The Soft X-Ray Counterpart of Hanny’s Voorwerp Near IC 2497

We report the detection in Chandra Advanced CCD Imaging Spectrometer archival data of an elongated soft (<3 keV) X-ray feature to the south of the Compton-thick active galactic nucleus (AGN) galaxy IC 2497, coincident with the emission-line feature known as Hanny’s Voorwerp. The data are consistent with the spatial correspondence between X-ray, optical emission-line, and radio features detected in nearby obscured AGNs (e.g., ESO 428-G014). The X-ray luminosity of the (0.3-3.0 keV) soft feature is ∼1.2 × 10⁴⁰ erg s^-1. We infer an [O III]/soft-X-ray ratio in the range of ∼200, consistent with the highest values measured in some of the clouds of NGC 4151. Overall, given the uncertainties, Hanny’s Voorwerp appears to be a feature consistent with the ionization cone emission of nearby AGNs. We estimate an X-ray recombination time of ∼2 × 10⁷ yr, longer than the [O III] recombination time (∼8000 yr). This suggests that extended soft X-ray components may be a better diagnostic of overall long-term activity, while detection of an [O III] HV would point to a time-limited activity burst.