arXiv subjects

Devansh Agarwal

Publications and source records attributed to Devansh Agarwal.

27 records · Page 2Linked to original sources

arXiv2020

FETCH: A deep-learning based classifier for fast transient classification

With the upcoming commensal surveys for Fast Radio Bursts (FRBs), and their high candidate rate, usage of machine learning algorithms for candidate classification is a necessity. Such algorithms will also play a pivotal role in sending real-time triggers for prompt follow-ups with other instruments. In this paper, we have used the technique of Transfer Learning to train the state-of-the-art deep neural networks for classification of FRB and Radio Frequency Interference (RFI) candidates. These are convolutional neural networks which work on radio frequency-time and dispersion measure-time images as the inputs. We trained these networks using simulated FRBs and real RFI candidates from telescopes at the Green Bank Observatory. We present 11 deep learning models, each with an accuracy and recall above 99.5% on our test dataset comprising of real RFI and pulsar candidates. As we demonstrate, these algorithms are telescope and frequency agnostic and are able to detect all FRBs with signal-to-noise ratios above 10 in ASKAP and Parkes data. We also provide an open-source python package FETCH (Fast Extragalactic Transient Candidate Hunter) for classification of candidates, using our models. Using FETCH, these models can be deployed along with any commensal search pipeline for real-time candidate classification.

astro-ph.IM↗

arXiv2020

Initial results from a realtime FRB search with the GBT

We present the data analysis pipeline, commissioning observations and initial results from the GREENBURST fast radio burst (FRB) detection system on the Robert C. Byrd Green Bank Telescope (GBT) previously described by Surnis et al. which uses the 21~cm receiver observing commensally with other projects. The pipeline makes use of a state-of-the-art deep learning classifier to winnow down the very large number of false positive single-pulse candidates that mostly result from radio frequency interference. In our observations totalling 156.5 days so far, we have detected individual pulses from 20 known radio pulsars which provide an excellent verification of the system performance. We also demonstrate, through blind injection analyses, that our pipeline is complete down to a signal-to-noise threshold of 12. Depending on the observing mode, this translates to peak flux sensitivities in the range 0.14--0.89~Jy. Although no FRBs have been detected to date, we have used our results to update the analysis of Lawrence et al. to constrain the FRB all-sky rate to be $1140^{+200}_{-180}$ per day above a peak flux density of 1~Jy. We also constrain the source count index $α=0.83\pm0.06$ which indicates that the source count distribution is substantially flatter than expected from a Euclidean distribution of standard candles (where $α=1.5$). We discuss this result in the context of the FRB redshift and luminosity distributions. Finally, we make predictions for detection rates with GREENBURST, as well as other ongoing and planned FRB experiments.

astro-ph.IM↗

arXiv2019

A fast radio burst in the direction of the Virgo cluster

The rate of fast radio bursts (FRBs) in the direction of nearby galaxy clusters is expected to be higher than the mean cosmological rate if intrinsically faint FRBs are numerous. In this paper, we describe a targeted search for faint FRBs near the core of the Virgo cluster using the Australian Square Kilometer Array Pathfinder telescope. During 300 hr of observations, we discovered one burst, FRB 180417, with dispersion measure DM $=474.8$ cm$^{-3}$pc. The FRB was promptly followed up by several radio telescopes for 27 h, but no repeat bursts were detected. An optical follow-up of FRB 180417 using the PROMPT5 telescope revealed no new sources down to an $R$-band magnitude of 20.1. We argue that FRB 180417 is likely behind the Virgo cluster as the Galactic and intracluster DM contribution are small compared to the DM of the FRB, and there are no galaxies in the line of sight. The non-detection of FRBs from Virgo constrains the faint-end slope, $α<1.52$ (at 68\% confidence limit), and the minimum luminosity, $L_{\rm min}\gtrsim 2\times 10^{40}$ erg s$^{-1}$ (at 68\% confidence limit), of the FRB luminosity function assuming cosmic FRB rate of $10^4$ FRBs sky$^{-1}$ day$^{-1}$ with flux above 1 Jy located out to redshift of 1. Further FRB surveys of galaxy clusters with high-sensitivity instruments will tighten the constraints on the faint end of the luminosity function and, thus, are strongly encouraged.

astro-ph.HE↗

arXiv2019

Non-detection of fast radio bursts from six gamma-ray burst remnants with possible magnetar engines

The analogy of the host galaxy of the repeating fast radio burst (FRB) source FRB 121102 and those of long gamma-ray bursts (GRBs) and super-luminous supernovae (SLSNe) has led to the suggestion that young magnetars born in GRBs and SLSNe could be the central engine of repeating FRBs. We test such a hypothesis by performing dedicated observations of the remnants of six GRBs with evidence of having a magnetar central engine using the Arecibo telescope and the Robert C. Byrd Green Bank Telescope (GBT). A total of $\sim 20$ hrs of observations of these sources did not detect any FRB from these remnants. Under the assumptions that all these GRBs left behind a long-lived magnetar and that the bursting rate of FRB 121102 is typical for a magnetar FRB engine, we estimate a non-detection probability of $8.9\times10^{-6}$. Even though these non-detections cannot exclude the young magnetar model of FRBs, we place constraints on the burst rate and luminosity function of FRBs from these GRB targets.

astro-ph.HE↗

arXiv2019

GBTrans: A commensal search for radio pulses with the Green Bank twenty metre telescope

We describe GBTrans, a real-time search system designed to find fast radio bursts (FRBs) using the 20-m radio telescope at the Green Bank Observatory. The telescope has been part of the Skynet educational program since 2015. We give details of the observing system and report on the non-detection of FRBs from a total observing time of 503 days. Single pulses from four known pulsars were detected as part of the commensal observing. The system is sensitive enough to detect approximately half of all currently known FRBs and we estimate that our survey probed redshifts out to about 0.3 corresponding to an effective survey volume of around 124,000~Mpc$^3$. Modeling the FRB rate as a function of fluence, $F$, as a power law with $F^{-α}$, we constrain the index $α< 2.5$ at the 90% confidence level. We discuss the implications of this result in the context of constraints from other FRB surveys.

astro-ph.HE↗

arXiv2019

GREENBURST: a commensal fast radio burst search back-end for the Green Bank Telescope

We describe the design and deployment of GREENBURST, a commensal Fast Radio Burst (FRB) search system at the Green Bank Telescope. GREENBURST uses the dedicated L-band receiver tap to search over the 960$-$1920 MHz frequency range for pulses with dispersion measures out to $10^4$ pc cm$^{-3}$. Due to its unique design, GREENBURST will obtain data even when the L-band receiver is not being used for scheduled observing. This makes it a sensitive single pixel detector capable of reaching deeper in the radio sky. While single pulses from Galactic pulsars and rotating radio transients will be detectable in our observations, and will form part of the database we archive, the primary goal is to detect and study FRBs. Based on recent determinations of the all-sky rate, we predict that the system will detect approximately one FRB for every 2$-$3 months of continuous operation. The high sensitivity of GREENBURST means that it will also be able to probe the slope of the FRB source function, which is currently uncertain in this observing band.

astro-ph.IM↗

arXiv2019

A Survey of the Galactic Plane for Dispersed Pulses with the Australian Square Kilometre Array Pathfinder

We report the results from a survey of the Galactic plane for dispersed single pulses using the Australian SKA Pathfinder (ASKAP). We searched for rare bright dispersed radio pulses comprising 160 pointings covering 4800 deg$^2$ of the Galactic plane within |b| $< 7 °$, each pointing with an exposure time of 10 hours. We detected one fast radio burst, FRB 180430, and single pulses from 11 pulsars. No rotating radio transients were detected. We detected FRB 180430 in the Galactic plane in the anticentre direction with a fluence of 216$\pm5$Jy ms a dispersion measure (DM) of 264.1 pc cm-3. We estimate the extragalactic DM of the object to be less than 86.7 $ \text{pc} \ \text{cm}^{-3} $ depending on the electron density model. One model suggests that this FRB may be a giant pulse within our galaxy; we discuss how this may not correctly represent the line-of-sight DM. Based on the single detection of FRB 180430 in 3.47 $\times 10^{4}$ deg$^2$ h we derive a FRB event rate in the Galactic plane at the 20 Jy ms threshold to be in the range 2-140 per sky per day at 95% confidence. Despite the necessarily large uncertainties from this single detection, this is consistent with the current ASKAP all-sky detection rate.

astro-ph.HE↗

arXiv2017

Initial Results from the ALFABURST Survey

Here, we present initial results from the ALFABURST radio transient survey, which is currently running in a commensal mode with the ALFA receiver at the Arecibo telescope. We observed for a total of 1400 hours and have detected single pulses from known pulsars but did not detect any FRBs. The non-detection of FRBs is consistent with the current FRB sky rates.

astro-ph.HE↗

arXiv2016

Everyday Radio Telescope

We have developed an affordable, portable college level radio telescope for amateur radio astronomy which can be used to provide hands-on experience with the fundamentals of a radio telescope and an insight into the realm of radio astronomy. With our set-up one can measure brightness temperature and flux of the Sun at 11.2 GHz and calculate the beam width of the antenna. The set-up uses commercially available satellite television receiving system and parabolic dish antenna. We report the detection of point sources like Saturn and extended sources like the galactic arm of the Milky way. We have also developed python pipeline, which are available for free download, for data acquisition and visualization.

physics.ed-ph↗