1,107 research outputs found
The intrinsic collective X-ray spectrum of luminous high-mass X-ray binaries
Using a sample of two hundred luminous (L_unabs>10^38 erg/s, where L_unabs is
the unabsorbed 0.25-8 keV luminosity) high-mass X-ray binary (HMXB) candidates
found with Chandra in 27 nearby galaxies, we have constructed the collective
X-ray spectrum of HMXBs in the local Universe per unit star formation rate,
corrected for observational biases associated with intrinsic diversity of HMXB
spectra and X-ray absorption in the interstellar medium. This spectrum is well
fit by a power law with a photon index Gamma=2.1+/-0.1 and is dominated by
ultraluminous X-ray sources with L_unabs>10^39 erg/s. Hard sources (those with
the 0.25-2 keV to 0.25-8 keV flux ratio of <0.6) dominate above ~2 keV, while
soft and supersoft sources (with the flux ratios of 0.6-0.95 and >0.95,
respectively) at lower energies. The derived spectrum probably represents the
angle-integrated X-ray emission of the near- and super-critically accreting
stellar mass black holes and neutron stars in the local Universe. It provides
an important constraint on supercritical accretion models and can be used as a
reference spectrum for calculations of the X-ray preheating of the Universe by
the first generations of X-ray binaries.Comment: 8 pages, 4 figues, accepted for publication in MNRA
Bright end of the luminosity function of high-mass X-ray binaries: contributions of hard, soft and supersoft sources
Using a spectral analysis of bright Chandra X-ray sources located in 27
nearby galaxies and maps of star-formation rate (SFR) and ISM surface densities
for these galaxies, we constructed the intrinsic X-ray luminosity function
(XLF) of luminous high-mass X-ray binaries (HMXBs), taking into account
absorption effects and the diversity of HMXB spectra. The XLF per unit SFR can
be described by a power law dN/d log L=2.0(L/10^39 erg/s)^(-0.6)
(M_Sun/yr)^(-1) from L=10^38 to 10^40.5 erg/s, where L is the unabsorbed
luminosity at 0.25-8 keV. The intrinsic number of luminous HMXBs per unit SFR
is a factor of ~2.3 larger than the observed number reported before. The
intrinsic XLF is composed of hard, soft and supersoft sources (defined here as
those with the 0.25-2 keV to 0.25-8 keV flux ratio of 0.95,
respectively) in ~2:1:1 proportion. We also constructed the intrinsic HMXB XLF
in the soft X-ray band (0.25-2 keV). Here, the numbers of hard, soft and
supersoft sources prove to be nearly equal. The cumulative present-day 0.25-2
keV emissivity of HMXBs with luminosities between 10^38 and 10^40.5 erg/s is ~5
10^39 erg/s (M_Sun/yr)^(-1), which may be relevant for studying the X-ray
preheating of the early Universe.Comment: 37 pages, 40 figures, accepted for publication in MNRA
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