The puzzling symbiotic X-ray system 4U1700+24

Abstract

Symbiotic X-ray binaries form a subclass of low-mass X-ray binary systems consisting of a neutron star accreting material from a red giant donor star via stellar wind or Roche lobe overflow. Only a few confirmed members are currently known; 4U 1700+24 is a good candidate as it is a relatively bright X-ray object, possibly associated with the late-type star V934 Her. We analysed the archive {\it XMM}-Newton and Swift/XRT observations of 4U 1700+24 in order to have a uniform high-energy ($0.3-10$ keV) view of the source. We confirmed the existence of a red-shifted O VIII Ly-$\alpha$ transition (already observed in the 2002 {\it XMM}-Newton data) in the high-resolution spectra collected via the RGS instruments. The red-shift of the line is found in all the analysed observations and, on average, it was estimated to be $\simeq 0.009$. We also observed a modulation of the centroid energy of the line on short time scales (a few days) and discuss the observations in the framework of different scenarios. If the modulation is due to the gravitational red-shift of the neutron star, it might arise from a sudden re-organization of the emitting $X$-ray matter on the scale of a few hundreds of km. Alternatively, we are witnessing a uni-polar jet of matter (with typical velocity of $1000-4000$ km s${}^{-1}$) possibly emitted by the neutron star in an almost face-on system. The second possibility seems to be required by the apparent lack of any modulation in the observed $X$-ray light curve. We also note also that the low-resolution spectra (both {\it XMM}-Newton and Swift/XRT in the $0.3-10$ keV band) show the existence of a black body radiation emitted by a region (possibly associated with the neutron star polar cap) with typical size from a few tens to hundreds of meters. The size of this spot-like region reduces as the overall luminosity of 4U 1700+24 decreases.

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References in corpus (9)

• On the origin of soft X-rays in obscured AGN: answers from high-resolution spectroscopy with XMM-Newton
• IGR J16194-2810: a new symbiotic X-ray binary
• M-type giants as optical counterparts of X-ray sources 4U 1700+24 and 4U 1954+319
• A Comparison of the Variability of the Symbiotic X-ray Binaries GX 1+4, 4U 1954+31, and 4U 1700+24 from Swift/BAT and RXTE/ASM Observations
• Wind-accreting Symbiotic X-ray Binaries
• X-ray broad-band study of the symbiotic X-ray binary 4U 1954+31
• A Possible Magnetar Nature for IGR J16358-4726
• A new symbiotic low mass X-ray binary system: 4U 1954+319
• XMM observation of 1RXS J180431.1-273932: a new M-type X-ray binary with a 494 s-pulse period neutron star?

Cited by in corpus (6)

• An Ultra Low Mass and Small Radius Compact Object in 4U 1746-37?
• Infrared Spectroscopy of Symbiotic Stars. XII. The Neutron Star SyXB System 4U 1700+24 = V934 Herculis
• Scientific Objectives of the Hot Universe Baryon Surveyor (HUBS) Mission
• A solution of the puzzling symbiotic X-ray system 4U 1700+24
• The Symbiotic X-ray binaries Sct X-1, 4U 1700+24 and IGR J17329-2731
• THA 15-31: Discovery with VLT/X-Shooter and Swift/UVOT of a new symbiotic star of the accreting-only variety