Astronomy Object of the Month: 2024, January
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PSR B0809+74 – a drifting subpulse pulsar reveals the secrets of the emission mechanism
Pulsars are fast-rotating neutron stars endowed with a very strong magnetic field. While more than 55 years have passed since their discovery, the mechanism responsible for their radiation still remains mysterious.
Illustration 1: A scheme of pulsar emission (NASA Scientific Visualization Studio)..
We know that radiate electrons accelerated along twisted magnetic field lines, which, along with the z pulsar rotation creates a "lighthouse" effect, but the details of the mechanism of radio emission formation remain largely unknown. One way to study this mechanism are observations of single pulses coming from pulsars, in which the phenomenon of "drifting pulses" is sometimes seen: with each successive pulse, the emission clearly shifts in phase, which is best visible in images of a series of pulses, revealing characteristic "drift bands".
Some pulsars also show other effects related to the emission mechanism, such as pulse nulling and radiation mode changes (moding). One such object is PSR B0809+74, which is regularly observed by a radio telescope belonging to the Jagiellonian University and being part of the pan-European LOFAR network in Łazy near Kraków. Observations of such objects are a key element in our attempts to understand the physical conditions in the magnetosphere of pulsars and the phenomena occurring there that lead to their radio emissions.
Illustration 2: Examples of the series of pulses observed in PSR B0809+74 with the LOFAR PL611 radio telescope in Łazy near Kraków. The observations were made at 150 MHz with a bandwidth of 72 MHz. The series of pulses reproduces the appearance of the shapes of successive consecutive pulses (from bottom to top), showing their varying brightness on a color scale. The series on the left shows the typical drift phenomenon -- in successive pulses the emission shifts to the left (it occurs progressively earlier in the pulse phase), creating characteristic and regular "drift bands." The middle image shows radiation decay (so-called nulling) -- the pulsar's emission has decayed over several pulses. In the right image, in addition to the pulse decay, there was also a change in the mode of radiation, as manifested by the disruption of the regularity of the drift bands. Source: Team publication.
Original publication:
Rahul Basu, Wojciech Lewandowski, Jarosław Kijak, Bartosz Śmierciak, Marian Soida, Leszek Błaszkiewicz, Andrzej Krankowski, Single pulse emission from PSR B0809+74 at 150 MHz using Polish LOFAR station, Monthly Notices of the Royal Astronomical Society, Vol 526, Issue 1, pp.691-699 (2023).
The publication was prepared as part of the POLFAR consortium (Polish consortium of the LOFAR network), with the participation of the Prof. Janusz Gil Institute of Astronomy at the University of Zielona Góra, the Astronomical Observatory of the Jagiellonian University in Kraków, and the Space Environment Radio Diagnostics Center belonging to the University of Warmia and Mazury in Olsztyn. The work received funding from NCN grant no. 2020/37/B/ST9/02215. Polish participation in the activities of the LOFAR network is funded by the Ministry of Science and Higher Education (LOFAR2. 0 upgrade, decision number: 2021/WK/2), which also funds the maintenance of the LOFAR PL-610 Borówiec, LOFAR PL-611 Łazy, and LOFAR PL-612 Bałdy radio telescopes (decisions nos. 30/530252/SPUB/SP/2022, 29/530358/SPUB/SP/2022, and 28/530020/SPUB/SP/2022).
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Marian Soida Astronomical Observatory Jagiellonian University Marian.Soida [@] uj.edu.pl |
