solver method. The A-solver method uses ray tracing to model the AIP as demonstrated for the VLA antennas. However it is a non-trivial process involving a significant development effort on the part of individual observatories to include their own AIP into the framework, requiring a precise description of the antenna geometry, feed locations and offsets etc. The algorithm was also shown to be lacking in it's modeling of off-axis polarization effects at lower frequencies and is quite computationally expensive (Jagannathan et al., 2018).

Using this new algorithm we have successfully modeled the AIP of EVLA, MeerKAT, and ALMA. We show that the imaging performance is comparable (or better) than beams derived from ray traced beams for Stokes-I and -V imaging, and significantly better for Stokes-Q and -U. Furthermore the A-to-Z solver directly models the electric field distribution of the AIP and works independently of antenna shape, feed basis etc. We also show that the efficacy of this approach is limited by the quality of the holographic data - although the requisite quality should be achievable by most observatories.
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The emergence of the three-dimensional structure of the cosmic web over the history of the Universe displays very distinctive features when observed in X-rays, where both the most massive collapsed structure (clusters of galaxies) and the most energetic events in the life of galaxies (AGN and Quasars) reveal themselves unambiguously. The next generation of wide-area, sensitive X-ray surveys designed to map the hot and energetic Universe will be heralded by eROSITA (extended ROentgen Survey with an Imaging Telescope Array), the core instrument on the Russian-German Spektrum-Roentgen-Gamma (SRG) mission, successfully launched in July 2019. The high sensitivity, large field of view, high spatial resolution and high survey efficiency of eROSITA is bound to revolutionize X-ray astronomy and deliver large legacy samples for many classes of astronomical objects in the energy range 0.2-8 keV. I will present an overview of the instrument capabilities, the current status of the mission, a few selected early science results and the expectations for the survey program, which has completed in June the first observation of the whole sky.

The solar atmosphere is a favorable medium for the generation and propagation of waves. Waves transport energy to the upper atmosphere and are tools for probing the magnetic field, which is difficult to measure directly. Atmospheric gravity waves (AGWs) are generated by overshooting convection on the Sun. However, they are ubiquitous in other stellar and planetary atmospheres. On Earth, these waves play a pivotal role in our general circulation models that predict weather and global climate. AGWs can propagate throughout the lower solar atmosphere and are suspected to reach chromospheric heights. Their characteristics are strongly affected by the magnetic field allowing them to be a new potential seismic diagnostic in addition to commonly studied waves, such as acoustic waves. We can harness their observed behavior at different heights to sense the magnetic field and atmospheric flows in a novel way. We investigate the propagation and behavior of these waves throughout the lower solar atmosphere. Using IBIS at the Dunn Solar Telescope in Sunspot, New Mexico, we present high-resolution, multi-wavelength observations to derive phase differences and construct k−ω diagnostic diagrams for combinations of various heights. The signatures of propagating AGWs are detected at disk center on the quiet Sun. This study will shape our knowledge of these waves, which will be observed in high resolution with the new 4 meter solar telescope, DKIST, in the upcoming years.
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From 1998 to 2000, three white anticyclonic storms in Jupiter' South Temperate Belt merged into the single storm Oval BA. This storm maintained the white color of the storms from which it formed until late 2005 when it began to redden. The new red color was confirmed by amateur astronomers and Hubble Space Telescope observations in late 2005 and 2006. Starting in 2008, Oval BA began gradually lightening back to white, appearing first as a white core surrounded by a red collar and then completely lightening back to white within the past year. Images taken by the Hubble Space Telescope in 2019 for the Outer Planet Atmospheres Legacy (OPAL) program show that Oval BA now appears to be nearly as white as when it first formed. In this work, we report on the analysis of hyperspectral image cubes of Jupiter obtained with the NMSU Acousto-Optic Imaging Camera (NAIC) on the Astrophysical Research Consortium's 3.5 meter telescope at Apache Point Observatory. These hyperspectral image cubes were acquired in support of the Juno mission, providing observations that are complementary to those acquired by Juno. During Juno's perijove passes of Jupiter, Juno passes over a narrow range of longitudes and is unable to capture the whole planet. The NAIC image cubes are taken at the same time as Juno's perijove passes and capture the full disk of Jupiter, providing contextual data for Juno's high spatial resolution imagery. The NAIC image cubes span the wavelengths 470 nm to 950 nm, covering the optical and very near infrared, with images taken every 2 nm, yielding 241 unique images of Jupiter in each image cube. The image cubes used in this work were acquired on the night of May 27, 2019 which corresponds to the 20th perijove pass made by Juno. Using these image cubes, we will characterize the optical spectrum of Oval BA in its re-whitened state. This will allow us to compare Oval BA's current spectrum to that during its reddened state, thereby establishing the temporal evolution of the color of this storm feature.

The subclass of magnetic Cataclysmic Variables (CV), known as asynchronous polars, are still relatively poorly understood. An asynchronous polar is a polar in which the spin period of the white dwarf is either shorter or longer than the binary orbital period. In order to search for a more complete understanding, we compared standard and asynchronous polars in order to examine the relationship between a CV's status and its hard to soft X-ray ratio. By cross referencing the Ritter and Kolb, Swift-BAT, and ROSAT data, we narrowed down the list to 14 polars, but the data proved to be inconclusive as far as a relationship between hardness ratios and asynchronicity is concerned.

Globular clusters (GCs) are very old group of stars. Their age and very dense stellar environment lead to a higher formation rate, compared to the Galactic field, of compact binaries (harboring black holes, neutron stars, and white dwarfs) in tight orbits. Of special interest are the Cataclysmic Variables (CVs), which are accreting white dwarfs from Hydrogen-rich companions. CVs deserve special attention as they are predicted to account for a large fraction of the compact binary population in GCs and can be used to test whether GCs are in fact the efficient factories of compact binaries that we think. We present an ongoing survey which uses archival Hubble Space Telescope data to find and characterize the putative sizable population of CVs and compact binaries in 7 globular clusters, and preliminary findings for the globular cluster NGC 6397.

GW170817 has been instrumental in providing important clues into the physics involved in mergers of neutron stars. Observations at different wavelengths of the electromagnetic spectrum have provided evidence for the formation of heavier elements, insights into jet physics, circum-merger environment etc. and accompanied with gravitational wave measurements, have changed the way we look at such transients. In particular, radio observations track the fastest moving ejecta and have helped to zero in on possible models that could explain the observed radiation. Continued observations can further constrain the allowed parameter, allowing for better modelling of the inherent physics. I will present a brief overview of all observations of GW170817 done till date and will also hint upon what we expect to observe from the source in the near future.

Los Alamos National Laboratory (LANL) has a long history of discovery in gamma-ray astronomy, from the first detection of gamma-ray bursts by the Vela satellites to extensive involvement in NASA's highly successful Swift and Fermi missions. Looking to the future, several exciting new opportunities are being pursued, leveraging LANL's unique expertise in space-based gamma-ray detector development and data analysis. We describe current experimental efforts at LANL, including: 1) a concept for a Lunar CubeSat mission to measure gamma-ray lines from nuclear processes; 2) development of an advanced Compton telescope based on diamond detectors and fast scintillators; 3) a high-altitude ballooning program to test advanced detector technologies in a near-space environment; and 4) contributions to proposed large-scale NASA missions, including AMEGO, LEAP, and LOX.

Quiescent black holes produce large amounts of synchrotron radiation within the radio band due to the presence of the black hole's powerful relativistic jets. Here, we describe a method of locating unknown stellar mass black holes by using two radio sky surveys: VLASS and NVSS. Matching the two sky surveys allows for the spectral index of each source to be determined which can then be used to identify evidence of synchrotron radiation. In an effort to analyze the spectral indices, an interesting offshoot became evident. The steep spectrum point sources within the list may be indicative of unknown pulsars. Matching the list of sources to the ATNF Pulsar Catalogue yielded around 60 sources with a significant number of steep spectrum sources. Although this is very much a work in progress, it illustrates a possible method of discovering previously unknown black holes and pulsars.

The origin of radio emission from radio-quiet quasi-stellar objects (QSOs) remains an elusive problem. It is clear AGN-powered jets drive the bulk of radio seen in radio-loud QSOs (RLQs), but generally all of the emission in radio-quiet QSOs (RQQs) is confined to the QSO host galaxy, making discerning any physical origins of the observed radio emission ambiguous to say the least. To untangle this ambiguity, we re-image the RQ subset of 129 RQQs from the volume-complete (0.2<z<0.3), optically selected sample of 178 QSOs introduced by Kimball et al. (2011). Using the VLA's highest resolution A-configuration (~0.33 arcsec or ~1.3kpc at z=0.25), we resolve notable sub-galactic extended structures in about half of the RQQs, suggesting that small-scale jet behavior may well play a pivotal role in shaping the radio-quiet population along with the radio-loud.

The Andromeda galaxy, Messier 31, has been extensively studied in wavebands including radio, optical, ultraviolet and X-ray. The previous UV survey of M31 with Galex had ~5 arcsec spatial resolution. Thus Astrosat with its ultraviolet imaging telescope (UVIT) has been utilized to produce a survey of M31 in near and far UV with spatial resolution of 1 arcsec. The higher resolution is allowing many single stars in M31 to be resolved, and a number of star clusters. The current work is an update on the status of the survey and new results from analysis of the survey data.

The "Spiderweb Galaxy" is a massive irregular radio galaxy located inside a proto-galaxy-cluster environment at z = 2.16 (10.7 Gyr look-back time). Previous studies have reported extreme source-frame Faraday rotation measure (RM) values of ~6000 rad/m/m in the system, revealing a massive reservoir of magnetized and ionized cluster gas, and providing an invaluable opportunity to study mass assembly and AGN feedback in the early-time Universe. Here we report preliminary results from a new broadband (8-12 + 29-37 GHz) full polarisation Jansky VLA study of this system, as follows: We have generated the best-ever spatially-resolved Faraday RM map, and magnetic field orientation map, of a high-z radio galaxy. We confirm the the presence of extreme rest-frame RMs, and may detect even higher values than previously reported (|RM|>1e4 rad/m/m). The RM map shows smooth and significant changes in structure on kpc-scales, including a possible transverse gradient along the length of the radio jet, which may trace jet-gas interactions. With the addition of deep Chandra X-ray data (in hand), we outline the prospects for a combined X-ray and radio-spectropolarimetric analysis to measure the cluster magnetic field strength and structure, as well as the energetics, ages, and pressures of relativistic particle in this high-z system.

The Bulge Asymmetries and Dynamical Evolution (BAaDE) survey is the largest ever SiO maser survey of 28,062 infrared-selected selected evolved stars throughout the Galactic plane. We have generated an IR catalogue from 0.79 microns to 70 microns by cross-matching the BAaDE sources with nine different surveys. With this, spectral energy distributions (SEDs) can be formed for our objects. Using this IR catalog and the resulting SEDs, we are attempting to estimate distances to the sources as well as infer properties of the stellar objects and their circumstellar envelopes. The method used to extract these properties is by modeling SEDs of the sources. By generating SED templates, which we can match to sources of known distances, we can subsequently estimate distances to the full set of BAaDE sources. To effectively use this method, an in-depth study of interstellar extinction in the Galactic plane is necessary and we are attempting to map the extinction.

With an unprecedentedly large sample of uniformly selected asymptotic giant branch (AGB) stars, we present results focused on understanding the intermediate-age stellar populations in the Milky Way. Via radio and mm observations, the Bulge Asymmetries and Dynamical Evolution (BAaDE) survey has detected SiO maser emission in about 10,000 AGB stars, effectively probing the AGB stellar kinematics via their velocities. Here we show how to best separate C-rich from O-rich stars in this set of thin-shelled AGBs using multiple IR colors. These data imply the possible existence of a much larger sample of C-rich stars in the bulge than previously has been reported, although distances are needed for confirmation. The data have also provided exceptionally detailed statistical information about SiO lines and their line ratios, including isotopologue transitions. Findings include situations where the 29SiO isotopologue lines can become stronger than the main 28SiO isotopologue line despite the fact that 28SiO is 15 times more abundant. Follow-up observations show this may not be persistent throughout the stellar cycle, further complicating our understanding of the origin of these unusually bright maser lines, and illustrating the need of extensive modeling.
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Recent observations indicate that organic molecules are prevalent toward starless and prestellar cores. Deuteration of these molecules has not been well-studied during the starless phase. Published observations of singly-deuterated methanol, CH2DOH, have only been observed in a couple of well-studied, dense and evolved prestellar cores (e.g. L1544). Since the formation of gas-phase methanol during this cold phase is believed to occur via desorption from icy grain surfaces, observations of CH2DOH may be useful as a probe of the deuterium fraction in the ice mantles of dust grains. We present a systematic survey of CH2DOH toward 12 starless and prestellar cores in the B10 region of the Taurus molecular cloud. Nine of the twelve cores are detected with [CH2DOH]/[CH3OH] ranging from <0.04 to 0.23(+0.12 −0.06) with a median value of 0.11. Sources not detected tend to have larger virial parameters and larger methanol linewidths than detected sources. The results of this survey indicate that deuterium fractionation of organic molecules, such as methanol, during the starless phase may be more easily detectable than previously thought.
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The ubiquitous multiple velocity components seen in turbulent molecular clouds pose a challenge to conventional spectral line analysis techniques. To this end we have developed a novel Bayesian methodology to determine the number of velocity components and estimate their model parameters in a statistically rigorous and automated way. We have written an open-source software implementation for community use, NestFit. The method selects models using Bayes factors computed with Nested Sampling Monte Carlo. Application to the GBT GAS synthetic test suite shows superior retrieval accuracy compared to leading automated methods. We present results from an analysis of the GBT KEYSTONE M17 and Mon R2 fields. The results agree well with previous analyses for spectra at high-SNR, but the new techniques produce substantial improvement at low-SNR due to (i) the numerical robustness of Nested Sampling and (ii) the conditioning of the data on empirically motivated priors. The Bayesian inference methods presented in this work enable reproducible analyses of large observational and simulated datasets in a flexible and automated fashion without being restricted to the specific model and training dataset used, as is the case for Neural Network based approaches. Further, the Bayesian analysis of spectra in the low-SNR regime enabled by NestFit represents a powerful new tool for studying the molecular ISM at low densities, such as: the environments of dense cores, large-scale converging flows, and magnetically sub-critical gas.

We present a large study of CIV absorption lines in high-resolution quasar spectra, in which we characterize the properties of over 1200 CIV absorbers at redshifts z=1-4.75 down to an equivalent width (EW) limit of W=0.05 A. The frequency distribution of these absorbers is well-described by an evolving Schechter function from high to low redshifts. The incidence of CIV rises with decreasing redshift, with the rate of increase being higher for larger EW absorbers. We establish that CIV-absorbing structures become more numerous and/or larger in physical size over the last ~13 Gyr of cosmic time. Assuming these absorbers are associated with galaxy halos, the weakest absorbers with W>0.05 A have a characteristic absorption radius of ~200-240 kpc at z~1-4 and ~300-450 kpc at z<1, implying that a significant fraction of them could be found in the intergalactic medium, far from their production sites in galactic centers. State-of-the-art cosmological simulations over-produce the observed abundance of absorbers with W<0.3 A at z=3-5, necessitating a more complete understanding of the physics of the gas cycle that regulates galaxy growth. Using an expanded spectral database, we are currently undertaking project CHIMERA (Cosmic History In Metal Enriched Redshifted Absorption) to characterize various metal ions like MgII and OVI as well as neutral hydrogen across cosmic dawn (z~4), cosmic noon (z~1.5-3), and cosmic afternoon (z<1). This work will significantly improve our knowledge of the chemical, ionization and kinematic conditions of gaseous galaxy ecosystems across cosmic time.
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Hydra A is one of the most luminous FR I radio galaxies known and amongst the most well-studied. The radio emission from this source shows extremely large Faraday rotation measures (RMs) ranging between 3000 rad/m^² and -12000 rad/m^². The majority of these high RMs are believed to originate from magnetized thermal gas external to the radio lobes. We present our preliminary results of our wideband (2 - 12 GHz) polarization study of Hydra A with the VLA. The data reveal interesting polarization behaviour: significant depolarization as a function of λ² (particularly at low frequencies), structure in the depolarization (e.g. sinc-like patterns), non-linearities in the position angle as a function of λ², and significant structure in the Faraday spectra. We find that the majority of these structures can be attributed to unresolved fluctuations on scales < 1500 pc, suggesting the presence of turbulent magnetic field/electron density structures within a Faraday rotating (FR) medium. The location of the turbulent FR medium is still uncertain.

The Drake Equation is a method to estimate the number of technological civilizations in a galaxy as a function of six factors. However, the Drake Equation does not take into account the coupling between those factors. We present a new approach to the Drake Equation which uses Monte Carlo modeling to take into account the coupling between parameters and their time dependence. We model the development of stars in the galaxy, their planetary systems, and potential complex life. The model generates a random host star from an initial mass function and a time-dependent star formation rate. The characteristics (mass and luminosity) of each star are used with a power law mass distribution function to form a planetary system. Each planet is randomly placed in a protoplanetary disk with constant density and is formed from the mass in an area around its radius. The placement of subsequent planets cannot overlap with the area of previously used mass, resulting in a realistic spacing of the planets. Then, based on the star and planet characteristics, the model determines which planets are in the habitable zone and if they will last long enough to develop a technological civilization. As a result, we are able to model the distribution of habitable planets and civilizations as a function of spectral class throughout the life of a galaxy. Through a form of variance reduction, we efficiently model the full life of a galaxy and therefore can determine the impact of each model input.
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