Search

Although neutron star–black hole binaries have been identified through mergers detected in gravitational waves, a pulsar–black hole binary has yet to be detected. While short-period binaries are detectable due to a clear signal in the pulsar's timing residuals, effects from a long-period binary could be masked by other timing effects, allowing them to go undetected. In particular, a long-period binary measured over a small subset of its orbital period could manifest via time derivatives of the spin frequency incompatible with isolated pulsar properties. We assess the possibility of pulsars having unknown companions in long-period binaries and put constraints on the range of binary properties that may remain undetected in current data, but that may be detectable with further observations. We find that for 35% of canonical pulsars with published higher-order derivatives, the precision of measurements is not enough to confidently reject binarity (period ≳2 kyr), and that a black hole binary companion could not be ruled out for a sample of pulsars without published constraints if the period is >1 kyr. While we find no convincing cases in the literature, we put more stringent limits on orbital period and longitude of periastron for the few pulsars with published higher-order frequency derivatives (n ≥ 3). We discuss the detectability of candidates and find that a sample pulsar in a 100 yr orbit could be detectable within 5–10 yr. [ABSTRACT FROM AUTHOR]

The phenomenon of pulsar nulling, observed as the temporary inactivity of a pulsar, remains poorly understood both observationally and theoretically. Most observational studies that quantify nulling employ a variant of Ritchings algorithm, which can suffer significant biases for pulsars where the emission is weak. Using a more robust mixture model method, we study pulsar nulling in a sample of 22 recently discovered pulsars, for which we publish the nulling fractions for the first time. These data clearly demonstrate biases of the former approach and show how an otherwise nonnulling pulsar can be classified as having significant nulls. We show that the population-wide studies that find a positive correlation of nulling with pulsar period/characteristic age can similarly be biased because of the bias in estimating the nulling fraction. We use our probabilistic approach to find the evidence for periodicity in the nulls in a subset of three pulsars in our sample. In addition, we also provide improved timing parameters for 17 of the 22 pulsars that had no prior follow-up. [ABSTRACT FROM AUTHOR]

GW170817 is the first binary neutron star (NS) merger detected in gravitational waves (GWs) and photons, and so far remains the only GW event of its class with a definitive electromagnetic counterpart. Radio emission from the structured jet associated with GW170817 has faded below the sensitivity achievable via deep radio observations with the most sensitive radio arrays currently in operation. Hence, we now have the opportunity to probe the radio re-brightening that some models predict, which should emerge at late times from the interaction of the dynamically stripped merger ejecta with the interstellar medium. Here we present the latest results from our deep radio observations of the GW170817 field with the Karl G. Jansky Very Large Array (VLA), 4.5 yr after the merger. Our new data at 3 GHz do not show any compelling evidence for emission in excess to the tail of the jet afterglow (<3.3 ÎĽ Jy), confirming our previous results. We thus set new constraints on the dynamical ejecta afterglow models. These constraints favor single-speed ejecta with energies ≲1050 erg (for an ejecta speed of β 0 = 0.5), or steeper energyâ€"speed distributions of the kilonova ejecta. Our results also suggest larger values of the cold, nonrotating maximum NS mass in equal-mass scenarios. However, without a detection of the dynamical ejecta afterglow, obtaining precise constraints on the NS equation of state remains challenging. [ABSTRACT FROM AUTHOR]

We report the independent discovery of PSR J0026-1955 with the Murchison Widefield Array (MWA) in the ongoing Southern-sky MWA Rapid Two-metre pulsar survey. J0026-1955 has a period of ∼1.306 s, a dispersion measure of ∼20.869 pc cmâˆ'3, and a nulling fraction of ∼77%. This pulsar highlights the advantages of the survey's long dwell times (∼80 minutes), which, when fully searched, will be sensitive to the expected population of similarly bright, intermittent pulsars with long nulls. A single-pulse analysis in the MWA's 140â€"170 MHz band also reveals a complex subpulse drifting behavior, including both rapid changes of the drift rate characteristic of mode switching pulsars, as well as a slow, consistent evolution of the drift rate within modes. In some longer drift sequences, interruptions in the otherwise smooth drift rate evolution occur preferentially at a particular phase, typically lasting a few pulses. These properties make this pulsar an ideal test bed for prevailing models of drifting behavior such as the carousel model. [ABSTRACT FROM AUTHOR]

We report the discovery of a highly circularly polarized, variable, steep-spectrum pulsar in the Australian Square Kilometre Array Pathfinder (ASKAP) Variables and Slow Transients (VAST) survey. The pulsar is located about 1° from the center of the Large Magellanic Cloud, and has a significant fractional circular polarization of ∼20%. We discovered pulsations with a period of 322.5 ms, dispersion measure (DM) of 157.5 pc cmâˆ'3, and rotation measure (RM) of +456 rad mâˆ'2 using observations from the MeerKAT and the Parkes telescopes. This DM firmly places the source, PSR J0523âˆ'7125, in the Large Magellanic Cloud (LMC). This RM is extreme compared to other pulsars in the LMC (more than twice that of the largest previously reported one). The average flux density of ∼1 mJy at 1400 MHz and ∼25 mJy at 400 MHz places it among the most luminous radio pulsars known. It likely evaded previous discovery because of its very steep radio spectrum (spectral index α ≈ âˆ'3, where S ν ∝ ν α ) and broad pulse profile (duty cycle ≳35%). We discuss implications for searches for unusual radio sources in continuum images, as well as extragalactic pulsars in the Magellanic Clouds and beyond. Our result highlighted the possibility of identifying pulsars, especially extreme pulsars, from radio continuum images. Future large-scale radio surveys will give us an unprecedented opportunity to discover more pulsars and potentially the most distant pulsars beyond the Magellanic Clouds. [ABSTRACT FROM AUTHOR]

We present nimbus: a hierarchical Bayesian framework to infer the intrinsic luminosity parameters of kilonovae (KNe) associated with gravitational-wave (GW) events, based purely on nondetections. This framework makes use of GW 3D distance information and electromagnetic upper limits from multiple surveys for multiple events and self-consistently accounts for the finite sky coverage and probability of astrophysical origin. The framework is agnostic to the brightness evolution assumed and can account for multiple electromagnetic passbands simultaneously. Our analyses highlight the importance of accounting for model selection effects, especially in the context of nondetections. We show our methodology using a simple, two-parameter linear brightness model, taking the follow-up of GW190425 with the Zwicky Transient Facility as a single-event test case for two different prior choices of model parameters: (i) uniform/uninformative priors and (ii) astrophysical priors based on surrogate models of Monte Carlo radiative-transfer simulations of KNe. We present results under the assumption that the KN is within the searched region to demonstrate functionality and the importance of prior choice. Our results show consistency with simsurveyâ€"an astronomical survey simulation tool used previously in the literature to constrain the population of KNe. While our results based on uniform priors strongly constrain the parameter space, those based on astrophysical priors are largely uninformative, highlighting the need for deeper constraints. Future studies with multiple events having electromagnetic follow-up from multiple surveys should make it possible to constrain the KN population further. [ABSTRACT FROM AUTHOR]