A recent study utilizing the Five-hundred-meter Aperture Spherical radio Telescope (FAST) has confirmed the "radio-quiet" characteristics of four magnetars and one magnetar-like pulsar. Conducted by Ph.D. student BAI Juntao under the supervision of Prof. WANG Na from the Xinjiang Astronomical Observatory of the Chinese Academy of Sciences, the study provides new insights into the radio emission properties of these extreme celestial objects. 

The results are published in The Astrophysical Journal.

The researchers utilized FAST's unparalleled sensitivity to observe four magnetars (SGR 0501+4516, Swift J1834.9–0846, 1E 1841–045, and SGR 1900+14) as well as the magnetar-like pulsar PSR J1846–0258 at 1250 MHz. These observations were conducted using the central beam of FAST's 19-beam receiver, with a total bandwidth of 500 MHz and a time resolution of 49.152 seconds.

To analyze the data, they employed the PRESTO software package to mitigate radio frequency interference (RFI), dedisperse signals, and performed both periodic pulsation searches and single pulse detections. Using previously measured X-ray timing results, they extrapolated the spin periods of these sources and searched for periodic signals. 

Additionally, blind searches in the Fourier domain were performed using accelsearch, and a comprehensive search for dispersed single pulses was conducted with single pulse search.

Despite the deep observations, no periodic radio pulsations or single pulses were detected. The derived strict upper limits on flux density at 1250 MHz (S1250 < 16.9 Jy) are significantly lower than the flux densities of known radio pulsars. This suggests that these objects may be intrinsically radio-quiet or their radio beams are not favorably aligned with Earth. Notably, PSR J1846–0258 was observed one month after its 2020 X-ray outburst, providing crucial constraints on the timing of potential transient radio emissions.

This study provides valuable insights into magnetar radio emission mechanisms and offers guidance for future radio surveys of high-magnetic-field neutron stars. Continued monitoring of magnetars post-outburst is essential to further investigate their radio behavior.

 The upper limits on flux density for the four magnetars and the magnetar-like pulsar are lower than measured radio flux densities (at 1.4 GHz) of pulsars. (Image by BAI Juntao)