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Long-period transients (LPTs) challenge our knowledge of the mechanism producing radio periodic pulsations in compact objects. Some LPTs have been associated with systems hosting a white dwarf and a low-mass star in a detached binary. Recently, a new LPT (ASKAP J174508.9-505149) has been classified as an accreting cataclysmic variable (CV). In the present Letter, we report on the detailed study of the X-ray variability of ASKAP J174508.9-505149 as observed byXMM-NewtonandEinstein Probebetween September 2025 and May 2026. Simultaneous optical and radio observations are also presented. We studied the timing variability of the source, and estimated an X-ray periodicity ofP = 4868(22) s, consistent with radio and optical periods. We also observe the same periodicity in the hardness ratio extracted from theXMM-Newtonobservation, peaking at the minimum of the modulation. A long-term modulation is also present in the X-rays and in the B-band photometry, but it is poorly constrained by the current dataset. Spectral X-ray analysis shows the presence of a black-body component (∼0.1 keV), a collisionally ionised plasma (∼15 keV), and an absorption feature at 0.77 keV (possibly due to Oxygen-VII). This is the third LPT detected in the X-ray band, the second with a detected X-ray periodicity and variable X-ray emission, and the first conclusively recognised as an accreting magnetic CV. 

Abstract Long-period radio transients (LPTs) are coherent bursts of polarized radio emission that repeat periodically on timescales of minutes to hours. Little is known about the physical origins of these systems. Astronomers have proposed magnetars that rotate slowly and white dwarfs that rapidly orbit with a companion star as potential explanations. While several recent examples appear to support the latter hypothesis, the mechanism generating these bright radio pulses remains poorly understood. Here we report our discovery and classification of the LPT ASKAP J174508.9-505149 as an accreting white dwarf binary. This object has an ~1.3 h spectroscopic orbital period and exhibits orbitally modulated X-ray emission and radio bursts. These elliptically polarized radio bursts drift in emission frequency, potentially due to a longer beat period, and turn off for several hours at a time. Some LPTs have been associated with non-interacting white dwarf binaries. We have spectroscopically confirmed this system as an accreting cataclysmic variable, identified through characteristic optical emission lines and an ongoing X-ray outburst. Our results strengthen the link between at least some LPTs and white dwarf binaries. 

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 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. 

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.