Over 15 years after the finding of fast radio bursts (FRBs), astronomers worldwide have been exploring the universe for answers about their origin. Most FRBs come from outside our Milky Way, but in April 2020, the first Galactic FRB (FRB 20200428) was detected, originating from a magnetar called SGR J1935+2154. This discovery sparked theories that even distant FRBs might be produced by magnetars, but the evidence, like the rotation period of the magnetar, remained elusive. Recent research, including UNLV astrophysicist Bing Zhang’s work, delves into this matter, shedding light on the peculiar discrepancy. In the journal Science Advances, an international team reports on their monitoring of SGR J1935+2154 after the April 2020 FRB, leading to the discovery of a radio pulsar phase five months later.
Unraveling a cosmological conundrum
Astronomers rely on powerful radio telescopes like China’s Five-hundred-meter Aperture Spherical radio Telescope (FAST) to track FRBs and other deep-space activity. Using FAST, they observed FRB 20200428 and a later pulsar phase originating from different regions within the magnetar’s scope, hinting at different origins.
Weiwei Zhu, lead author from the National Astronomical Observatory of China (NAOC), explained that FAST detected 795 pulses from the source over 13 days, showing different properties from the bursts observed.
These emissions from a magnetosphere’s region help astronomers understand how and where FRBs and related phenomena occur in our galaxy and potentially in cosmological distances.
Radio pulses, similar to FRBs, emit much less brightness and are typically observed in rotating neutron stars called pulsars, not magnetars. Most magnetars don’t emit radio pulses most of the time due to their strong magnetic fields, but some, like SGR J1935+2154, become temporary radio pulsars after bursting activities.
The bursts and pulses have different emission “phases” within each period, with magnetar pulses emitted in a narrow window. The April 2020 FRB and later bursts were emitted randomly outside this pulse window identified in the pulsar phase, suggesting different emission mechanisms and origins.
Implications for cosmological FRBs
Studying a Galactic FRB source in such detail has illuminated the mysterious nature of cosmological FRBs, occurring beyond our galaxy. Many cosmological FRB sources have been observed to repeat, with FAST detecting thousands of repeated bursts from a few sources. Previous searches for periodicity in seconds-level intervals have yielded no results.
According to Zhang, this challenges the prevailing idea that repeating FRBs are powered by magnetars. The discovery that bursts are generated in random phases offers a natural explanation for the absence of periodicity in repeating FRBs. Bursts seem to emanate in all directions from a magnetar, making it difficult to identify specific periods from FRB sources due to unknown reasons.
Source: University of Nevada, Las Vegas