We introduce new modules in the open-source PyCBC gravitational-wave astronomy toolkit that implement Bayesian inference for compact-object binary mergers. We review the Bayesian inference methods ...implemented and describe the structure of the modules. We demonstrate that the PyCBC Inference modules produce unbiased estimates of the parameters of a simulated population of binary black hole mergers. We show that the parameters' posterior distributions obtained using our new code agree well with the published estimates for binary black holes in the first Advanced LIGO-Virgo observing run.
We describe an ongoing search for pulsars and dispersed pulses of radio emission, such as those from rotating radio transients (RRATs) and fast radio bursts, at 350 MHz using the Green Bank ...Telescope. With the Green Bank Ultimate Pulsar Processing Instrument, we record 100 MHz of bandwidth divided into 4096 channels every 81.92 mu s. This survey will cover the entire sky visible to the Green Bank Telescope ( delta > -40degrees, or 82% of the sky) and outside of the Galactic Plane will be sensitive enough to detect slow pulsars and low dispersion measure (<30 pc cm super(-3)) millisecond pulsars (MSPs) with a 0.08 duty cycle down to 1.1 mJy. For pulsars with a spectral index of -1.6, we will be 2.5 times more sensitive than previous and ongoing surveys over much of our survey region. Here we describe the survey, the data analysis pipeline, initial discovery parameters for 62 pulsars, and timing solutions for 5 new pulsars. PSR J0214 + 5222 is an MSP in a long-period (512 days) orbit and has an optical counterpart identified in archival data. PSR J0636 + 5129 is an MSP in a very short-period (96 minutes) orbit with a very low mass companion (8 M sub(J)). PSR J0645 + 5158 is an isolated MSP with a timing residual RMS of 500 ns and has been added to pulsar timing array experiments. PSR J1434 + 7257 is an isolated, intermediate-period pulsar that has been partially recycled. PSR J1816 + 4510 is an eclipsing MSP in a short-period orbit (8.7 hr) and may have recently completed its spin-up phase.
Synopsis
Epigenetic mechanisms such as DNA methylation modulate gene expression in a complex fashion are consequently recognized as among the most important contributors to phenotypic variation in ...natural populations of plants, animals, and microorganisms. Interactions between genetics and epigenetics are multifaceted and epigenetic variation stands at the crossroad between genetic and environmental variance, which make these mechanisms prominent in the processes of adaptive evolution. DNA methylation patterns depend on the genotype and can be reshaped by environmental conditions, while transgenerational epigenetic inheritance has been reported in various species. On the other hand, DNA methylation can influence the genetic mutation rate and directly affect the evolutionary potential of a population. The origin of epigenetic variance can be attributed to genetic, environmental, or stochastic factors. Generally less investigated than the first two components, variation lacking any predictable order is nevertheless present in natural populations and stochastic epigenetic variation, also referred to spontaneous epimutations, can sustain phenotypic diversity. Here, potential sources of such stochastic epigenetic variability in animals are explored, with a focus on DNA methylation. To this day, quantifying the importance of stochasticity in epigenetic variability remains a challenge. However, comparisons between the mutation and the epimutation rates showed a high level of the latter, suggesting a significant role of spontaneous epimutations in adaptation. The implications of stochastic epigenetic variability are multifold: by affecting development and subsequently phenotype, random changes in epigenetic marks may provide additional phenotypic diversity, which can help natural populations when facing fluctuating environments. In isogenic lineages and asexually reproducing organisms, poor or absent genetic diversity can hence be tolerated. Further implication of stochastic epigenetic variability in adaptation is found in bottlenecked invasive species populations and populations using a bet-hedging strategy.
Hardware injections are simulated gravitational-wave signals added to the Laser Interferometer Gravitational-wave Observatory (LIGO). The detectors’ test masses are physically displaced by an ...actuator in order to simulate the effects of a gravitational wave. The simulated signal initiates a control-system response which mimics that of a true gravitational wave. This provides an end-to-end test of LIGO’s ability to observe gravitational waves. The gravitational-wave analyses used to detect and characterize signals are exercised with hardware injections. By looking for discrepancies between the injected and recovered signals, we are able to characterize the performance of analyses and the coupling of instrumental subsystems to the detectors’ output channels. This paper describes the hardware injection system and the recovery of injected signals representing binary black hole mergers, a stochastic gravitational wave background, spinning neutron stars, and sine-Gaussians.
Modern radio pulsar surveys produce a large volume of prospective candidates, the majority of which are polluted by human-created radio frequency interference or other forms of noise. Typically, ...large numbers of candidates need to be visually inspected in order to determine if they are real pulsars. This process can be labour intensive. In this paper, we introduce an algorithm called Pulsar Evaluation Algorithm for Candidate Extraction (peace) which improves the efficiency of identifying pulsar signals. The algorithm ranks the candidates based on a score function. Unlike popular machine-learning-based algorithms, no prior training data sets are required. This algorithm has been applied to data from several large-scale radio pulsar surveys. Using the human-based ranking results generated by students in the Arecibo Remote Command Center programme, the statistical performance of peace was evaluated. It was found that peace ranked 68 per cent of the student-identified pulsars within the top 0.17 per cent of sorted candidates, 95 per cent within the top 0.34 per cent and 100 per cent within the top 3.7 per cent. This clearly demonstrates that peace significantly increases the pulsar identification rate by a factor of about 50 to 1000. To date, peace has been directly responsible for the discovery of 47 new pulsars, 5 of which are millisecond pulsars that may be useful for pulsar timing based gravitational-wave detection projects.
The energetic, eclipsing millisecond pulsar J1816+4510 was recently discovered in a low-frequency radio survey with the Green Bank Telescope. With an orbital period of 8.7 hr and a minimum companion ...mass of 0.16 M sub(middot in circle), it appears to belong to an increasingly important class of pulsars that are ablating their low-mass companions. We report the discovery of the gamma -ray counterpart to this pulsar and present a likely optical/ultraviolet counterpart as well. Using the radio ephemeris, we detect pulsations in the unclassified gamma -ray source 2FGL J1816.5+4511, implying an efficiency of ~25% in converting the pulsar's spin-down luminosity into gamma -rays and adding PSR J1816+4510 to the large number of millisecond pulsars detected by Fermi. The likely optical/UV counterpart was identified through position coincidence (<0".1) and unusual colors. Assuming that it is the companion, with R = 18.27 + or - 0.03 mag and effective temperature > ~15,000 K, it would be among the brightest and hottest of low-mass pulsar companions and appears qualitatively different from other eclipsing pulsar systems. In particular, current data suggest that it is a factor of two larger than most white dwarfs of its mass but a factor of four smaller than its Roche lobe. We discuss possible reasons for its high temperature and odd size, and suggest that it recently underwent a violent episode of mass loss. Regardless of origin, its brightness and the relative unimportance of irradiation make it an ideal target for a mass, and hence a neutron star mass, determination.
We present timing solutions for 10 pulsars discovered in 350 MHz searches with the Green Bank Telescope. Nine of these were discovered in the Green Bank Northern Celestial Cap survey and one was ...discovered by students in the Pulsar Search Collaboratory program during an analysis of drift-scan data. Following the discovery and confirmation with the Green Bank Telescope, timing has yielded phase-connected solutions with high-precision measurements of rotational and astrometric parameters. Eight of the pulsars are slow and isolated, including PSR J0930−2301, a pulsar with a nulling fraction lower limit of ∼30% and a nulling timescale of seconds to minutes. This pulsar also shows evidence of mode changing. The remaining two pulsars have undergone recycling, accreting material from binary companions, resulting in higher spin frequencies. PSR J0557−2948 is an isolated, 44 ms pulsar that has been partially recycled and is likely a former member of a binary system that was disrupted by a second supernova. The paucity of such so-called "disrupted binary pulsars" (DRPs) compared to double neutron star (DNS) binaries can be used to test current evolutionary scenarios, especially the kicks imparted on the neutron stars in the second supernova. There is some evidence that DRPs have larger space velocities, which could explain their small numbers. PSR J1806+2819 is a 15 ms pulsar in a 44-day orbit with a low-mass white dwarf companion. We did not detect the companion in archival optical data, indicating that it must be older than 1200 Myr.
We present timing solutions for four pulsars discovered in the Green Bank Northern Celestial Cap survey. All four pulsars are isolated with spin periods between 0.26 and 1.84 s. PSR J0038−2501 has a ...0.26 s period and a period derivative of 7.6 × 10−19 s s−1, which is unusually low for isolated pulsars with similar periods. This low period derivative may be simply an extreme value for an isolated pulsar or it could indicate an unusual evolution path for PSR J0038−2501, such as a disrupted recycled pulsar from a binary system or an orphaned central compact object (CCO). Correcting the observed spin-down rate for the Shklovskii effect suggests that this pulsar may have an unusually low space velocity, which is consistent with expectations for DRPs. There is no X-ray emission detected from PSR J0038−2501 in an archival Swift observation, which suggests that it is not a young orphaned CCO. The high dispersion measure of PSR J1949+3426 suggests a distance of 12.3 kpc. This distance indicates that PSR J1949+3426 is among the most distant 7% of Galactic field pulsars, and is one of the most luminous pulsars.
Many important aspects of the dynamic thermo-mechanical response of materials occur at the mesoscale, i.e. a physical scale of interactions smaller than what can be adequately described by homogenous ...behaviors, yet larger than the scale of the atomic lattice. Concurrent advancements in computational power, continuum theory, and experimental diagnostics are enabling unprecedented understanding of such interactions. However, we cannot develop a sufficient level of confidence in such mesoscale capability until the constitutive description of the underlying constituents is reliably representative of their actual physical behavior. Therefore, there is a strong need to combine experimental, modeling, and data-science techniques to validate models of the thermomechanical response of individual single crystals. One experimental diagnostic with high potential impact to shock physics and materials science is in-situ x-ray diffraction. This paper is primarily focused on simulation of x-ray diffraction in shock physics, but with an aim toward quantifying parametric uncertainty of simulation models. We develop and demonstrate a data-science and model-driven approach to constrain the parameterization of continuum models of crystal lattice deformation associated with the shock response of crystalline materials. The framework is built around the connection between continuum hydrodynamic simulations of lattice deformation and a new Bragg diffraction simulation code, BarberShop. The dynamic deformation of a crystal lattice is modeled using the DiscoFlux model within an arbitrary Lagrangian-Eulerian hydrodynamic code, FLAG. These detailed continuum simulations of lattice deformation can be computationally slow, thus a statistical model is used to emulate the evolution of lattice deformation fields in time and across the considered model parameter space. Emulated lattice deformation fields can then be generated rapidly for any combination of physics model parameters. In turn, these fields can be fed into BarberShop to realize a rapid prediction of Bragg diffraction patterns associated with particular values of physics model parameters. The framework enables parameterization of the single crystal model to obtain Bragg diffraction patterns that most closely resemble a corresponding measurement. Furthermore, the framework naturally provides sensitivities of the lattice deformation to the physics parameters. We highlight the utility of this framework through the application to a synthetic closed-loop inverse problem leading to the parameterization of a single crystal material model. As a model problem, we consider the dynamic response of the energetic molecular crystal, cyclotrimethylenetrinitramine (or RDX), under dynamic compression induced by simulated flyer plate impact experiments.
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