Evidence of Compton cooling during an X-ray flare supports a neutron star nature of the compact object in 4U1700-37

Abstract

Based on new Chandra X-ray telescope data, we present empirical evidence of plasma Compton cooling during a flare in the non pulsating massive X-ray binary 4U1700-37. This behaviour might be explained by quasispherical accretion onto a slowly rotating magnetised neutron star. In quiescence, the neutron star in 4U1700-37 is surrounded by a hot radiatively cooling shell. Its presence is supported by the detection of mHz quasi periodic oscillations likely produced by its convection cells. The high plasma temperature and the relatively low X-ray luminosity observed during the quiescence, point to a small emitting area about 1 km, compatible with a hot spot on a NS surface. The sudden transition from a radiative to a significantly more efficient Compton cooling regime triggers an episode of enhanced accretion resulting in a flare. During the flare, the plasma temperature drops quickly. The predicted luminosity for such transitions, Lx = 3 x 10^35 erg s-1, is very close to the luminosity of 4U1700-37 during quiescence. The transition may be caused by the accretion of a clump in the stellar wind of the donor star. Thus, a magnetised NS nature of the compact object is strongly favoured.

Accepted for publication in MNRAS

References in corpus (3)

• Towards a unified view of inhomogeneous stellar winds in isolated supergiant stars and supergiant high mass X-ray binaries
• High variability in Vela X-1: giant flares and off states
• Very Low Frequency QPO in 4U1700-37

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• The stellar and wind parameters of six prototypical HMXBs and their evolutionary status
• A Comparative Study of Machine Learning Methods for X-ray Binary Classification
• First Detection of X-ray Polarization and Its Short-term Increase Pre- and Post-Eclipse in HMXB 4U 1700-377
• Constraints on cyclotron features and accretion regime in the high-mass X-ray binary 4U 1700-37 from NuSTAR