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 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. We 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, we find there are at least a handful of promising candidates for Galactic ULPMs. The detections of these objects imply a substantial number, N ≳ 13000 and N ≳ 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 Myr, distinct from the inferred behaviour in confirmed Galactic magnetars. ULPMs may also constitute a second class of FRB progenitors which could naturally exhibit very long periodic activity windows. Finally, we 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. We estimate that ${\cal O}(100)$ more such objects should be detected with SKA-MID and DSA-2000.

Ultrafast Compact Binary Mergers

“…However, the ultrafast kick-induced delay time tail for regular collapses discussed here means that there would be a nonnegligible fraction of mergers in which one of the NSs is strongly magnetized during the merger. Furthermore, as recently shown by Beniamini et al (2023), there is growing evidence of a large population of ultra-long-period magnetars, whose fields decay on a much longer (∼10 6 yr) timescale, making them favorable candidates for being involved in mergers involving a highly magnetized NS. Several authors (Lipunov & Panchenko 1996;Lyutikov 2019;Cooper et al 2023) have suggested that such mergers could result in detectable coherent radio precursors of BNS mergers.…”

A Luminous Precursor in the Extremely Bright GRB 230307A

“…A common theme for many of these models is the requirement that at least one NS in the binary be very strongly magnetized (surface dipole field strength 10 15 G) in order to reach a luminosity 10 50 erg s −1 . Thus, if GRB 230307A is originated in a binary NS merger, the energetic of this precursor strongly suggests that the NS can maintain a strong magnetic field over the duration of the inspiral phase (e.g., Beniamini et al 2023), indicating that it is preserved by some specific mechanism (e.g., it could be frozen into the superfluid NS core; see Ho et al 2017).…”

Evolutionary Origin of Ultralong-period Radio Transients

“…Because of long spin periods, longperiod pulsars have been proposed to most likely be white dwarfs (Katz 2022) or hot subdwarfs (proto-white dwarf, Loeb & Maoz 2022). However, Beniamini et al (2023) demonstrated that the observations of J1627 are unlikely to be explained by either a magnetically or a rotationally powered white dwarf. Kou et al (2019) proposed that the long period of J0250 is related to the magnetospheric evolution and magnetic field decay.…”