Log LX Research Articles

A Wrist-Worn Internet of Things Sensor Node for Wearable Equivalent Daylight Illuminance Monitoring.

Light exposure is a vital regulator of physiology and behavior in humans. However, monitoring of light exposure is not included in current wearable Internet of Things (IoT) devices, and only recently have international standards defined [Formula: see text] -optic equivalent daylight illuminance (EDI) measures for how the eye responds to light. This article reports a wearable light sensor node that can be incorporated into the IoT to provide monitoring of EDI exposure in real-world settings. We present the system design, electronic performance testing, and accuracy of EDI measurements when compared to a calibrated spectral source. This includes consideration of the directional response of the sensor, and a comparison of performance when placed on different parts of the body, and a demonstration of practical use over 7 days. Our device operates for 3.5 days between charges, with a sampling period of 30 s. It has 10 channels of measurement, over the range 415-910 nm, balancing accuracy and cost considerations. Measured [Formula: see text]-opic EDI results for 13 devices show a mean absolute error of less than 0.07 log lx, and a minimum between device correlation of 0.99. These findings demonstrate that accurate light sensing is feasible, including at wrist worn locations. We provide an experimental platform for use in future investigations in real-world light exposure monitoring and IoT-based lighting control.

Hall-magnetohydrodynamic simulations of X-ray photoevaporative protoplanetary disc winds

ABSTRACT Understanding the evolution and dispersal via energetic stellar radiation of protoplanetary discs (PPDs) is a prominent challenge in astrophysics. It has been established that X-ray luminosity from the central protostar can significantly heat the surface of the disc, causing powerful photoevaporative winds that eject a considerable fraction of the disc’s mass. Recent work in the field has moreover shown the importance of global PPD simulations that simultaneously take into account non-ideal magnetohydrodynamic (MHD) effects and detailed thermochemistry. In this paper, we combine these two aspects and figure out how they interact. Focus is put on the Hall Effect (HE) and the impact it has on the overall field topology and mass-loss/accretion rates. Utilizing a novel X-ray temperature parametrization, we perform 2D-axisymmetric MHD simulations with the nirvana-iii fluid code, covering all non-ideal effects. We find that, in the aligned orientation, the HE causes prominent inward displacement of the poloidal field lines that increase the accretion rate through a laminar Maxwell stress. We find that outflows are mainly driven by photoevaporation – unless the magnetic field strength is considerable (i.e. βp ≤ 103) or the X-ray luminosity low enough (i.e. log LX ≤ 29.3). Inferred mass-loss rate are in the range of the expected values 10−8–$10^{-7}\, M_\odot \, {\rm yr}^{-1}$. Moreover, we performed pure hydrodynamic (HD) runs and compared them with the equivalent MHD runs. We concluded that the magnetic field does indeed contribute to the mass-loss rate, albeit only discernibly so for low enough LX (i.e. log LX ≤ 30.8).

Complete X-ray census of M dwarfs in the solar neighborhood

Context. X-ray emission is the most sensitive diagnostic of magnetic activity in M dwarfs and, hence, of the dynamo in low-mass stars. Moreover it is crucial for quantifying the influence of the stellar irradiation on the evolution of planet atmospheres. Aims. We have embarked in a systematic study of the X-ray emission in a volume-limited sample of M dwarf stars to explore the full range of activity levels present in their coronae. We look to obtain a better understanding of the conditions in their outer atmospheres and their possible impact on the circumstellar environment. Methods. Based on a recent catalog of Gaia objects within 10 pc from the Sun, we identified all its stars with spectral types between M0 and M4 and we carried out a systematic search for X-ray measurements of this sample. To this end, we used both archival data from ROSAT, XMM-Newton, and the ROentgen Survey with an Imaging Telescope Array (eROSITA) on board the Russian Spektrum-Roentgen-Gamma mission, as well as our own dedicated XMM-Newton observations. To make inferences on the properties of the M dwarf corona, we compared the range of their observed X-ray emission levels to the flux radiated by the Sun from different types of magnetic structures: coronal holes, background corona, active regions, and cores of active regions. In this work, we focus on the properties of stars with the faintest X-ray emission. Results. At the current state of our project, with more than 90% of the 10 pc M dwarf sample observed in the X-ray, there is only one star that has had no detections: GJ 745 A. With an upper limit luminosity of log Lx (erg s−1) < 25.4 and an X-ray surface flux of log FX,SURF (erg cm−2 s−1) < 3.6, GJ 745 A defines the lower boundary of the X-ray emission level for M dwarfs. Together with its proper motion companion (GJ 745 B), it is the only star in this volume-complete sample located in the range of X-ray surface flux that corresponds to the faintest solar coronal structures, namely: coronal holes. The fact that the ultra-low X-ray emission level of GJ 745 B (log Lx (erg s−1) = 25.6 and log FX,SURF (erg cm−2 s−1) = 3.8) is entirely attributed to flaring activity indicates that while its corona is dominated by “holes,” at least one magnetically active structure is present. This structure determines the total X-ray brightness and the coronal temperature of the star.

X-ray emission of contact binary variables within 1 kpc

Aims. The X-ray emission of contact binaries (EW-type) is an important facet of such systems. Thus, X-ray emitting EW-type binaries (EWXs) are ideal laboratories for studying the X-ray radiation saturation mechanisms as well as binary evolution. By assembling the largest sample to date of EWXs with periods of less than 1 day from the All-Sky Automated Survey for Supernovae Variable Stars Database and X-ray catalogs from the XMM-Newton and ROSAT missions, we aim to conduct a systematic population study of X-ray emission properties of EWXs within 1 kpc. Methods. We carried out correlation analyses for the X-ray luminosity, log LX, and X-ray activity level log(LX/Lbol) versus the orbital period, P, effective temperature, Teff, metallicity [Fe/H], and the surface gravity log g of EWXs. We investigated the relation between X-ray emission and the mass of component stars in the binary systems. We also performed sample simulations to explore the degeneracy between period, mass, and effective temperature for EWXs. Results. We find strong P–log LX and P–log(LX/Lbol) correlations for EWXs with P ≲ 0.44 days and we provide the linear parametrizations for these relations, on the basis of which the orbital period can be treated as a good predictor for log LX and log(LX/Lbol). The aforementioned binary stellar parameters are all correlated with log LX, while only Teff exhibits a strong correlation with log(LX/Lbol). Then, EWXs with higher temperature show lower X-ray activity level, which could indicate the thinning of the convective area related to the magnetic dynamo mechanism. The total X-ray luminosity of an EWX is essentially consistent with that of an X-ray saturated main sequence star with the same mass as its primary, which may imply that the primary star dominates the X-ray emission. The monotonically decreasing P–log(LX/Lbol) relation and the short orbital periods indicate that EWXs could all be in the X-ray saturated state, and they may inherit the changing trend of the saturated X-ray luminosities along with the mass shown by single stars. For EWXs, the orbital period, mass, and effective temperature increase in concordance. We demonstrate that the period P = 0.44 days corresponds to the primary mass of ∼1.1 M⊙, beyond which the saturated X-ray luminosity of single stars will not continue to increase with mass. This explains the break in the positive P–log LX relation for EWXs with P > 0.44 days.

The Fundamental Planes of black hole activity for radio-loud and radio-quiet quasars

ABSTRACT We examine the Fundamental Plane of black hole activity for correlations with redshift and radio loudness in both radio-loud and radio-quiet quasar populations. Sources are compiled from archival data of both radio-loud and radio-quiet quasars over redshifts 0.1 < z < 5.0 to produce a sample of 353 sources with known X-ray, radio, and black hole mass measurements. A Fundamental Plane of accretion activity is fit to a sample of radio-loud and radio-quiet quasars, and we find a dichotomy between radio-loud and radio-quiet sources. The set of best-fitting equations that best describe the two samples are log LR = (1.12 ± 0.06)log LX − (0.20 ± 0.07)log M − (5.64 ± 2.99) for our radio-loud sample and log LR = (0.48 ± 0.06)log LX + (0.50 ± 0.08)log M + (15.26 ± 2.66) for our radio-quiet sample. Our results suggest that the average radio-quiet quasar emission is consistent with advection-dominated accretion, while a combination of jet and disc emission dominates in radio-loud quasars. We additionally examine redshift trends amongst the radio-loud and radio-quiet samples, and we observe a redshift dependence for the Fundamental Plane of radio-loud quasars. Lastly, we utilize the Fundamental Plane as a black hole mass estimation method and determine it useful in studying systems where standard spectral modelling techniques are not viable.

Chandra X-Ray Observations of V830 Tau: A T Tauri Star Hosting an Evanescent Planet

Abstract The radial velocity study by Donati et al. (2016) reported the detection of a close-in giant planet in a 4.93 day orbit around the ∼2 Myr old weak-lined T Tauri star V830 Tau. Because of the stringent timescale constraints that a very young host star like V830 Tau would place on hot-Jupiter formation models and inward-migration mechanisms, independent confirmation of the planet’s existence is needed but so far has not been obtained. We present new Chandra X-ray observations of V830 Tau. The Chandra observations in combination with previous XMM-Newton observations reveal strong, variable X-ray emission with an X-ray luminosity spanning the range log L x = 30.10–30.87 erg s−1. Chandra High Energy Transmission Grating spectra show emission lines formed over a range of plasma temperatures from ∼4 MK (Ne ix) to ∼16 MK (S xv). At the separation of the reported planet (0.057 au) the X-ray flux is ∼106–107 times greater than the Sun’s X-ray flux at Jupiter. We provide estimates of the X-ray ionization and atmospheric heating rates at the planet’s separation and identify areas of uncertainty that will need to be addressed in any future atmospheric models.

X-ray flux in SED modelling: An application of X-CIGALE in the XMM-XXL field

X-CIGALE is built on the spectral energy distribution (SED) code of CIGALE and implements important new features: the code accounts for obscuring material in the poles of AGNs and has the ability to fit X-ray fluxes. In this work, we used ∼2500 spectroscopic X-ray AGNs from the XMM-XXL-north field and examined the improvements the new features bring to the SED modelling analysis. Based on our results, X-CIGALE successfully connects the X-ray with the UV luminosity in the whole range spanned by our sample (log LX(2−10 keV) = (42−46) erg s−1). The addition of the new features generally improves the efficiency of X-CIGALE in the estimation and characterisation of the AGN component. Classification as type 1 or type 2 based on their inclination angle is improved, especially at redshifts lower than 1. The statistical significance of AGN fraction, fracAGN, measurements is increased, in particular for luminous X-ray sources (LX > 1045 erg s−1). These conclusions hold under the condition that (mid-) IR photometry is available in the SED fitting process. The addition of polar dust increases the AGN fraction and the efficiency of the SED decomposition to detect AGNs among X-ray selected sources. X-CIGALE estimates a strong AGN (fracAGN > 0.3) in more than 90% of the IR-selected AGNs and 75% of X-ray-detected AGNs not selected by IR colour criteria. The latter drops to ∼50% when polar dust is not included. The ability of X-CIGALE to include X-ray information in the SED fitting process can be instrumental in the optimal exploitation of the wealth of data that current (eROSITA) and future (ATHENA) missions will provide us.

GJ 357 b

Aims. In this paper we present a deep X-ray observation of the nearby M dwarf GJ 357 and use it to put constraints on the atmospheric evolution of its planet, GJ 357 b. We also analyse the systematic errors in the stellar parameters of GJ 357 in order to see how they affect the perceived planetary properties. Methods. By comparing the observed X-ray luminosity of its host star, we estimate the age of GJ 357 b as derived from a recent XMM-Newton observation (log Lx [erg s−1] = 25.73), with Lx− age relations for M dwarfs. We find that GJ 357 presents one of the lowest X-ray activity levels ever measured for an M dwarf, and we put a lower limit on its age of 5 Gyr. Using this age limit, we performed a backwards reconstruction of the original primordial atmospheric reservoir. Furthermore, by considering the systematic errors in the stellar parameters, we find a range of possible planetary masses, radii, and densities. Results. From the backwards reconstruction of the irradiation history of GJ 357 b’s we find that the upper limit of its initial primordial atmospheric mass is ~38 M⊕. An initial atmospheric reservoir significantly larger than this may have survived through the X-ray and ultraviolet irradiation history, which would not be consistent with current observations that suggest a telluric composition. However, given the relatively small mass of GJ 357 b, even accreting a primordial envelope ≳10 M⊕ would have been improbable as an unusually low protoplanetary disc opacity, large-scale migration, and a weak interior luminosity would have been required. For this reason, we discard the possibility that GJ 357 b was born as a Neptunian- or Jovian-sized body. In spite of the unlikelihood of a currently existing primordial envelope, volcanism and outgassing may have contributed to a secondary atmosphere. Under this assumption, we present three different synthetic IR spectra for GJ 357 b that one might expect, consisting of 100% CO2, 100% SO2, and 75% N2, 24% CO2 and 1% H2O, respectively. Future observations with space-based IR spectroscopy missions will be able to test these models. Finally, we show that the uncertainties in the stellar and planetary quantities do not have a significant effect on the estimated mass or radius of GJ 357 b.

X-ray irradiation and evaporation of the four young planets around V1298 Tau

ABSTRACT Planets around young stars are thought to undergo atmospheric evaporation due to the high magnetic activity of the host stars. Here we report on X-ray observations of V1298 Tau, a young star with four transiting exoplanets. We use X-ray observations of the host star with Chandra and ROSAT to measure the current high-energy irradiation level of the planets and employ a model for the stellar activity evolution together with exoplanetary mass-loss to estimate the possible evolution of the planets. We find that V1298 Tau is X-ray bright with log LX [erg s−1] = 30.1 and has a mean coronal temperature of ≈9 MK. This places the star amongst the more X-ray luminous ones at this stellar age. We estimate the radiation-driven mass-loss of the exoplanets and find that it depends sensitively on the possible evolutionary spin-down tracks of the star as well as on the current planetary densities. Assuming the planets are of low density due to their youth, we find that the innermost two planets can lose significant parts of their gaseous envelopes and could be evaporated down to their rocky cores depending on the stellar spin evolution. However, if the planets are heavier and follow the mass–radius relation of older planets, then even in the highest XUV irradiation scenario none of the planets is expected to cross the radius gap into the rocky regime until the system reaches an age of 5 Gyr.

The origin of X-ray emission in Low-Excitation Radio Galaxies

AbstractIn previous works, the radio-X-ray slope in FRI radio galaxies is found to be steeper compared with that in low-luminosity AGNs, indicating different origin of the X-ray emission. Here we reinvestigate this point by compiling a sample of 13 low-excitation radio galaxies (LERG) from 3CR radio catalog of galaxies, where the central engine in LERG is accepted to be a radiatively inefficient accretion flow (RIAF). The core radio and X-ray emissions in all the objects of our sample are detected by VLA/VLBI/VLBA and Chandra/XMM-Newton, respectively. Surprisingly, a shallower slope of Lr – Lx relation () is given by our sample, which demonstrates that the X-ray emission in LERG may come from accretion disk rather than a jet as suggested by previous works. In addition, the slope in the fundamental plane ((log LR = 0.52 log LX + 0.84 log MBH + 10.84) of LERG is found to be well consistent with that reported by Merloni et al. (2003).

Disentangling the AGN and star formation connection using XMM-Newton

There is growing evidence supporting the coeval growth of galaxies and their resident super-massive black hole (SMBH). Most studies also claim a correlation between the activity of the SMBH and the star formation of the host galaxy. It is unclear, however, whether this correlation extends to all redshifts and X-ray luminosities. Some studies find a weaker dependence at lower luminosities and/or a suppression of the star formation at high luminosities. We here use data from the X-ATLAS and XMM-XXL North fields and compile the largest X-ray sample up to date to investigate how X-ray selected AGN affect the star formation of their host galaxies in a wide redshift and luminosity baseline of 0.03 < z < 3 and log LX(2−10 keV) = (41−45.5) erg s−1. Our sample consists of 3336 AGN. 1872 of our sources have spectroscopic redshifts. For the remaining sources we calculate photometric redshifts using TPZ, a machine-learning algorithm. We estimate stellar masses (M⋆) and star formation rates (SFRs) by applying spectral energy distribution fitting through the CIGALE code, using optical, near-IR, and mid-IR photometry (SDSS, VISTA, and WISE). Of our sources, 608 also have far-IR photometry (Herschel). We use these sources to calibrate the SFR calculations of our remaining X-ray sample. Our results show a correlation between the X-ray luminosity (LX) and the SFR of the host galaxy at all redshifts and luminosities spanned by our sample. We also find a dependence of the specific SFR (sSFR) on redshift, while there are indications that the X-ray luminosity enhances the sSFR even at low redshifts. We then disentangle the effects of stellar mass and redshift on the SFR and again study its dependence on the X-ray luminosity. Towards this end, we estimate the SFR of main-sequence galaxies that have the same stellar mass and redshift as our X-ray AGN and compare them with the SFR of our X-ray AGN. Our analysis reveals that the AGN enhances the star formation of its host galaxy when the galaxy lies below the main sequence and quenches the star formation of the galaxy it lives in when the host lies above the main sequence. Therefore, the effect of AGN on the SFR of the host galaxy depends on the location of the galaxy relative to the main sequence.

The black hole fundamental plane in low-excitation radio galaxies

ABSTRACT The radio–X-ray slope in the fundamental plane of radio-loud active galactic nuclei (AGNs) has been found to be steeper than that of radio-quiet AGNs in previous studies. In this paper, we reinvestigate the fundamental plane in radio-loud AGNs by compiling a sample of 13 low-excitation radio galaxies (LERGs) from the 3CR radio galaxies, for the reason that the accretion mode in LERGs is believed to be a radiatively inefficient accretion flow. All the sources in our sample have data available both at the 5-GHz core radio luminosity as detected by VLA/VLBI/VLBA and at the core X-ray luminosity as detected by Chandra/XMM–Newton. Surprisingly, we find that the slope in the fundamental plane (logLR = 0.52log LX + 0.84log MBH + 10.84) of LERGs is consistent with that reported by Merloni et al. However, the normalization is found to be shifted by about 0.7 dex, which could be due to the difference in the magnetic field strength in different objects. A shallower slope of the LR−LX relationship ($L_{\rm R}\sim L_{\rm X}^{0.63}$) is also found for our sample, which demonstrates that the X-ray emission in LERGs may come from the accretion disc, rather than jets suggested by previous works.

15-GHz radio emission from nearby low-luminosity active galactic nuclei

We present a sub-arcsec resolution radio imaging survey of a sample of 76 low-luminosity active galactic nuclei (LLAGN) that were previously not detected with the Very Large Array at 15 GHz. Compact, parsec-scale radio emission has been detected above a flux density of 40 μ Jy in 60% (45 of 76) of the LLAGN sample. We detect 20 out of 31 (64%) low-ionization nuclear emission-line region (LINER) nuclei, ten out of 14 (71%) low-luminosity Seyfert galaxies, and 15 out of 31 (48%) transition objects. We use this sample to explore correlations between different emission lines and the radio luminosity. We also populate the X-ray and the optical fundamental plane of black hole activity and further refine its parameters. We obtain a fundamental plane relation of log LR = 0.48 (±0.04) log LX + 0.79 (±0.03) log M and an optical fundamental plane relation of log LR = 0.63 (±0.05) log L[O III] + 0.67 (±0.03) log M after including all the LLAGN detected at high resolution at 15 GHz, and the best-studied hard-state X-ray binaries (luminosities are given in erg s−1 while the masses are in units of solar mass). Finally, we find conclusive evidence that the nuclear 15 GHz radio luminosity function (RLF) of all the detected Palomar Sample LLAGN has a turnover at the low-luminosity end, and is best-fitted with a broken power law. The break in the power law occurs at a critical mass accretion rate of 1.2 × 10−3 M⊙ yr−1, which translates to an Eddington ratio of ṁEdd ~ 5.1 × 10−5, assuming a black hole mass of 109 M⊙. The local group stands closer to the extrapolation of the higher-luminosity sources, and the classical Seyferts agree with the nuclear RLF of the LLAGN in the local universe.

Determination of Cosmological Parameters with a Sample of Quasars

We use a sample of 808 quasars selected by Risaliti and Lusso to estimate two important cosmological parameters: the percentage of matter in the Universe Ωm and the Hubble constant. The method is based on an auxiliary experimental correlation between the luminosity of quasars in the Xray band and UV band in the form log LX = β + γ log LUV. For the flat ΛCDM model our fit gives Ω m = 0.21 ± 0.12. Our main results are the following: firstly, the fraction of matter (baryonic + dark) contained in the Universe is 21% according to our estimate and is smaller than the one found by other authors using Type Ia Supernovae (though, considering the large error, our result is consistent with the supernova data). Secondly, the Einstein–de Sitter model is outside the 95% confidence interval of our best fit curve. In order to determine also the Hubble constant, we were compelled to fix one of the free parameters (β, γ,H0,Ω m ) and to determine the others with the non-linear least square method. We have proceeded in two different ways. Increasing h0 = H0/100 with a step of 0.01 in the range from 0.65 to 0.95, we obtain a Hubble constant H0 = 74.6± 2.4 (km/s)/Mpc in agreement with the values found using CMB, supernovae and cepheids. On the other hand, increasing the parameter m = β/γ with a step of 0.03 in the range from 13.4 to 14.4, we obtain the same result (but with a greater statistical error), and hence a self-consistentmodel, only assuming β ≥ 8.21.

X-ray emission from the giant magnetosphere of the magnetic O-type star NGC 1624-2

We observed NGC 1624-2, the O-type star with the largest known magnetic field Bp~20 kG), in X-rays with the ACIS-S camera onboard the Chandra X-ray Observatory. Our two observations were obtained at the minimum and maximum of the periodic Halpha emission cycle, corresponding to the rotational phases where the magnetic field is the closest to equator-on and pole-on, respectively. With these observations, we aim to characterise the star's magnetosphere via the X-ray emission produced by magnetically confined wind shocks. Our main findings are: (i) The observed spectrum of NGC 1624-2 is hard, similar to the magnetic O-type star Theta 1 Ori C, with only a few photons detected below 0.8 keV. The emergent X-ray flux is 30% lower at the Halpha minimum phase. (ii) Our modelling indicated that this seemingly hard spectrum is in fact a consequence of relatively soft intrinsic emission, similar to other magnetic Of?p stars, combined with a large amount of local absorption (~1-3 x 10^22 cm^-2). This combination is necessary to reproduce both the prominent Mg and Si spectral features, and the lack of flux at low energies. NGC 1624-2 is intrinsically luminous in X-rays (log LX emission ~ 33.4) but 70-95% of the X-ray emission produced by magnetically confined wind shocks is absorbed before it escapes the magnetosphere (log LX ISM corrected ~ 32.5). (iii) The high X-ray luminosity, its variation with stellar rotation, and its large attenuation are all consistent with a large dynamical magnetosphere with magnetically confined wind shocks.

X-RAYING THE CORONAE OF HD 155555

We present an analysis of the high-resolution Chandra observation of the multiple system, HD 155555 (an RS CVn type binary system, HD 155555 AB, and its spatially resolved low-mass companion HD 155555 C). This is an intriguing system which shows properties of both an active pre-main sequence star and a synchronised (main sequence) binary. We obtain the emission measure distribution, temperature structures, plasma densities, and abundances of this system and compare them with the coronal properties of other young/active stars. HD 155555 AB and HD 155555 C produce copious X-ray emission with log Lx of 30.54 and 29.30, respectively, in the 0.3-6.0 keV energy band. The light curves of individual stars show variability on timescales of few minutes to hours. We analyse the dispersed spectra and reconstruct the emission measure distribution using spectral line analysis. The resulting elemental abundances exhibit inverse first ionisation potential effect in both cases. An analysis of He-like triplets yields a range of coronal electron densities ~10^10-10^13 cm-3. Since HD 155555 AB is classified both as an RS CVn and a PMS star, we compare our results with those of other slightly older active main-sequence stars and T Tauri stars, which indicates that the coronal properties of HD 155555 AB closely resemble that of an older RS CVn binary rather than a younger PMS star. Our results also suggests that the properties of HD 155555 C is very similar to those of other active M dwarfs.

DETAILED SHAPE AND EVOLUTIONARY BEHAVIOR OF THE X-RAY LUMINOSITY FUNCTION OF ACTIVE GALACTIC NUCLEI

We construct the rest-frame 2--10 keV intrinsic X-ray luminosity function of Active Galactic Nuclei (AGNs) from a combination of X-ray surveys from the all-sky Swift BAT survey to the Chandra Deep Field-South. We use ~3200 AGNs in our analysis, which covers six orders of magnitude in flux. The inclusion of the XMM and Chandra COSMOS data has allowed us to investigate the detailed behavior of the XLF and evolution. In deriving our XLF, we take into account realistic AGN spectrum templates, absorption corrections, and probability density distributions in photometric redshift. We present an analytical expression for the overall behavior of the XLF in terms of the luminosity-dependent density evolution, smoothed two power-law expressions in 11 redshift shells, three-segment power-law expression of the number density evolution in four luminosity classes, and binned XLF. We observe a sudden flattening of the low luminosity end slope of the XLF slope at z>~0.6. Detailed structures of the AGN downsizing have been also revealed, where the number density curves have two clear breaks at all luminosity classes above log LX>43. The two break structure is suggestive of two-phase AGN evolution, consisting of major merger triggering and secular processes.

The X-ray spectral evolution and radio–X-ray correlation in radiatively efficient black-hole sources

AbstractWe explore X-ray spectral evolution and radio–X-ray correlation simultaneously for four X-ray binaries (XRBs). We find that hard X-ray photon indices, Γ, are anti- and positively correlated to X-ray fluxes when the X-ray flux, F3–9keV, is below and above a critical flux, FX,crit, which may be regulated by ADAF and disk-corona respectively. We find that the data points with anti-correlation of Γ-F3–9keV follow the universal radio–X-ray correlation of FR ∝ FXb (b ~ 0.5-0.7), while the data points with positive X-ray spectral evolution follow a steeper radio–X-ray correlation (b ~ 1.4, the so-called ‘outliers track’). The bright active galactic nuclei (AGNs) share similar X-ray spectral evolution and radio–X-ray correlation as XRBs in ‘outliers’ track, and we present a new fundamental plane of log LR=1.59+0.28−0.22 log LX−0.22+0.19−0.20 log MBH−28.97+0.45−0.45 for these radiatively efficient BH sources.

X-ray activity cycle on the active ultra-fast rotator AB Doradus A?

Although chromospheric activity cycles have been studied in a larger number of late-type stars for quite some time, very little is known about coronal activity-cycles in other stars and their similarities or dissimilarities with the solar activity cycle. While it is usually assumed that cyclic activity is present only in stars of low to moderate activity, we investigate whether the ultra-fast rotator AB Dor, a K dwarf exhibiting signs of substantial magnetic activity in essentially all wavelength bands, exhibits a X-ray activity cycle in analogy to its photospheric activity cycle of about 17 years and possible correlations between these bands. We analysed the combined optical photometric data of AB Dor A, which span ~35 years. Additionally, we used ROSAT and XMM-Newton X-ray observations of AB Dor A to study the long-term evolution of magnetic activity in this active K dwarf over nearly three decades and searched for X-ray activity cycles and related photometric brightness changes. AB Dor A exhibits photometric brightness variations ranging between 6.75 < Vmag < 7.15 while the X-ray luminosities range between 29.8 < log LX [erg/s] < 30.2 in the 0.3-2.5 keV. As a very active star, AB Dor A shows frequent X-ray flaring, but, in the long XMM-Newton observations a kind of basal state is attained very often. This basal state probably varies with the photospheric activity-cycle of AB Dor A which has a period of ~17 years, but, the X-ray variability amounts at most to a factor of ~2, which is, much lower than the typical cycle amplitudes found on the Sun.

X-RAY OBSERVATIONS OF DISRUPTED RECYCLED PULSARS: NO REFUGE FOR ORPHANED CENTRAL COMPACT OBJECTS

We present a Chandra X-ray survey of the disrupted recycled pulsars (DRPs), isolated radio pulsars with P > 20 ms and B_s < 3E10 G. These observations were motivated as a search for the immediate descendants of the approx. 10 central compact objects (CCOs) in supernova remnants, three of which have similar timing and magnetic properties as the DRPs, but are bright, thermal X-ray sources consistent with minimal neutron star cooling curves. Since none of the DPRs were detected, there is no evidence that they are "orphaned" CCOs, neutron stars whose supernova remnants has dissipated. Upper limits on their thermal X-ray luminosities are in the range log Lx[erg/s] = 31.8-32.8, which implies cooling ages > 1E4 - 1E5 yr, roughly 10 times the ages of the approximately 10 known CCOs in a similar volume of the Galaxy. The order of a hundred CCO descendants that could be detected by this method are thus either intrinsically radio quiet, or occupy a different region of (P,B_s) parameter space from the DRPs. This motivates a new X-ray search for orphaned CCOs among radio pulsars with larger B-fields, which could verify the theory that their fields are buried by fall-back of supernova ejecta, but quickly regrow to join the normal pulsar population.