arXiv subjects

John M. Sarkissian

Publications and source records attributed to John M. Sarkissian.

5 recordsLinked to original sources

arXiv2026

Transient narrowband radio bursts from the magnetar 1E 1547.0-5408

Radio-loud magnetars are well known for exhibiting radiative behaviors that are seldom seen among the wider pulsar population. Yet one form of emission that remains elusive among pulsars and magnetars is narrowband bursts of radio waves. Such emission is a hallmark of repeating sources of fast radio bursts (FRBs), intense radio flashes that originate from distant galaxies. Here, we report the detection of 84 narrowband radio bursts during observations of the magnetar 1E 1547.0-5408 by the Murriyang telescope. They were confined to a transient profile component that appeared between 2009 February 23 to 25, one month after its 2009 outburst. Their appearance coincided with both dramatic changes in the magnetar line-of-sight magnetic-field geometry, and an emergent pulsed hard X-ray component detected by the Rossi X-ray Timing Explorer. The leading edge of the hard X-ray emission was phase-aligned with the narrowband component. This may indicate the bursts originated from pair cascades along closed field lines, though open-field line emission remains valid. Our characterization of the bursts suggests they may represent a low-energy analogue of the repeating FRB mechanism, further linking FRB progenitors to young, highly magnetized neutron stars.

astro-ph.HE↗

arXiv2024

Linear to circular conversion in the polarized radio emission of a magnetar

Radio emission from magnetars provides a unique probe of the relativistic, magnetized plasma within the near-field environment of these ultra-magnetic neutron stars. The transmitted waves can undergo birefringent and dispersive propagation effects that result in frequency-dependent conversions of linear to circularly polarized radiation and vice-versa, thus necessitating classification when relating the measured polarization to the intrinsic properties of neutron star and fast radio burst (FRB) emission sites. We report the detection of such behavior in 0.7-4 GHz observations of the P = 5.54 s radio magnetar XTE J1810$-$197 following its 2018 outburst. The phenomenon is restricted to a narrow range of pulse phase centered around the magnetic meridian. Its temporal evolution is closely coupled to large-scale variations in magnetic topology that originate from either plastic motion of an active region on the magnetar surface or free precession of the neutron star crust. Our model of the effect deviates from simple theoretical expectations for radio waves propagating through a magnetized plasma. Birefringent self-coupling between the transmitted wave modes, line-of-sight variations in the magnetic field direction and differences in particle charge or energy distributions above the magnetic pole are explored as possible explanations. We discuss potential links between the immediate magneto-ionic environments of magnetars and those of FRB progenitors.

astro-ph.HE↗

arXiv2023

The Parkes Pulsar Timing Array Third Data Release

We present the third data release from the Parkes Pulsar Timing Array (PPTA) project. The release contains observations of 32 pulsars obtained using the 64-m Parkes "Murriyang" radio telescope. The data span is up to 18 years with a typical cadence of 3 weeks. This data release is formed by combining an updated version of our second data release with $\sim 3$ years of more recent data primarily obtained using an ultra-wide-bandwidth receiver system that operates between 704 and 4032 MHz. We provide calibrated pulse profiles, flux-density dynamic spectra, pulse times of arrival, and initial pulsar timing models. We describe methods for processing such wide-bandwidth observations, and compare this data release with our previous release.

astro-ph.HE↗

arXiv2023

The 2022 high-energy outburst and radio disappearing act of the magnetar 1E 1547.0-5408

We report the radio and high-energy properties of a new outburst from the radio-loud magnetar 1E 1547.0$-$5408. Following the detection of a short burst from the source with Swift-BAT on 2022 April 7, observations by NICER detected an increased flux peaking at $(6.0 \pm 0.4) \times 10^{-11}$ erg s$^{-1}$ cm$^{-2}$ in the soft X-ray band, falling to the baseline level of $1.7\times10^{-11}$ erg s$^{-1}$ cm$^{-2}$ over a 17-day period. Joint spectroscopic measurements by NICER and NuSTAR indicated no change in the hard non-thermal tail despite the prominent increase in soft X-rays. Observations at radio wavelengths with Murriyang, the 64-m Parkes radio telescope, revealed that the persistent radio emission from the magnetar disappeared at least 22 days prior to the initial Swift-BAT detection and was re-detected two weeks later. Such behavior is unprecedented in a radio-loud magnetar, and may point to an unnoticed slow rise in the high-energy activity prior to the detected short-bursts. Finally, our combined radio and X-ray timing revealed the outburst coincided with a spin-up glitch, where the spin-frequency and spin-down rate increased by $0.2 \pm 0.1$ $μ$Hz and $(-2.4 \pm 0.1) \times 10^{-12}$ s$^{-2}$ respectively. A linear increase in spin-down rate of $(-2.0 \pm 0.1) \times 10^{-19}$ s$^{-3}$ was also observed over 147 d of post-outburst timing. Our results suggest that the outburst may have been associated with a reconfiguration of the quasi-polar field lines, likely signalling a changing twist, accompanied by spatially broader heating of the surface and a brief quenching of the radio signal, yet without any measurable impact on the hard X-ray properties.

astro-ph.HE↗

arXiv2017

One year of monitoring the Vela pulsar using a Phased Array Feed

We have observed the Vela pulsar for one year using a Phased Array Feed (PAF) receiver on the 12-metre antenna of the Parkes Test-Bed Facility. These observations have allowed us to investigate the stability of the PAF beam-weights over time, to demonstrate that pulsars can be timed over long periods using PAF technology and to detect and study the most recent glitch event that occurred on 12 December 2016. The beam-weights are shown to be stable to 1% on time scales on the order of three weeks. We discuss the implications of this for monitoring pulsars using PAFs on single dish telescopes.

astro-ph.HE↗