10 research outputs found
Separation of pulsar signals from noise with supervised machine learning algorithms
We evaluate the performance of four different machine learning (ML)
algorithms: an Artificial Neural Network Multi-Layer Perceptron (ANN MLP ),
Adaboost, Gradient Boosting Classifier (GBC), XGBoost, for the separation of
pulsars from radio frequency interference (RFI) and other sources of noise,
using a dataset obtained from the post-processing of a pulsar search pi peline.
This dataset was previously used for cross-validation of the SPINN-based
machine learning engine, used for the reprocessing of HTRU-S survey data
arXiv:1406.3627. We have used Synthetic Minority Over-sampling Technique
(SMOTE) to deal with high class imbalance in the dataset. We report a variety
of quality scores from all four of these algorithms on both the non-SMOTE and
SMOTE datasets. For all the above ML methods, we report high accuracy and
G-mean in both the non-SMOTE and SMOTE cases. We study the feature importances
using Adaboost, GBC, and XGBoost and also from the minimum Redundancy Maximum
Relevance approach to report algorithm-agnostic feature ranking. From these
methods, we find that the signal to noise of the folded profile to be the best
feature. We find that all the ML algorithms report FPRs about an order of
magnitude lower than the corresponding FPRs obtained in arXiv:1406.3627, for
the same recall value.Comment: 14 pages, 2 figures. Accepted for publication in Astronomy and
Computin
Searching for Low Frequency Fast Radio Bursts with VLITE
The VLITE (VLA Low Band Ionosphere and Transient Experiment; http://vlite.nrao.edu) program performs commensal observations using 16 antennas of the Very Large Array radio telescope from 320-384 MHz. The VLITE-Fast program searches for short time-scale (\u3c100ms) transients, such as Fast Radio Bursts (FRBs), in real time and triggers recording of baseband voltages for offline imaging. Searches are made possible by a 12 node cluster, each housing GPUs for digital signal processing. A real-time Message Passing Interface (MPI)-based co-adder incoherently sums the data streams from all the antennas to boost the signal-to-noise. To undo the dispersion effects of signal propagation through the ionized interstellar medium, the co-added stream is de-dispersed and matched-filtered to search for transients. This operation is completely performed on GPUs by the software package Heimdall . A selection logic is applied to the candidates and interesting candidates with their corresponding data are processed and packaged in a binary file along with a diagnostic plot. Furthermore, a Machine Learning classification is applied on the reduced data product and, based on its decision, baseband voltages are recorded. Reduced data products collected over 126 days of on-sky operation form the VLITE-Fast Pathfinder Survey (VFPS). This pipeline has triggered on single pulses from 7 known radio pulsars. Lastly, the pipeline capabilities are tested against pure random noise and simulated injected signals
Multiwavelength Constraints on the Origin of a Nearby Repeating Fast Radio Burst Source in a Globular Cluster
Since fast radio bursts (FRBs) were discovered, their precise origins have
remained a mystery. Multiwavelength observations of nearby FRB sources provide
one of the best ways to make rapid progress in our understanding of the
enigmatic FRB phenomenon. We present results from a sensitive, broadband
multiwavelength X-ray and radio observational campaign of FRB 20200120E, the
closest known extragalactic repeating FRB source. At a distance of 3.63 Mpc,
FRB 20200120E resides in an exceptional location, within a ~10 Gyr-old globular
cluster in the M81 galactic system. We place deep limits on both the persistent
X-ray luminosity and prompt X-ray emission at the time of radio bursts from FRB
20200120E, which we use to constrain possible progenitors for the source. We
compare our results to various classes of X-ray sources and transients. In
particular, we find that FRB 20200120E is unlikely to be associated with:
ultraluminous X-ray bursts (ULXBs), similar to those observed from objects of
unknown origin in other extragalactic globular clusters; giant flares, like
those observed from Galactic and extragalactic magnetars; or most intermediate
flares and very bright short X-ray bursts, similar to those seen from magnetars
in the Milky Way. We show that FRB 20200120E is also unlikely to be powered by
a persistent or transient ultraluminous X-ray (ULX) source or a young,
extragalactic pulsar embedded in a Crab-like nebula. We also provide new
constraints on the compatibility of FRB 20200120E with accretion-based FRB
models involving X-ray binaries and models that require a synchrotron maser
process from relativistic shocks to generate FRB emission. These results
highlight the power that multiwavelength observations of nearby FRBs can
provide for discriminating between potential FRB progenitor models.Comment: 58 pages, 10 figures, 7 tables, submitte
Patterned Colouring via Variable-Speed Single Stretching
We demonstrate a cost-effective, highly reliable/stable and environmentally friendly approach for the patterned colouring of a commercial transparent polyethylene terephthalate (PET). We show that different colour patterns (transparent, white/translucent, complete white/silver and different combinations of these three colours) can be realised in PET strips upon varying the speed during continuous stretching. The conditions for good quality colour patterns are investigated, and the length of transient region during speed change is investigated
Patterned Colouring via Variable-Speed Single Stretching
We demonstrate a cost-effective, highly reliable/stable and environmentally friendly approach for the patterned colouring of a commercial transparent polyethylene terephthalate (PET). We show that different colour patterns (transparent, white/translucent, complete white/silver and different combinations of these three colours) can be realised in PET strips upon varying the speed during continuous stretching. The conditions for good quality colour patterns are investigated, and the length of transient region during speed change is investigated
Precision pulsar timing with the ORT and the GMRT and its applications in pulsar astrophysics
Radio pulsars show remarkable clock-like stability, which make them useful astronomy tools in experiments to test equation of state of neutron stars and detecting gravitational waves using pulsar timing techniques. A brief review of relevant astrophysical experiments is provided in this paper highlighting the current state-of-the-art of these experiments. A program to monitor frequently glitching pulsars with Indian radio telescopes using high cadence observations is presented, with illustrations of glitches detected in this program, including the largest ever glitch in PSR B0531+21. An Indian initiative to discover sub-μ Hz gravitational waves, called Indian Pulsar Timing Array (InPTA), is also described briefly, where time-of-arrival uncertainties and post-fit residuals of the order of μs are already achievable, comparable to other international pulsar timing array experiments. While timing the glitches and their recoveries are likely to provide constraints on the structure of neutron stars, InPTA will provide upper limits on sub-μ Hz gravitational waves apart from auxiliary pulsar science. Future directions for these experiments are outlined
Precision pulsar timing with the ORT and the GMRT and its applications in pulsar astrophysics
Joshi BC, Arumugasamy P, Bagchi M, et al. Precision pulsar timing with the ORT and the GMRT and its applications in pulsar astrophysics. Journal of Astrophysics and Astronomy. 2018;39(4): 51.Radio pulsars show remarkable clock-like stability, which make them useful astronomy tools in experiments to test equation of state of neutron stars and detecting gravitational waves using pulsar timing techniques. A brief review of relevant astrophysical experiments is provided in this paper highlighting the current state-of-the-art of these experiments. A program to monitor frequently glitching pulsars with Indian radio telescopes using high cadence observations is presented, with illustrations of glitches detected in this program, including the largest ever glitch in PSR B0531+21. An Indian initiative to discover sub-μHz gravitational waves, called Indian Pulsar Timing Array (InPTA), is also described briefly, where time-of-arrival uncertainties and post-fit residuals of the order of μs are already achievable, comparable to other international pulsar timing array experiments. While timing the glitches and their recoveries are likely to provide constraints on the structure of neutron stars, InPTA will provide upper limits on sub-μHz gravitational waves apart from auxiliary pulsar science. Future directions for these experiments are outlined