Sample of a single pulse of PSR J0628+0909 with one of the highest signal-to-noise (S/N) ratio. Credit: Hsu et al, 2022
Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), Chinese astronomers have inspected single-pulse behavior of a rotating radio transient (RRAT) known as PSR J0628+0909. Results of the study, published November 22 in Monthly Notices of the Royal Astronomical Society, could help us better understand the mysterious nature of RRATs.
RRATs are a subclass of pulsars characterized by sporadic emission. First objects of this type were identified in 2006 as sporadically appearing dispersed pulses, with frequencies varying from several minutes to several hours. However, the nature of these transients is still unclear. In general, it is assumed that they are ordinary radio pulsars that experience strong pulses and can only be detected through single-pulse searches.
PSR J0628+0909 was initially discovered in 2006 as single pulses in the Pulsar survey using the Arecibo L-band Feed Array (PALFA). Six years later, the source was classified as an RRAT and its precise position was measured using the Karl G. Jansky Very Large Array (VLA). PSR J0628+0909 has a pulse period of approximately 1.24 seconds and dispersion measure of 88 pc/cm3. Previous observations have found that this pulsar has a burst rate of about 141 per hour and a pulse width at half maximum of 10 milliseconds.
A team of astronomers led by Jui-An Hsu of Peking University in Beijing, China, investigated single pulses of PSR J0628+0909, hoping to shed more light on the nature of this source. For this purpose they used FAST’s L-band 19-beam receiver, which covers the frequency range from 1.0 to 1.5 GHz.
“In this work, we analyzed the half-hour FAST observation of PSR J0628+0909 with a central frequency of 1,250 MHz and a bandwidth of 500 MHz. We conducted single-pulse studies and measured the polarization properties of the source,” the researchers wrote in the paper.
By analyzing the peak flux distribution of single pulses, it was found that three log-normal components are required to describe the distribution. The detected components are at least a few times weaker when compared with previous results. These results suggest that the intrinsic pulse peak flux or energy distributions are more complex if observed with higher sensitivity.
Furthermore, the astronomers identified weaker pulse signals buried under the radiometer noise floor. Similar weak pulses were reported in other RRATs, therefore, this finding provides evidence supporting the hypothesis that RRATs are in general low-flux pulsars.
The study also found that the correlation between the waiting-time and the pulse energy is relatively weak. This indicates that RRATs may have different mechanisms to produce the strong single pulses rather than via the energy store-release scenario. It was added that the event rate for single pulses of PSR J0628+0909 with signal-to-noise ratio (S/N) over 7.0 was calculated to be approximately 270 per hour.
“We find that the pulse waiting-time is not correlated with the pulse energy and conclude that the strong transient emission of RRAT is not generated by the energy store-release mechanism,” the authors of the paper concluded.
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