New candidates for magnetar counterparts from a deep search with the Hubble Space Telescope

Chrimes, A A and Levan, A J and Fruchter, A S and Groot, P J and Kouveliotou, C and Lyman, J D and Tanvir, N R and Wiersema, K (2022) New candidates for magnetar counterparts from a deep search with the Hubble Space Telescope. Monthly Notices of the Royal Astronomical Society, 512 (4). pp. 6093-6103. ISSN 0035-8711

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Abstract

We report the discovery of six new magnetar counterpart candidates from deep near-infrared Hubble Space Telescope imaging. The new candidates are among a sample of nineteen magnetars for which we present HST data obtained between 2018–2020. We confirm the variability of previously established near-infrared counterparts, and newly identify candidates for PSR J1622-4950, Swift J1822.3-1606, CXOU J171405.7-381031, Swift J1833-0832, Swift J1834.9-0846 and AX J1818.8-1559 based on their proximity to X-ray localisations. The new candidates are compared with the existing counterpart population in terms of their colours, magnitudes, and near-infrared to X-ray spectral indices. We find two candidates for AX J1818 which are both consistent with previously established counterparts. The other new candidates are likely to be chance alignments, or otherwise have a different origin for their near-infrared emission not previously seen in magnetar counterparts. Further observations and studies of these candidates are needed to firmly establish their nature.