Magnetar spin-down glitch clearing the way for FRB-like bursts and a pulsed radio episode G. Younes12 M. G. Baring3 A. K. Harding4 T. Enoto5 Z. Wadiasingh167 A. B. Pearlman8910

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Magnetar spin-down glitch clearing the way for FRB-like bursts

and a pulsed radio episode

G. Younes1,2, M. G. Baring3, A. K. Harding4, T. Enoto5, Z. Wadiasingh1,6,7, A. B. Pearlman8,9,10,

W. C. G. Ho11, S. Guillot12,13, Z. Arzoumanian1, A. Borghese14,15, K. Gendreau1, E. G¨

o˘

g¨

us¸16,

T. G¨

uver17, A. J. van der Horst2, C.-P. Hu18, G. K. Jaisawal19, C. Kouveliotou2, L. Lin20, W. A. Majid21,10

1 Astrophysics Science Division, NASA/GSFC, Greenbelt, MD 20771, USA

2 Department of Physics, The George Washington University, 725 21st St. NW, Washington,

DC 20052, USA

3 Department of Physics and Astronomy - MS 108, Rice University, 6100 Main Street, Hous-

ton, Texas 77251-1892, USA

4 Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

5 Extreme Natural Phenomena RIKEN Hakubi Research Team, Cluster for Pioneering Re-

search, RIKEN, Wako, Saitama 351-0198, Japan

6 Department of Astronomy, University of Maryland, College Park, Maryland 20742, USA

7 Center for Research and Exploration in Space Science and Technology, NASA/GSFC, Green-

belt, Maryland 20771, USA

8 Department of Physics, McGill University, 3600 rue University, Montr´

eal, QC H3A 2T8,

Canada

arXiv:2210.11518v1 [astro-ph.HE] 20 Oct 2022

9 McGill Space Institute, McGill University, 3550 rue University, Montr´

eal, QC H3A 2A7,

Canada

10 Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena,

CA 91125, USA

11 Department of Physics and Astronomy, Haverford College, 370 Lancaster Avenue, Haver-

ford, PA 19041, USA

12 IRAP, CNRS, 9 avenue du Colonel Roche, BP 44346, F-31028 Toulouse Cedex 4, France

13 Universit´

e de Toulouse, CNES, UPS-OMP, F-31028 Toulouse, France

14 Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, E-

08193, Barcelona, Spain

15 Institut d’Estudis Espacials de Catalunya (IEEC), Carrer Gran Capit. 2–4, E-08034 Barcelona,

Spain

16 Sabancı University, Faculty of Engineering and Natural Sciences, 34956, ˙

Istanbul, Turkey

17 Istanbul University, Science Faculty, Department of Astronomy and Space Sciences, Beyazıt,

34119, Istanbul, Turkey

18 Department of Physics, National Changhua University of Education, Changhua, 50007, Tai-

wan

19 National Space Institute, Technical University of Denmark, Elektrovej 327-328, DK-2800

Lyngby, Denmark

20 Department of Astronomy, Beijing Normal University, Beijing 100875, People’s Republic

of China

21 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA

Magnetars are a special subset of the isolated neutron star family, with X-ray and radio

emission mainly powered by the decay of their immense magnetic ﬁelds. Many attributes

of magnetars remain poorly understood: spin-down glitches or the sudden reductions

in the star’s angular momentum, radio bursts reminiscent of extra-galactic Fast Radio

Bursts (FRBs), and transient pulsed radio emission lasting months to years. Here we un-

veil the detection of a large spin-down glitch event (|∆ν/ν|= 5.8+2.6

−1.6×10−6) from the

magnetar SGR 1935+2154 on 2020 October 5 (+/- 1 day). We ﬁnd no change to the source

persistent surface thermal or magnetospheric X-ray behavior, nor is there evidence of

strong X-ray bursting activity. Yet, in the subsequent days, the magnetar emitted three

FRB-like radio bursts followed by a month long episode of pulsed radio emission. Given

the rarity of spin-down glitches and radio signals from magnetars, their approximate

synchronicity suggests an association, providing pivotal clues to their origin and trigger-

ing mechanisms, with ramiﬁcations to the broader magnetar and FRB populations. We

postulate that impulsive crustal plasma shedding close to the magnetic pole generates a

wind that combs out magnetic ﬁeld lines, rapidly reducing the star’s angular momentum,

while temporarily altering the magnetospheric ﬁeld geometry to permit the pair creation

needed to precipitate radio emission.

SGR 1935+2154 is an isolated neutron star displaying hot and luminous soft X-ray emis-

sion pulsed1at a spin frequency ν≈0.308 Hz while slowing down at a nominal rate of about

−1.4×10−12 Hz s−1. If attributed to magnetic dipole braking, these spin properties imply a dipole

magnetic ﬁeld strength B≈2.2×1014 G at the equator and a young spin-down age τ≈3.6kyr.

SGR 1935+2154 is also a proliﬁc burster, capable of displaying in a matter of minutes hundreds of

bright millisecond-duration X-ray bursts2, with luminosities exceeding 1.0×1041 erg s−1. Hence,

SGR 1935+2154 belongs to the small, special group of isolated neutron stars known as magne-

tars, for which the very strong magnetic ﬁeld powers their many emission characteristics. Due to

their extreme variable nature and large magnetic energy budget, magnetars are the leading suspect

for the sources of enigmatic bright millisecond radio ﬂashes of extragalactic origin known as Fast

Radio Bursts (FRBs)3. Indeed, in a rare occurrence to date, on 2020 April 28 during a period of

intense X-ray bursting activity2, SGR 1935+2154 emitted a radio burst with a luminosity approach-

ing extragalactic FRBs. This discovery provided the ﬁrst evidence for the nature of the progenitor

of at least some FRBs 4, 5.

Since this event, we have been monitoring SGR 1935+2154 regularly with several X-ray in-

struments, most notably in the soft, 1–3 keV band with the NICER and XMM-Newton telescopes.

In this band, X-rays from the source are dominated by the pulsed, surface thermal emission, en-

abling us to track the evolution of its spin ephemerides. During a particularly heavy cadence

observational period covering the October 1st to November 27th dates, we were able to employ a

phase-coherent timing analysis, i.e., tracking the time-of-arrival (TOA) of X-ray pulses from the

source with a precise timing model. The pulse arrival time of SGR 1935+2154 from October 6th to

November 27th is well predicted, with an accuracy that is a few percent of the source spin-period,

from a simple timing model that includes the frequency and its ﬁrst and second derivatives. How-

ever, this model fails to predict the pulse arrival time from the 1st and the 2nd of October, showing

an offset of about half a rotation just 3.5 to 5 days later. Attempting to model these residuals with

the inclusion of higher order frequency derivatives fails to provide a statistically acceptable ﬁt (See

methods, Figure 2).

The sharp and large pulse-phase offset observed in the early October data is reminiscent

of the glitching behavior observed in pulsars and magnetars when they exhibit a sudden jump in

spin-frequency (i.e., ∆ν) at a well-deﬁned epoch tg. Indeed, a timing model that includes a glitch

provides an accurate prediction of the pulse TOA for the full October and November time period

(Figure 1 and Table1). In this model, we ﬁnd that a frequency jump ∆ν= 1.8+0.7

−0.5×10−6Hz

(corresponding to a fractional change ∆ν/ν = 5.8+2.6

−1.6×10−6) occurred at a glitch epoch tg=

59127.2+1.0

−0.7MJD or October 5th. We note that the positive frequency jump is required to ex-

plain the early TOAs relative to our reference epoch (59141.0 MJD), implying that the source

experienced a negative ∆νfrequency jump at tg. The corresponding loss of the magnetar rota-

tional kinetic energy due to this abrupt spin-down event is of the order of 3.0×1040 erg. This

phenomenon of a spin-down glitch, also referred to as ”anti-glitch”, has been conclusively ob-

served from one other magnetar, 1E 2259+5866, 7. The spin-down glitch magnitude, as well as the

fractional change in the case of SGR 1935+2154, are about one order of magnitude larger com-

pared to the three spin-down glitches observed so far from 1E 2259+586 over a period of 20 years

of observations7, 8. Other potential spin-down glitches have been reported from other magnetars,

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Magnetarspin-downglitchclearingthewayforFRB-likeburstsandapulsedradioepisodeG.Younes1;2,M.G.Baring3,A.K.Harding4,T.Enoto5,Z.Wadiasingh1;6;7,A.B.Pearlman8;9;10,W.C.G.Ho11,S.Guillot12;13,Z.Arzoumanian1,A.Borghese14;15,K.Gendreau1,E.G¨og¨us¸16,T.G¨uver17,A.J.vanderHorst2,C.-P.Hu18,G.K.Jaisawal19,C.Kou...

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Magnetar spin-down glitch clearing the way for FRB-like bursts and a pulsed radio episode G. Younes12 M. G. Baring3 A. K. Harding4 T. Enoto5 Z. Wadiasingh167 A. B. Pearlman8910

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