Giant radio pulses in the magnetar XTE J1810-197 detected with the IAR's telescopes

Abstract

[...] We observed XTE J1810-197 between 29 September 2022 and 14 July 2023 with the radio telescopes at the Argentine Institute of Radioastronomy (IAR). We searched for single pulses in time series at a DM range of 100-400 pc cm-3 , with a threshold in signal-to-noise ratio (S/N) of 8. [...] We found 249 giant pulses at a DM mean value of 178.8$\pm$0.1 pc cm-3 . We measured peak flux densities up to 119 Jy, and fluences up to 58 Jy ms. We fitted a power law distribution to the flux density, obtaining an index of -4.0$\pm$0.3. We observed a maximum rate of approximately 15 pulses per hour on 20 February 2023, followed by an abrupt disappearance of transient radio emission, indicating a transition to a less active state. The brightest single pulses are limited to a $\sim$2$\%$ of the rotational phase and have similar fluence values to the reported intermediate FRB-like bursts of SGR 1935+2154. No significant X-ray activity in the MAXI data was detected during the radio observing period. This is the first study of single radio pulses of a magnetar using IAR data, showing the potential of the upgraded telescopes for investigating the transient radio sky. The properties of the single pulses detected here show the magnetar transient nature and capability to emit high-luminosity pulses. We compared the detected emission to FRB-like bursts and single pulses emitted by SGR 1935+2154. Even though the mechanism producing all the events should be coherent, the luminosity of the events, features on the dynamic spectra, and the difference between being phase confined or not, indicate that XTE J1810-197 presents GP emission, while SGR 1935+2154 only shows normal single pulses or FRB bursts. This could indicate that the conditions for producing each type of event differ.

Figures (12)

• Figure 1: Observable time of XTE J1810$-$197 for different telescopes that have conducted high-cadence campaigns. The arc matching the telescope's color represents the source's possible observation time for that telescope. We highlight the very short overlap between the IAR and other observatories.
• Figure 2: Single pulse search made with PRESTO on 19 November 2022 for the DM range. Time = 0 corresponds to the start of the observation. Each circle represents a pulse detected with a S/N $\geq$ 8, with its size proportional to its $\mathrm{S/N}$. The dashed horizontal line marks the DM of the magnetar (178 pc cm$^{-3}$). Pulses align in elongated islands centered around the magnetar DM. Pulses that are farther from that line (as the one at $\sim$6200 s) are more likely to be RFIs. Inset: distribution of the pulses' $\mathrm{S/N}$ as a function of DM. The pink vertical line marks the DM of the magnetar. The distribution of the pulses' $\mathrm{S/N}$ is also centered at the magnetar DM.
• Figure 3: S/N vs DM distribution of one pulse detected on 25 November 2022, at time 7128.940 s from the start of the observation. It appeared at two "different" times: 7128.939 s and 7128.940 s. It was detected in 75 different time series across a DM range of 127--210 pc cm$^{-3}$, peaking in S/N at $\mathrm{DM} = 179$ pc cm$^{-3}$.
• Figure 4: Residuals with respect to the timing model presented in Table \ref{['tab: timing-solution']}.
• Figure 5: Rate of pulses per hour of observation against days of observation. The upper panel shows the rate considering only pulses of $\mathrm{S/N} \geq8$ and the lower panel only of $\mathrm{S/N}\geq15$. In circles we represent the rate and in filled triangles the upper limits.