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

ABSTRACT Two recent discoveries, namely PSR J0901?4046 and GLEAM-X J162759.5?523504.3 (hereafter J1627), have corroborated an extant population of radio-loud periodic sources with long periods (76 1091 s, respectively) whose emission can hardly be explained by rotation losses. We argue that J1627 is a highly magnetized object consistent magnetar (an ultra-long period magnetar, ULPM), demonstrate it unlikely to either magnetically or rotationally powered white dwarf. By studying these together previously detected objects, we find there are at least handful promising candidates for Galactic ULPMs. The detections objects imply substantial number, N ? 13 000 500 like respectively, within our Galaxy. These source densities, as well cooling age limits from non-detection thermal X-rays, offsets, timing stability dipole spin-down limits, all the ULPM substantially older than confirmed magnetars their formation channel common one. Their existence implies widespread survival magnetar-like fields several Myr, distinct inferred behaviour in magnetars. ULPMs may also constitute second class FRB progenitors which could naturally exhibit very activity windows. Finally, show existing radio campaigns biased against detecting discuss strategies future X-ray surveys identify more such objects. estimate ${\cal O}(100)$ should SKA-MID DSA-2000.