# Evidence for an abundant old population of Galactic ultra long period magnetars and implications for fast radio bursts

**Authors:** P. Beniamini, Z. Wadiasingh, J. Hare, K. Rajwade, G. Younes, A. J. van der Horst  
**arXiv:** [2210.09323](https://arxiv.org/abs/2210.09323)  
**Date:** 2022-10-17  
**Summary page:** https://www.summarizepaper.com/en/paper/2210.09323v3/

## Key points

- Radio astronomy has been important in astrophysics for 90 years
- Much of the parameter space for radio detections remains unexplored
- Two recent discoveries have revealed a population of radio-loud periodic sources with long periods
- These sources are consistent with ultra long period magnetars (ULPMs)
- There are at least a handful of promising candidates for Galactic ULPMs
- The existence of ULPMs implies widespread survival of magnetar-like fields for several million years
- ULPMs may constitute a second class of Fast Radio Burst progenitors
- Existing radio campaigns are biased against detecting objects like these
- Future surveys could identify more such objects, estimating O(100) more should be detected with SKA-MID and DSA 2000.

## Summary

Radio astronomy has been a major pillar in astrophysics since the first radio detection of an astronomical object by Karl Jansky about 90 years ago. While radio astronomy has revealed classes of objects and types of radiation that were previously unknown, much of the parameter space for radio detections remains unexplored, particularly for rare or intermittent transients that are currently being discovered. Two recent discoveries, namely PSR J0901–4046 and GLEAM-X J162759.5–523504.3 (hereafter GLEAM-X J1627), have corroborated an extant population of radio-loud periodic sources with long periods (76 s and 1091 s respectively) whose emission can hardly be explained by rotation losses. The authors argue that GLEAM-X J1627 is a highly-magnetized object consistent with a magnetar (an ultra long period magnetar - ULPM), and demonstrate it is unlikely to be either a magnetically or a rotationally-powered white dwarf. By studying these sources together with previously detected objects, they find there are at least a handful of promising candidates for Galactic ULPMs. The detections of these objects imply a substantial number, 𝑁 (cid:38) 13000 and 𝑁 (cid:38) 500 for PSR J0901–4046 like and GLEAM-X J1627 like objects, respectively, within our Galaxy. These source densities as well as cooling age limits from non-detection of thermal X-rays, Galactic offsets, timing stability and dipole spindown limits all imply the ULPM candidates are substantially older than confirmed Galactic magnetars and that their formation channel is a common one. Their existence implies widespread survival of magnetar-like fields for several million years distinct from the inferred behaviour in confirmed Galactic magnetars. ULPMs may also constitute a second class of Fast Radio Burst progenitors which could naturally exhibit very long periodic activity windows. Furthermore, the authors show that existing radio campaigns are biased against detecting objects like these and discuss strategies for future radio and X-ray surveys to identify more such objects; they estimate that O(100) more should be detected with SKA Mid Frequency Array (SKA-MID) and Deep Space Array 2000 (DSA 2000). In conclusion, this study provides evidence for an abundant old population of Galactic ULPMs which could have implications on our understanding on Fast Radio Bursts as well as other aspects in astrophysics research.