arXiv subjects

Yang-Yang Lin

Publications and source records attributed to Yang-Yang Lin.

3 recordsLinked to original sources

arXiv2026

Extended 2.25/8.60 GHz Observations of the Magnetar Swift J1818.0-1607

We present the long-term rotational evolution and radio emission properties of the magnetar Swift~J1818.0$-$1607, using simultaneous 2.25/8.60~GHz observations obtained with the Shanghai Tian Ma Radio Telescope from MJD~58936 to 59427. The average pulse profiles exhibit significant evolution with time and frequency, attributable to relative changes in the leading, central, and trailing emission components. The magnetar generally spins down with an average rate of $-1.65(4)\times10^{-11}\,\mathrm{s^{-2}}$, with the magnitude of the spin-down rate first increasing and then decreasing over the monitoring span. The overall flux density shows an initial rise followed by a decline, with sporadic variability superimposed; the variations at 2.25 and 8.60~GHz are broadly consistent across most epochs. The two-point spectral index increased from $α\simeq-1.8$ shortly after the outburst to near-zero values around MJD~59030--59050, followed by repeated decreases and increases. Despite this variability, 41 of the 54 two-point spectral-index measurements in the later campaign have $α>-1$. Three component-dependent types of mode changing are identified: Type~I, involving primarily intensity changes in the central component; Type~II, involving central and trailing components; and Type~III, involving leading and central components. All three classes include events showing a corresponding component response in the other observing band, with event-dependent response strengths and directions. Type~I variations are generally more pronounced at 8.60~GHz than at 2.25~GHz.

astro-ph.HE↗

arXiv2026

PSR~B0355+54: An Unexpected Compendium of Nearly All Scintillation Arc Morphologies

Scintillation arcs are sensitive probes of multipath propagation, offering a window into the distribution of scattering material in the interstellar medium. Contrary to the common observational finding that individual pulsars exhibit only a limited range of scintillation arc morphologies, we report that PSR~B0355+54, observed simultaneously at 2.25/8.60~GHz with the Shanghai Tianma Radio Telescope, displays nearly the full range of known arc patterns, many of which evolve rapidly. Across 54 observations from 2020 to 2026, we detect scintillation arcs in 53/53 usable observations at 2.25~GHz and 33/49 at 8.60~GHz. At 2.25~GHz, the secondary spectra exhibit five broad morphological types: forward arcs, inverted arclets, diffuse arcs, diffuse power, and irregular structures, with prominent displaced arclets appearing in several observations. In contrast, the 8.60-GHz spectra are generally dominated by faint forward arcs. Despite these marked morphological differences, the scaled curvatures and their annual variations agree between the two frequencies, showing that both trace the same dominant scattering screen at a fractional distance of $s=0.069^{+0.015}_{-0.014}$ near the pulsar, further supporting a possible association with the \ion{H}{ii} region Sh~2-205. Simulations show that this diversity can arise from variations in the scattered-image distribution within this screen, while brightness reconstructions at 2.25~GHz resolve localized structure down to $\sim0.02~\mathrm{mas}$. Tracking four arclets over 10~h at 8.60~GHz, including two displaced arclets, reveals a common evolutionary trend consistent with the line of sight sweeping across small-scale scattering structure, helping explain the rapid arc evolution.

astro-ph.GA↗

arXiv2025

Long-term simultaneous 2.25/8.60~GHz monitoring of the newly-discovered repeating FRB~20240114A

We report on the simultaneous monitoring of the repeating fast radio burst (FRB) 20240114A at 2.25 and 8.60~GHz, conducted 66 times between 2024 January 29 and 2025 February 15 with the Shanghai Tianma Radio Telescope (TMRT). In about 180 hours of observation, we detected 155 bursts at 2.25~GHz above a fluence threshold of 0.72~Jy~ms, but none at 8.60~GHz above a fluence threshold of 0.27~Jy~ms. FRB~20240114A exhibited frequency-dependent activity, as evidenced by the non-detections in 14.3 hours of observations at 2.25~GHz prior to 2024 February 24, despite its reported activity below 2~GHz. In contrast to its low-activity state reported below 1.4~GHz between 2024 June and December, FRB~20240114A exhibited high activity at 2.25~GHz in 2024 July with a mean burst rate of $1.72^{+0.18}_{-0.16}~\rm{hr}^{-1}$, followed by a low-activity state. We also detected a short-term reactivation at 2.25~GHz around 2025 January 20, about two weeks after renewed activity was reported below 1.4~GHz by other telescopes. The median burst width at 2.25~GHz is 3~ms, which is narrower than that at lower frequencies. The waiting time distribution peaks at 1019~s, and burst arrivals on hourly timescales consistent with a Poisson process. The isotropic-equivalent energy of bursts spans $10^{37} -10^{39}$~erg. The distribution of burst energy above the completeness threshold ($7.5\times10^{37}$~erg) follows a power-law relation with an index of $γ=-1.20\pm0.03\pm0.02$. Finally, we find that FRB~20240114A is at least two orders of magnitude less active at 8.60~GHz than at 2.25~GHz, and we constrain the broadband spectra of the detected bursts.

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