IXPE Observations of the Pulsar 4U 1626-67
: Ng Mason, Marshall Herman, Rogantini Daniele, Heyl Jeremy, Tsygankov Sergey, Poutanen Juri, Costa Enrico, Zane Silvia, Malacaria Christian, Chakrabarty Deepto, Schulz Norbert
: Home High Energy Astrophysics Division Meetings
Publisher: American Institute of Physics
: 2023
: Bulletin of the American Astronomical Society
: HEAD20 Abstracts : The 20th Meeting of the High Energy Astrophysics Division
: 55
: 4
: 0002-7537
: 2330-9458
: https://baas.aas.org/pub/2023n4i109p05/release/1
: https://research.utu.fi/converis/portal/detail/Publication/387031781
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).