Hitomi X-ray observation of the pulsar wind nebula G21.5−0.9

Abstract

We present results from the Hitomi X-ray observation of a young composite-type supernova remnant (SNR) G21.5−0.9, whose emission is dominated by the pulsar wind nebula (PWN) contribution. The X-ray spectra in the 0.8–80 keV range obtained with the Soft X-ray Spectrometer (SXS), Soft X-ray Imager, and Hard X-ray Imager (HXI) show a significant break in the continuum as previously found with the NuSTAR observation. After taking into account all known emissions from the SNR other than the PWN itself, we find that the Hitomi spectra can be fitted with a broken power law with photon indices of Γ1 = 1.74 ± 0.02 and Γ2 = 2.14 ± 0.01 below and above the break at 7.1 ± 0.3 keV, which is significantly lower than the NuSTAR result (∼9.0 keV). The spectral break cannot be reproduced by time-dependent particle injection one-zone spectral energy distribution models, which strongly indicates that a more complex emission model is needed, as suggested by recent theoretical models. We also search for narrow emission or absorption lines with the SXS, and perform a timing analysis of PSR J1833−1034 with the HXI and the Soft Gamma-ray Detector. No significant pulsation is found from the pulsar. However, unexpectedly, narrow absorption line features are detected in the SXS data at 4.2345 keV and 9.296 keV with a significance of 3.65 σ. While the origin of these features is not understood, their mere detection opens up a new field of research and was only possible with the high resolution, sensitivity, and ability to measure extended sources provided by an X-ray microcalorimeter.

The deepestChandraX-ray study of the plerionic supernova remnant G21.5−0.9

“…Seward et al 2006;Hester 2008). It is found that the standard MHD model ran into problems to explain the spectral index distribution and surface brightness profile in the outer part of the nebula (Amato et al 2000;Slane et al 2004). The polarization measurements (e.g.…”

“…Nynka et al (2014) used NuSTAR observations up to 40 keV and found evidence of the knot and limb features indicating non-thermal emission processes, with a break at 9 keV in the PWN spectrum. This break was most recently refined to 7.1 keV using Hitomi's broadband coverage (Aharonian et al (2018)). The distance to the SNR has been estimated by several authors to be in the 4.3-5.1 kpc range (e.g., Safi-Harb et al (2001); Camilo et al (2006); Bietenholz & Bartel (2008); Kilpatrick et al (2016)).…”

“…Nynka et al (2014) used NuSTAR observations up to 40 keV and found evidence of the knot and limb features indicating non-thermal emission processes, with a break at 9 keV in the PWN spectrum. This break was most recently refined to 7.1 keV using Hitomi's broadband coverage (Aharonian et al (2018)).…”

Splitting of a photon by an atomic ion

“…A strongly pronounced effect of the angular anisotropy of the scattered radiation in the corresponding proposed experimental schemes is established. The theory allows modification by replacing the δ-Dirac-function in Fermi's 'golden rule' with the Gaussian-Laplace spectral function to account for the nonzero spectral resolution width of the proposed experiment (see, for example, Γ beam ∼ = 5 eV in astrophysics [14]). Extension beyond the dipole approximation framework for the contact interaction operator, and as a result, taking into account the Tamm-Dancoff approximation for N > 2 'particles' in the Feynman diagram dissections, is a subject of future investigations.…”

The scientific results from the X-ray observatory Hitomi

“…G21.5−0.9 is one of the composite-type supernova remnants (SNRs) whose emission is dominated by a pulsar wind nebula. A blind search for the emission/absorption line detected a couple of absorption lines at 4.235 keV and 9.296 keV at more than 3σ level [37]. The spectra in these…”