Harsha Blumer
A5086794065- Pulsars and Gravitational Waves Research
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Geophysics and Gravity Measurements
- Astrophysics and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Cosmology and Gravitation Theories
- High-pressure geophysics and materials
- Astronomical Observations and Instrumentation
- Solar and Space Plasma Dynamics
- Advanced Frequency and Time Standards
- Particle Accelerators and Free-Electron Lasers
- Particle Detector Development and Performance
- Dark Matter and Cosmic Phenomena
- Astronomy and Astrophysical Research
- Inertial Sensor and Navigation
- Neutrino Physics Research
- Stellar, planetary, and galactic studies
- Cold Atom Physics and Bose-Einstein Condensates
- Superconducting and THz Device Technology
- Atomic and Subatomic Physics Research
- Particle accelerators and beam dynamics
- GNSS positioning and interference
- Black Holes and Theoretical Physics
- Galaxies: Formation, Evolution, Phenomena
West Virginia University
2017-2024
New Mexico Institute of Mining and Technology
2022
Abstract We search for an isotropic stochastic gravitational-wave background (GWB) in the 12.5 yr pulsar-timing data set collected by North American Nanohertz Observatory Gravitational Waves. Our analysis finds strong evidence of a process, modeled as power law, with common amplitude and spectral slope across pulsars. Under our fiducial model, Bayesian posterior f −2/3 power-law spectrum, expressed characteristic GW strain, has median 1.92 × 10 −15 5%–95% quantiles 1.37–2.67 at reference...
The All-sky Medium Energy Gamma-ray Observatory (AMEGO) is a probe class mission concept that will provide essential contributions to multimessenger astrophysics in the late 2020s and beyond. AMEGO combines high sensitivity 200 keV 10 GeV energy range with wide field of view, good spectral resolution, polarization sensitivity. Therefore, key study astrophysical objects have unique signatures gamma-ray regime, such as neutron star mergers, supernovae, flaring active galactic nuclei....
We report results from continued timing observations of PSR J0740+6620, a high-mass, 2.8-ms radio pulsar in orbit with likely ultra-cool white dwarf companion. Our data set consists combined pulse arrival-time measurements made the 100-m Green Bank Telescope and Canadian Hydrogen Intensity Mapping Experiment telescope. explore significance timing-based phenomena arising general-relativistic dynamics variations dispersion. When using various statistical methods, we find that combining $\sim...
Pulsar timing array collaborations, such as the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), are seeking to detect nanohertz gravitational waves emitted by supermassive black hole binaries formed in aftermath of galaxy mergers. We have searched continuous from individual circular using NANOGrav's recent 12.5-year data set. created new methods accurately model uncertainties on pulsar distances our analysis, and we implemented techniques account a common red noise...
Abstract We present the results of a Bayesian search for gravitational wave (GW) memory in NANOGrav 12.5 yr data set. find no convincing evidence any signals this Bayes factor 2.8 favor model that includes signal and common spatially uncorrelated red noise (CURN) compared to including only CURN. However, further investigation shows disproportionate amount support comes from three dubious pulsars. Using more flexible red-noise these pulsars reduces 1.3. Having found compelling evidence, we go...
We search NANOGrav's 12.5-year data set for evidence of a gravitational wave background (GWB) with all the spatial correlations allowed by general metric theories gravity. find no substantial in favor existence such our data. that scalar-transverse (ST) yield signal-to-noise ratios and Bayes factors are higher than quadrupolar (tensor transverse, TT) correlations. Specifically, we ST ratio 2.8 preferred over TT (Hellings Downs correlations) Bayesian odds about 20:1. However, significance is...
Low-frequency gravitational-wave experiments require the highest timing precision from an array of most stable millisecond pulsars. Several known sources noise on short timescales in single radio-pulsar observations are well described by a simple model three components: template-fitting finite signal-to-noise ratio, pulse phase/amplitude jitter single-pulse stochasticity, and scintillation errors short-timescale interstellar scattering variations. Currently dominate, but as radio telescopes...
Abstract The Green Bank North Celestial Cap (GBNCC) pulsar survey will cover the entire northern sky ( δ > −40°) at 350 MHz, and is one of most uniform sensitive all-sky surveys to date. We have created a pipeline reanalyze GBNCC data take MHz census all pulsars detected by survey, regardless their discovery survey. Of 1413 in region, we were able recover 670. For these present measured signal-to-noise ratios (S/N), flux densities, pulse widths, profiles, where appropriate, refined...
We present time-of-arrival (TOA) measurements and timing models of 47 millisecond pulsars (MSPs) observed from 2004 to 2017 at the Arecibo Observatory Green Bank Telescope by North American Nanohertz for Gravitational Waves (NANOGrav). The observing cadence was three four weeks most over this time span, with weekly observations six sources. These data were collected use in low-frequency gravitational wave searches other astrophysical purposes. detail our observational methods a set TOA...
Abstract The millisecond pulsar J1713+0747 underwent a sudden and significant pulse shape change between 2021 April 16 17 (MJDs 59320 59321). Subsequently, the gradually recovered over course of several months. We report results continued multifrequency radio observations made using Canadian Hydrogen Intensity Mapping Experiment 100 m Green Bank Telescope in 3 yr period encompassing event, 2020 February 2023 February. As February, had returned to state similar that seen before but with...
We present a new analysis of the profile data from 47 millisecond pulsars comprising 12.5-year set North American Nanohertz Observatory for Gravitational Waves (NANOGrav), which is presented in parallel paper (Alam et al. 2021a; NG12.5). Our reprocessing performed using "wideband" timing methods, use frequency-dependent template profiles, simultaneous time-of-arrival (TOA) and dispersion measure (DM) measurements broadband observations, novel techniques. In particular, wideband DM are used...
Abstract We report the first discovery of a fast radio burst (FRB), FRB 20200125A, by Green Bank Northern Celestial Cap (GBNCC) Pulsar Survey conducted with Telescope at 350 MHz. 20200125A was detected Galactic latitude 58.°43 dispersion measure 179 pc cm 3 , while electron density models predict maximum contribution 25 along this line sight. Moreover, no apparent foreground sources ionized gas that could account for excess DM are visible in multiwavelength surveys region. This argues source...
Pulsar timing array collaborations, such as the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), are seeking to detect nanohertz gravitational waves emitted by supermassive black hole binaries formed in aftermath of galaxy mergers. We have searched continuous from individual circular using NANOGrav's recent 12.5-year data set. created new methods accurately model uncertainties on pulsar distances our analysis, and we implemented techniques account a common red noise...
Abstract We report on X-ray limits observations of FRB 20190520B during simultaneous with the Green Bank Telescope and Chandra Observatory. is an outlier in fast radio burst (FRB) population due to its excess source-local dispersion, association compact persistent emission, high line-of-sight magnetic field variability. One was detected overlapping observing time, no emission detected. find density duration 20190520B’s luminosity, interpreting nondetection context known populations that...
The frequency dependence of radio pulse arrival times provides a probe structures in the intervening media. Demorest et al. 2013 was first to show short-term (~100-200 days) reduction electron content along line sight PSR J1713+0747 data from 2008 (approximately MJD 54750) based on an apparent dip dispersion measure pulsar. We report similar event 2016 57510), with average residual pulse-arrival approximately 3.0,-1.3, and -0.7 microseconds at 820, 1400, 2300 MHz, respectively. Timing...
The Green Bank North Celestial Cap (GBNCC) survey is a 350-MHz all-sky for pulsars and fast radio transients using the Robert C. Byrd Telescope. To date, has discovered over 190 pulsars, including 33 millisecond (MSPs) 24 rotating transients(RRATs). Several exotic have been in survey, PSR J1759+5036, binary pulsar with 176-ms spin period an orbit of 2.04 days, eccentricity 0.3,and projected semi-major axis 6.8 light seconds. Using seven years timing data, we are able to measure one...
Abstract The radio galaxy 3C 66B has been hypothesized to host a supermassive black hole binary (SMBHB) at its center based on electromagnetic observations. Its apparent 1.05 yr period and low redshift (∼0.02) make it an interesting testbed search for low-frequency gravitational waves (GWs) using pulsar timing array (PTA) experiments. This source subjected multiple searches continuous GWs from circular SMBHB, resulting in progressively more stringent constraints GW amplitude chirp mass. In...
Abstract The Neutron Star Interior Composition Explorer ( NICER ) is an X-ray astrophysics payload on the International Space Station. It enables unprecedented high-precision timing of millisecond pulsars (MSPs) without pulse broadening and delays due to dispersion scattering within interstellar medium that plague radio timing. We present initial results from a year data MSPs PSR B1937+21 J0218+4232, nine months B1821−24. time-of-arrival uncertainties for three are consistent with...
Abstract We report the discovery of a new 5.78 ms period millisecond pulsar (MSP), PSR J1740−5340B (NGC 6397B), in an eclipsing binary system discovered with Parkes radio telescope (now also known as Murriyang) Australia and confirmed MeerKAT South Africa. The measured orbital period, 1.97 days, is longest among all binaries globular clusters (GCs) consistent that coincident X-ray source U18, previously suggested to be “hidden MSP.” Our XMM-Newton observations during NGC 6397B’s...
We extract interstellar scintillation parameters for pulsars observed by the NANOGrav radio pulsar timing program. Dynamic spectra observing epochs of each were used to obtain estimates timescales, bandwidths, and corresponding scattering delays using a stretching algorithm account frequency-dependent scaling. able measure bandwidths 28 at 1500 MHz 15 820 MHz. examine scaling behavior 17 find power-law indices ranging from $-0.7$ $-3.6$, though these may be biased shallow due insufficient...
We search for a first-order phase transition gravitational wave signal in 45 pulsars from the NANOGrav 12.5-year dataset. find that data can be modeled terms of strong first order taking place at temperatures below electroweak scale. However, we do not observe any preference phase-transition interpretation over standard astrophysical supermassive black hole mergers; but expect to gain additional discriminating power with future datasets, improving noise ratio and extending sensitivity window...