Learning about the magnetar Swift J1834.9-0846 from its wind nebula

Jonathan Granot, Ramandeep Gill, George Younes, Joseph (Yosi) Gelfand, Alice Harding, Chryssa Kouveliotou, Matthew G. Baring

Research output: Contribution to journalArticle

Abstract

The first wind nebula around a magnetar was recently discovered in X-rays around Swift J1834.9-0846. We study this magnetar's global energetics and the properties of its particle wind or outflows. At a distance of ~4 kpc, Swift J1834.9-0846 is located at the centre of the supernova remnant (SNR) W41 whose radius is ~19 pc, an order of magnitude larger than that of the X-ray nebula (~2 pc). The association with SNR W41 suggests a common age of ~5-100 kyr, while its spin-down age is 4.9 kyr. A small natal kick velocity may partly explain why a wind nebula was detected around this magnetar but not around other magnetars, most of which appear to have larger kick velocities and may have exited their birth SNR. We find that the GeV and TeV source detected by Fermi/Large Area Telescope (LAT) and High Energy Spectroscopic System (H.E.S.S.), respectively, of radius ~11 pc is most likely of hadronic origin. The dynamics and internal structure of the nebula are examined analytically to explain the nebula's current properties. Its size may naturally correspond to the diffusiondominated cooling length of the X-ray emitting e+e- pairs. This may also account for the spectral softening of the X-ray emission from the nebula's inner to outer parts. The analysis of the X-ray synchrotron nebula implies that (i) the nebular magnetic field is ≳11 μG (and likely ≲30 μG), and (ii) the nebula is not powered predominantly by the magnetar's quiescent spin-down-powered MHD wind, but by other outflows that contribute most of its energy. The latter are most likely associated with the magnetar's bursting activity, and possibly dominated by outflows associated with its past giant flares. The energy source for the required outflows cannot be the decay of the magnetar's dipole field alone, and is most likely the decay of its much stronger internal magnetic field.

Original languageEnglish (US)
Pages (from-to)4895-4926
Number of pages32
JournalMonthly Notices of the Royal Astronomical Society
Volume464
Issue number4
DOIs
StatePublished - Jan 1 2017

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magnetars
nebulae
learning
outflow
supernova remnants
magnetic field
x rays
softening
energy
energetics
radii
cooling
decay
energy sources
magnetic fields
flares
synchrotrons
telescopes
dipoles

Keywords

  • Diffusion
  • Hydrodynamics
  • ISM: supernova remnants
  • Magnetic fields
  • Outflows
  • Stars: magnetars
  • Stars: winds

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Learning about the magnetar Swift J1834.9-0846 from its wind nebula. / Granot, Jonathan; Gill, Ramandeep; Younes, George; Gelfand, Joseph (Yosi); Harding, Alice; Kouveliotou, Chryssa; Baring, Matthew G.

In: Monthly Notices of the Royal Astronomical Society, Vol. 464, No. 4, 01.01.2017, p. 4895-4926.

Research output: Contribution to journalArticle

Granot, J, Gill, R, Younes, G, Gelfand, JY, Harding, A, Kouveliotou, C & Baring, MG 2017, 'Learning about the magnetar Swift J1834.9-0846 from its wind nebula', Monthly Notices of the Royal Astronomical Society, vol. 464, no. 4, pp. 4895-4926. https://doi.org/10.1093/mnras/stw2554
Granot, Jonathan ; Gill, Ramandeep ; Younes, George ; Gelfand, Joseph (Yosi) ; Harding, Alice ; Kouveliotou, Chryssa ; Baring, Matthew G. / Learning about the magnetar Swift J1834.9-0846 from its wind nebula. In: Monthly Notices of the Royal Astronomical Society. 2017 ; Vol. 464, No. 4. pp. 4895-4926.
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AB - The first wind nebula around a magnetar was recently discovered in X-rays around Swift J1834.9-0846. We study this magnetar's global energetics and the properties of its particle wind or outflows. At a distance of ~4 kpc, Swift J1834.9-0846 is located at the centre of the supernova remnant (SNR) W41 whose radius is ~19 pc, an order of magnitude larger than that of the X-ray nebula (~2 pc). The association with SNR W41 suggests a common age of ~5-100 kyr, while its spin-down age is 4.9 kyr. A small natal kick velocity may partly explain why a wind nebula was detected around this magnetar but not around other magnetars, most of which appear to have larger kick velocities and may have exited their birth SNR. We find that the GeV and TeV source detected by Fermi/Large Area Telescope (LAT) and High Energy Spectroscopic System (H.E.S.S.), respectively, of radius ~11 pc is most likely of hadronic origin. The dynamics and internal structure of the nebula are examined analytically to explain the nebula's current properties. Its size may naturally correspond to the diffusiondominated cooling length of the X-ray emitting e+e- pairs. This may also account for the spectral softening of the X-ray emission from the nebula's inner to outer parts. The analysis of the X-ray synchrotron nebula implies that (i) the nebular magnetic field is ≳11 μG (and likely ≲30 μG), and (ii) the nebula is not powered predominantly by the magnetar's quiescent spin-down-powered MHD wind, but by other outflows that contribute most of its energy. The latter are most likely associated with the magnetar's bursting activity, and possibly dominated by outflows associated with its past giant flares. The energy source for the required outflows cannot be the decay of the magnetar's dipole field alone, and is most likely the decay of its much stronger internal magnetic field.

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