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Evidence for 1.01 s Pulsations of the Central Compact Object in the Supernova Remnant RCW 103 with ASCA, XMM-Newton, and NuSTAR

Kazuo Makishima, Nagomi Uchida, Teruaki Enoto

TL;DR

This study addresses the puzzling long-period variability of the Central Compact Object 1E 1613 in RCW 103 by testing for a fast ~1.01 s spin period hidden by a 6.67 hr modulation. Using six archival X-ray datasets (ASCA93, XMM01/05/16, NuS16/17) and two complementary timing techniques—phase-sorted periodograms and demodulation with a fixed long-period T—the authors uncover consistent ~1.01 s pulsations that line up on a linear spin-down trend: $P(t) = 1.0094300(2) + 1.097(2) imes10^{-12} t$ s. The inferred spin-down rate, characteristic age $ au_c oughly 14.7$ kyr, dipole field $B_d oughly 4.6 imes10^{13}$ G, and toroidal field $B_t oughly 7 imes10^{15}$ G support a magnetar-like, magnetically powered neutron star, with the long 6.67 hr cycle explained as a beat between rotation and free precession in a mildly aspherical star. Across energy bands and epochs, the pulsation is revealed most clearly in harder X-ray emission and via careful timing corrections, underscoring complex emission geometry and evolution during 2016 activity. The findings constrain NS deformation, precession, and magneto-rotational energy budgets, and provide a framework for applying similar demodulation techniques to other slow-rotating compact objects. This advances our understanding of the magnetar–CCO connection and the role of precession in shaping X-ray timing signals in young neutron stars.

Abstract

The neutron-star X-ray source 1E 161348-5055, associated with the supernova remnant RCW 103, exhibits clear intensity variations with a period of 6.67 hr. To clarify the nature of this object and its long periodicity, detailed timing studies were applied to its archival X-ray data, taken with ASCA (in 1993), XMM-Newton (in 2001, 2005, and 2016), and NuSTAR (2016 and 2017). It was assumed that the 6.67 hr period arises due to the beat between the rotation and free precession periods of the star that is slightly aspherical. By removing timing perturbations to be caused by this long periodicity, the six data sets consistently yielded evidence for pulsations at periods of P~1.01 s, to be interpreted as the objects' spin period, although the optimum energy range differed among the data sets. The measured six periods accurately line up on a linear spin-down trend of dP/dt = 1.097x 10^{-12} s/s. The object is implied to have a characteristic age of 14.7 kyr, a spin-down luminosity of 4.2x10^{34} erg/s, which is insufficient to power the X-ray luminosity, a dipole magnetic field of ~4.6x10^{13} G, and a toroidal field of ~7 x10^{15} G. Its similarity and dissimilarity to magnetars are discussed. An emission geometry, which crudely explain these results, is presented.

Evidence for 1.01 s Pulsations of the Central Compact Object in the Supernova Remnant RCW 103 with ASCA, XMM-Newton, and NuSTAR

TL;DR

This study addresses the puzzling long-period variability of the Central Compact Object 1E 1613 in RCW 103 by testing for a fast ~1.01 s spin period hidden by a 6.67 hr modulation. Using six archival X-ray datasets (ASCA93, XMM01/05/16, NuS16/17) and two complementary timing techniques—phase-sorted periodograms and demodulation with a fixed long-period T—the authors uncover consistent ~1.01 s pulsations that line up on a linear spin-down trend: s. The inferred spin-down rate, characteristic age kyr, dipole field G, and toroidal field G support a magnetar-like, magnetically powered neutron star, with the long 6.67 hr cycle explained as a beat between rotation and free precession in a mildly aspherical star. Across energy bands and epochs, the pulsation is revealed most clearly in harder X-ray emission and via careful timing corrections, underscoring complex emission geometry and evolution during 2016 activity. The findings constrain NS deformation, precession, and magneto-rotational energy budgets, and provide a framework for applying similar demodulation techniques to other slow-rotating compact objects. This advances our understanding of the magnetar–CCO connection and the role of precession in shaping X-ray timing signals in young neutron stars.

Abstract

The neutron-star X-ray source 1E 161348-5055, associated with the supernova remnant RCW 103, exhibits clear intensity variations with a period of 6.67 hr. To clarify the nature of this object and its long periodicity, detailed timing studies were applied to its archival X-ray data, taken with ASCA (in 1993), XMM-Newton (in 2001, 2005, and 2016), and NuSTAR (2016 and 2017). It was assumed that the 6.67 hr period arises due to the beat between the rotation and free precession periods of the star that is slightly aspherical. By removing timing perturbations to be caused by this long periodicity, the six data sets consistently yielded evidence for pulsations at periods of P~1.01 s, to be interpreted as the objects' spin period, although the optimum energy range differed among the data sets. The measured six periods accurately line up on a linear spin-down trend of dP/dt = 1.097x 10^{-12} s/s. The object is implied to have a characteristic age of 14.7 kyr, a spin-down luminosity of 4.2x10^{34} erg/s, which is insufficient to power the X-ray luminosity, a dipole magnetic field of ~4.6x10^{13} G, and a toroidal field of ~7 x10^{15} G. Its similarity and dissimilarity to magnetars are discussed. An emission geometry, which crudely explain these results, is presented.
Paper Structure (46 sections, 29 equations, 17 figures, 2 tables)

This paper contains 46 sections, 29 equations, 17 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Observations
  3. Data selection
  4. ASCA observation
  5. XMM-Newton observations
  6. NuSTAR observations
  7. Data analysis and results
  8. Basic strategy
  9. Period search range
  10. Periodograms (PGs) and $Z_m^2$ statistics
  11. Period increment steps
  12. Period change rate
  13. The 69 ms pulsar
  14. 1E 1613 in the 1993 ASCA data (ASCA93)
  15. Raw periodograms
  16. ...and 31 more sections

Figures (17)

  • Figure 1: A PG ($m=2$) of the 69 ms pulsar AXS J161730$-$505505, from the 3--10 keV ASCA93 data. The ordinate is logarithmic, to show side lobes. Alt Text: A periodogram of the 69 millisecond pulsar from ASCA93.
  • Figure 2: (a) A phase-sorted PG for 2.5--12 keV CCO photons in ASCA93, calculated employing $m=4$ and $M_{\rm seg}=5$. The 10--30 s region is truncated. (b) Same, but derived using the demodulation method assuming $T=24.0$ ks. (c) Details of the PG in (a) around Peak B. Results with $M_{\rm seg}=1$ (brown with dots), $5$ (solid black), and $10$ (dashed green) are overlaid. The ordinate refers to equation (\ref{['eq:scaled_Z2']}). A horizontal arrow shows the expected fringe separation. (d) Details of the PG in (c) around Peak B. The amplitude $A$ is shown in dashed blue (right ordinate). The dotted brown curve labeled "raw" is the result before demodulation. Alt Text: Four periodograms of 1E 1613 obtained with ASCA, in photon energies of 2.5 to 12 kilo-electronvolts. Top two cover the 0.3 to 30 second period range, whereas bottom two are their expanded views.
  • Figure 3: (a) Demodulated $Z_m^2$ values from the ASCA93 CCO data in 2.5--12 keV, calculated with different $m$ and shown against the assumed value of $T$. The pulse period is constrained to a vicinity of $P_{93}$. (b) A control study using the 69 ms pulsar in ASCA93, in the same energy range. The optimum value of $A$ is shown in the lower trace (blue), using the right ordinate. Alt Text: Top panel shows the significance of the 1.01 second pulsation with ASCA, as a function of the modulation period from 7 to 100 kilo-seconds. Bottom panel is a control study using the 69 millisecond pulsar.
  • Figure 4: Pulse profiles of 1E 1613 in ASCA93. (a) Results in 2.5--12 keV folded at $P_{93}$, before (dashed black) and after (solid red) the demodulation using $T=24.0$ ks. (b) Demodulated pulse profiles in the 2.5--3.0 keV and 3.5--12 keV energy ranges. Alt Text: Folded pulse profiles with ASCA.
  • Figure 5: Results on 1E 1613 from the 2.7--10 keV XMM01 data. (a) A demodulated PG with $m=4$, derived in the same way as figure \ref{['fig:f2_Pscan_ASCA93']}b but over a more limited period range of equation (\ref{['eq:P_search_range']}). The downward arrow indicates $P_{93}$. (b) An expanded view (in solid black) of panel (a) around the peak, and the optimum $A$ in dotted blue (right ordinate). The $m=4$ PG before the demodulation (labeled "raw") is superposed as an ocher line. Alt Text: Periodograms with XMM-Newton in 2001, in 2.7 to 10 kilo-elecronvolts.
  • ...and 12 more figures