A summary of extreme scattering events and a descriptive model

Fiedler, Russell; Dennison, B.; Johnston, K. J.; Waltman, E. B.; Simon, R. S.

doi:10.1086/174432

Cited by 115 publications

(151 citation statements)

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“…Recently, however, Walker (2007) has suggested that the lenses must be associated with neutral, self-gravitating gas clouds and may be the source of the Galaxy's dark matter. Very little new data on the phenomenon has been obtained since the early work of Fiedler et al (1987aFiedler et al ( , 1994 and the field has stagnated. The allsky monitoring capability of ASKAP will address this problem in a comprehensive way.…”

Section: The Transient Radio Skymentioning

confidence: 99%

Science with the Australian Square Kilometre Array Pathfinder

Johnston

Bailes

Bartel

et al. 2007

Publ. – Astron. Soc. Aust

313

174

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The future of cm and m-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries that will be 50 times more sensitive than any existing radio facility. Most of the key science for the SKA will be addressed through largearea imaging of the Universe at frequencies from a few hundred MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is a technology demonstrator aimed in the mid-frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phased-array feed systems on parabolic reflectors. The large field-of-view makes ASKAP an unprecedented synoptic telescope that will make substantial advances in SKA key science. ASKAP will be located at the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of two sites selected by the international community as a potential location for the SKA. In this paper, we outline an ambitious science program for ASKAP, examining key science such as understanding the evolution, formation and population of galaxies including our own, understanding the magnetic Universe, revealing the transient radio sky and searching for gravitational waves.

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Section: The Transient Radio Skymentioning

confidence: 99%

Science with the Australian Square Kilometre Array Pathfinder

Johnston

Bailes

Bartel

et al. 2007

Publ. – Astron. Soc. Aust

313

174

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“…INTRODUCTION The discovery of extreme scattering events (ESEs; Fiedler et al 1987) in the late 1980s provided evidence of ultracompact (Շ1 AU) ionized objects in the interstellar medium. Despite more than 15 years of observational and interpretive work, the physical conditions, origin, and lifetime of these compact refractors are not well established (Romani et al 1987;Fiedler et al 1994;Rickett et al 1997;Walker & Wardle 1998). Furthermore, their space density and possible contribution to the mass distribution in the Galaxy are poorly known.…”

mentioning

confidence: 99%

Deflection of Pulsar Signal Reveals Compact Structures in the Galaxy

Hill

Stinebring

Asplund

et al. 2005

ApJ

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We have detected a strong deflection of radio waves from the pulsar PSR B0834ϩ06 in scintillation observations. Interference between the undeflected pulsar image and deflected subimages allows single-dish interferometry of the interstellar medium with submilliarcsecond resolution. We infer the presence of scattering structure(s) similar to those that are thought to cause extreme scattering events in quasar flux monitoring programs: size ∼0.2 AU (an angular size of 0.1 mas) with an electron overdensity of տ10 3 compared to the warm ionized medium. The deflectors are nearly stationary in a scattering screen that is thin (Շ5% of the pulsar-observer distance in extent), is located 70% of the way from the Earth to the pulsar, and has been seen consistently in observations dating back 20 years. The pulsar scans the scattering screen at a velocity of 110 km s Ϫ1 with a detection radius of 15 mas. Pulsar observations such as these-particularly with a new generation of low-frequency radio telescopes with large collecting areas-hold promise for improving constraints on the poorly understood physical characteristics and space density of the deflecting structures. Such observations may also prove useful in correcting deviations that the deflectors produce in high-precision timing of millisecond pulsars.

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“…However, it follows from the ESE rate (Fiedler et al 1994), in the context of this physical model, that the neutral gas clouds constitute a large fraction of the mass of the Galaxy. In other words, since they are not present in our current inventories of visible matter, they are a major component of dark matter.…”

Section: Extreme Scattering Eventsmentioning

confidence: 96%

“…We begin with a brief overview of current activity directed towards identifying dark matter (Section 2), then focus on a model in which the Galactic dark matter is composed of planetary-mass gas clouds-a picture that can be drawn directly from the radio-wave lensing of quasars reported by Fiedler et al (1987Fiedler et al ( , 1994. A lensing event (extreme scattering event, or ESE) occurs when a cloud in the Galactic halo crosses the line of sight: radio waves are refracted by an ionised wind which is evaporated from the neutral cloud by UV radiation (Section 3).…”

Section: Introductionmentioning

confidence: 99%

The Cloudy Universe

Walker

Wardle

1999

Publ. – Astron. Soc. Aust

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Abstract:Modelling of extreme scattering events suggests that the Galaxy's dark matter is an undetected population of cold, AU-sized, planetary-mass gas clouds. None of the direct observational constraints on this picture-thermal/non-thermal emission, extinction and lensing-are problematic. The theoretical situation is less comfortable, but still satisfactory. Galactic clouds can survive in their current condition for billions of years, but we do not have a firm description for either their origin or their evolution to the present epoch. We hypothesise that the proto-clouds formed during the quark-hadron phase transition, thereby introducing the inhomogeneity necessary for compatibility with light element nucleosynthesis in a purely baryonic universe. We outline the prospects for directly detecting the inferred cloud population. The most promising signatures are cosmic-ray-induced Hα emission from clouds in the solar neighbourhood, optical and X-ray flashes arising from cloud-cloud collisions, ultraviolet extinction, and three varieties of lensing phenomena.

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A summary of extreme scattering events and a descriptive model

Cited by 115 publications

References 0 publications

Science with the Australian Square Kilometre Array Pathfinder

Science with the Australian Square Kilometre Array Pathfinder

Deflection of Pulsar Signal Reveals Compact Structures in the Galaxy

The Cloudy Universe

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