We observed the neutron star (NS) ultra-compact X-ray binary 4U 0614+091 quasi-simultaneously in the radio band (Very Large Array), mid-infrared (IR)/IR (Spitzer/Multiband Imaging Photometer for ...Spitzer and Infrared Array Camera), near-IR/optical (Small and Moderate Aperture Research Telescope System), optical-UV (Swift/UV-Optical Telescope), soft and hard X-rays (Swift/X-ray Telescope and Rossi-X-ray Timing Explorer). The source was steadily in its 'hard state'. We detected the source in the whole range, for the first time in the radio band at 4.86 and 8.46 GHz and in the mid-IR at 24 {mu}m, up to 100 keV. The optically thick synchrotron spectrum of the jet is consistent with being flat from the radio to the mid-IR band. The flat jet spectrum breaks in the range {approx}(1-4) x 10{sup 13} Hz to an optically thin power-law synchrotron spectrum with spectral index {approx}-0.5. These observations allow us to estimate a lower limit on the jet radiative power of {approx}3 x 10{sup 32} erg s{sup -1} and a total jet power L{sub J} {approx} 10{sup 34}mu{sup -1}{sub 0.05} E {sup 0.53}{sub c} erg s{sup -1} (where E{sub c} is the high-energy cutoff of the synchrotron spectrum in eV and mu{sub 0.05} is the radiative efficiency in units of 0.05). The contemporaneous detection of the optically thin part of the compact jet and the X-ray tail above 30 keV allows us to assess the contribution of the jet to the hard X-ray tail by synchrotron self-Compton (SSC) processes. We conclude that, for realistic jet size, boosting, viewing angle, and energy partition, the SSC emission alone, from the post-shock, accelerated, non-thermal population in the jet, is not a viable mechanism to explain the observed hard X-ray tail of the NS 4U 0614+091.
Current atmospheric models underestimate the production of organic acids in the troposphere. We report a detailed kinetic model of the photochemistry of acetaldehyde (ethanal) under tropospheric ...conditions. The rate constants are benchmarked to collision-free experiments, where extensive photo-isomerization is observed upon irradiation with actinic ultraviolet radiation (310 to 330 nanometers). The model quantitatively reproduces the experiments and shows unequivocally that keto-enol photo-tautomerization, forming vinyl alcohol (ethenol), is the crucial first step. When collisions at atmospheric pressure are included, the model quantitatively reproduces previously reported quantum yields for photodissociation at all pressures and wavelengths. The model also predicts that 21 ± 4% of the initially excited acetaldehyde forms stable vinyl alcohol, a known precursor to organic acid formation, which may help to account for the production of organic acids in the troposphere.
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Deep observations with the Very Large Array of A0620-00, performed in 2005 August, resulted in the first detection of radio emission from a black hole binary at X-ray luminosities as low as 10−8.5 ...times the Eddington limit. The measured radio flux density, of 51 ± 7 μJy at 8.5 GHz, is the lowest reported for an X-ray binary system so far, and is interpreted in terms of partially self-absorbed synchrotron emission from outflowing plasma. Making use of the estimated outer accretion rate of A0620−00 in quiescence, we demonstrate that the outflow kinetic power must be energetically comparable to the total accretion power associated with such rate, if it was to reach the black hole with the standard radiative efficiency of 10 per cent. This favours a model for quiescence in which a radiatively inefficient outflow accounts for a sizable fraction of the missing energy, and, in turn, substantially affects the overall dynamics of the accretion flow. Simultaneous observations in the X-ray band, with Chandra, confirm the validity of a non-linear radio/X-ray correlation for hard state black hole binaries down to low quiescent luminosities, thereby contradicting some theoretical expectations. Taking the mass term into account, the A0620−00 data lie on the extrapolation of the so-called Fundamental Plane of black hole activity, which has thus been extended by more than two orders of magnitude in radio and X-ray luminosity. With the addition of the A0620−00 point, the plane relation provides an empirical proof for the scale invariance of the jet-accretion coupling in accreting black holes over the entire parameter space observable with current instrumentation.
We report on the results of a four-year long X-ray monitoring campaign of the central 1.2 square degrees of our Galaxy, performed with Chandra and XMM-Newton between 2005 and 2008. Our study focuses ...on the properties of transient X-ray sources that reach 2–10 keV luminosities of LX ≳ 1034 erg s-1 for an assumed distance of 8 kpc. There are 17 known X-ray transients within the field of view of our campaign, eight of which were detected in outburst during our observations: the transient neutron star low-mass X-ray binaries GRS 1741–2853, AX J1745.6–2901, SAX J1747.0–2853, KS 1741–293 (all four are also known X-ray bursters), and GRO J1744–28 (a 2.1 Hz X-ray pulsar), and the unclassified X-ray transients XMM J174457–2850.3, CXOGC J174535.5–290124 and CXOGC J174541.0–290014. We present their X-ray spectra and flux evolution during our campaign, and discuss our results in light of their historic activity. Our main results include the detection of two thermonuclear X-ray bursts from SAX J1747.0–2853 that were separated by an unusually short time interval of 3.8 min. Investigation of the lightcurves of AX J1745.6–2901 revealed one thermonuclear X-ray burst and a ~1600-s long X-ray eclipse. We found that both XMM J174457–2850.3 and GRO J1744–28 displayed weak X-ray activity above their quiescent levels at LX ~ 1033−34 erg s-1, which is indicative of low-level accretion. We compare this kind of activity with the behaviour of low-luminosity X-ray transients that display 2–10 keV peak luminosities of LX ~ 1034 erg s-1 and have never been seen to become brighter. In addition to the eight known X-ray transients, we discovered a previously unknown X-ray source that we designate XMMU J174654.1–291542. This object emits most of its photons above 2 keV and appears to be persistent at a luminosity of LX ~ 1034 erg s-1, although it exhibits strong spectral variability on a time scale of months. Based on its X-ray properties and the possible association with an infrared source, we tentatively classify this object as a cataclysmic variable. No new transients were found during our campaign, reinforcing the conclusion of previous authors that most X-ray transients recurring on a time scale of less than a decade have now been identified near the Galactic centre.
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ABSTRACT
What determines the nuclear radio emission in local galaxies? To address this question, we combine optical O iii line emission, robust black hole (BH) mass estimates, and high-resolution ...e-MERLIN 1.5-GHz data, from the LeMMINGs survey, of a statistically complete sample of 280 nearby optically active (LINER and Seyfert) and inactive H ii and absorption line galaxies (ALGs) galaxies. Using O iii luminosity ($L_{\rm O\, \small {III}}$) as a proxy for the accretion power, local galaxies follow distinct sequences in the optical–radio planes of BH activity, which suggest different origins of the nuclear radio emission for the optical classes. The 1.5-GHz radio luminosity of their parsec-scale cores (Lcore) is found to scale with BH mass (MBH) and O iii luminosity. Below MBH ∼ 106.5 M⊙, stellar processes from non-jetted H ii galaxies dominate with $L_{\rm core} \propto M_{\rm BH}^{0.61\pm 0.33}$ and $L_{\rm core} \propto L_{\rm O\, \small {III}}^{0.79\pm 0.30}$. Above MBH ∼ 106.5 M⊙, accretion-driven processes dominate with $L_{\rm core} \propto M_{\rm BH}^{1.5-1.65}$ and $L_{\rm core} \propto L_{\rm O\, \small {III}}^{0.99-1.31}$ for active galaxies: radio-quiet/loud LINERs, Seyferts, and jetted H ii galaxies always display (although low) signatures of radio-emitting BH activity, with $L_{\rm 1.5\, GHz}\gtrsim 10^{19.8}$ W Hz−1 and MBH ≳ 107 M⊙, on a broad range of Eddington-scaled accretion rates ($\dot{m}$). Radio-quiet and radio-loud LINERs are powered by low-$\dot{m}$ discs launching sub-relativistic and relativistic jets, respectively. Low-power slow jets and disc/corona winds from moderately high to high-$\dot{m}$ discs account for the compact and edge-brightened jets of Seyferts, respectively. Jetted H ii galaxies may host weakly active BHs. Fuel-starved BHs and recurrent activity account for ALG properties. In conclusion, specific accretion–ejection states of active BHs determine the radio production and the optical classification of local active galaxies.
Abstract
Intermediate-mass black holes (IMBHs) by definition have masses of
M
IMBH
∼ 10
2−5
M
⊙
, a range with few observational constraints. Finding IMBHs in globular star clusters (GCs) would ...validate a formation channel for massive black-hole seeds in the early universe. Here, we simulate a 60 hr observation with the next-generation Very Large Array (ngVLA) of 728 GC candidates in the Virgo Cluster galaxy NGC 4472. Interpreting the radio detection thresholds as signatures of accretion onto IMBHs, we benchmark IMBH mass thresholds in three scenarios and find the following: (1) radio analogs of ESO 243-49 HLX-1, a strong IMBH candidate with
M
IMBH
HLX
∼
10
4
−
5
M
⊙
in a star cluster, are easy to access in all 728 GC candidates. (2) For the 30 GC candidates with extant X-ray detections, the empirical fundamental-plane relation involving black-hole mass plus X-ray and radio luminosities suggests access to
M
IMBH
FP
∼
10
1.7
−
3.6
M
⊙
, with an uncertainty of 0.44 dex. (3) A fiducial Bondi accretion model was applied to all 728 GC candidates and to radio stacks of the GC candidates. This model suggests access to IMBH masses, with a statistical uncertainty of 0.39 dex, of
M
IMBH
B
∼
10
4.9
−
5.1
M
⊙
for individual GC candidates, and
M
IMBH
B
,
stack
∼
10
4.5
M
⊙
for radio stacks of about 100–200 GC candidates. The fiducial Bondi model offers initial guidance, but is subject to additional systematic uncertainties and should be superseded by hydrodynamical simulations of gas flows in GCs.
We present the discovery of a powerful candidate microquasar in NGC 300, associated with the S 10 optical nebula (previously classified as a supernova remnant). Chandra images show four discrete ...X-ray knots aligned in the plane of the sky over a length of ≈150 pc. The X-ray emission from the knots is well fitted with a thermal plasma model at a temperature of ≈0.6 keV and a combined 0.3–8 keV luminosity of ≈10^37 erg s^−1. The X-ray core, if present at all, does not stand out above the thermal emission of the knots: this suggests that the accreting compact object is either currently in a dim state or occulted from our view. We interpret the emission from the knots as the result of shocks from the interaction of a jet with the interstellar medium (possibly over different epochs of enhanced activity). Cooler shock-heated gas is likely the origin also of the optical bubble and lobes near the X-ray structure, detected in images from the Hubble Space Telescope and the Very Large Telescope. In the radio bands, we observed the region with the Australia Telescope Compact Array, and discovered an elongated radio nebula (about 170 × 55 pc in size) with its major axis aligned with the chain of Chandra sources. The radio nebula has an integrated 5.5 GHz radio luminosity of |${\approx }10^{34}\, \rm{erg\,s^{-1}}$| for a distance of 1.88 Mpc. The morphology, size, and luminosity of the extended X-ray, optical, and radio structure suggest that NGC 300-S 10 belongs to the same class of powerful (P_jet > 10^39 erg s^−1) microquasars as SS 433, Ho II X-1, and NGC 7793-S 26.
In this paper, we present a combined analysis of data obtained with the Hubble Space Telescope (HST), Very Large Telescope (VLT) and Swift X-ray telescope of the intermediate-mass black hole ESO ...243−49 HLX-1 that were taken two months apart between 2010 September and November. Previous separate analyses of these data found that they were consistent with an irradiated accretion disc with contribution from either a very young or very old stellar population, and also indicated that the optical flux of the HLX-1 counterpart could be variable. Such variability could only be attributed to a varying accretion disc, so simultaneous analysis of all data sets should break the degeneracies in the model fits. We thus simultaneously fit the broad-band spectral energy distribution (SED) from near-infrared through to X-ray wavelengths of the two epochs of data with a model consisting of an irradiated accretion disc and a stellar population. We show that this combined analysis rules out an old stellar population, finding that the SED is dominated by emission from an accretion disc with moderate reprocessing in the outer disc around an intermediate-mass black hole imbedded in a young (∼20 Myr) stellar cluster with a mass of ∼105 M. We also place an upper limit on the mass of an additional hidden old stellar population of ∼106 M. However, optical r
′-band observations of HLX-1 obtained with the Gemini-South telescope covering part of the decay from a later X-ray outburst are consistent with constant optical flux, indicating that the observed variability between the HST and VLT observations could be spurious caused by differences in the background subtraction applied to the two optical data sets. In this scenario, the contribution of the stellar population, and thus the stellar mass of the cluster, may be higher. Nonetheless, variability of <50 per cent cannot be ruled out by the Gemini data and thus they are still consistent within the errors with an exponential decay similar to that observed in X-rays.
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