We report the discovery of 1.97 ms period gamma-ray pulsations from the 75 minute orbital-period binary pulsar now named PSR J1653−0158. The associated Fermi Large Area Telescope gamma-ray source ...4FGL J1653.6−0158 has long been expected to harbor a binary millisecond pulsar. Despite the pulsar-like gamma-ray spectrum and candidate optical/X-ray associations-whose periodic brightness modulations suggested an orbit-no radio pulsations had been found in many searches. The pulsar was discovered by directly searching the gamma-ray data using the GPU-accelerated Einstein@Home distributed volunteer computing system. The multidimensional parameter space was bounded by positional and orbital constraints obtained from the optical counterpart. More sensitive analyses of archival and new radio data using knowledge of the pulsar timing solution yield very stringent upper limits on radio emission. Any radio emission is thus either exceptionally weak, or eclipsed for a large fraction of the time. The pulsar has one of the three lowest inferred surface magnetic-field strengths of any known pulsar with Bsurf 4 × 107 G. The resulting mass function, combined with models of the companion star's optical light curve and spectra, suggests a pulsar mass 2 M . The companion is lightweight with mass ∼0.01 M , and the orbital period is the shortest known for any rotation-powered binary pulsar. This discovery demonstrates the Fermi Large Area Telescope's potential to discover extreme pulsars that would otherwise remain undetected.
ABSTRACT
LOFAR (LOw Frequency ARray) has previously detected bursts from the periodically active, repeating fast radio burst (FRB) source FRB 20180916B down to unprecedentedly low radio frequencies ...of 110 MHz. Here, we present 11 new bursts in 223 more hours of continued monitoring of FRB 20180916B in the 110–188 MHz band with LOFAR. We place new constraints on the source’s activity window $w =4.3^{+0.7}_{-0.2}$ d and phase centre $\phi _{\mathrm{c}}^{\mathrm{LOFAR}} = 0.67^{+0.03}_{-0.02}$ in its 16.33-d activity cycle, strengthening evidence for its frequency-dependent activity cycle. Propagation effects like Faraday rotation and scattering are especially pronounced at low frequencies and constrain properties of FRB 20180916B’s local environment. We track variations in scattering and time–frequency drift rates, and find no evidence for trends in time or activity phase. Faraday rotation measure (RM) variations seen between June 2021 and August 2022 show a fractional change >50 per cent with hints of flattening of the gradient of the previously reported secular trend seen at 600 MHz. The frequency-dependent window of activity at LOFAR appears stable despite the significant changes in RM, leading us to deduce that these two effects have different causes. Depolarization of and within individual bursts towards lower radio frequencies is quantified using LOFAR’s large fractional bandwidth, with some bursts showing no detectable polarization. However, the degree of depolarization seems uncorrelated to the scattering time-scales, allowing us to evaluate different depolarization models. We discuss these results in the context of models that invoke rotation, precession, or binary orbital motion to explain the periodic activity of FRB 20180916B.
Abstract
We investigate whether the sky rate of fast radio bursts (FRBs) depends on Galactic latitude using the first catalog of FRBs detected by the Canadian Hydrogen Intensity Mapping Experiment ...Fast Radio Burst (CHIME/FRB) Project. We first select CHIME/FRB events above a specified sensitivity threshold in consideration of the radiometer equation, and then we compare these detections with the expected cumulative time-weighted exposure using Anderson–Darling and Kolmogorov–Smirnov tests. These tests are consistent with the null hypothesis that FRBs are distributed without Galactic latitude dependence (
p
-values distributed from 0.05 to 0.99, depending on completeness threshold). Additionally, we compare rates in intermediate latitudes (∣
b
∣ < 15°) with high latitudes using a Bayesian framework, treating the question as a biased coin-flipping experiment–again for a range of completeness thresholds. In these tests the isotropic model is significantly favored (Bayes factors ranging from 3.3 to 14.2). Our results are consistent with FRBs originating from an isotropic population of extragalactic sources.
Abstract
We report the discovery of seven new Galactic pulsars with the Canadian Hydrogen Intensity Mapping Experiment’s Fast Radio Burst (CHIME/FRB) backend. These sources were first identified via ...single pulses in CHIME/FRB, then followed up with CHIME/Pulsar. Four sources appear to be rotating radio transients, pulsar-like sources with occasional single-pulse emission with an underlying periodicity. Of those four sources, three have detected periods ranging from 220 ms to 2.726 s. Three sources have more persistent but still intermittent emission and are likely intermittent or nulling pulsars. We have determined phase-coherent timing solutions for the latter two. These seven sources are the first discovery of previously unknown Galactic sources with CHIME/FRB and highlight the potential of fast radio burst detection instruments to search for intermittent Galactic radio sources.
We present a new single-pulse pipeline for the PALFA survey to efficiently identify single radio pulses from pulsars, rotating radio transients (RRATs), and fast radio bursts (FRBs). We conducted a ...sensitivity analysis of this new pipeline in which many single pulses were injected into PALFA data and run through the pipeline. We find that for single pulse widths <5 ms, the sensitivity of our new pipeline is at most a factor of ∼2 less sensitive than theoretically predicted. For pulse widths >10 ms, as the DM decreases, the degradation in sensitivity gets worse and can increase up to a factor of ∼4.5. Using this pipeline, we have discovered seven pulsars and two RRATs, and identified three candidate RRATs and one candidate FRB. The confirmed pulsars and RRATs have DMs ranging from 133 to 386 pc cm−3 and flux densities ranging from 20 to 160 mJy. The pulsar periods range from 0.4 to 2.1 s. We report on candidate FRB 141113, which is likely astrophysical and extragalactic, having DM 400 pc cm−3, which is over the Galactic maximum along this line of sight by ∼100-200 pc cm−3. We consider implications for the FRB population and show via simulations that if FRB 141113 is real and extragalactic, the slope of the distribution of integral source counts as a function of flux density (N(>S) ∝ S− ) is 1.4 0.5 (95% confidence range). However, this conclusion is dependent on assumptions that require verification.
Multifrequency observations of SGR J1935+2154 Bailes, M; Bassa, C G; Bernardi, G ...
Monthly notices of the Royal Astronomical Society,
06/2021, Letnik:
503, Številka:
4
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
Magnetars are a promising candidate for the origin of fast radio bursts (FRBs). The detection of an extremely luminous radio burst from the Galactic magnetar SGR J1935+2154 on 2020 April 28 ...added credence to this hypothesis. We report on simultaneous and non-simultaneous observing campaigns using the Arecibo, Effelsberg, LOFAR, MeerKAT, MK2, and Northern Cross radio telescopes and the MeerLICHT optical telescope in the days and months after the April 28 event. We did not detect any significant single radio pulses down to fluence limits between 25 mJy ms and 18 Jy ms. Some observing epochs overlapped with times when X-ray bursts were detected. Radio images made on 4 d using the MeerKAT telescope revealed no point-like persistent or transient emission at the location of the magnetar. No transient or persistent optical emission was detected over seven days. Using the multicolour MeerLICHT images combined with relations between DM, NH, and reddening, we constrain the distance to SGR J1935+2154, to be between 1.5 and 6.5 kpc. The upper limit is consistent with some other distance indicators and suggests that the April 28 burst is closer to two orders of magnitude less energetic than the least energetic FRBs. The lack of single-pulse radio detections shows that the single pulses detected over a range of fluences are either rare, or highly clustered, or both. It may also indicate that the magnetar lies somewhere between being radio-quiet and radio-loud in terms of its ability to produce radio emission efficiently.
ABSTRACT
We present LOFAR imaging observations from the April/May 2020 active episode of magnetar SGR 1935 + 2154. We place the earliest radio limits on persistent emission following the ...low-luminosity fast radio burst FRB 200428 from the magnetar. We also perform an image-plane search for transient emission and find no radio flares during our observations. We examine post-FRB radio upper limits in the literature and find that all are consistent with the multiwavelength afterglow predicted by the synchrotron maser shock model interpretation of FRB 200428. However, early optical observations appear to rule out the simple versions of the afterglow model with constant-density circumburst media. We show that these constraints may be mitigated by adapting the model for a wind-like environment, but only for a limited parameter range. In addition, we suggest that late-time non-thermal particle acceleration occurs within the afterglow model when the shock is no longer relativistic, which may prove vital for detecting afterglows from other Galactic FRBs. We also discuss future observing strategies for verifying either magnetospheric or maser shock FRB models via rapid radio observations of Galactic magnetars and nearby FRBs.
The Pulsar Arecibo L-Band Feed Array (PALFA) survey, the most sensitive blind search for radio pulsars yet conducted, is ongoing at the Arecibo Observatory in Puerto Rico. The vast majority of the ...180 pulsars discovered by PALFA have spin periods shorter than 2 s. Pulsar surveys may miss long-period radio pulsars owing to the summing of a finite number of harmonic components in conventional Fourier analyses (typically ∼16), or as a result of the strong effect of red noise at low modulation frequencies. We address this reduction in sensitivity by using a time-domain search technique: the fast-folding algorithm (FFA). We designed a program that implements an FFA-based search in the PALFA processing pipeline and tested the efficiency of the algorithm by performing tests under both ideal, white-noise conditions, as well as with real PALFA observational data. In the two scenarios, we show that the time-domain algorithm has the ability to outperform the FFT-based periodicity search implemented in the survey. We perform simulations to compare the previously reported PALFA sensitivity with that obtained using our new FFA implementation. These simulations show that for a pulsar having a pulse duty cycle of roughly 3%, the performance of our FFA pipeline exceeds that of our FFT pipeline for pulses with dispersion measure 40 pc cm−3 and for periods as short as ∼500 ms, and that the survey sensitivity is improved by at least a factor of two for periods 6 s. Early results from the implementation of the algorithm in PALFA, including discoveries, are also presented in this paper.
Using LOFAR, we have performed a very-low-frequency (115−155 MHz) radio survey for millisecond pulsars (MSPs). The survey targeted 52 unidentified Fermi γ-ray sources. Employing a combination of ...coherent and incoherent dedispersion, we have mitigated the dispersive effects of the interstellar medium while maintaining sensitivity to fast-spinning pulsars. Toward 3FGL J1553.1+5437 we have found PSR J1552+5437, the first MSP to be discovered (through its pulsations) at a radio frequency <200 MHz. PSR J1552+5437 is an isolated MSP with a 2.43 ms spin period and a dispersion measure of 22.9 pc cm−3. The pulsar has a very steep radio spectral index ( 2.8 0.4). We obtain a phase-connected timing solution combining the 0.74 years of radio observations with γ-ray photon arrival times covering 7.5 years of Fermi observations. We find that the radio and γ-ray pulse profiles of PSR J1552+5437 appear to be nearly aligned. The very steep spectrum of PSR J1552+5437, along with other recent discoveries, hints at a population of radio MSPs that have been missed in surveys using higher observing frequencies. Detecting such steep spectrum sources is important for mapping the population of MSPs down to the shortest spin periods, understanding their emission in comparison to slow pulsars, and quantifying the prospects for future surveys with low-frequency radio telescopes like SKA-Low and its precursors.
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