The Nonstandard Properties of a "Standard" PWN: Unveiling the Mysteries of PWN G21.5-0.9 Using its IR and X-ray emission

Abstract

The evolution of a pulsar wind nebula (PWN) depends on properties of the progenitor star, supernova, and surrounding environment. As some of these quantities are difficult to measure, reproducing the observed dynamical properties and spectral energy distribution (SED) with an evolutionary model is often the best approach in estimating their values. G21.5-0.9, powered by the pulsar J1833-1034, is a well observed PWN for which previous modeling efforts have struggled to reproduce the observed SED. In this study, we reanalyze archival infrared (IR; Herschel, Spitzer) and X-ray (Chandra, NuSTAR, Hitomi) observations. The similar morphology observed between IR line and continuum images of this source indicates that a significant portion of this emission is generated by surrounding dust and gas, and not synchrotron radiation from the PWN. Furthermore, we find the broadband X-ray spectrum of this source is best described by a series of power laws fit over distinct energy bands. For all X-ray detectors, we find significant softening and decreasing unabsorbed flux at higher energy bands. Our model for the evolution of a PWN is able to reproduce the properties of this source when the supernova ejecta has a low initial kinetic energy $E_{\mathrm{sn}}\approx 1.2\times 10^{50}\mathrm{ergs}$ and the spectrum of particles injected into the PWN at the termination shock is softer at low energies. Lastly, our hydrodynamical modeling of the SNR can reproduce its morphology if there is a significant density increase of the ambient medium $\sim 1.8$ pc north of the explosion center.

24 pages, 15 figures, accepted for publication in The Astrophysical Journal (accepted manuscript); corrected typo in standard deviation equation of appendix

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• Spectral Break of Energetic Pulsar Wind Nebulae Detected with Wideband X-ray Observations
• Pulsar Wind Nebulae
• Fermi-LAT Gamma-ray Emission Discovered from the Composite Supernova Remnant B0453-685 in the Large Magellanic Cloud
• Spatio-spectral-temporal Modelling of Two Young Pulsar Wind Nebulae
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• New Hard X-Ray and Multiwavelength Study of the PeVatron Candidate PWN G0.9+0.1 in the Galactic Center Region