Search for: All records

Abstract Long-period radio transients are an emerging class of extreme astrophysical events of which only three are known. These objects emit highly polarized, coherent pulses of typically a few tens of seconds duration, and minutes to approximately hour-long periods. Although magnetic white dwarfs and magnetars, either isolated or in binary systems, have been invoked to explain these objects, a consensus has not emerged. Here we report on the discovery of ASKAP J193505.1+214841.0 (henceforth ASKAP J1935+2148) with a period of 53.8 minutes showing 3 distinct emission states—a bright pulse state with highly linearly polarized pulses with widths of 10–50 seconds; a weak pulse state that is about 26 times fainter than the bright state with highly circularly polarized pulses of widths of approximately 370 milliseconds; and a quiescent or quenched state with no pulses. The first two states have been observed to progressively evolve over the course of 8 months with the quenched state interspersed between them suggesting physical changes in the region producing the emission. A constraint on the radius of the source for the observed period rules out an isolated magnetic white-dwarf origin. Unlike other long-period sources, ASKAP 1935+2148 shows marked variations in emission modes reminiscent of neutron stars. However, its radio properties challenge our current understanding of neutron-star emission and evolution. 

ABSTRACT With unparalleled rotational stability, millisecond pulsars (MSPs) serve as ideal laboratories for numerous astrophysical studies, many of which require precise knowledge of the distance and/or velocity of the MSP. Here, we present the astrometric results for 18 MSPs of the ‘MSPSR$$\pi$$’ project focusing exclusively on astrometry of MSPs, which includes the re-analysis of three previously published sources. On top of a standardized data reduction protocol, more complex strategies (i.e. normal and inverse-referenced 1D interpolation) were employed where possible to further improve astrometric precision. We derived astrometric parameters using sterne, a new Bayesian astrometry inference package that allows the incorporation of prior information based on pulsar timing where applicable. We measured significant ($${>}3\, \sigma$$) parallax-based distances for 15 MSPs, including 0.81 ± 0.02 kpc for PSR J1518+4904 – the most significant model-independent distance ever measured for a double neutron star system. For each MSP with a well-constrained distance, we estimated its transverse space velocity and radial acceleration. Among the estimated radial accelerations, the updated ones of PSR J1012+5307 and PSR J1738+0333 impose new constraints on dipole gravitational radiation and the time derivative of Newton’s gravitational constant. Additionally, significant angular broadening was detected for PSR J1643−1224, which offers an independent check of the postulated association between the HII region Sh 2-27 and the main scattering screen of PSR J1643−1224. Finally, the upper limit of the death line of γ-ray-emitting pulsars is refined with the new radial acceleration of the hitherto least energetic γ-ray pulsar PSR J1730−2304. 

Abstract The Green Bank 820 MHz pulsar survey covers ≃173 deg²in the Cygnus X region of the Galaxy, centered onl= 84.°5 andb= 1.°5. Significant star formation is present in this region, and lines of sight pass through three arms of the Galaxy (Orion–Cygnus, Perseus, and an outer arm). Using the Green Bank Telescope, we recorded 200 MHz of bandwidth for 4.5 minutes at 81.92μs resolution for each of 3457 observed survey pointings during 2016 and 2017, covering about two-thirds of the total area. We searched these data for pulsars and report the discovery of six new pulsars—PSRs J2016+3820, J2016+4231, J2019+3810, J2035+3538, J2035+3655, and J2041+4551—and the codiscovery of PSR J2057+4701. PSR J2035+3655 is in a short (4.5 hr) binary orbit; we report the full binary solution and weakly constrain the mass of the pulsar via a marginal (2σ) detection of the Shapiro delay. We also searched the survey data for known pulsars to estimate the survey’s sensitivity and measured 820 MHz pulse widths and flux density for 20 detected sources. For sources that were also detected in the Green Bank North Celestial Cap survey at 350 MHz, we measure scattering parameters and compare to expectations for the region. With these results, we revisit the population estimates that motivated this survey and consider the impact of the survey’s yield on their underlying models. We note an apparent underestimate in dispersion measure predictions from typical Galactic electron density models in the survey region, and discuss future observation strategies. 

Abstract We present timing solutions for 21 pulsars discovered in 350 MHz surveys using the Green Bank Telescope (GBT). All were discovered in the Green Bank North Celestial Cap pulsar survey, with the exception of PSR J0957−0619, which was found in the GBT 350 MHz Drift-scan pulsar survey. The majority of our timing observations were made with the GBT at 820 MHz. With a spin period of 37 ms and a 528 days orbit, PSR J0032+6946 joins a small group of five other mildly recycled wide binary pulsars, for which the duration of recycling through accretion is limited by the length of the companion’s giant phase. PSRs J0141+6303 and J1327+3423 are new disrupted recycled pulsars. We incorporate Arecibo observations from the NANOGrav pulsar timing array into our analysis of the latter. We also observed PSR J1327+3423 with the Long Wavelength Array, and our data suggest a frequency-dependent dispersion measure. PSR J0957−0619 was discovered as a rotating radio transient, but is a nulling pulsar at 820 MHz. PSR J1239+3239 is a new millisecond pulsar (MSP) in a 4 days orbit with a low-mass companion. Four of our pulsars already have published timing solutions, which we update in this work: the recycled wide binary PSR J0214+5222, the noneclipsing black widow PSR J0636+5128, the disrupted recycled pulsar J1434+7257, and the eclipsing binary MSP J1816+4510, which is in an 8.7 hr orbit with a redback-mass companion. 

Abstract We present and evaluate the prospects for detecting coherent radio counterparts to gravitational wave (GW) events using Murchison Widefield Array (MWA) triggered observations. The MWA rapid-response system, combined with its buffering mode ($$\sim$$4 min negative latency), enables us to catch any radio signals produced from seconds prior to hours after a binary neutron star (BNS) merger. The large field of view of the MWA ($$\sim$$$$1\,000\,\textrm{deg}^2$$at 120 MHz) and its location under the high sensitivity sky region of the LIGO-Virgo-KAGRA (LVK) detector network, forecast a high chance of being on-target for a GW event. We consider three observing configurations for the MWA to follow up GW BNS merger events, including a single dipole per tile, the full array, and four sub-arrays. We then perform a population synthesis of BNS systems to predict the radio detectable fraction of GW events using these configurations. We find that the configuration with four sub-arrays is the best compromise between sky coverage and sensitivity as it is capable of placing meaningful constraints on the radio emission from 12.6% of GW BNS detections. Based on the timescales of four BNS merger coherent radio emission models, we propose an observing strategy that involves triggering the buffering mode to target coherent signals emitted prior to, during or shortly following the merger, which is then followed by continued recording for up to three hours to target later time post-merger emission. We expect MWA to trigger on$$\sim$$$$5-22$$BNS merger events during the LVK O4 observing run, which could potentially result in two detections of predicted coherent emission. 

In the present work, four, well-studied, model peptides ( e.g. , substance P, bradykinin, angiotensin I and AT-Hook 3) were used to correlate structural information provided by ion mobility and ECD/CID fragmentation in a TIMS-q-EMS-ToF MS/MS platform, incorporporating an electromagnetostatic cell (EMS). The structural heterogeneity of the model peptides was observed by (i) multi-component ion mobility profiles (high ion mobility resolving power, R ∼115–145), and (ii) fast online characteristic ECD fragmentation patterns per ion mobility band (∼0.2 min). Particularly, it was demonstrated that all investigated species were probably conformers, involving cis / trans -isomerizations at X-Pro peptide bond, following the same protonation schemes, in good agreement with previous ion mobility and single point mutation experiments. The comparison between ion mobility selected ECD spectra and traditional FT-ICR ECD MS/MS spectra showed comparable ECD fragmentation efficiencies but differences in the ratio of radical (˙)/prime (′) fragment species (H˙ transfer), which were associated with the differences in detection time after the electron capture event. The analysis of model peptides using online TIMS-q-EMSToF MS/MS provided complementary structural information on the intramolecular interactions that stabilize the different gas-phase conformations to those obtained by ion mobility or ECD alone. 

ABSTRACT We present results from a search for the radio counterpart to the possible neutron star–black hole merger GW190814 with the Australian Square Kilometre Array Pathfinder. We have carried out 10 epochs of observation spanning 2–655 d post-merger at a frequency of 944 MHz. Each observation covered 30 deg2, corresponding to 87 per cent of the posterior distribution of the merger’s sky location. We conducted an untargeted search for radio transients in the field, as well as a targeted search for transients associated with known galaxies. We find one radio transient, ASKAP J005022.3−230349, but conclude that it is unlikely to be associated with the merger. We use our observations to place constraints on the inclination angle of the merger and the density of the surrounding environment by comparing our non-detection to model predictions for radio emission from compact binary coalescences. This survey is also the most comprehensive widefield search (in terms of sensitivity and both areal and temporal coverage) for radio transients to-date and we calculate the radio transient surface density at 944 MHz. 

ABSTRACT We present a low-frequency (170–200 MHz) search for prompt radio emission associated with the long GRB 210419A using the rapid-response mode of the Murchison Widefield Array (MWA), triggering observations with the Voltage Capture System for the first time. The MWA began observing GRB 210419A within 89 s of its detection by Swift, enabling us to capture any dispersion delayed signal emitted by this gamma-ray burst (GRB) for a typical range of redshifts. We conducted a standard single pulse search with a temporal and spectral resolution of $$100\, \mu$$s and 10 kHz over a broad range of dispersion measures from 1 to $$5000\, \text{pc}\, \text{cm}^{-3}$$, but none were detected. However, fluence upper limits of 77–224 Jy ms derived over a pulse width of 0.5–10 ms and a redshift of 0.6 < z < 4 are some of the most stringent at low radio frequencies. We compared these fluence limits to the GRB jet–interstellar medium interaction model, placing constraints on the fraction of magnetic energy (ϵB ≲ [0.05–0.1]). We also searched for signals during the X-ray flaring activity of GRB 210419A on minute time-scales in the image domain and found no emission, resulting in an intensity upper limit of $$0.57\, \text{Jy}\, \text{beam}^{-1}$$, corresponding to a constraint of ϵB ≲ 10−3. Our non-detection could imply that GRB 210419A was at a high redshift, there was not enough magnetic energy for low-frequency emission, or the radio waves did not escape from the GRB environment. 

Abstract We present timing solutions for 12 pulsars discovered in the Green Bank North Celestial Cap 350 MHz pulsar survey, including six millisecond pulsars (MSPs), a double neutron star (DNS) system, and a pulsar orbiting a massive white dwarf companion. Timing solutions presented here include 350 and 820 MHz Green Bank Telescope data from initial confirmation and follow-up, as well as a dedicated timing campaign spanning 1 ryr PSR J1122−3546 is an isolated MSP, PSRs J1221−0633 and J1317−0157 are MSPs in black widow systems and regularly exhibit eclipses, and PSRs J2022+2534 and J2039−3616 are MSPs that can be timed with high precision and have been included in pulsar timing array experiments seeking to detect low-frequency gravitational waves. PSRs J1221−0633 and J2039−3616 have Fermi Large Area Telescope gamma-ray counterparts and also exhibit significant gamma-ray pulsations. We measure proper motions for three of the MSPs in this sample and estimate their space velocities, which are typical compared to those of other MSPs. We have detected the advance of periastron for PSR J1018−1523 and therefore measure the total mass of the DNS system, m tot = 2.3 ± 0.3 M ⊙ . Long-term pulsar timing with data spanning more than 1 yr is critical for classifying recycled pulsars, carrying out detailed astrometry studies, and shedding light on the wealth of information in these systems post-discovery.