NICER Observation of the Temporal and Spectral Evolution of Swift J1818.0−1607: A Missing Link between Magnetars and Rotation-powered Pulsars
Abstract
We report on the hard X-ray burst and the first ~100 days of NICER monitoring of the soft X-ray temporal and spectral evolution of the newly discovered magnetar Swift J1818.0−1607. The burst properties are typical of magnetars with a duration of T₉₀ = 10 ± 4 ms and a temperature of kT = 8.4 ± 0.7 keV. The 2–8 keV pulse shows a broad, single-peak profile with a pulse fraction increasing with time from 30% to 43%. The NICER observations reveal strong timing noise with varying erratically by a factor of 10, with an average long-term spin-down rate of ν = (−2.48±0.03)×10⁻¹¹~s⁻², implying an equatorial surface magnetic field of 2.5 × 10¹⁴ G and a young characteristic age of ~470 yr. We detect a large spin-up glitch at MJD 58928.56 followed by a candidate spin-down glitch at MJD 58934.81, with no accompanying flux enhancements. The persistent soft X-ray spectrum of Swift J1818.0−1607 can be modeled as an absorbed blackbody with a temperature of ~1 keV. Its flux decayed by ~60% while the modeled emitting area decreased by ~30% over the NICER observing campaign. This decrease, coupled with the increase in the pulse fraction, points to a shrinking hot spot on the neutron star surface. Assuming a distance of 6.5 kpc, we measure a peak X-ray luminosity of 1.9 × 10³⁵ erg s⁻¹, lower than its spin-down luminosity of 7.2 × 10³⁵ erg s⁻¹. Its quiescent thermal luminosity is ≾1.7 × 10³⁴ erg s⁻¹, lower than those of canonical young magnetars. We conclude that Swift J1818.0−1607 is an important link between regular magnetars and high-magnetic-field, rotation-powered pulsars.
Additional Information
© 2020 The American Astronomical Society. Received 2020 June 6; revised 2020 August 18; accepted 2020 August 27; published 2020 October 7. We thank Professor Victoria Kaspi for useful discussions and the anonymous reviewer for valuable comments that improved this paper. This work was supported by the National Aeronautics and Space Administration (NASA) through the NICER mission and the Astrophysics Explorers Program. The NICER observation campaign was performed under the NICER GO2 program 3056 "Magnetic Energy Dissipation of Magnetar Outbursts Studied via Multiwavelength Follow-up Observation" (PI: Teruaki Enoto). This work partly made use of data supplied by the UK Swift Science Data Centre at the University of Leicester, and observations obtained with XMM-Newton and the ESA science mission with instruments and contributions directly funded by the ESA member states and NASA. C.-P.H. acknowledges support from the Japan Society for the Promotion of Science (JSPS; ID: P18318). T.G. has been supported in part by the Royal Society Newton Advanced Fellowship, NAF\R2\180592, and the Turkish Republic, Directorate of Presidential Strategy and Budget project, 2016K121370. T.E. has been supported by the JSPS/MEXT KAKENHI grant Nos. 16H02198 18H01246 and the Hakubi projects of Kyoto University and RIKEN. C.M. is supported by the NASA Postdoctoral Program at the Marshall Space Flight Center, administered by the Universities Space Research Association under contract with NASA. Z.W. acknowledges support from the NASA postdoctoral program. A portion of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This work has made use of the NASA Astrophysics Data System. Facility: NICER. - Software: HEASoft, XSPEC.Attached Files
Published - Hu_2020_ApJ_902_1.pdf
Accepted Version - 2009.00231.pdf
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Additional details
- Eprint ID
- 105908
- Resolver ID
- CaltechAUTHORS:20201008-073229255
- NASA/JPL/Caltech
- ESA Member States
- P18318
- Japan Society for the Promotion of Science (JSPS)
- NAF\R2\180592
- Royal Society
- 2016K121370
- Turkish Republic, Directorate of Presidential Strategy and Budget
- 16H02198
- Japan Society for the Promotion of Science (JSPS)
- 18H01246
- Japan Society for the Promotion of Science (JSPS)
- Kyoto University
- RIKEN
- NASA Postdoctoral Program
- Created
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2020-10-08Created from EPrint's datestamp field
- Updated
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2021-11-16Created from EPrint's last_modified field