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IXPE Observations of the Pulsar 4U 1626-67




AuthorsNg Mason, Marshall Herman, Rogantini Daniele, Heyl Jeremy, Tsygankov Sergey, Poutanen Juri, Costa Enrico, Zane Silvia, Malacaria Christian, Chakrabarty Deepto, Schulz Norbert

Conference nameHome High Energy Astrophysics Division Meetings

PublisherAmerican Institute of Physics

Publication year2023

JournalBulletin of the American Astronomical Society

Book title HEAD20 Abstracts : The 20th Meeting of the High Energy Astrophysics Division

Volume55

Issue4

ISSN0002-7537

eISSN2330-9458

Web address https://baas.aas.org/pub/2023n4i109p05/release/1

Self-archived copy’s web addresshttps://research.utu.fi/converis/portal/detail/Publication/387031781


Abstract

We report on new X-ray spectropolarimetric observations from the recently launched Imaging X-ray Polarimetry Explorer (IXPE) of the ultracompact low-mass X-ray binary system 4U 1626-67. We also report on supplementary observations taken by NICER and Chandra/HETGS around the IXPE observation window. We will present energy-resolved and pulse phase-resolved spectropolarimetric 2-8 keV IXPE observations of 4U 1626-67 and discuss implications for our understanding of accretion geometries in accreting pulsars. NICER provided complementary spectral and timing results over the 0.3-10 keV band, with an emphasis on the soft band; Chandra/HETGS allowed for detailed characterization of the plasma in the accretion disk. 4U 1626-67 is an interesting system as it hosts a slowly spinning accretion-powered pulsar (~7.7 s) with a strong magnetic field (B ~ 1012 G) in a ~42 minute ultracompact orbit around a very low mass hydrogen-depleted companion. It has exhibited two episodes of long-term torque reversals in 1990 and 2008, and it is currently in the spin-up state; the pulse profiles also exhibit strong energy dependence. The quiescent state is also occasionally punctured by >100 s-long flaring episodes. In addition, the system hosts a highly collisionally-ionized plasma in the accretion disk and complex emission line phenomena around 1 keV (attributed to Ne X and O VIII).


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