A5005359878- Pulsars and Gravitational Waves Research
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Stellar, planetary, and galactic studies
- Geophysics and Gravity Measurements
- Astronomy and Astrophysical Research
- Cosmology and Gravitation Theories
- GNSS positioning and interference
- Astrophysics and Star Formation Studies
- Advanced Frequency and Time Standards
- Astronomical Observations and Instrumentation
- Solar and Space Plasma Dynamics
- Adaptive optics and wavefront sensing
- Superconducting and THz Device Technology
- Geophysics and Sensor Technology
- Statistical and numerical algorithms
- Seismic Waves and Analysis
- Inertial Sensor and Navigation
- Particle accelerators and beam dynamics
- Advanced Optical Sensing Technologies
- Robotic Mechanisms and Dynamics
- Astro and Planetary Science
California Institute of Technology
2015-2024
Loma Linda University
2024
Madras Medical College
2024
Caltech Submillimeter Observatory
2023
Center for Astrophysics Harvard & Smithsonian
2019-2022
University of San Francisco
2020-2021
Harvard University
2020
ARC Centre of Excellence for All-sky Astrophysics
2017
Swinburne University of Technology
2015-2017
The University of Sydney
2017
A "pulsar timing array" (PTA), in which observations of a large sample pulsars spread across the celestial sphere are combined, allows investigation "global" phenomena such as background gravitational waves or instabilities atomic timescales that produce correlated residuals array. The Parkes Pulsar Timing Array (PPTA) is an implementation PTA concept based on with 64-m radio telescope. 20 millisecond being observed at three radio-frequency bands, 50cm (~700 MHz), 20cm (~1400 MHz) and 10cm...
Placing bounds on gravitational wave detection Gravitational waves are expected to be generated by the interaction of massive bodies in black-hole binary systems. As distort spacetime, it should possible verify their existence as they interfere with pulses emitted millisecond pulsars. However, after monitoring 24 pulsars Parkes radio telescope for 12 years, Shannon et al. found no detectable variation pulsar records. This nondetection result indicates that a new strategy is needed. Science ,...
We present timing models for 20 millisecond pulsars in the Parkes Pulsar Timing Array. The precision of parameter measurements these has been improved over earlier results by using longer data sets and modelling non-stationary noise. describe a new noise procedure demonstrate its effectiveness simulated data. Our methodology includes addition annual dispersion measure (DM) variations to some pulsars. first significant parallax PSRs J1024−0719, J1045−4509, J1600−3053, J1603−7202, J1730−2304,...
Quantum fluctuations of the gravitational field in early Universe, amplified by inflation, produce a primordial gravitational-wave background across broad frequency band. We derive constraints on spectrum this radiation, and hence theories combining experiments that cover 29 orders magnitude frequency. These include Planck observations cosmic microwave temperature polarization power spectra lensing, together with baryon acoustic oscillations big bang nucleosynthesis measurements, as well new...
Abstract We conduct a systematic tidal disruption event (TDE) demographics analysis using the largest sample of optically selected TDEs. A flux-limited, spectroscopically complete 33 TDEs is constructed Zwicky Transient Facility over 3 yr (from 2018 October to 2021 September). infer black hole (BH) mass ( M BH ) with host galaxy scaling relations, showing that ranges from 10 5.1 ⊙ 8.2 . developed survey efficiency corrected maximum volume method rates. The rest-frame g -band luminosity...
We report the detection and interferometric localization of repeating fast radio burst (FRB) source FRB 20220912A during commissioning observations with Deep Synoptic Array (DSA-110). Two bursts were detected from 20220912A, one each on 2022 October 18 25. The best-fit position is (R.A. J2000, decl. J2000) = (23:09:04.9, +48:42:25.4), a 90% confidence error ellipse $\pm2$ arcsec $\pm1$ in right ascension declination respectively. two have disparate polarization properties temporal profiles....
Abstract Fast radio bursts (FRBs) are a powerful and mysterious new class of transients that luminous enough to be detected at cosmological distances. By associating FRBs host galaxies, we can measure intrinsic environmental properties test FRB origin models, in addition using them as precise probes distant cosmic gas. The Deep Synoptic Array (DSA-110) is interferometer built maximize the rate which it simultaneously detect localize FRBs. Here, present first sample galaxies discovered by...
Signals from radio pulsars show a wavelength-dependent delay due to dispersion in the interstellar plasma. At typical observing wavelength, this can vary by tens of microseconds on five-year time scales, far excess signals interest pulsar timing arrays, such as that induced gravitational-wave background. Measurement these variations is not only crucial for detection signals, but also provides an unparallelled measurement turbulent plasma at au scales. In paper we demonstrate without...
Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA) project we develop first pulsar-based timescale that has a precision comparable to uncertainties in international atomic timescales.Our ensemble provides an Ensemble Scale (EPS) analogous free Échelle Atomique Libre (EAL).The EPS can be used detect fluctuations timescales and therefore lead new realisation Terrestrial Time, TT(PPTA11).We successfully follow features known affect frequency International Atomic Timescale...
Timing observations from the Parkes 64-m radio telescope for 165 pulsars between 1990 and 2011 have been searched period glitches. A total of 107 glitches were identified in 36 pulsars, where 61 previously reported 46 are new discoveries. Glitch parameters measured by fitting timing residual data. Observed relative glitch sizes \Delta\nu_g/\nu range 10^-10 10^-5, \nu = 1/P is pulse frequency. We confirm that distribution bimodal with peaks at approximately 10^-9 10^-6. Glitches mostly...
The formation and growth processes of supermassive black holes (SMBHs) are not well constrained. SMBH population models, however, provide specific predictions for the properties gravitational-wave background (GWB) from binary SMBHs in merging galaxies throughout Universe. Using observations Parkes Pulsar Timing Array, we constrain fractional GWB energy density with 95% confidence to be ${\Omega}_{GW}(H_0/73 {\rm km} s}^{-1} Mpc}^{-1})^2 < 1.3 \times 10^{-9}$ at a frequency 2.8 nHz, which is...
Recent observations of short gamma-ray bursts (SGRBs) suggest that binary neutron star (NS) mergers can create highly magnetized, millisecond NSs. Sharp cut-offs in X-ray afterglow plateaus some SGRBs hint at the gravitational collapse these remnant NSs to black holes. The such 'supramassive' also describes blitzar model, a leading candidate for progenitors fast radio (FRBs). observation an FRB associated with SGRB would provide compelling evidence model and NS merger scenario SGRBs, lead...
The favoured progenitor model for short $\gamma$-ray bursts (SGRBs) is the merger of two neutron stars that triggers an explosion with a burst collimated $\gamma$-rays. Following initial prompt emission, some SGRBs exhibit plateau phase in their $X$-ray light curves indicates additional energy injection from central engine, believed to be rapidly rotating, highly magnetised star. collapse this `protomagnetar' black hole likely responsible steep decay flux observed at end plateau. In letter,...
We report the real-time discovery of a fast radio burst (FRB 131104) with Parkes telescope in targeted observation Carina dwarf spheroidal galaxy. The dispersion measure is 779 cm$^{-3}$ pc, exceeding predictions for maximum line-of-sight Galactic contribution by factor 11. temporal structure characterized an exponential scattering tail timescale 2.0$^{+0.8}_{-0.5}$ ms at 1582 MHz that scales as frequency to power $-$4.4$^{+1.6}_{-1.8}$ (all uncertainties represent 95% confidence intervals)....
We present high signal-to-noise ratio, multifrequency polarization pulse profiles for 24 millisecond pulsars that are being observed as part of the Parkes Pulsar Timing Array project. The in three bands, centred close to 730, 1400 and 3100 MHz, using a dual-band 10 cm/50 cm receiver central beam 20-cm multibeam receiver. Observations spanning approximately six years have been carefully calibrated summed produce S/N profiles. This allows us study individual profile components particular how...
We present the first interferometric detections of Fast Radio Bursts (FRBs), an enigmatic new class astrophysical transient. In a 180-day survey Southern sky we discovered 3 FRBs at 843 MHz with UTMOST array, as part commissioning science during major ongoing upgrade. The wide field view ($\approx 9$ deg$^{2}$) is well suited to FRB searches. primary beam covered by 352 partially overlapping fan-beams, each which searched for in real time pulse widths range 0.655 42 ms, and dispersion...
Abstract We present detailed submillimeter- through centimeter-wave observations of the extraordinary extragalactic transient AT2018cow. The apparent characteristics—the high radio luminosity, rise and long-lived emission plateau at millimeter bands, sub-relativistic velocity—have no precedent. A basic interpretation data suggests coupled to a fast but ( ) shock in dense medium. find that X-ray is not naturally explained by an extension radio-submm synchrotron spectrum, nor inverse Compton...
We report a new Fast Radio Burst (FRB) discovered in real-time as part of the UTMOST project at Molonglo Observatory Synthesis Telescope (MOST). FRB170827 is first detected with our low-latency ($< 24$ s), machine-learning-based FRB detection system. The discovery was accompanied by capture voltage data native time and frequency resolution observing system, enabling coherent dedispersion detailed off-line analysis, which have unveiled fine temporal structure. dispersion measure (DM) 176.80...
We present results of an all-sky search in the Parkes Pulsar Timing Array (PPTA) Data Release 1 data set for continuous gravitational waves (GWs) frequency range from 5 × 10−9 to 2 10−7 Hz. Such signals could be produced by individual supermassive binary black hole systems early stage coalescence. phase up pulsar timing array form, each position on sky, two streams that correspond GW polarizations and then carry out optimal these streams. Since no statistically significant GWs were detected,...
High-sensitivity radio-frequency observations of millisecond pulsars usually show stochastic, broadband, pulse-shape variations intrinsic to the pulsar emission process. These induce jitter noise in timing observations; understanding properties this is particular importance for effort detect gravitational waves with arrays. We assess short-term profile and stability 22 that are part Parkes Pulsar Timing Array sample by examining intra-observation arrival time variability single-pulse...
We report the discovery of a multiply imaged, gravitationally lensed type Ia supernova, iPTF16geu (SN 2016geu), at redshift z = 0.409. This phenomenon was identified because light from stellar explosion magnified more than 50 times by curvature space around matter in an intervening galaxy. used high-spatial-resolution observations to resolve four images approximately 0.3 arc seconds center foreground The probe physical scale ~1 kiloparsec, smaller is typical other studies extragalactic...
Anisotropic bursts of gravitational radiation produced by events such as supermassive black hole mergers leave permanent imprints on space. Such wave 'memory' (GWM) signals are, in principle, detectable through pulsar timing sudden changes the apparent pulse frequency a pulsar. If an array pulsars is monitored GWM signal passes over Earth, would simultaneously appear to change amount that varies with their sky position quadrupolar fashion. Here, we describe search algorithm for and apply...
It is widely accepted that dark matter contributes about a quarter of the critical mass-energy density in our Universe. The nature currently unknown, with mass possible constituents spanning nearly one hundred orders magnitude. ultralight scalar field matter, consisting extremely light bosons m∼10−22 eV and often called “fuzzy” provides intriguing solutions to some challenges at sub-Galactic scales for standard cold model. As shown by Khmelnitsky Rubakov, such Galaxy would produce an...