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Post Info TOPIC: Rotating RAdio Transients
Blobrana


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RE: Rotating RAdio Transients
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After confirmation of their celestial nature, studies have revealed that 10 of the 11 sources have underlying periods of between 0.4 seconds and seven seconds.

"The periodicities found suggest that these new sources are also rotating neutron stars, but different from radio pulsars. It is for this reason that we call them Rotating Radio Transients or RRATs. It's as if, following a flash, a RRAT has to gather its strength during perhaps a thousand rotations before it can do it again!" - Professor Andrew Lyne.

RRATs are a new flavour of neutron stars in addition to the conventional radio pulsars and to the magnetars, which are also believed to be rotating neutron stars and are known to give off powerful X-ray and gamma-ray bursts. It is possible that RRATs represent a different evolutionary phase of neutron stars to or from magnetars.


Transient radio bursts from rotating neutron stars
Authors: M. A. McLaughlin, A. G. Lyne, D. R. Lorimer, M. Kramer, A. J. Faulkner, R. N. Manchester, J. M. Cordes, F. Camilo, A. Possenti, I. H. Stairs, G. Hobbs, N. D'Amico, M. Burgay, J. T. O'Brien

The `radio sky' is relatively unexplored for transient signals, although the potential of radio-transient searches is high, as demonstrated recently by the discovery of a previously unknown type of source which varies on timescales of minutes to hours. Here we report a new large-scale search for radio sources varying on much shorter timescales. This has revealed 11 objects characterized by single, dispersed bursts having durations between 2 and 30 ms. The average time intervals between bursts range from 4 minutes to 3 hours, with radio emission typically detectable for < 1 s per day. From an analysis of the burst arrival times, we have identified periodicities in the range 0.4 - 7 s for ten of the 11 sources, suggesting a rotating neutron star origin. Despite the small number of sources presently detected, their ephemeral nature implies a total Galactic population which significantly exceeds that of the regularly pulsing radio pulsars. Five of the ten sources have periods greater than 4 s, and period derivatives have been measured for three of the sources, with one having a very high inferred magnetic field of 5e13 G, suggesting that this new population is related to other classes of isolated neutron stars observed at X-ray and gamma-ray wavelengths.


Measured and derived parameters for the 11 sources. For each, we give the Right Ascension, Declination, Galactic longitude, Galactic latitude, DM, inferred distance, average burst duration at 50% of the maximum, peak 1400-MHz flux density of brightest detected burst, ratio of the total number of bursts detected to the total observation time, and the ratio of the number of observations in which at least one burst was detected to the total number of observations.
Estimated 1-o errors are given in parentheses where relevant and refer to the last quoted digit. The mean latitudes and longitudes are comparable to those of the pulsars detected in the Parkes survey. The distances are inferred from their DMs, positions and a model for the Galactic free electron density. The mean distance of 4.2 kpc is comparable to that of 5.8 kpc for the pulsars detected in the Parkes survey. The extremely sporadic nature of the bursts makes localisation difficult, with most positions known only to within the 1400-MHz 14-arcminute beam of the Parkes Telescope.
For the three sources for which we have measured period derivatives, more accurate positions have been derived through radio timing. Burst durations for each source remain constant, within the uncertainties, and are all much larger than those measured for pulsar giant pulses

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Blobrana


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An international team of researchers spotted the new stars, called rotating radio transients, or RRATs, using the Parkes radio telescope in Australia. They were searching for radio pulsars — rotating neutron stars emitting radiation — at the time, but couldn't help noticing the blazingly bright flashing objects.

While the team found more than 800 pulsars, they discovered 11 of the previously unknown RRATs. The researchers, lead by Maura McLaughlin of the University of Manchester's Jodrell Bank Observatory, determined that RRATs are a type radio pulsars, although they don't emit radiation as uniformly as the conventional version.

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Blobrana


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The `radio sky' is relatively unexplored for transient signals, as demonstrated recently by the discovery of a previously unknown type of source which varies on timescales of minutes to hours.

An international team has announced that a huge number of neutron stars, ultra dense stellar remnants, emit sporadic but extraordinarily powerful bursts of radio waves. These bursts last just fractions of a second, but during that fleeting interval they are among the brightest radio sources in the sky, even outshining the Sun.
The bursting neutron stars were discovered by an international team of radio astronomers led by Maura A. McLaughlin, University of Manchester, England.
The researchers looked at the data taken by the 64-meter Parkes radio telescope in Australia from 1998 to 2002. The team were looking for pulsars, neutron stars that emit regular, periodic pulses of radio waves as they spin. Besides finding lots of pulsars, the team's computer algorithm identified 11 bursting radio sources coming from various directions near the galactic plane. T
he team spent the next three years observing the sky coordinates of these objects to confirm the discovery and to measure their properties.

On average these bursting objects are visible just from 0.1 to 1 second per day. The bursts last between 2 and 30 milliseconds, with intervals between bursts ranging from 4 minutes to 3 hours. Previous astronomers may have interpreted such signals as radio interference.

The group found periodicities for 10 of the 11 sources, falling between 0.4 and 7 seconds. This regularity strongly suggests that the radio bursts come from rotating neutron stars.
McLaughlin's team has named these objects RRATs, short for Rotating RAdio Transients.

During the bursts, the RRATs are the brightest radio sources ever observed except for giant radio pulses observed from the Crab Nebula pulsar and another pulsar named B1937+21. Given the short duration, the source objects probably emit these radio bursts in narrow beams from small areas tied to the stars' surfaces or magnetospheres. But the exact cause of the bursts remains unknown.

Given their transient nature, RRATs are extremely difficult to study, which means astronomers can engage in little more than informed speculation until further information is available. One of the RRATs has spin properties that resemble those of a class of highly magnetized neutron stars known as magnetars. These observations indicate that at least some highly magnetized RRATs are at most a few tens of thousands of years old.

But two other RRATs have rotation characteristics that suggest they are middle-aged, like ordinary pulsars. This may indicate that RRATs have a wide variety of properties.

Knowing the spatial coverage and sensitivity of the Parkes data, and the ephemeral nature of the sources, McLaughlin and her colleagues estimate that there could be roughly 400,000 RRATs in the Milky Way Galaxy, which means they would outnumber the familiar radio pulsars by a ratio of about 4 to 1.

The implied high number of RRATs might help explain the mystery of why relatively few supernova remnants have associated neutron stars. Neutron stars are created in the explosions, but unlike the famous Crab Nebula, for example, more than half of known supernova remnants have no observed pulsars.

"I don't find it too outrageous to think the majority of neutron stars are born in a very different state than the Crab pulsar, and it is these objects that could make up the parent population of these RRATs" - David Helfand, Columbia University, a leading neutron-star observer.

Over the next few decades astronomers should learn much more about RRATs as they build new wide-field radio-telescope arrays, such as the Square Kilometre Array (SKA). The SKA could discover tens of thousands of RRATs.

Besides picking up many more RRATs, these telescopes might also discover entire new classes of radio-emitting objects.

"The transient radio sky is relatively unexplored" - Joseph Lazio, Naval Research Laboratory, who codiscovered a bright, bursting radio object near the galactic centre that was announced earlier this year.
The nature of that source has not yet been explained.

Read More (PDF, 166kb)

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