Geminga's pulsar halo: an X-ray view

Abstract

Geminga is the first pulsar around which a remarkable TeV gamma-ray halo extending over a few degrees was discovered by MILAGRO, HAWC and later by H.E.S.S., and by Fermi-LAT in the GeV band. More middle-aged pulsars have exhibited gamma-ray halos, and they are now recognized as an emerging class of Galactic gamma-ray sources. The emission appears in the late evolution stage of pulsars, and is most plausibly explained by inverse Compton scattering of CMB and interstellar photons by relativistic electrons and positrons escaping from the pulsar wind nebulae. These observations pose a number of theoretical challenges. Tackling these questions requires constraining the ambient magnetic field properties, which can be achieved through X-ray observations. If the gamma-ray halos originate from a distribution of highly energetic electrons, synchrotron losses in the ambient magnetic fields of the same particles are expected to produce a diffuse X-ray emission with a similar spatial extension. We present the most comprehensive X-ray study of the Geminga pulsar halo to date, utilising archival data from XMM-Newton and NuSTAR. Our X-ray analysis covers a broad bandwidth ($0.5-79$ keV) and large field of view ($\sim 4^{\circ }$) for the first time. This is achieved by accurately measuring the background over the entire field of view, and taking into account both focused and stray-light X-ray photons with NuSTAR. We find no significant emission and set robust constraints on the X-ray halo flux. These are translated to stringent constraints on the ambient magnetic field strength and the diffusion coefficient by using a physical model considering particle injection, diffusion and cooling over the pulsar's lifetime, which is tuned by fitting multi-wavelength data. Our novel methodology for modelling and searching for synchrotron X-ray halos can be applied to other pulsar halo candidates.

15 pages, 11 figures. Comments are welcomed. v2: Few comments added. Matches version submitted to A&A

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Cited by in corpus (10)

• Disclosing the catalog pulsars dominating the Galactic positron flux
• Anisotropic Diffusion of $e^{\pm }$ in Pulsar Halos over Multiple Coherence of Magnetic Fields
• On the origin of the X-ray emission surrounding PSR B0656+14 in the eROSITA Cal-PV data
• The environment of TeV halo progenitors
• PHECT: A lightweight computation tool for pulsar halo emission
• The Potential for Hadronic Particle Acceleration in Galactic Pulsar Wind Nebulae
• Investigating the mysterious nature of 1LHAASO J1740+0948u through deep XMM-Newton observations
• Diagnosing Interstellar Magnetic Turbulence with TeV Pulsar Halos
• Possible evidence for extended X-ray emission surrounding PSR B0656+14 with eROSITA
• Method for testing diffusive shock acceleration and diffusion propagation of 1-100 TeV cosmic electrons with multiwavelength observations of the Geminga halo and pulsar wind nebula