Based on a homogeneous set of X-ray, infrared and ultraviolet observations from Chandra, Spitzer, GALEX and 2MASS archives, we study populations of high-mass X-ray binaries (HMXBs) in a sample of 29 ...nearby star-forming galaxies and their relation to the star-formation rate (SFR). In agreement with previous results, we find that HMXBs are a good tracer of the recent star-formation activity in the host galaxy and their collective luminosity and number scale with the SFR: in particular,
. However, the scaling relations still bear a rather large dispersion of rms ∼ 0.4 dex, which we believe is of a physical origin.
We present the catalogue of 1055 X-ray sources detected within the D25 ellipse for galaxies of our sample and construct the average X-ray luminosity function (XLF) of HMXBs with substantially improved statistical accuracy and better control of systematic effects than achieved in previous studies. The XLF follows a power law with a slope of 1.6 in the log (L
X) ∼ 35-40 luminosity range with moderately significant evidence for a break or cut-off at L
X∼ 1040 erg s−1. As before, we did not find any features at the Eddington limit for a neutron star or a stellar-mass black hole.
We discuss the implications of our results for the theory of binary evolution. In particular we estimate the fraction of compact objects that once in their lifetime experienced an X-ray active phase powered by accretion from a high-mass companion and obtain a rather large number, f
X∼ 0.2 × (0.1 Myr/τX), where τX is the lifetime of the X-ray active phase. This is ∼4 orders of magnitude more frequent than in low-mass X-ray binaries (LMXBs). We also derive constraints on the mass distribution of the secondary star in HMXBs.
Abstract
Using results of Chandra observations of old stellar systems in 11 nearby galaxies of various morphological types and the census of low-mass X-ray binaries (LMXBs) in the Milky Way, we study ...the population of LMXBs and their relation to the mass of the host galaxy. We show that the azimuthally averaged spatial distributions of the number of LMXBs and, in the majority of cases, of their collective luminosity closely follow that of the near-infrared light. Considering galaxies as a whole, we find that, in a broad stellar mass range, log(M
*) ∼ 9-11.5, the total number of LMXBs and their combined luminosity are proportional to the stellar mass of the host galaxy. Within the accuracy of the light-to-mass conversion, we cannot rule out the possibility of a weak dependence of the X/M
* ratio on morphological type. However, the effect of such a dependence, if any, does not exceed a factor of ∼1.5-2.
The luminosity distributions of LMXBs observed in different galaxies are similar to each other and, with the possible exception of NGC 1553, are consistent with the average luminosity function derived from all data. The average X-ray luminosity function of LMXBs in nearby galaxies has a complex shape and is significantly different from that of high-mass X-ray binaries (HMXBs). It follows a power law with a differential slope of ≈1 at low luminosities, gradually steepens at log(L
X) ≳ 37.0-37.5 and has a rather abrupt cut-off at log(L
X) ∼ 39.0-39.5. This value of the cut-off luminosity is significantly, by an order of magnitude, lower than found for HMXBs.
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BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
We study the emission from the hot interstellar medium (ISM) in a sample of nearby late-type galaxies defined in Paper I. Our sample covers a broad range of star formation rates (SFRs) from ...∼0.1 to ∼17 M⊙ yr−1 and stellar masses from ∼3 × 108 to ∼6 × 1010 M⊙. We take special care of systematic effects and contamination from bright and faint compact sources. We find that in all galaxies at least one optically thin thermal emission component is present in the unresolved emission, with the average temperature of 〈kT〉 = 0.24 keV. In about ∼1/3 of galaxies, a second, higher temperature component is required, with 〈kT〉 = 0.71 keV. Although statistically significant variations in temperature between galaxies are present, we do not find any meaningful trends with the stellar mass or SFR of the host galaxy. The apparent luminosity of the diffuse emission in the 0.5-2 keV band linearly correlates with the SFR with the scale factor of L
x
/SFR≈8.3×1038ergs−1(M⊙yr−1)−1, of which in average ∼30-40 per cent is likely produced by faint compact sources of various types. We attempt to estimate the bolometric luminosity of the gas and obtain results differing by an order of magnitude, log(L
bol/SFR) ∼ 39−40, depending on whether intrinsic absorption in star-forming galaxies is allowed or not. Our theoretically most accurate, but in practice the most model-dependent result for the intrinsic bolometric luminosity of the ISM is L
bol/SFR ∼ 1.5×1040erg s−1(M⊙yr−1)−1. Assuming that core-collapse supernovae are the main source of energy, it is implied that ϵSN ∼ 5×10−2(ESN/1051)−1 of mechanical energy of supernovae is converted into thermal energy of the ISM.
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BFBNIB, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
The halo of the Milky Way provides a laboratory to study the properties of the shocked hot gas that is predicted by models of galaxy formation. There is observational evidence of energy injection ...into the halo from past activity in the nucleus of the Milky Way
; however, the origin of this energy (star formation or supermassive-black-hole activity) is uncertain, and the causal connection between nuclear structures and large-scale features has not been established unequivocally. Here we report soft-X-ray-emitting bubbles that extend approximately 14 kiloparsecs above and below the Galactic centre and include a structure in the southern sky analogous to the North Polar Spur. The sharp boundaries of these bubbles trace collisionless and non-radiative shocks, and corroborate the idea that the bubbles are not a remnant of a local supernova
but part of a vast Galaxy-scale structure closely related to features seen in γ-rays
. Large energy injections from the Galactic centre
are the most likely cause of both the γ-ray and X-ray bubbles. The latter have an estimated energy of around 10
erg, which is sufficient to perturb the structure, energy content and chemical enrichment of the circumgalactic medium of the Milky Way.
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FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Aims.
We study populations of soft and super-soft X-ray sources (SSSs) in nearby galaxies of various morphological types with particular emphasis on characterizing populations of stable nuclear ...burning, accreting white dwarfs (WDs).
Methods.
Analyzing the content of the
Chandra
archive, we assembled a sample of nearby galaxies suitable for studying populations of SSSs. Our sample includes four spiral galaxies, two lenticular galaxies, and three ellipticals with stellar mass exceeding 10
10
M
⊙
and X-ray sensitivity of the order of a few × 10
36
erg s
−1
. We used a combination of hardness ratio and median energy to pre-select X-ray sources with soft spectra, and used the temperature–X-ray luminosity diagram to identify SSSs, likely nuclear-burning, accreting WDs.
Results.
For spiral galaxies, there is a distinct and rare population of super-soft sources that are largely detached from the rest of the sources on the
kT
bb
−
L
X
plane. The boundary between these sources and the much more numerous population of harder (but still soft) sources is consistent with the boundary of stable hydrogen burning on the surface of WDs. The combined spectrum of soft sources located outside this boundary shows clear emission lines of Mg and S, the equivalent width of which is similar to that in the combined spectrum of a large number of confirmed supernova remnants in M 83. This supports earlier suggestions that the vast majority of the so-called quasi-soft sources are supernova remnants. In early-type galaxies, populations of super-soft sources are about a factor of eight less abundant, in broad agreement with the population synthesis calculations. Specific frequencies of super-soft sources are (2.08 ± 0.46) × 10
−10
M
⊙
−1
in spiral galaxies and (2.47 ± 1.34) × 10
−11
M
⊙
−1
in lenticular and elliptical galaxies, with the ratio of the latter to the former being 0.12 ± 0.05.
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FMFMET, NUK, UL, UM, UPUK
ABSTRACT
We present the first sample of tidal disruption events (TDEs) discovered during the SRG all-sky survey. These 13 events were selected among X-ray transients detected in the 0° < l < 180° ...hemisphere by eROSITA during its second sky survey (2020 June 10 to December 14) and confirmed by optical follow-up observations. The most distant event occurred at z = 0.581. One TDE continued to brighten at least 6 months. The X-ray spectra are consistent with nearly critical accretion on to black holes of a few ×103 to $10^8\, \mathrm{ M}_\odot$, although supercritical accretion is possibly taking place. In two TDEs, a spectral hardening is observed 6 months after the discovery. Four TDEs showed an optical brightening apart from the X-ray outburst. The other nine TDEs demonstrate no optical activity. All 13 TDEs are optically faint, with Lg/LX < 0.3 (Lg and LX being the g band and 0.2–6 keV luminosity, respectively). We have constructed a TDE X-ray luminosity function, which can be fit by a power law with a slope of −0.6 ± 0.2, similar to the trend observed for optically selected TDEs. The total rate is estimated at (1.1 ± 0.5) × 10−5 TDEs per galaxy per year, an order of magnitude lower than inferred from optical studies. This suggests that X-ray bright events constitute a minority of TDEs, consistent with models predicting that X-rays can only be observed from directions close to the axis of a thick accretion disc formed from the stellar debris. Our TDE detection threshold can be lowered by a factor of ∼2, which should allow a detection of ∼700 TDEs by the end of the SRG survey.
ABSTRACT
Symbiotic stars are long-period interacting binaries where the compact object, most commonly a white dwarf, is embedded in the dense stellar wind of an evolved companion star. Ultraviolet ...and soft X-ray emission of the accretion disc and the nuclear-burning white dwarf plays a major role in shaping the ionization balance of the surrounding wind material, giving rise to the rich line emission. In this paper, we employ two-dimensional photoionization calculations based on the cloudy code to study the ionization state of the circumbinary material in symbiotic systems and to predict their emission-line spectra. Our simulations are parametrized via the orbital parameters of the binary and the wind mass-loss rate of the donor star, while the mass accretion rate, temperature and luminosity of the white dwarf are computed self-consistently. We explore the parameter space of symbiotic binaries and compute luminosities of various astrophysically important emission lines. The line ratios are compared with traditional diagnostic diagrams used to distinguish symbiotic binaries from other types of sources, and it is shown how the binary system parameters shape these diagrams. In the significant part of the parameter space, the wind material is nearly fully ionized, except for the ‘shadow’ behind the donor star, so the white dwarf emission is typically freely escaping the system.
ABSTRACT
We report the discovery of X-ray emission from CFHQS J142952+544717, the most distant known radio-loud quasar at z = 6.18, on 2019 December 10–11 with the eROSITA telescope on board the SRG ...satellite during its ongoing all-sky survey. The object was identified by cross-matching an intermediate SRG/eROSITA source catalogue with the Pan-STARRS1 distant quasar sample at 5.6 < z < 6.7. The measured flux ∼8 × 10−14 erg cm−2 s−1 in the 0.3–2 keV energy band corresponds to an X-ray luminosity of $2.6^{+1.7}_{-1.0}\times 10^{46}$ erg s−1 in the 2–10 keV rest-frame energy band, which renders CFHQS J142952+544717 the most X-ray luminous quasar ever observed at z > 6. Combining our X-ray measurements with archival and new photometric measurements in other wavebands (radio to optical), we estimate the bolometric luminosity of this quasar at ∼(2–3) × 1047 erg s−1. Assuming Eddington limited accretion and isotropic emission, we infer a lower limit on the mass of the supermassive black hole of ∼2 × 109 M⊙. The most salient feature of CFHQS J142952+544717 is its X-ray brightness relative to the optical/UV emission. We argue that it may be linked to its radio-loudness (although the object is not a blazar according to its radio properties), specifically to a contribution of inverse Compton scattering of cosmic microwave background photons off relativistic electrons in the jets. If so, CFHQS J142952+544717 might be the tip of the iceberg of high-z quasars with enhanced X-ray emission, and SRG/eROSITA may find many more such objects during its 4-yr all-sky survey.
To date, the question of which progenitor channel can reproduce the observed rate of Type Ia supernovae (SNe Ia) remains unresolved, with the single and double degenerate scenarios remaining the ...leading contenders. The former implies a large population of hot accreting white dwarfs with photospheric temperatures of T ∼ 105-106 K during some part of their accretion history. We show that in early-type galaxies, a population of accreting white dwarfs large enough to reproduce the SN Ia rate would contribute significantly to the ionizing ultraviolet (UV) radiation expected from the stellar population. For mean stellar ages 5 Gyr, single degenerate progenitors would dominate the ionizing background produced by stars, increasing the continuum beyond the He ii-ionizing limit more than 10-fold. This opens a new avenue for constraining the progenitors of SNe Ia, through consideration of the spatially extended low-ionization emission-line regions now found in many early-type galaxies. Modelling the expected emission, we show that one can constrain the contribution of the single degenerate channel to the SN Ia rate in E/S0 galaxies from upper limits on the luminosity of He ii recombination lines in the optical and far-ultraviolet (FUV). We discuss future directions, as well as possible implications for the evolution of SNe Ia in old stellar populations.
ABSTRACT
We present results from a 20 ks XMM–Newton director’s discretionary time observation of the radio-loud quasar CFHQS J142952 + 544717 at z = 6.18, whose extreme X-ray luminosity was recently ...revealed by the SRG/eROSITA telescope in the course of its first all-sky survey. The quasar has been confidently detected with a total of ∼1400 net counts in the 0.2–10 keV energy band (1.4–72 keV in the object’s rest frame). Its measured spectrum is unusually soft and can be described by an absorbed power-law model with a photon index of Γ = 2.5 ± 0.2. There are no signs of a high-energy cut-off or reflected component, with a 90 per cent upper limit on the fluorescence iron K α equivalent width of ≈290 eV and the corresponding upper limit on the iron K-edge absorption depth of 0.6. We have detected, at the >95 per cent confidence level, an excess absorption above the Galactic value, corresponding to a column density NH = 3 ± 2 × 1022 cm−2 of material located at z = 6.18. The intrinsic luminosity of CFHQS J142952 + 544717 in the 1.4–72 keV energy band is found to be $5.5_{-0.6}^{+0.8} \times 10^{46}$ erg s−1. We did not detect statistically significant flux changes between two SRG scans and the XMM–Newton observation, spanning over ∼7.5 months, implying that the quasar remained at this extremely high-luminosity level for at least a month in its rest frame. We put forward the hypothesis that the extreme X-ray properties of CFHQS J142952 + 544717 are associated with inverse Compton scattering of cosmic microwave background photons (at z = 6.18) in its relativistic jets.
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