J. Y. Koay

The Commensal Real-Time ASKAP Fast-Transients (CRAFT) Survey

We are developing a purely commensal survey experiment for fast (<5 s) transient radio sources. Short-timescale transients are associated with the most energetic and brightest single events in the Universe. Our objective is to cover the enormous volume of transients parameter space made available by ASKAP, with an unprecedented combination of sensitivity and field of view. Fast timescale transients open new vistas on the physics of high brightness temperature emission, extreme states of matter and the physics of strong gravitational fields. In addition, the detection of extragalactic objects affords us an entirely new and extremely sensitive probe on the huge reservoir of baryons present in the IGM. We outline here our approach to the considerable challenge involved in detecting fast transients, particularly the development of hardware fast enough to dedisperse and search the ASKAP data stream at or near real-time rates. Through CRAFT, ASKAP will provide the testbed of many of the key technologies and survey modes proposed for high time resolution science with the SKA.

Detection of six rapidly scintillating active galactic nuclei and the diminished variability of J1819+3845

The extreme, intra-hour and >10% rms flux density scintillation observed in AGNs such as PKS 0405-385, J1819+3845 and PKS 1257-326 at cm wavelengths has been attributed to scattering in highly turbulent, nearby regions in the interstellar medium. Such behavior has been found to be rare. We searched for rapid scintillators among 128 flat spectrum AGNs and analyzed their properties to determine the origin of such rapid and large amplitude radio scintillation. The sources were observed at the VLA at 4.9 and 8.4 GHz simultaneously at two hour intervals over 11 days. We detected six rapid scintillators with characteristic time-scales of 10%. We found strong lines of evidence linking rapid scintillation to the presence of nearby scattering regions, estimated to be 11 day variations, suggesting that the highly turbulent cloud responsible for its extreme scintillation has moved away, with its scintillation now caused by a more distant screen ≈50 to 150 pc away.

Scatter broadening of compact radio sources by the ionized intergalactic medium: prospects for detection with Space VLBI and the Square Kilometre Array

We investigate the feasibility of detecting and probing various components of the ionized intergalactic medium (IGM) and their turbulent properties at radio frequencies through observations of scatter broadening of compact sources. There is a strong case for conducting targeted observations to resolve scatter broadening (where the angular size scales as

The Micro-Arcsecond Scintillation-Induced Variability (MASIV) Survey III. Optical Identifications and New Redshifts

\sim \nu^{-2}

Time domain studies of Active Galactic Nuclei with the Square Kilometre Array

) of compact background sources intersected by foreground galaxy haloes and rich clusters of galaxies to probe the turbulence of the ionized gas in these objects, particularly using Space VLBI with baselines of 350,000 km at frequencies below 800 MHz. The sensitivity of the Square Kilometre Array (SKA) allows multifrequency surveys of interstellar scintillation (ISS) of

Interstellar scattering as a cosmological probe

\sim 100 \,\mu

The MASIV legacy: Surveying AGN intra-day variability at radio wavelengths

Jy sources to detect or place very strong constraints on IGM scatter broadening down to

Interstellar Scintillation as a Cosmological Probe: Prospects and Challenges

\sim 1\, \mu

Temporal Smearing of Transient Radio Sources by the Intergalactic Medium

as scales at 5 GHz. Scatter broadening in the warm-hot component of the IGM with typical overdensities of

DUAL-FREQUENCY OBSERVATIONS OF 140 COMPACT, FLAT-SPECTRUM ACTIVE GALACTIC NUCLEI FOR SCINTILLATION-INDUCED VARIABILITY

\sim 30