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Register a new userEstimating fast transient detection pipeline efficiencies at UTMOST via real-time injection of mock FRBs
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Dedicated surveys using different detection pipelines are being carried out at multiple observatories to find more Fast Radio Bursts (FRBs). Understanding the efficiency of detection algorithms and the survey completeness function is important to enable unbiased estimation of the underlying FRB population properties. One method to achieve end-to-end testing of the system is by injecting mock FRBs in the live data-stream and searching for them blindly. Mock FRB injection is particularly effective for machine-learning-based classifiers, for which analytic characterisation is impractical. We describe a first-of-its-kind implementation of a real-time mock FRB injection system at the upgraded Molonglo Observatory Synthesis Telescope (UTMOST) and present our results for a set of 20,000 mock FRB injections. The injections have yielded clear insight into the detection efficiencies and have provided a survey completeness function for pulse width, fluence and DM. Mock FRBs are recovered with uniform efficiency over the full range of injected DMs, however the recovery fraction is found to be a strong function of the width and Signal-to-Noise (SNR). For low widths ($lesssim 20$ ms) and high SNR ($gtrsim$ 9) the recovery is highly effective with recovery fractions exceeding 90%. We find that the presence of radio frequency interference causes the recovered SNR values to be systematically lower by up to 20% compared to the injected values. We find that wider FRBs become increasingly hard to recover for the machine-learning-based classifier employed at UTMOST. We encourage other observatories to implement live injection set-ups for similar testing of their surveys.
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We report the first radio interferometric search at 843 MHz for fast transients, particularly Fast Radio Bursts (FRBs). The recently recommissioned Swinburne University of Technologys digital backend for the Molonglo Observatory Synthesis Telescope array (the UTMOST) with its large collecting area (18,000 $mathrm{m^2}$) and wide instantaneous field of view (7.80 $mathrm{deg^2}$) is expected to be an efficient tool to detect FRBs. As an interferometer it will be capable of discerning whether the FRBs are truly a celestial population. We show that UTMOST at full design sensitivity can detect an event approximately every few days. We report on 2 preliminary FRB surveys at about 7% and 14% respectively of the arrays final sensitivity. Several pulsars have been detected via single pulses and no FRBs were discovered with pulse widths ($W$), in the range 655.36 $mu$s $< W < 41.9$ ms and dispersion measures (DMs) in the range $100 < $DM$< 2000$ $mathrm{pc,cm^{-3}}$. This non-detection sets a 2$sigma$ upper limit of the sky rate of not more than 1000 events $mathrm{sky^{-1}}$ $mathrm{day^{-1}}$ at 843 MHz down to a flux limit of 11 Jy for 1 ms FRBs. We show that this limit is consistent with previous survey limits at 1.4 GHz and 145 MHz and set a lower limit on the mean spectral index of FRBs of $alpha > -3.2$.
Glitches are the observational manifestations of superfluidity inside neutron stars. The aim of this paper is to describe an automated glitch detection pipeline, which can alert the observers on possible real-time detection of rotational glitches in pulsars. Post alert, the pulsars can be monitored at a higher cadence to measure the post-glitch recovery phase. Two algorithms namely, Median Absolute Deviation (MAD) and polynomial regression have been explored to detect glitches in real time. The pipeline has been optimized with the help of simulated timing residuals for both the algorithms. Based on the simulations, we conclude that the polynomial regression algorithm is significantly more effective for real time glitch detection. The pipeline has been tested on a few published glitches. This pipeline is presently implemented at the Ooty Radio Telescope. In the era of upcoming large telescopes like SKA, several hundreds of pulsars will be observed regularly and such a tool will be useful for both real-time detection as well as optimal utilization of observation time for such glitching pulsars.
We describe the ongoing `Survey for Magnetars, Intermittent pulsars, Rotating radio transients and Fast radio bursts (SMIRF), performed using the newly refurbished UTMOST telescope. SMIRF repeatedly sweeps the southern Galactic plane performing real-time periodicity and single-pulse searches, and is the first survey of its kind carried out with an interferometer. SMIRF is facilitated by a robotic scheduler which is capable of fully autonomous commensal operations. We report on the SMIRF observational parameters, the data analysis methods, the surveys sensitivities to pulsars, techniques to mitigate radio frequency interference and present some early survey results. UTMOSTs wide field of view permits a full sweep of the Galactic plane to be performed every fortnight, two orders of magnitude faster than previous surveys. In the six months of operations from January to June 2018, we have performed $sim 10$ sweeps of the Galactic plane with SMIRF. Notable blind re-detections include the magnetar PSR J1622$-$4950, the RRAT PSR J0941$-$3942 and the eclipsing pulsar PSR J1748$-$2446A. We also report the discovery of a new pulsar, PSR J1705$-$54. Our follow-up of this pulsar with the UTMOST and Parkes telescopes at an average flux limit of $leq 20$ mJy and $leq 0.16$ mJy respectively, categorizes this as an intermittent pulsar with a high nulling fraction of $< 0.002$
Fast Radio Bursts (FRBs) are bright enigmatic radio pulses of roughly millisecond duration that come from extragalactic distances. As part of the MeerTRAP project, we use the MeerKAT telescope array in South Africa to search for and localise those bursts to high precision in real-time. We aim to pinpoint FRBs to their host galaxies and, thereby, to understand how they are created. However, the transient nature of FRBs presents various challenges, e.g. in system design, raw compute power and real-time communication, where the real-time requirements are reasonably strict (a few tens of seconds). Rapid data processing is essential for us to be able to retain high-resolution data of the bursts, to localise them, and to minimise the delay for follow-up observations. We give a short overview of the data analysis pipeline, describe the challenges faced, and elaborate on our initial design and implementation of a real-time triggering infrastructure for FRBs at the MeerKAT telescope.
We detail a new fast radio burst (FRB) survey with the Molonglo Radio Telescope, in which six FRBs were detected between June 2017 and December 2018. By using a real-time FRB detection system, we captured raw voltages for five of the six events, which allowed for coherent dedispersion and very high time resolution (10.24 $mu$s) studies of the bursts. Five of the FRBs show temporal broadening consistent with interstellar and/or intergalactic scattering, with scattering timescales ranging from 0.16 to 29.1 ms. One burst, FRB181017, shows remarkable temporal structure, with 3 peaks each separated by 1 ms. We searched for phase-coherence between the leading and trailing peaks and found none, ruling out lensing scenarios. Based on this survey, we calculate an all-sky rate at 843 MHz of $98^{+59}_{-39}$ events sky$^{-1}$ day$^{-1}$ to a fluence limit of 8 Jy-ms: a factor of 7 below the rates estimated from the Parkes and ASKAP telescopes at 1.4 GHz assuming the ASKAP-derived spectral index $alpha=-1.6$ ($F_{ u}propto u^{alpha}$). Our results suggest that FRB spectra may turn over below 1 GHz. Optical, radio and X-ray followup has been made for most of the reported bursts, with no associated transients found. No repeat bursts were found in the survey.
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