Settling accretion on to isolated neutron stars from interstellar medium

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We apply the model of subsonic settling accretion on to isolated neutron stars accreting from the interstellar medium (AINS). We show that in this regime the expected mean X-ray luminosity from AINS turns out to be 2-3 orders of magnitude as small as the maximum possible Bondi value, i.e. 10²⁷-10²⁸ erg s⁻¹. The intrinsically unstable character of settling accretion due to long plasma cooling time leads to regular appearance of X-ray flares with a duration of about one hour and a maximum luminosity of about the Bondi value, 10³¹ erg s⁻¹. This feature can be used to distinguished AINS from other dim X-ray sources. With the sensitivity of the forthcoming all-sky X-ray surveys the expected number of the potentially detectable AINS can be from a few to ten.