95 research outputs found
Discovery and characterisation of fast radio transients
No full textMany types of astronomical objects are detectable through the radio waves that they produce. The observed properties of sources in the 'radio sky' can vary on a wide range of timescales, both for intrinsic and extrinsic reasons. Transients are those sources whose observed properties change drastically within a timescale that a human astronomer can measure. Traditionally, the qualifier 'fast' refers to transients whose emission properties change significantly over less than a second, and most commonly on millisecond timescales. The two classes of fast radio transients studied in this thesis are pulsars and fast radio bursts. We are motivated to study these sources because they probe extreme astrophysical environments as well as the intervening magnetised and ionised medium between observer and source. Furthermore, the origin of the relatively recently discovered fast radio bursts remains enigmatic, though the properties of these signals share traits of pulsar emission. Thus, we aim to better understand the physical nature of fast radio bursts and their possible link to pulsar emission. We discuss the characteristics of these source classes and outline some of the outstanding scientific questions we can address through observations with a radio telescope and other complementary, multi-wavelength information
Discovery and characterisation of fast radio transients
No full textMany types of astronomical objects are detectable through the radio waves that they produce. The observed properties of sources in the 'radio sky' can vary on a wide range of timescales, both for intrinsic and extrinsic reasons. Transients are those sources whose observed properties change drastically within a timescale that a human astronomer can measure. Traditionally, the qualifier 'fast' refers to transients whose emission properties change significantly over less than a second, and most commonly on millisecond timescales. The two classes of fast radio transients studied in this thesis are pulsars and fast radio bursts. We are motivated to study these sources because they probe extreme astrophysical environments as well as the intervening magnetised and ionised medium between observer and source. Furthermore, the origin of the relatively recently discovered fast radio bursts remains enigmatic, though the properties of these signals share traits of pulsar emission. Thus, we aim to better understand the physical nature of fast radio bursts and their possible link to pulsar emission. We discuss the characteristics of these source classes and outline some of the outstanding scientific questions we can address through observations with a radio telescope and other complementary, multi-wavelength information
The northern cross fast radio burst project - II. Monitoring of repeating FRB 20180916B, 20181030A, 20200120E, and 20201124A
No full textIn this work, we report the results of a 19-month fast radio burst observational campaign carried out with the north–south arm of the Medicina Northern Cross radio telescope at 408 MHz in which we monitored four repeating sources: FRB20180916B, FRB20181030A, FRB20200120E, and FRB20201124A. We present the current state of the instrument and the detection and characterization of three bursts from FRB20180916B. Given our observing time, our detections are consistent with the event number we expect from the known burst rate (2.7 ± 1.9 above our 10σ, 38 Jy ms detection threshold) in the 5.2 d active window of the source, further confirming the source periodicity. We detect no bursts from the other sources. We turn this result into a 95 per cent confidence level lower limit on the slope of the differential fluence distribution α to be α > 2.1 and α > 2.2 for FRB20181030A and FRB20200120E, respectively. Given the known rate for FRB20201124A, we expect 1.0 ± 1.1 bursts from our campaign, consistent with our non-detection
Sub-second periodicity in a fast radio burst
No full textFast radio bursts (FRBs) are millisecond-duration flashes of radio waves that are visible at distances of billions of light years1. The nature of their progenitors and their emission mechanism remain open astrophysical questions2. Here we report the detection of the multicomponent FRB 20191221A and the identification of a periodic separation of 216.8(1) ms between its components, with a significance of 6.5σ. The long (roughly 3 s) duration and nine or more components forming the pulse profile make this source an outlier in the FRB population. Such short periodicity provides strong evidence for a neutron-star origin of the event. Moreover, our detection favours emission arising from the neutron-star magnetosphere3,4, as opposed to emission regions located further away from the star, as predicted by some models5
Sub-second periodicity in a fast radio burst
No full textFast radio bursts (FRBs) are millisecond-duration flashes of radio waves that are visible at distances of billions of light years1. The nature of their progenitors and their emission mechanism remain open astrophysical questions2. Here we report the detection of the multicomponent FRB 20191221A and the identification of a periodic separation of 216.8(1) ms between its components, with a significance of 6.5σ. The long (roughly 3 s) duration and nine or more components forming the pulse profile make this source an outlier in the FRB population. Such short periodicity provides strong evidence for a neutron-star origin of the event. Moreover, our detection favours emission arising from the neutron-star magnetosphere3,4, as opposed to emission regions located further away from the star, as predicted by some models5
Do patients with open spina bifida always need a shunt for lifetime? A long-term follow-up
No full textCHIME/FRB Discovery of 25 Repeating Fast Radio Burst Sources
No full textWe present the discovery of 25 new repeating fast radio burst (FRB) sources found among CHIME/FRB events detected between 2019 September 30 and 2021 May 1. The sources were found using a new clustering algorithm that looks for multiple events colocated on the sky having similar dispersion measures (DMs). The new repeaters have DMs ranging from ∼220 to ∼1700 pc cm−3, and include sources having exhibited as few as two bursts to as many as twelve. We report a statistically significant difference in both the DM and extragalactic DM (eDM) distributions between repeating and apparently nonrepeating sources, with repeaters having a lower mean DM and eDM, and we discuss the implications. We find no clear bimodality between the repetition rates of repeaters and upper limits on repetition from apparently nonrepeating sources after correcting for sensitivity and exposure effects, although some active repeating sources stand out as anomalous. We measure the repeater fraction over time and find that it tends to an equilibrium of 2.6+2.9-2.6% over our total time-on-sky thus far. We also report on 14 more sources, which are promising repeating FRB candidates and which merit follow-up observations for confirmation
The First CHIME/FRB Fast Radio Burst Catalog
No full textWe present a catalog of 536 fast radio bursts (FRBs) detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) Project between 400 and 800 MHz from 2018 July 25 to 2019 July 1, including 62 bursts from 18 previously reported repeating sources. The catalog represents the first large sample, including bursts from repeaters and nonrepeaters, observed in a single survey with uniform selection effects. This facilitates comparative and absolute studies of the FRB population. We show that repeaters and apparent nonrepeaters have sky locations and dispersion measures (DMs) that are consistent with being drawn from the same distribution. However, bursts from repeating sources differ from apparent nonrepeaters in intrinsic temporal width and spectral bandwidth. Through injection of simulated events into our detection pipeline, we perform an absolute calibration of selection effects to account for systematic biases. We find evidence for a population of FRBs—composing a large fraction of the overall population—with a scattering time at 600 MHz in excess of 10 ms, of which only a small fraction are observed by CHIME/FRB. We infer a power-law index for the cumulative fluence distribution of α =-1.40 ± 0.11 (stat.)+0.06-0.09 (sys.), consistent with the −3/2 expectation for a nonevolving population in Euclidean space. We find that α is steeper for high-DM events and shallower for low-DM events, which is what would be expected when DM is correlated with distance. We infer a sky rate of [820± 60(stat.)+220-200 (sys.)]/sky / day above a fluence of 5 Jy ms at 600 MHz, with a scattering time at 600 MHz under 10 ms and DM above 100 pc cm−3
Propagation effects at low frequencies seen in the LOFAR long-term monitoring of the periodically active FRB 20180916B
No full textLOFAR (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 φ LOFARc = 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
- …
