Discovery of Low Dm Fast Radio Transients: Geminga Pulsar Caught in the Act

Leeuwen

et al. 2020

A&A

Context. Repeating fast radio bursts (FRBs) present excellent opportunities to identify FRB progenitors and host environments, as well as decipher the underlying emission mechanism. Detailed studies of repeating FRBs might also hold clues to the origin of FRBs as a population. Aims. We aim to detect bursts from the first two repeating FRBs: FRB 121102 (R1) and FRB 180814.J0422+73 (R2), and characterise their repeat statistics. We also want to significantly improve the sky localisation of R2 and identify its host galaxy. Methods. We use the Westerbork Synthesis Radio Telescope to conduct extensive follow-up of these two repeating FRBs. The new phased-array feed system, Apertif, allows covering the entire sky position uncertainty of R2 with fine spatial resolution in a single pointing. The data were searched for bursts around the known dispersion measures of the two sources. We characterise the energy distribution and the clustering of detected R1 bursts. Results. We detected 30 bursts from R1. The non-Poissonian nature is clearly evident from the burst arrival times, consistent with earlier claims. Our measurements indicate a dispersion measure of 563.5(2) pc cm −3 , suggesting a significant increase in DM over the past few years. Assuming a constant position angle across the burst, we place an upper limit of 8% on the linear polarisation fraction for the brightest burst in our sample. We did not detect any bursts from R2. Conclusions. A single power-law might not fit the R1 burst energy distribution across the full energy range or widely separated detections. Our observations provide improved constraints on the clustering of R1 bursts. Our stringent upper limits on the linear polarisation fraction imply a significant depolarisation, either intrinsic to the emission mechanism or caused by the intervening medium, at 1400 MHz that is not observed at higher frequencies. The non-detection of any bursts from R2, despite nearly 300 hrs of observations, implies either a highly clustered nature of the bursts, a steep spectral index, or a combination of both assuming the source is still active. Another possibility is that R2 has turned off completely, either permanently or for an extended period of time.

Section: Polarisation Propertiesmentioning

confidence: 99%

Repeating fast radio bursts with WSRT/Apertif

Oostrum

Leeuwen

et al. 2020

A&A

“…Since ORT is receptive to only a single linear polarization, the differential Faraday rotation of a linearly polarized signal manifests itself in the form of spectral intensity modulation within the observation bandwidth. This spectral modulation can be exploited to deduce RM and linear polarization properties (Ramkumar & Deshpande 1999;Maan 2015). However, this is possible only for reasonably high RMs and significantly linearly polarized sources, and the above mentioned search involving RM would require computing time several orders of magnitude longer than that spent in the current search limited to DM, period and acceleration domains.…”

Section: Aligned or Nearly Aligned Rotatorsmentioning

confidence: 99%

A Search for Pulsars in Steep Spectrum Radio Sources

Bassa

Leeuwen

et al. 2018

ApJ

Self Cite

We report on a time-domain search for pulsars in 44 steep spectrum radio sources originally identified from recent imaging surveys. The time-domain search was conducted at 327 MHz using the Ooty radio telescope, and utilized a semi-coherent dedispersion scheme, retaining the sensitivity even for sub-millisecond periods up to reasonably high dispersion measures. No new pulsars were found. We discuss the nature of these steep spectrum sources and argue that majority of the sources in our sample should either be pulsars or a new category of Galactic sources. Several possibilities that could hinder detection of these sources as pulsars, including anomalously high scattering or alignment of the rotation and magnetic axes, are discussed in detail, and we suggest unconventional search methods to further probe these possibilities.

“…There are hints that the current outburst also exhibits millisecond-width bright pulses (Dai et al 2019). A number of similar emission components from other classes of pulsar population are known, e.g., the giantpulses (Staelin & Reifenstein 1968;Wolszczan et al 1984;Joshi et al 2004;Maan et al 2012;Maan 2015), the giant micropulses from the Vela pulsar (Johnston et al 2001), spiky emission from PSR B0656+14 (Weltevrede et al 2006), PSR J0437−4715 (Ables et al 1997;Vivekanand 2000), and rotating radio transients (McLaughlin et al 2006). Any similarity between the spiky emission from the magnetar and the above mentioned emission components could provide an important link between the corresponding emission mechanisms.…”

Section: Introductionmentioning

confidence: 95%

Distinct Properties of the Radio Burst Emission from the Magnetar XTE J1810–197

Joshi

Surnis

et al. 2019

ApJL

Self Cite

XTE J1810−197 (PSR J1809−1943 was the first ever magnetar which was found to emit transient radio emission. It has recently undergone another radio and high-energy outburst. This is only the second radio outburst that has been observed from this source. We observed J1810−197 soon after its recent radio outburst at low radio frequencies using the Giant Metrewave Radio Telescope. We present the 650 MHz flux density evolution of the source in the early phases of the outburst, and its radio spectrum down to frequencies as low as 300 MHz. The magnetar also exhibits radio emission in the form of strong, narrow bursts. We show that the bursts have a characteristic intrinsic width of the order of 0.5−0.7 ms, and discuss their properties in the context of giant pulses and giant micropulses from other pulsars. We also show that the bursts exhibit spectral structures which cannot be explained by interstellar propagation effects. These structures might indicate a phenomenological link with the repeating fast radio bursts which also show interesting, more detailed frequency structures. While the spectral structures are particularly noticeable in the early phases of the outburst, these seem to be less prominent as well as less frequent in the later phases, suggesting an evolution of the underlying cause of these spectral structures.