FLAGCAL:A flagging and calibration package for radio interferometric data

We describe a flagging and calibration pipeline intended for making quick look images from GMRT data. The package identifies and flags corrupted visibilities, computes calibration solutions and interpolates these onto the target source. These flagged calibrated visibilities can be directly imaged using any standard imaging package. The pipeline is written in "C" with the most compute intensive algorithms being parallelized using OpenMP.Comment: 15 Pages, 6 figures, 2 Tables, Accepted for publication in the Experimental Astronomy Journa

A morphological algorithm for improving radio-frequency interference detection

A technique is described that is used to improve the detection of radio-frequency interference in astronomical radio observatories. It is applied on a two-dimensional interference mask after regular detection in the time-frequency domain with existing techniques. The scale-invariant rank (SIR) operator is defined, which is a one-dimensional mathematical morphology technique that can be used to find adjacent intervals in the time or frequency domain that are likely to be affected by RFI. The technique might also be applicable in other areas in which morphological scale-invariant behaviour is desired, such as source detection. A new algorithm is described, that is shown to perform quite well, has linear time complexity and is fast enough to be applied in modern high resolution observatories. It is used in the default pipeline of the LOFAR observatory.Comment: Accepted for publication in A&

A fast radio burst associated with a Galactic magnetar

Since their discovery in 2007, much effort has been devoted to uncovering the sources of the extragalactic, millisecond-duration fast radio bursts (FRBs). A class of neutron stars known as magnetars is a leading candidate source of FRBs. Magnetars have surface magnetic fields in excess of 10¹⁴ gauss, the decay of which powers a range of high-energy phenomena5. Here we report observations of a millisecond-duration radio burst from the Galactic magnetar SGR 1935+2154, with a fluence of 1.5 ± 0.3 megajansky milliseconds. This event, FRB 200428 (ST 200428A), was detected on 28 April 2020 by the STARE2 radio array in the 1,281–1,468 megahertz band. The isotropic-equivalent energy released in FRB 200428 is 4 × 10³ times greater than that of any radio pulse from the Crab pulsar—previously the source of the brightest Galactic radio bursts observed on similar timescales7. FRB 200428 is just 30 times less energetic than the weakest extragalactic FRB observed so far, and is drawn from the same population as the observed FRB sample. The coincidence of FRB 200428 with an X-ray burst favours emission models that describe synchrotron masers or electromagnetic pulses powered by magnetar bursts and giant flares. The discovery of FRB 200428 implies that active magnetars such as SGR 1935+2154 can produce FRBs at extragalactic distances

Detection of Crab Giant Pulses Using the Mileura Widefield Array Low Frequency Demonstrator Field Prototype System

We report on the detection of giant pulses from the Crab Nebula pulsar at a frequency of 200 MHz using the field deployment system designed for the Mileura Widefield Array's Low Frequency Demonstrator (MWA-LFD). Our observations are among the first high-quality detections at such low frequencies. The measured pulse shapes are deconvolved for interstellar pulse broadening, yielding a pulse-broadening time of 670$\pm$100 $\mu$s, and the implied strength of scattering (scattering measure) is the lowest that is estimated towards the Crab nebula from observations made so far. The sensitivity of the system is largely dictated by the sky background, and our simple equipment is capable of detecting pulses that are brighter than $\sim$9 kJy in amplitude. The brightest giant pulse detected in our data has a peak amplitude of $\sim$50 kJy, and the implied brightness temperature is $10^{31.6}$ K. We discuss the giant pulse detection prospects with the full MWA-LFD system. With a sensitivity over two orders of magnitude larger than the prototype equipment, the full system will be capable of detecting such bright giant pulses out to a wide range of Galactic distances; from $\sim$8 to $\sim$30 kpc depending on the frequency. The MWA-LFD will thus be a highly promising instrument for the studies of giant pulses and other fast radio transients at low frequencies.Comment: 10 pages, 6 figures, Accepted for publication in the Astrophysical Journa