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Added by
Mallory S. E. Roberts
Publication date
2015
fields
Physics
and research's language is
English
Authors
Mallory S.E. Roberts
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We consider the X-ray properties of the redback class of eclipsing millisecond pulsars. These are transitional systems between accreting low-mass X-ray binaries and binary millisecond pulsars orbiting white dwarfs, and hence their companions are non-degenerate and nearly Roche-lobe filling. The X-ray luminosity seems to scale with the fraction of the pulsar sky subtended by the companion, suggesting the shock region is not much larger than the companion, which is supported by modeling of the orbital light curves. The typical X-ray photon spectral index is $sim 1$ and the typical 0.3-8 keV X-ray efficiency, assuming a shock size on the order of the companions Roche lobe cross-section, is on the order of 10%. We present an overview of previous investigations, and present new observations of two redbacks, a Chandra observation of PSR J1628$-$3205 and a XMM-Newton observation of PSR J2129$-$0429. The latter shows a clearly double peaked orbital light curve with variation of the non-thermal flux by a factor of $sim 11$, with peaks around orbital phases 0.6 and 0.9. We suggest the magnetic field of the companion plays a significant role in the X-ray emission from intrabinary shocks in redbacks.
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Black widows and redbacks are binary systems consisting of a millisecond pulsar in a close binary with a companion having matter driven off of its surface by the pulsar wind. X-rays due to an intra-binary shock have been observed from many of these systems, as well as orbital variations in the optical emission from the companion due to heating and tidal distortion. We have been systematically studying these systems in radio, optical and X-rays. Here we will present an overview of X-ray and optical studies of these systems, including new XMM-Newton and NuStar data obtained from several of them, along with new optical photometry.
Black widow and redback systems are compact binaries in which a millisecond pulsar heats and may even ablate its low-mass companion by its intense wind of relativistic particles and radiation. In such systems, an intrabinary shock can form as a site of particle acceleration and associated non-thermal emission. We model the X-ray and gamma-ray synchrotron and inverse-Compton spectral components for select spider binaries, including diffusion, convection and radiative energy losses in an axially-symmetric, steady-state approach. Our new multi-zone code simultaneously yields energy-dependent light curves and orbital phase-resolved spectra. Using parameter studies and matching the observed X-ray spectra and light curves, and Fermi Large Area Telescope spectra where available, with a synchrotron component, we can constrain certain model parameters. For PSR J1723--2837 these are notably the magnetic field and bulk flow speed of plasma moving along the shock tangent, the shock acceleration efficiency, and the multiplicity and spectrum of pairs accelerated by the pulsar. This affords a more robust prediction of the expected high-energy and very-high-energy gamma-ray flux. We find that nearby pulsars with hot or flaring companions may be promising targets for the future Cherenkov Telescope Array. Moreover, many spiders are likely to be of significant interest to future MeV-band missions such as AMEGO and e-ASTROGAM.
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This article reports the results of X-ray studies of the extended TeV $gamma$-ray source VER J2019+368. Suzaku observations conducted to examine properties of the X-ray pulsar wind nebula (PWN) around PSR J2021+3651 revealed that the western region of the X-ray PWN has a source extent of $15 times 10$ with the major axis oriented to that of the TeV emission. The PWN-west spectrum was closely fitted by a power-law for absorption at $N({rm H}) = (8.2^{+1.3}_{-1.1}) times 10^{21}~{rm cm^{-2}}$ and a photon index of $Gamma = 2.05pm0.12$, with no obvious change in the index within the X-ray PWN. The measured X-ray absorption indicates that the distance to the source is much less than $10~{rm kpc}$ inferred by radio data. Aside from the PWN, no extended emission was observed around PSR J2021+3651 even by Suzaku. Archival data from the XMM-Newton were also analyzed to complement the Suzaku observations, indicating that the eastern region of the X-ray PWN has a similar spectrum ($N(rm H)=(7.5 pm 0.9) times 10^{21}~{rm cm^{-2}}$ and $Gamma=2.03 pm 0.10$) and source extent up to at least $12$ along the major axis. The lack of significant change in the photon index and the source extent in X-ray are used to constrain the advection velocity or the diffusion coefficient for accelerated X-ray-producing electrons. A mean magnetic field of ${sim}3~mu{rm G}$ is required to account for the measured X-ray spectrum and reported TeV $gamma$-ray spectrum. A model calculation of synchrotron radiation and inverse Compton scattering was able to explain ${sim}80%$ of the reported TeV flux, indicating that the X-ray PWN is a major contributor of VER J2019+368.
This is a white paper submitted in response to the call from the Astro2020 Decadal Survey Committee. We outline the scientific progress that will be made in the next few decades in the study of supernova remnants in the X-ray band, using observatories like Athena, Lynx, and AXIS.
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