The Astrophysical Journal, 989:89 (11pp), 2025 August 10
© 2025. The Author(s). Published by the American Astronomical Society.
Timing and Spectral Evolution of the Magnetar 1E 1841-045 in Outburst
George Younes1,2,3 aa, Samuel K. Lander4, Matthew G. Baring5 aa, Marlon L. Bause6 aa, Rachael Stewart7 aa,
Zaven Arzoumanian2 aa, Hoa Dinh Thi5 aa, Teruaki Enoto8 aa, Keith C. Gendreau2 aa, Tolga Güver9,10 aa, Alice K. Harding11 aa,
Wynn C. G. Ho12 aa, Chin-Ping Hu13 aa, Alex Van Kooten7 aa, Chryssa Kouveliotou7,14 aa, Niccolò Di Lalla15 aa,
Alexander McEwen1, Michela Negro16 aa, Mason Ng17,18 aa, David M. Palmer19,20 aa, Laura G. Spitler6 aa, and
Zorawar Wadiasingh2,3,21 aa
1		Center for Space Sciences and Technology, University of Maryland, Baltimore County, Baltimore, MD 21250, USA; george.a.younes@nasa.gov
2		Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
3		Center for Research and Exploration in Space Science and Technology, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
4		School of Engineering, Mathematics and Physics, University of East Anglia, Norwich NR4 7TJ, UK
5		Department of Physics and Astronomy—MS 108, Rice University, 6100 Main Street, Houston, TX 77251-1892, USA
6		Max Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
7		Department of Physics, The George Washington University, Washington, DC 20052, USA
8		Department of Physics, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 606-8502, Japan
9		Istanbul University, Science Faculty, Department of Astronomy and Space Sciences, Beyazıt, 34119 Istanbul, Turkey
10		Istanbul University Observatory Research and Application Center, Istanbul University, 34119 Istanbul, Turkey
11		Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
12		Department of Physics and Astronomy, Haverford College, 370 Lancaster Avenue, Haverford, PA 19041, USA
13		Department of Physics, National Changhua University of Education, Changhua 50007, Taiwan
14		Astronomy, Physics and Statistics Institute of Sciences (APSIS), The George Washington University, Washington, DC 20052, USA
15		Department of Physics and Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305, USA
16		Department of Physics & Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA
17		Department of Physics, McGill University, 3600 rue University, Montréal, QC H3A 2T8, Canada
18		Trottier Space Institute, McGill University, 3550 rue University, Montréal, QC H3A 2A7, Canada
19		Los Alamos National Laboratory, Los Alamos, NM 87544, USA
20		New Mexico Consortium, Los Alamos, NM 87544, USA
21	Department of Astronomy, University of Maryland, College Park, MD 20742, USA
Received 2025 February 27; revised 2025 June 13; accepted 2025 June 19; published 2025 August 6
Abstract
We present timing and spectral analyses of Neutron star Interior Composition Explorer (NICER), Nuclear
Spectroscopic Telescope Array (NuSTAR), and IXPE observations of the magnetar 1E 1841-045 covering 82 days following its 2024 August bursting activity as well as radio observations utilizing MeerKAT and Effelsberg. We supplement our study with a historical NuSTAR observation and all 2024 preoutburst NICER observations. The outburst is marked by an X-ray flux enhancement of a factor of 1.6 compared to the historical level, predominantly driven by a newly formed nonthermal emitting component with a photon index Γ = 1.5. This flux showed a 20% decay at the end of our monitoring campaign. The radio monitoring did not reveal any pulsed radio emission with an upper limit of 20 mJy and 50 mJy ms on the mean flux density and single pulse fluence, respectively. We detect a spin-up glitch at outburst onset with Δν = 6.1 × 10-8 Hz and = 1.4 × 10 14 Hz s-1, consistent with the near universality of this behavior among the continuously monitored magnetars. Most intriguingly, the 1E 1841-045 2–10 keV pulse profile is markedly different compared to preoutburst: it shows a new, narrow (0.1 cycle) peak that appears to shift toward merging with the main, persistently present, pulse. This is the second case of pulse-peak migration observed in magnetars after SGR 1830-0645, and the two sources exhibit a similar rate of phase shift. This implies that this phenomenon is not unique and might present itself in the broader population. The newly formed peak for 1E 1841-045 is nonthermal, with emission extending to ≳20 keV, in contrast to the case of SGR 1830-0645. Our results are consistent with an untwisting magnetic field bundle with migration toward the magnetic pole, perhaps accompanied by plastic motion of the crust.
Unified Astronomy Thesaurus concepts: High energy astrophysics (739)

1.		Introduction
Magnetars represent a subset of the isolated neutron star (INS) population, possessing dipole magnetic fields with strengths reaching 1015 G (C. Kouveliotou et al. 1998). This large magnetic energy reservoir gives magnetars unique characteristics rarely present in other types of INSs, chief among them are their outburst episodes. The onset of such is
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
commonly manifested by the emission of a few to several hundred bright (EX ∼ 1037-41 erg), short (duration in the range 0.01–1 s), hard X-ray bursts (A. C. Collazzi et al. 2015). Concurrently, the magnetar soft and hard X-ray quiescent emission increases by as much as 3 orders of magnitude (F. Coti Zelati et al. 2018), accompanied by significantly higher surface temperatures and strong temporal variability in the form of timing noise, glitch activity, and altered pulse shape and fraction. This diverse phenomenology is typically interpreted in the context of the decay of strong crustal B fields, causing magnetic stresses on the star surface that could exceed the yield strain of the solid crust (e.g., S. K. Lander et al. 2015). This, in turn, can result in crustal deformation, thermal energy deposition leading to new hot spots on the star surface, and twisted external B-field loops (see, e.g., C. Thompson & R. C. Duncan 1996; A. K. Harding et al. 1999; C. Thompson et al. 2002; D. Viganò et al. 2013). For a review of magnetars see, e.g., V. M. Kaspi & A. Beloborodov (2017).
1E 1841-045 is a persistently X-ray bright magnetar discovered with the Advanced Satellite for Cosmology and Astrophysics (G. Vasisht & E. V. Gotthelf 1997). Its timing characteristics imply a surface dipolar field of about 7 × 1014 G, a spin-down age of about 4.6 kyr, and a rotational-energy loss ∼ 1033 erg s-1. Its soft and hard X-ray luminosities exceed 1035 erg s-1 (e.g., L. Kuiper et al. 2004), well in excess of its E . It is located at the center of the X-ray and radio-bright supernova remnant (SNR) Kes 73, confirming its spin-down inferred young age. The 1E 1841-045 broadband X-ray spectrum is well described with the canonical quasi-thermal soft X-ray and nonthermal hard X-ray tail model (L. Kuiper et al. 2004; H. An et al. 2013, 2015; T. Enoto et al. 2017).
Since its discovery, 1E 1841-045 has displayed several episodes of magnetar bursting activity including the one that established it as part of the magnetar family (F. P. Gavriil et al. 2002), yet never was its persistent emission observed to be in an enhanced state (H. S. Kumar & S. Safi-Harb 2010; L. Lin et al. 2011; R. Dib & V. M. Kaspi 2014). On 2024 August 21, 1E 1841-045 entered another active period which was first observed with the Neil Gehrels Swift Observatory (Swift) Burst Alert Telescope (BAT; S. Dichiara & D. M. Palmer 2024), and later confirmed with the Fermi Gamma-ray Burst Monitor (GBM) and Neutron star Interior Composition Explorer (NICER; M. Ng et al. 2024; O. J. Roberts et al. 2024), among other high-energy instruments. Follow-up NICER, Nuclear Spectroscopic Telescope Array (NuSTAR), and Swift observations revealed an enhanced 2–70 keV flux and noticeably more complex soft and hard X-ray pulse profiles (G. Younes et al. 2024), highlighting the first radiative outburst from the source in conjunction with its bursting emission.
In this paper, we report on the X-ray timing and spectral evolution of the magnetar 1E 1841-045 during its 2024 August outburst through the analysis of NICER, NuSTAR, and IXPE observations covering the period 2024 August 21 to November 11. For completeness and comparison purposes, we also analyze all the NICER observations conducted in 2024, and a historical NuSTAR observation taken in 2012. Lastly, we report on 2024 radio observations of the source taken with MeerKAT and Effelsberg. Section 2 summarizes the observations and data reduction procedures. Section 3 details our findings. Section 4 discusses our results in the context of surface and magnetospheric dynamics during magnetar outbursts.
2.		Observations, Data Reduction, and Analysis Procedures
2.1.		X-Rays
We analyze the four NuSTAR (F. A. Harrison et al. 2013) observations of 1E 1841-045 that were taken postoutburst, which occurred over the course of 2.5 months from 2024 August 29, 8 days after the Swift-BAT announcement of the most recent activity from 1E 1841-045, until November 11. Each observation is roughly 50 ks in exposure. For comparison with the quiescent state, we also analyze the NuSTAR observation from 2012 November 9 (ID 30001025002), which also had an exposure of about 50 ks (Table 2). We perform the data reduction, calibration, and high-level product extraction, e.g., source and background cleaned event files, spectra, and light curves, utilizing NuSTARDAS software version 2.1.2 as part of HEASoft (version 6.33.1). We utilize a circular region with a radius of 45″ centered on the central brightest pixel to extract source events, while background events were considered from a source-free circular region with a radius of 60″, on the same CCD as the source. The photon flux from NuSTAR is likely contaminated by Kes 73 especially at ≲5 keV (H. An et al. 2013, 2015), yet, since we do not consider any cross-instrument spectral analysis, this contamination does not affect our results (see below and Section 3.2).
NICER (K. C. Gendreau et al. 2016) has performed biweekly observations of the magnetar 1E 1841-045 since 2018 as part of a long-term monitoring program for a systematic study of magnetar activity (e.g., G. Younes et al. 2020b). At the start of the 2024 August outburst, NICER's cadence was increased to closely follow-up the evolution of the source. In this paper, we report on all the 2024 NICER observations which spanned the dates 2024 February 13 to 2024 November 11. We create cleaned and calibrated event files using nicerl2, part of NICERDAS version v12. To increase the NICER data available for our analysis, we retain both night and daytime exposures with the flag thresh- filter set to ALL. Moreover, we excise any flaring intervals due to strong particle activity by visually inspecting the 12–15 keV light curve, where events are predominantly from the high-energy particle background. We only utilize NICER for timing analysis; spectral analysis with the available data is complicated by the strong contamination to the source flux from the X-ray bright Kes 73 SNR.
To increase our data statistics, we also utilize the IXPE observations presented in R. Stewart et al. (2025), primarily for timing analysis. We refer the reader to that work for details on the data reduction procedure.
We correct all photon arrival times to the solar system barycenter using the HEASoft tool barycorr, the JPL ephemerides DE430, and the source coordinates as established in S. Wachter et al. (2004). Subsequently, we perform our timing analysis utilizing the Code for Rotational-analysis of Isolated Magnetars and Pulsars (CRIMP) (version 0.1.0). Specifically, we use CRIMP to perform period searches using the Z2 statistics, perform model fitting to pulse profiles, deliver rms pulsed fraction, measure pulse times of arrival (TOAs), and derive the corresponding rotational phase of each photon arrival time. For the TOA measurement, CRIMP allows for a variable template model, an important feature in magnetar timing during outbursts, and relevant to the case of 1E 1841 -045 as we detail below. To model the pulse TOAs and create a phase-coherent timing solution throughout the 2024 observational campaign, we utilize Tempo2 (G. B. Hobbs et al. 2006) and PINT (J. Luo et al. 2021). The two software packages resulted in near-identical timing solutions; hereafter, we report the Tempo2 results.
For spectral analysis, we utilize Xspec version 12.14.0c. We group all spectra to 5 counts per energy bin and use the W statistic (statistic cstat in Xspec) as our fitting statistic.

We restrict the spectra to the energy range 3–70 keV since we only consider NuSTAR. Accordingly, we fix the absorbing column density NH to 2.6 × 1022 cm2 as derived in H. S. Kumar et al. (2014) utilizing high-resolution, soft X-ray imaging instruments. For consistency with the latter work, we adopt the E. Anders & N. Grevesse (1989) elemental abundances (angr in Xspec) along with the photoelectric cross sections of D. A. Verner et al. (1996). Lastly, we model the calibration discrepancy between the two NuSTAR detectors FPMA and FPMB with a multiplicative constant normalization, which we find to be in the 1%-3% range.
2.2.		Radio
1E 1841-045 has been observed as part of two monitoring campaigns that target radio-quiet magnetars in the search for radio emission independent of X-ray outbursts. These campaigns were started in 2024 February with the MeerKAT radio telescope and in 2024 May with the Effelsberg 100 m radio telescope. MeerKAT is a 64-dish interferometer located in the Karoo desert in South Africa, while Effelsberg is a single-dish instrument located near Bonn in Germany. For MeerKAT, seven epochs have been observed as part of an open time proposal with a monthly cadence while six more have been observed as part of Director’s Discretionary Time (DDT) time with an increased cadence after the outburst. With Effelsberg, two observations, one each in May and June, were taken. Beam- formed search-mode data were recorded for both telescopes. Each MeerKAT observation was taken with a time resolution of 38 μs, full polarization information, and 1024 frequency channels. Five of the open time observations were taken in L band (856–1712 MHz) and the other two and all DDT observations were taken in the S1 band (1968–2843 MHz). The Effelsberg observations were taken with the new ultrabroad band receiver covering the frequency range from 1300 to 6000 MHz with five subbands (Band 1: 1290–1940 MHz; Band 2: 1940–2590 MHz; Band 3: 2975–4100 MHz; Band 4: 4100–5225 MHz; and Band 5: 5225–5975 MHz). The data were recorded using the Effelsberg Direct Digitisation (EDD) backend (E. D. Barr et al. 2023) independently in each subband at a frequency and time resolution of 1 MHz and 32 μs, respectively, and full polarization information. The duration of the observation varies by telescope and observing band. Table 4 gives an overview of all radio observations of 1E 1841-045 presented in this work. Given that no radio emission has been observed from 1E 1841-045, we estimated the amount of dispersion expected, the dispersion measure (DM), to be 746 pc cm-3 using the NE2001 model (J. M. Cordes & T. J. W. Lazio 2002). This value is used for coherent dedispersion at the time the data are taken for both telescopes, with the exception of the first Effelsberg observation, where no coherent de-dispersion has been applied. The observations of the other sources targeted by the survey and the imaging data of MeerKAT are presented in separate, forthcoming publications.
All MeerKAT and Effelsberg data are searched for radio emission in the form of single pulses as well as for periodic pulsations. For the Effelsberg observations, each subband of the UBB is searched individually. The single pulse search is based on the software package TransientX (Y. Men & E. Barr 2024),23 which offers inbuilt mitigation techniques for radio frequency interference (RFI). We searched over a DM range of 20–10,000 pc cm-3, a width range from the native time resolution of the data to the period of the magnetar and applied a minimum signal-to-noise ratio (S/N) of six. Each candidate is inspected visually and classified as real single pulse or noise/RFI. For the periodic pulsation search, we use the PRESTO software suite (S. M. Ransom 2001).24 First a mask is generated to mitigate RFI in the data using rfifind. The data are then folded using the timing solution of the X-ray observations provided in this work and with 128 profile bins. The folds are thus only searching for the DM and cover the range from 00 to 22,145 pc cm-3.
3.		Results
3.1.		Timing Analysis
To build a long-term, phase-coherent timing solution that encompasses the outburst, we rely on the full 2024 NICER monitoring of 1E 1841-045, first establishing a coherent timing model from February and up to the outburst onset. We build a template by fitting a preoutburst high-S/N NICER profile to a Fourier series with three harmonics. We then establish the time intervals that define each TOA by merging consecutive 2 × 104 NICER events detected within a <2 day period. Finally, we fit the unbinned, folded profile of each of these time intervals to the same template only allowing the global phase shift Δf and normalization constant to vary, utilizing the extended maximum likelihood fitting method with a Poisson probability density function. We find that a simple timing model consisting of a spin frequency and its first derivative is adequate to fit the phase shifts, or equivalently, the pulse TOAs with a χ2 of 9 for seven degrees of freedom (DOF). The resulting rms residuals is 130 ms (1.3% of the source spin cycle).
Our preliminary timing analysis of the earliest postoutburst NICER and NuSTAR data (taken between August 21 and August 29) reveals a prominent change to the soft X-ray pulse profile shape, namely the appearance of a narrow peak with a width of about 0.1 cycles. The peak was also present in the later observations when folded with local ephemerides, yet it showed a noticeable shift toward merger with the main pulse. Given this drastic change, we build a separate template for the postoutburst data, utilizing the earliest NuSTAR pulse profile, which we fit with an increasing number of von Mises (wrapped Gaussian) functions and assess the quality of the fit according to the χ2 test. We find that a model consisting of three von Mises components or fewer cannot satisfactorily fit the data resulting in a reduced χ2 ≫ 2. A model consisting of four von Mises components provides an acceptable fit to the pulse profile with a reduced χ2 of 1.6. Adding one extra component results in a reduced χ2 of approximately one, and an improvement at the 3.5σ level according to an F-test. In the remainder, we utilize the latter template, yet we note that none of our conclusions change if we employ the former.
We construct time intervals that define each postoutburst TOA by merging consecutive 2 × 104 NICER events (104 for NuSTAR and 5000 for IXPE) detected within a <2 day period. We fold these events with the preoutburst timing solution established above, and fit the resulting profiles with the von Mises template while allowing the phase shift Δf, normalization constant, and the centroid of the newly formed peak to vary (we restrict the latter to only vary between –0.1 and

Figure 1. Upper panel: spin residuals of the 1E 1841-045 pulse TOA covering the full 2024 time period, after subtracting a timing model fit to the preoutburst data (left of the vertical dashed line) consisting of a spin frequency and its first derivative. The residuals postoutburst are reminiscent of a spin-up glitch. Lower panel: same as above but after incorporating a glitch to the timing solution.

Table 1
Phase-coherent Spin Parameters of 1E 1841-045

Parameters	Values	
R.A. (J2000)	18:41:19.343	
Decl. (J2000)	-04:56:11.16	
Timescale	TDB	
Ephemeris	DE430	
MJD range	60353–60625	
Epoch (MJD)	60450	
ν (Hz)	0.084702008(1)	
(Hz s-1)	-2.938(2) × 10-13	
tg (MJD)	60543 (fixed)	
Δν (Hz)	6.1(4) × 10-8	
(Hz s-1)	-1.42(9) × 10-14	
Δν/ν	7.6(5) × 10-7	
χ2/DOF	89/58	
rms residual (ms)	188	

Notes. The 1σ uncertainty on each parameter is given in parentheses.

0.1 cycles). The residuals of these TOAs are presented in Figure 1. The sudden, and quasi-linear shift in residuals, followed by a quadratic turn, is consistent with a spin-up glitch. Indeed, fitting the full 2024 TOAs with a model including a glitch in frequency and its derivative provides a good fit to the data with a reduced χ2 of 1.5 for 58 DOF, and an rms residual of 188 ms. We summarize our timing fit in Table 1. We find Δν = (6.1 ± 0.4) × 10-8 Hz and = ( 1.4 ± 0.1) × 10 14 Hz s-1. We note that we fixed the glitch epoch to the first reported BAT burst in August, i.e., MJD 60543.
We display the folded NuSTAR pulse profiles with the full phase-coherent solution, in three separate energy ranges, in Figure 2. In addition to the noticeable change at soft X-rays, the pulse also exhibits variability at hard X-rays. The usually flat-topped pulse profile at energies > 10 keV (e.g., H. An et al. 2013) shows a more prominent peaked profile with a maximum at around a phase of 0.75. The high-energy pulse returns to its preoutburst shape in the last NuSTAR observation of November 11. We also show the folded 2–8 keV NICER data in Figure 3, which present a consistent picture compared to the NuSTAR data in the 3–10 keV range. Finally, we measure the rms pulse fraction (PF) of each of these profiles. We do not find strong variation with time: the NuSTAR rms PF is 11%, 13%, and 15% in 3–10, 10–20, and 20–70 keV, respectively, while the NICER PF is around 6% throughout the outburst (smaller than NuSTAR partly due to the strong contamination from the bright SNR Kes 73). These values are also consistent with the preoutburst measurements.
Finally, to quantify the phase shift of the newly formed peak, we fit each NICER, NuSTAR, and IXPE profile (presented in Figures 2 and 3 and in R. Stewart et al. 2025) with the von Mises model with five components that best fitted the first NuSTAR profile (utilizing four components does not impact our results). We allow the centroid of the component that fits the newly formed peak, the overall normalization, and the overall pulsed fraction (i.e., one multiplicative constant normalization applied to the amplitude of each of the von Mises components) to vary. The latter takes into account the differing level of background in the different detectors, which impacts the level of pulsed flux observed. These fits are displayed as dashed lines in Figures 2 and 3 for NuSTAR and NICER, respectively. We show the corresponding phase shifts in the newly formed peak in Figure 4. There is a clear trend of an increasing pulse phase with time. We fit this evolution with a linear function, which resulted in a slope of 4.6(3) × 10-3 rad day-1, or 7.3(5) × 10-4 cycles day-1, and a reduced χ2 of 3.1 for eight DOF (dotted line). We also fit the evolution with an exponential-decay function of the increasing form a (1 exp ( t/ )) + b , where t is the time in days, τ is the exponential-decay timescale also in days, and b the initial phase of the newly formed peak at t = 0 (MJD 60543). We find a = 0.45+00..0068 rad, = 43+1230 days, and b = 1.45 ± 0.02 rad (dotted–dashed line). The fit results in a reduced χ2 of 1.0 for seven DOF, which is a slight improvement compared to the linear fit. We also present in Figure 4 the 2024 to 2025 February burst history of 1E 1841-045 as observed with Swift-BAT (D. M. Palmer 2024).
3.2.		Spectral Analysis
We solely rely on the NuSTAR observations to present the spectral evolution of 1E 1841-045 during its 2024 August outburst, mainly due to its nearly equal spread over the first 3 months of outburst and its hard spectral coverage (>3 keV), which limits the SNR contribution to the point source flux. As a baseline, we analyze the historical 2012 NuSTAR observation (ID 30001025002), which has a similar exposure of about 50 ks, with the postoutburst data sets. We fit the spectrum of this latter observation to an absorbed double power-law (2PL) model with a fixed NH (see Section 2). This model provides a statistically good fit with a W statistic of 1400 for 1464 DOF. Adding another component, e.g., a blackbody (BB) does not significantly improve the quality of the fit with a W statistic of 1390 for 1462 DOF. We also test the validity of a BB and a power-law (PL) fit to the data, yet this combination results in a worse fit with a W statistic of 1507 for the same DOF. Lastly, neither a broken PL nor an exponential-cutoff PL provide a satisfactory fit to the data. Hence, we deduce that a 2PL model

Figure 2. Energy-resolved pulse profiles as observed with NuSTAR postoutburst. Each row represents a single observation, while columns show the pulse profiles in increasing energy bins. Data are folded with the full phase-coherent timing solution covering the entirety of the 2024 data sets (Table 1). The shaded areas delimitate the intervals we used for phase-resolved spectroscopy. The dashed vertical lines in the 3–10 keV pulse profiles represent the centroid of the best-fit von Mises component to the newly formed peak as derived for the earliest NuSTAR observation. The dashed black lines are the best-fit von Mises model (with four components) to each epoch. See text for more details.

is an adequate representation of the NuSTAR spectra preoutburst. We note that prior analyses of the broadband X-ray spectrum of 1E 1841-045 indicate that the emission at energies > 3 keV is dominated by nonthermal components (H. An et al. 2013, 2015; T. Enoto et al. 2017).
We then fit the 2PL model to each of the postoutburst spectra, which we also find to be an adequate spectral decomposition to the data. We present these results in Table 2, while the best-fit model and residuals in terms of σ are shown in Figure 5. We find largely similar photon indices when comparing the post- and preoutburst spectral fits. On the other hand, the source flux 1 week from outburst onset is about 60% larger than the baseline. This increase is predominantly observed in the hard X-rays, where the hard X-ray tail contributes. The flux declines by about 10% over the course of our NuSTAR monitoring.
We also investigate adding the preoutburst best-fit model (2PL) to the spectral analysis of the postoutburst spectra, with the assumption that the former is unchanged during outbursts, i.e., as a fixed contribution to the total spectrum of the source. In this scenario, fitting the postoutburst enhanced emission with a 2PL results in a soft component with a photon index Γ ≈ 5, which implies a thermal nature for the soft X-ray enhancement. Hence, we also fit the data with a BB + PL model (Table 2). We find a BB temperature of about 0.43 keV and an average effective emitting area of about 36 km2 adopting an 8.5 kpc distance. We find an average PL photon index Γ ≈ 1.5, which is somewhat softer than the persistent hard X-ray tail. We observe a significant flux decrease in this nonthermal component between the first and last NuSTAR observation from 2.7 × 10-11 to 1.9 × 10-11 erg s-1 cm-2. We do not identify any strong variability in the spectral curvature, however.
Lastly, we perform phase-resolved spectroscopy to identify the spectral properties of each of the features in the source pulse profile. Our pulse phase binning is presented in Figure 2, where the green shaded area represents the off-pulse spectrum (considered as background), while the pink, blue, and purple shaded areas correspond to the newly formed peak, the main soft X-ray pulse, and its trailing edge, respectively, and are referred to as intervals 1, 2, and 3 in Table 3 (note that the pink shaded area is slightly shifted rightward in the later NuSTAR data to accommodate the pulse-peak shift we identify in Section 3.1). We find that the pulsed spectra in each of these intervals are best fit with a nonthermal PL model; a BB model results in temperatures of about 2 keV, too high to correspond to surface thermal emission. Moreover, we find that a second component is not required by the data. We summarize the photon indices for each peak during each of the NuSTAR postoutburst observations in Table 3. We find a consistent PL index between intervals 1 and 2, while interval 3 exhibits a harder PL. Moreover, the latter softens with time. This is consistent with the picture emerging from our energy-resolved pulse profile analysis, which indicates brighter emission at hard X-rays in the trailing edge of the main pulse at the early times of the outburst.
3.3.		Radio Upper Limits
After reducing the data from all observations, no single pulse or pulsed signal was found. Hence, our observations

Phase

Figure 3. NICER pulse profiles of 1E 1841-045 as observed preoutburst (upper panel) and postoutburst. Day 0 corresponds to 2024 August 21. Data are folded with the full phase-coherent timing solution covering the entirety of the 2024 data sets. The vertical dashed lines in the bottom four pulse profiles represent the centroid of the best-fit von Mises component to the newly formed peak as derived for the earliest NICER data (days 0–6). The dashed blue lines, on the other hand, are the best-fit von Mises model (with four components) to each epoch. See text for more details.

provide a time series of upper limits on the radio flux density before and after the outburst shown in Table 4. To estimate the upper limits for the flux density of folded profile Smean, as well as the fluence of single pulses FSP, we use the radiometer equation as derived in D. R. Lorimer & M. Kramer (2004) and derived the limit for FSP:

mean

FSP

(S/N) Tsys	X
G n pol tobs B	1 X
(S/N) Tsys w
G npolB
where S/N pertains to the folded profile or single pulse, Tsys is the system temperature, G is the gain of the receiving system, npol is the number of polarization data points summed (always two for our observations), tobs is the duration of the

Time (days since 2024 August 21)

Figure 4. Upper panel: daily burst history of 1E 1841-045 in 2024 and up to 2025 February as observed with Swift-BAT. Lower panel: pulse phase, in radians, of the newly formed peak in the soft X-ray band as a function of time. The dotted line is a linear fit to the data, while the dotted–dashed line is an exponential decay in the increasing form.

observation, B is the bandwidth of the receiving system, X is the duty cycle of the magnetar, and w is the pulse width of the single pulse.
For estimating the upper limits we assume fiducial values of X = 10% (folded profile) and w = 1 ms (single pulse), but other duty cycles and widths can easily be adopted by scaling the limits accordingly. The minimal S/N of six for a single pulse follows directly from the single pulse search. To find the minimal S/N of the folded profile that we could have detected, we investigate the S/N levels of residual RFI contributions. For MeerKAT, the RFI contribution is very low after the mitigation applied, making detections down to an S/N of five possible in each observation, which would make the signal significantly brighter than the RFI pulses in the data (except the observation on September 23, which is heavily affected by RFI and thus not considered). For the L-band observations, we adopt the sensitivity from W. Chen et al. (2023; G = 2.65 K Jy–1 and Tsys = 26 K), while for S band we estimate the SEFD = Tsys/G for 56 antennas to be 8.6 Jy. For Effelsberg, the RFI situation is worse. Here, we estimate the minimal detectable S/N of a folded profile to be eight. For Effelsberg, G is 1.3 K Jy-1 for each subband, while Tsys for Bands 1–5 is 20.6 K, 16.1 K, 16.5 K, 18.8 K, and 19 K, respectively. We note that our upper limit estimates to pulsed emission do not take into account the contribution of red noise, which can increase the minimum detectable flux density by a factor of a few (e.g., P. Lazarus et al. 2015). Quantifying this requires injecting synthetic pulses into the data, which is beyond the scope of this paper.
4.		Discussion
4.1.		High-energy Outburst
We have presented the timing and spectral evolution of the magnetar 1E 1841-045 during the first 82 days of its 2024

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4
10
2
0
2
4
Energy (keV)
Figure 5. Upper-left panel: best-fit 2PL models for the preoutburst NuSTAR data (black) and postoutburst NuSTAR spectra (colored lines), shown in νFν space. The total model flux is shown as a solid line while individual components are shown as dashed (soft power-law, SPL) and dotted (hard power-law, HPL) lines. Lower-left panel: residuals of the fit in units of one standard deviation. Upper-right panel: best-fit 2PL model for the preoutburst NuSTAR data (black) while adding a BB + PL model to the postoutburst NuSTAR spectra (colored lines), shown in νFν space. The total model flux is shown as a solid line while individual components are shown as dashed (SPL for the preoutburst and BB for the postoutburst) and dotted (HPL) lines. Lower-right panel: residuals of the fit in units of one standard deviation.
2
0
2
4
Energy (keV)

Table 2
Best-fit Spectral Parameters of the NuSTAR Observations
Observation ID	Date (UT)	Exposure (ks)	kT (keV)	2a RBB (km2)	ΓS	ΓH	b FS	b FH	b Ftot	
All Observations Treated Separately	
30001025002	2012-11-09	49	…	…	3.9 ± 0.1	1.32 ± 0.04	2.53 ± 0.06	5.7 ± 0.1	8.24 ± 0.08	
91001330002	2024-08-29	50			4.1 ± 0.1	1.32 ± 0.03	3.00 ± 0.05	8.8 ± 0.1	11.7 ± 0.1	
91001335002	2024-09-28	56			4.1 ± 0.1	1.29 ± 0.03	3.07 ± 0.06	8.2 ± 0.1	11.3 ± 0.1	
81002306002	2024-10-26	53			3.9 ± 0.1	1.26 ± 0.03	3.0 ± 0.1	7.6 ± 0.1	10.6 ± 0.1	
81002306004	2024-11-10	51			3.7 ± 0.1	1.21 ± 0.04	3.07 ± 0.06	7.6 ± 0.1	10.7 ± 0.1	
Postoutburst Spectral Parameters of the Enhanced Emission Onlyc	
91001330002	2024-08-29	50	0.43 ± 0.05	+48
28 17	…	1.50 ± 0.04	0.4 ± 0.1	2.7 ± 0.2	3.1 ± 0.2	
91001335002	2024-09-28	56	0.38 ± 0.05	+200
85 55	…	1.53 ± 0.05	0.6 ± 0.2	2.4 ± 0.3	3.0 ± 0.3	
81002306002	2024-10-26	53	0.43 ± 0.05	+52
26 16	…	1.56 ± 0.07	0.4 ± 0.1	+0.4
1.8 0.2	2.2 ± 0.3	
81002306004	2024-11-10	51	0.53 ± 0.08	+10 53	…	1.55 ± 0.08	0.27 ± 0.05	1.9 ± 0.3	2.2 ± 0.3	

Notes.
a Derived by adopting an 8.5 kpc distance.
b Derived in the 2–70 keV range in units of 10-11 erg s-1 cm-2. Listed uncertainties are at the 1σ level.
c These components and their corresponding spectral parameters only model the enhanced emission of the total postoutburst spectra; the preoutburst 2PL model is included as a fixed contribution, and assumed unchanged during outbursts.

outburst (S. Dichiara & D. M. Palmer 2024). We observe a clear increase in flux, by about 20% at soft energies and 60% at hard X-rays, with minimal decay. The flux enhancement is predominantly driven by the presence of a hard X-ray component that is well fit with a PL having a photon index Γ ≈ 1.5. In magnetar outburst theory, this component is typically attributed to newly formed, magnetospheric twisted B-field loops driven by plastic motion of the corresponding crustal foot points (C. Thompson et al. 2002). These twisted field bundles are capable of accelerating particles to high Lorentz factors. Bulk surface thermal photons with temperatures of about 0.5 keV can resonantly up-scatter off of these accelerated particles, resulting in inverted hard X-ray spectra (M. G. Baring & A. K. Harding 2007; R. Fernández & C. Thompson 2007; Z. Wadiasingh et al. 2018). Additionally, if the particles’ Lorentz factor exceeds ∼10, single photon pair creation could ignite, resulting in pair cascades (M. G. Baring &A. K. Harding 2001; K. Hu et al. 2019; Z. Wadiasingh et al. 2019; A. K. Harding et al. 2025, in preparation). These pairs, if created in high Landau states at higher altitudes, emit synchrotron emission from the outer parts of equatorial field loops. The highly polarized hard X-ray tail recently reported in R. Stewart et al. (2025) and M. Rigoselli et al. (2025) indeed suggests that synchrotron emission might play a significant role in shaping the spectrum of the hard X-ray emission (R. Stewart et al. 2025). Surface bombardment by return currents from twisted field loops could accommodate the increase that is observed at soft X-rays. Finally, the modest enhancement that is exhibited by 1E 1841-045 is largely due to its bright X-ray persistent state (H. An et al. 2015), and consistent with the maximal soft and hard X-ray luminosity expected from magnetar surfaces and magnetospheres,
Table 3
Phase-resolved Pulsed Spectral Modeling
Date (UT)	Interval 1	Interval 2 Γ	Interval 3	
2024-08-29	2.2 ± 0.2	2.2 ± 0.1	1.33 ± 0.05	
2024-09-28	1.7 ± 0.2	2.3 ± 0.1	1.39 ± 0.05	
2024-10-26	1.8 ± 0.1	2.1 ± 0.1	1.42 ± 0.06	
2024-11-10	2.1 ± 0.2	2.1 ± 0.1	1.56 ± 0.06	
Notes. The intervals refer to the shaded areas in Figure 2; interval 1 in pink, interval 2 in cyan, and interval 3 in purple. Observation IDs and exposures are reported in Table 2.

Table 4
Overview of the Radio Observations of 1E 1841-045
Obs. Date	MJD	tobs (s)	Telescope	mean (μJy)	FSP (mJy ms)	
2024-02-03	60343.345	730	MKT L band	17	52	
2024-03-03	60372.265	668	MKT S band	13	39	
2024-04-05	60405.159	730	MKT L band	17	52	
2024-05-01	60431.033	730	MKT L band	17	52	
2024-05-09	60439.143	1200	EFF UBB B1	34	84	
	⋯	⋯	EFF UBB B2	27	66	
	⋯	⋯	EFF UBB B3	RFI	51	
	⋯	⋯	EFF UBB B4	24	58	
	⋯	⋯	EFF UBB B5	30	72	
2024-06-01	60462.023	730	MKT L band	17	52	
2024-06-12	60473.144	1200	EFF UBB B1	34	84	
	⋯	⋯	EFF UBB B2	27	66	
	⋯	⋯	EFF UBB B3	21	51	
	⋯	⋯	EFF UBB B4	24	58	
	⋯	⋯	EFF UBB B5	30	72	
2024-07-12	60503.881	924	MKT S band	11	39	
2024-08-28	60550.724	922	MKT L band	15	52	
2024-09-17	60570.796	1200	MKT S band	10	39	
2024-09-22	60575.681	1200	MKT S band	10	39	
2024-09-23	60576.871	1200	MKT S band	RFI	39	
2024-09-28	60581.765	1200	MKT S band	10	39	
2024-10-11	60594.712	1200	MKT S band	10	39	
2024-10-28	60611.651	1200	MKT S band	10	39	
Note. For each observation, the date, MJD of the topocentric start of the observation, duration of the observation (tobs), telescope name (Effelsberg (EFF) and MeerKAT (MKT)) and observing band, and the limits on the mean flux density Smean and single pulse fluence FSP are given.

respectively. For the surface, the electromagnetic radiation is regulated through neutrino emission and cannot exceed ∼1036 erg s-1 whereas hard X-rays from a maximally twisted, axisymmetric field loop could reach a similar luminosity (A. M. Beloborodov 2009; J. A. Pons & N. Rea 2012).
The spin-up glitch observed in 1E 1841-045 at outburst onset is an almost ubiquitous feature of the continuously monitored members of the X-ray magnetar family (e.g., R. Dib & V. M. Kaspi 2014). Its size and the sudden change to are also on par with other measurements (e.g., R. Dib & V. M. Kaspi 2014; C.-P. Hu et al. 2024). In standard pulsar glitch theory, spin-up glitches occur when the superfluid component of the inner crust transfers part of its larger angular momentum to the outer crust, which suffers from magnetic dipole braking (see B. Haskell & A. Melatos 2015; D. Antonopoulou et al. 2022, and references therein). Under this assumption, the fact that the majority of magnetar outbursts from the monitored bunch are accompanied by glitching activity may indicate that their trigger mechanism is intimately connected to the inner crust. Yet, the accompanying and profound radiative changes, which are rarely observed in canonical rotation-powered pulsars (J. Palfreyman et al. 2018), argue for a link between internal instabilities causing the glitch and crustal and magnetospheric energy deposition that lead to the observed outbursts. It is worth noting that spin-up glitches can also occur without any obvious signs of activity such as the emission of short bursts (e.g., R. Dib & V. M. Kaspi 2014; G. Younes et al. 2020b). It is unclear whether this attribute is intrinsic to the population or due to some observational bias such as our incompleteness to sample the full magnetar burst luminosity function, especially with the current large field-of- view missions such as Swift-BAT and Fermi-GBM (A. C. Collazzi et al. 2015; L. Lin et al. 2020; G. Younes et al. 2020a).
Arguably, the most intriguing result of our 1E 1841-045 investigation is the apparent shift of the source newly formed pulse peak, the second observation of its kind, following SGR 1830-0645 (G. Younes et al. 2022). Assuming the shift is occurring along the great circle at the equator of a sphere with an ∼10 km radius (observed edge on with respect to the spin axis), the rate of this apparent shift implies a speed of ≲50 m day-1, about half the rate of SGR 1830-0645. Yet, this relatively small difference can easily be accounted for when considering the large systematic uncertainties due to the exact shape of the emitting regions, the full geometry of the system, and the compactness of the stars. The two observations share other similarities as well. For instance, similar to SGR 1830 -0645, the shift in 1E 1841-045 is linear in time, and in the direction to simplify the pulse shape (a common trait of magnetars; e.g., F. P. Gavriil et al. 2011; P. Scholz et al. 2012). Moreover, the newly formed peak is narrow with a width of about 0.1 cycles, comparable to the width of the shifting peaks in SGR 1830-0645.
There are also some apparent differences between the outbursts for these two magnetars. Notably, the spectral shape of the newly formed peak in 1E 1841-045 is nonthermal, similar to the overall enhancement we observe. By contrast, the SGR 1830-0645 phase-averaged and phase-resolved spectra were favorably fit with a thermal model (G. Younes et al. 2022), without a prominent nonthermal component above around 5 keV. For 1E 1841-045, such a nonthermal signal likely originates in the inner magnetosphere from a coronal magnetic-field flux tube activated by currents and hot plasma. The weakness of any similar hard X-ray component in SGR 1830-0645 may partly be attributed to unfavorable observing geometries that could partially occult an activated flux tube. In addition, an equatorial activated region would be smaller, leading to a fainter hard X-ray component even if not occulted. On the other hand, a transient thermal X-ray component in 1E 1841-045 could easily be masked by the bright quiescent soft X-ray flux, LX ≳ 2 × 1035 erg s-1, in contrast to the much lower quiescent luminosity of SGR 1830 -0645, LX < 1033 erg s-1. In short, the spectral differences of the newly formed peaks between the two sources might reflect simple geometrical and intrinsic discrepancies in the two sources, yet the underlying physical pictures of the outbursts are similar.
The pulse-peak migration in SGR 1830-0645 was interpreted as either plastic motion of the crust, or relaxation of twisted coronal field loops. We consider these two scenarios again here for 1E 1841-045 although one should bear in mind that even if one region—the interior or the exterior—is the driver of the observed pulse-peak motion, ultimately the crust and corona are dynamically coupled through the magnetic- field lines that thread them both.
A slow plastic failure or “flow” of the crust comes about when stresses build up to beyond the elastic yield stress, meaning the crust can no longer absorb further stress while remaining static. Magnetic-field evolution in the crust, for field strengths ≳ 1014 G, naturally leads to the development of such large stresses at the age of a typical magnetar, as a consequence of Hall drift (R. Perna & J. A. Pons 2011; S. K. Lander & K. N. Gourgouliatos 2019; C. Dehman et al. 2020; Y. Kojima 2022). In the scenario that attributes pulsepeak migration to this plastic crustal motion, the observed motion is simply the plastic velocity of the crust—subject to the caveats about viewing geometry discussed above—which for a slow and steady flow is proportional to how far above the yield stress the crust is, and inversely proportional to the viscosity of the crust in this phase (S. K. Lander 2016; Y. Kojima et al. 2021). The former factor might seem to indicate that the plastic velocity should decrease gradually as stress is relieved by the plastic flow, rather than remaining roughly constant as indicated by the linear change in the pulsepeak location as a function of phase. However, the interplay between plastic flow and Hall drift is complex, with plastic flow not able to remove stress efficiently; simulations show that plastic flow can be relatively steady, or even increase stresses locally (K. N. Gourgouliatos & S. K. Lander 2021). It is not sensible to draw strong conclusions from the inferred surface velocity for 1E 1841-045 being half that of SGR 1830–0645. It is, however, worth remarking that this is not unexpected within the plastic-flow scenario. Slower plastic motion suggests a higher viscosity for the plastic phase, which in turn suggests the failing region is deeper in the crust, since this viscosity likely scales with mass density (S. K. Lander & K. N. Gourgouliatos 2019). Crustal failures at greater depths release more energy (S. K. Lander et al. 2015), which is consistent with previous observations of X-ray bursts from 1E 1841-045 above 1039 erg (L. Lin et al. 2011), in contrast with the relatively feeble bursts seen from SGR 1830–0645.
In conjunction with such plastic motions, one expects that surface and magnetospheric field lines will be mobile, exhibiting time-varying departures from a pure dipolar morphology. This interconnection was alluded to for the first observed migration of pulse peaks seen in SGR 1830-0645 (G. Younes et al. 2022). Departures from dipolar fields in magnetars were postulated in C. Thompson et al. (2002), wherein a current-activated magnetosphere adds toroidal components Bf to generate a twisted field morphology, a picture based on solar coronal loop contexts (R. Wolfson 1995). This activation could well be triggered during outbursts by subsurface energy release associated with glitches, plastic flow, or crustal failure. Currents in twisted magnetospheres are concentrated in restricted zones (A. M. Beloborodov 2009) that assume quasi-toroidal shapes in the axisymmetric, ideal MHD approximation (A. Y. Chen & A. M. Beloborodov 2017). Charges can then release their energy by bombarding the surface at the field line foot points in the twist regions and thereby generate X-ray hot spots (A. M. Beloborodov & X. Li 2016). Prior to this, these leptonic charges can radiate in the magnetosphere, colliding with the hot surface emission via the resonant inverse Compton scattering process, and if this signal extends to above a few MeV in energy, it can create e+e- pairs that can subsequently emit synchrotron radiation in the ∼1–50 keV band. These mechanisms for hard X-ray generation are discussed above, and are addressed extensively for this epoch for 1E 1841-045 in R. Stewart et al. (2025). The pulse peaks observed for 1E 1841-045 in the NuSTAR data of Figure 2 very probably correspond to such emission from somewhat confined magnetospheric regions.
Once the activation energy source abates, the radiative dissipation and surface bombardment de-energizes the plasma- loaded magnetosphere, and it is expected (A. M. Beloborodov & C. Thompson 2007; A. M. Beloborodov 2009) that the twisted fields slowly unwind and the volume of the current loops declines due to ohmic dissipation. The timescale for this decay is nominally a year or so (A. M. Beloborodov 2009) for global, axisymmetric twisted configurations, and putatively shorter for more constricted twist volumes. The fields relax progressively toward the long-term field morphology, which may possess some twist and not be purely dipolar in magnetars that exhibit persistent hard X-ray emission, as 1E 1841-045 does. During this relaxation, the surface locale of the twist foot points can shrink and migrate toward the polar regions, nominally the first and last locale of enhanced plasma loading of magnetospheres. The magnetospheric twist zones will similarly migrate and volumetrically shrink, consistent with the observed evolution and merging of pulse peaks in Figures 2 and 3. The timescale for this pulse profile evolution is somewhat longer for 1E 1841-045 than that for SGR 1830 -0645, suggesting that 1E 1841-045 possessed the larger twist field volume or energy content (or both) during this burst active phase. Future detailed simulations of nonaxisymmetric twist setups and temporal evolution are therefore highly motivated. Such theoretical studies will have the goal of assessing the connections between the pulse-peak phase separations, the evolution timescales, and the twist enhancement to the net field energy and geometry.
Finally, it is worth noting that while this is the first reported radiative outburst from 1E 1841-045, it might be due to observational biases. Previous pointed X-ray observations of the source following bursting activity, most prominently in 2010, suffered from a limited S/N or coverage in the soft and hard X-ray band. For instance, the outburst was followed up with the Swift X-Ray Telescope (XRT) providing information on the soft X-ray band, within which we only observe a 20% flux increase with our NuSTAR monitoring (Table 2; H. S. Kumar & S. Safi-Harb 2010; L. Lin et al. 2011). Given the typical short exposures of XRT and its low effective area, such an increase could easily be missed. Moreover, few RXTE observations were acquired in the aftermath of the outburst (R. Dib & V. M. Kaspi 2014), and these also suffered from a large background and short integration, which may hinder its ability to observe the pulse profile changes we report. Hence, our results highlight the importance of large throughput, low background broadband instruments such as NICER and NuSTAR. Future generation satellites such as Strobe-X (P. S. Ray et al. 2019) and HEX-P (J. A. J. Alford et al. 2024) could provide data with unprecedented quality even for such a modest outburst. This is critical to increase the sample of observed magnetar outbursts from the younger, brighter members of the population for completeness and enable population-level studies of, e.g., pulse-peak migration that is poised to grow.
4.2.		Radio Nondetection
The absence of any detectable radio emission could be explained by the following reasons: the radio emission is too faint to be detectable, the emission is beamed away from our line of sight, or the magnetar is simply not emitting at radio wavelengths. In the first case, the distance and the expected scattering from multipath propagation could reduce the radio luminosity below the sensitivity of the telescopes used in this work. The distance of 1E 1841-045 is about a factor of 2 larger than the radio-loud magnetars XTE J1810-197 (F. Camilo et al. 2006) and Swift J1818-1607 (P. Esposito et al. 2020) but similar to the radio-loud magnetars PSR J1622 -4950 (L. Levin et al. 2010) and SGR J1745-2900 (R. P. Eatough et al. 2013). Hence, the radio luminosity must be significantly lower than the known sources or impacted by other effects, such as scattering. We estimate the expected scattering timescale using the NE2001 model (J. M. Cordes & T. J. W. Lazio 2002) to be around 15 ms at 1.4 GHz (MeerKAT L band and Band 1 of the Effelsberg UBB), which is ∼0.1% of the pulse period and would not significantly impact the folded profile. Scattering impacts the detectability of faint single pulses as long as the pulse broadening timescale is longer than the intrinsic duration. The scattering at 1.4 GHz would reduce the observed fluence of a single pulse with an intrinsic duration of ∼1 ms by a factor of a few. At higher frequencies the scattering time decreases to ∼1 ms for >2.8 GHz (MeerKAT S-band and Effelsberg Band 2–5 observations) and would only impact very narrow pulses. Additionally, the radio beam might have a geometrical orientation that does not allow us to see into the radio beam, i.e., the radio beam rotates such that the line of sight does not intersect the point at which the radio emission is emitted (D. R. Lorimer & M. Kramer 2012; V. M. Kaspi & A. Beloborodov 2017).
However, the magnetar might also be intrinsically radio quiet. According to the fundamental plane of radio emission in magnetars (N. Rea et al. 2012), 1E 1841-045 lies in the radioquiet zone as its X-ray luminosity significantly exceeds the spin-down luminosity. One exception to this observational constraint is SGR 1935+2154, which showed luminous millisecond-scale radio bursts, and a month-long, faint pulsed radio component albeit having an X-ray luminosity exceeding its spin-down luminosity. Interestingly, these appeared following a spin-down glitch (G. Younes et al. 2023) event indicating that the state of the magnetosphere may play a crucial role in the ignition of magnetar radio emission (C. Thompson 2008). Despite the many more spin-up glitches observed from magnetars (R. Dib & V. M. Kaspi 2014), no subsequent radio activation has been observed. Finally, we note that the searches for radio emission presented in this work were more likely to detect pulsar-like (i.e., spin-down powered) emission than the rare, luminous, millisecond-scale radio bursts observed from SGR 1935+2154 (C. D. Bochenek et al. 2020; CHIME/FRB Collaboration et al. 2020), which have provided evidence for a magnetar origin to fast radio bursts (FRBs). Such FRB-like bursts are exceedingly rare from Galactic magnetars, and therefore unlikely to occur during the short observations presented here, but also ∼MJy flux densities may be so large as to saturate the receiving system.
Acknowledgments
This material is based upon work supported by the National Aeronautics and Space Administration under Agreement No. 80GSFC24M0006 issued through the Office of Science. G.Y. acknowledges support through NASA grants 80NSSC21K1997, 80NSSC23K1114, and 80NSSC25K7257, which are partly funding PhD students R.S. and A.V.K., and postdoctoral fellow A.M. M.G.B. thanks NASA for generous support under awards 80NSSC24K0589 and 80NSSC25K7257. W.C.G.H. acknowledges support through grant 80NSSC23K0078 from NASA. M. Ng is a Fonds de Recherche du Quebec—Nature et Technologies (FRQNT) postdoctoral fellow. L.G.S. is a Lise Meitner Group Leader, and together with M.L.B. acknowledge support from the Max Planck Society. The MeerKAT telescope is operated by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation. This work has made use of the “MPIfR S-band receiver system” designed, constructed, and maintained by funding of the MPI für Radioastronomy and the Max Planck Society. Observations used PTUSE for data acquisition, storage, and analysis, which was partly funded by the Max-Planck-Institut für Radioastronomie (MPIfR). Based on observations with the 100 m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) at Effelsberg. The UBB receiver and the Effelsberg Direct Digitisation (EDD) system are developed and maintained by the Max Planck Institute for Radioastronomy (MPIfR) and are funded by the Max Planck Gesellschaft (MPG). G.Y. thanks Alexander Philippov for the enlightening discussions pertaining to the results presented in this manuscript.
ORCID iDs
George Younesaa https://orcid.org/0000-0002-7991-028X Matthew G. Baringaa https: /orcid.org/0000-0003-4433-1365 Marlon L. Bauseaa https://orcid.org/0009-0006-3567-981X Rachael Stewartaa https: /orcid.org/0000-0002-0254-5915 Zaven Arzoumanianaa https: /orcid.org/0009-0008-6187-8753 Hoa Dinh Thiaa https: /orcid.org/0000-0001-9268-5577 Teruaki Enotoaa https://orcid.org/0000-0003-1244-3100
Keith C. Gendreauaa https: /orcid.org/0000-0001-7115-2819 Tolga Güveraa https: /orcid.org/0000-0002-3531-9842
Alice K. Hardingaa https://orcid.org/0000-0001-6119-859X
Wynn C. G. Hoaa https://orcid.org/0000-0002-6089-6836
Chin-Ping Huaa https://orcid.org/0000-0001-8551-2002
Alex Van Kootenaa https://orcid.org/0000-0002-3905-4853
Chryssa Kouveliotouaa https: /orcid.org/0000-0003-1443-593X
Niccolò Di Lallaaa https://orcid.org/0000-0002-7574-1298
Michela Negroaa https: /orcid.org/0000-0002-6548-5622
Mason Ngaa https: /orcid.org/0000-0002-0940-6563
David M. Palmeraa https://orcid.org/0000-0001-7128-0802
Laura G. Spitleraa https: /orcid.org/0000-0002-3775-8291
Zorawar Wadiasinghaa https: /orcid.org/0000-0002-9249-0515
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