A wide-field X-ray search for the Geminga pulsar halo with SRG/ART-XC

TL;DR

This study uses wide-field X-ray observations with SRG/ART-XC to image the Geminga pulsar region, setting new constraints on its X-ray halo and magnetic environment through simulations and modeling.

Contribution

First wide-field imaging of Geminga's X-ray halo with SRG/ART-XC, providing new constraints and methodology for pulsar halo searches.

Findings

No significant X-ray halo detected, setting upper limits.

Constraints on Geminga's magnetic field strength are consistent with other studies.

Simulation shows 68% detection probability with 20-day exposure for certain magnetic fields.

Abstract

Searches for the putative large-scale X-ray halo around the Geminga pulsar have been extensively performed using various narrow field-of-view X-ray telescopes. In this paper, we present wide-field scanning observation of Geminga with SRG/ART-XC. Our X-ray analysis provides, for the first time, direct imaging of a $3.5^\circ \times 3.5^\circ$ region in the $4-12$ keV energy band, comparable in extent to the expected Geminga emission. The ART-XC observation provides a highly uniform sky coverage without strong vignetting effects. The synchrotron X-ray halo flux was predicted using a physical model based on particle injection, diffusion, and cooling over the pulsar's lifetime, as well as the spectral and spatial properties of the synchrotron X-ray and inverse-Compton gamma-ray emissions. The model is tuned to reproduce existing multiwavelength data from X-ray upper limits and GeV to TeV gamma-ray observations. After accounting for the high particle background and its uncertainties, no significant emission is found in the assumed source region, and X-ray flux upper limits are derived. These limits are less constraining by up to a factor of three with respect to existing results obtained with narrow field-of-view telescopes and longer exposure times. Nonetheless, we place direct and independent constraints on Geminga's ambient magnetic field strength, which are compatible with other studies. Our methodology, including simulation for longer observation times, is applied for the first time to the wide field-of-view search for pulsar halos. Using extensive simulations, we also show that a 68% probability of detecting the Geminga pulsar halo can be achieved with a 20-day SRG/ART-XC exposure for a 3 $\mu G$ magnetic field.