A 2-d orbital period for a redback millisecond pulsar candidate in the globular cluster NGC 6397. Issue 1 (11th March 2021)

• Record Type: Journal Article
• Authors: Marcano, Manuel Pichardo; Rivera Sandoval, Liliana E; Maccarone, Thomas J; Zhao, Yue; Heinke, Craig O
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 503:Issue 1(2021)
• Page Start: L51
• Page End: L55
• Publication Date: 2021-03-11
• Subjects: globular clusters: general -- globular clusters: individual (NGC 6397) -- X-rays: binaries pulsars; Astronomy -- Research -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnrasl/slab024
• Languages: English
• ISSNs: 1745-3933

Abstract

ABSTRACT: We report optical modulation of the companion to the X-ray source U18 in the globular cluster NGC 6397. U18, with combined evidence from radio and X-ray measurements, is a strong candidate as the second redback in this cluster, initially missed in pulsar searches. This object is a bright variable star with an anomalous red colour and optical variability (∼0.2 mag in amplitude) with a periodicity ∼1.96 d that can be interpreted as the orbital period. This value corresponds to the longest orbital period for known redback candidates and confirmed systems in Galactic globular clusters and one of the few with a period longer than 1 d.