X-Ray Characterization of the Pulsar PSR J1849−0001 and Its Wind Nebula G32.64+0.53 Associated with TeV Sources Detected by H.E.S.S., HAWC, Tibet ASγ, and LHAASO

Abstract

We report on the X-ray emission properties of the pulsar PSR J1849−0001 and its wind nebula (PWN), as measured by Chandra, XMM-Newton, NICER, Swift, and NuSTAR. In the X-ray data, we detected the 38 ms pulsations of the pulsar up to ∼60 keV with high significance. Additionally, we found that the pulsar's on-pulse spectral energy distribution displays significant curvature, peaking at ≈60 keV. Comparing the phase-averaged and on-pulse spectra of the pulsar, we found that the pulsar's off-pulse emission exhibits a spectral shape that is very similar to its on-pulse emission. This characterization of the off-pulse emission enabled us to measure the >10 keV spectrum of the faint and extended PWN using NuSTAR's off-pulse data. We measured both the X-ray spectrum and the radial profiles of the PWN’s brightness and photon index, and we combined these X-ray measurements with published TeV results. We then employed a multizone emission scenario to model the broadband data. The results of the modeling suggest that the magnetic field within the PWN is relatively low (≈7 μG) and that electrons are accelerated to energies ≳400 TeV within this PWN. The electrons responsible for the TeV emission outside the X-ray PWN may propagate to ∼30 pc from the pulsar in ∼10 kyr.

Efficiency of Nonthermal Pulsed Emission from Eight MeV Pulsars

“…The s-pl model provides an acceptable fitting result (Table 2), and its parameters are N H = 5.1(3) × 10 22 cm 2 and Γ 1 = 1.48(5). Although the obtained N H is smaller than N H = 8.1(2) × 10 22 cm 2 reported in Kim et al (2024), who use the same XMM-Newton and NuSTAR data as we did, the photon index is consistent with their Γ 1 = 1.42(3) within the error. The bk-pl model improves the fitting results with an Fstatistic value of 8.2 (p = 0.00031), and the photon index (Γ 1 = 0.8(4)) below the break energy (E b = 4.9(8) keV) is consistent with ∼1.1 in previous studies (Gotthelf et al 2011;Kuiper & Hermsen 2015), in which XMM-Newton data were fit by an s-pw model.…”

“…Assuming a distance of 7 kpc to the source (Gotthelf et al 2011), the efficiency in the 0.3-150 keV bands is estimated to be η X ∼ 0.025. Kim et al (2024) suggest the existence of a peak in the spectrum at ∼60 keV, which is lower than the ∼1-5 MeV of PSRs B1509-58 and J1846-0258. As the left panel in Figure B4 shows, on the other hand, our extracted spectrum may indicate an absorption feature at around 40 keV rather than a peaking of the spectrum.…”

“…It has been discussed that the nonthermal X-ray emission is produced by the synchrotron radiation from the secondary electron/positron pairs that are produced by the pair-creation process of the GeV gamma rays (Kisaka & Tanaka 2017). For MeV pulsars, on the other hand, previous X-ray studies have collected evidence that the broadband X-ray spectrum is described by a single power law with a photon index of Γ 1 < 1.5 or by a power law with a turnover in the 1-10 keV bands (see, e.g., Chen et al 2016;Hu et al 2017; and references therein for PSR B1509-58; Kargaltsev et al 2009 for PSR J1617-5055; Madsen et al 2020for PSR J1811-1925Kuiper & Hermsen 2015 for PSR J1813-1749; Lin et al 2009 and references therein for PSR J1838-0655; Gotthelf et al 2021 for PSR J1846-0258; Gotthelf et al 2011 andKim et al 2024 for PSR J1849-0001; and Lu et al 2007 for PSR J1930+1852). We also refer to Kuiper & Hermsen (2015) for a comprehensive observational study of the hard X-ray/soft gamma-ray emission of the young pulsars.…”

Multiband Nonthermal Radiative Study of PeVatron Candidate Pulsar Wind Nebula HESS J1849-000

“…Here, the value of δ depends on the property of turbulence in the ambient medium, and the different values of δ represent different diffusion forms (for details, see Zhu et al 2021Zhu et al , 2023. Following Kim et al (2024), we assumed that the turbulence is a classical Kolmogorov turbulence within the nebula, and so the value of δ was chosen to be one-third. According to Parker (1965), the diffusion timescale of particles τ diff is described by…”

“…To date, there is no known radio PWN coincident with HESS J1849-000 (Green 2014;Anderson et al 2017;Green 2019). Very recently, Kim et al (2024) used Chandra, XMM-Newton, NICER, Swift, and NuSTAR to measure both the X-ray spectrum and the radial profiles of the PWN's brightness and photon index, and then employed a spatially dependent emission scenario to explain the broadband data. In addition, Gagnon et al (2023) also explored the PWN morphology on arcsecond and arcminute scales and measured the spectra of different regions of the PWN by analyzing the new and old Chandra data.…”