The Intrabinary Shock and Companion Star of Redback Pulsar J2215+5135

Abstract

PSR J2215+5135 (J2215) is a `redback' spider pulsar, where the intrabinary shock (IBS) wraps around the pulsar rather than the stellar-mass companion. Spider orbital light curves are modulated, dominated by their binary companion thermal emission in the optical bands and by IBS synchrotron emission in the X-rays. We report on new XMM-Newton X-ray and U-band observations of J2215. We produce orbital light curves and use them to model the system properties. Our best-fit optical light model gives a neutron star mass $M_{NS}=1.98\pm 0.08$ M${}_{\odot }$, lower than previously reported. However, uncertainty in the stellar atmosphere metallicity, a parameter to which J2215 is unusually sensitive, requires us to consider an acceptable systematic plus statistical range of $M_{NS}\sim 1.85-2.3$ M${}_{\odot }$. From the X-ray analysis, we find that the IBS wraps around the pulsar, but with a pulsar wind to companion wind momentum ratio unusually close to unity, implying a flatter IBS geometry than seen in other spiders. Estimating the companion wind momentum and speed from the X-ray light curve, we find a companion mass-loss rate of ${\dot{M}}_c\gtrsim 10^{-10}$ M${}_{\odot }$ yr${}^{-1}$, so that J2215 may become an isolated millisecond pulsar in $\sim 1$ Gyr. Our X-ray analyses place constraints on the magnetization and particle density of the pulsar wind and support models of magnetic reconnection and particle acceleration in the highly magnetized relativistic IBS.

9 pages, 5 figures, 3 tables; Version to appear in ApJ

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• New Insights into Supradense Matter from Dissecting Scaled Stellar Structure Equations
• The Spider Stellar Engine: a Fully Steerable Extraterrestrial Design?
• Reconstruction of spider system's observables from orbital period modulations via the Applegate mechanism
• Neutron Star Equation of State with Nucleon Short-Range Correlations: A Concise Review and Open Issues
• Nature of 4FGL J2249.4+6229: Evidence for a redback system with a cool companion and low X-ray and $\gamma$-ray luminosities
• Structure of Anisotropic Magnetized Neutron Stars in f(R,T) Gravity with Realistic Equation of State