Variable hard x-ray emission from the central star of the Eskimo nebula

• Main Authors: Guerrero, Martín A., Toalá, J. A., Chu, You-Hua
• Other Authors: Ministerio de Economía y Competitividad (España), European Commission, Ministerio de Ciencia, Innovación y Universidades (España), Universidad Nacional Autónoma de México, Ministry of Science and Technology (Taiwan)
• Format: Article in Journal/Newspaper
• Language: English
• Published: IOP Publishing 2019
• Subjects: Papiit; eskimo*
• Online Access: http://hdl.handle.net/10261/198858; https://doi.org/10.3847/1538-4357/ab4256; https://doi.org/10.13039/501100003329; https://doi.org/10.13039/501100005739; https://doi.org/10.13039/501100000780

The central star of NGC 2392 shows the hardest X-ray emission among central stars of planetary nebulae (CSPNe). The recent discovery of a spectroscopic companion with an orbital period of 1.9 days could provide an explanation for its hard X-ray emission, as well as for the collimation of its fast outflow. Here, we analyze the available Chandra and XMM-Newton X-ray observations to determine accurately the spectral and temporal variation properties of the CSPN of NGC 2392. The X-ray emission can be described by an absorbed thermal plasma model with temperature 26(-5)(+8) MK and X-ray luminosity (8.7 +/- 1.0) x 10(30) erg s(-1). No long-term variability is detected in the X-ray emission level, but the Chandra light curve is suggestive of short-term variations with a period similar to 0.26 days. The possible origins of this X-ray emission are discussed. X-ray emission from the coronal activity of a companion or shocks in the stellar wind can be ruled out. Accretion of material from an unseen main-sequence companion onto the CSPN or from the CSPN wind onto a white dwarf companion are the most plausible origins for its hard X-ray emission, although the mismatch between the rotational period of the CSPN and the modulation timescale of the X-ray emission seems to preclude the former possibility. © 2019. The American Astronomical Society. All rights reserved. M.A.G. acknowledges financial support by grants AYA 2014-57280-P and PGC2018-102184-B-I00, co-funded with FEDER funds, and from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709). J.A.T. and M.A.G. are funded by UNAM DGAPA PAPIIT project IA100318. Y.H.C. is supported by Taiwanese Ministry of Science and Technology grant MOST 108-2811-M-001-587. Peer reviewed