Optical Flux Ratio Research Articles

Simultaneous Chandra and HST observations of the quiescent neutron star low-mass X-ray binaries in 47 Tucanae

ABSTRACT We present simultaneous Chandra X-ray Observatory and Hubble Space Telescope observations of three certain (X5, X7, W37) and two likely (X4, W17) quiescent neutron star low-mass X-ray binaries (qLMXBs) in the globular cluster 47 Tuc. We study these systems in the X-ray, optical, and near-ultraviolet (NUV) using the simultaneous data and additional non-contemporaneous HST data. We have discovered a blue and variable NUV counterpart to W17. We have not securely identified the eclipsing qLMXB W37 in the optical or NUV. Deeper high-resolution imaging is needed to further investigate the faint NUV excess near the centre of the W37 error circle. We suggest that a previously identified optical astrometric match to X7 is likely the true counterpart. The H α emission and the location of the counterpart in the colour–magnitude diagram, indicate that the secondary is probably a non-degenerate, H-rich star. This is consistent with previous results from fitting X7’s X-ray spectrum. In X4, the simultaneous X-ray and optical behaviour supports the earlier suggestion that the X-ray variability is driven by changes in accretion rate. The X-ray eclipses in X5 coincide with minima in the optical/NUV light curves. Comparison of the 47 Tuc qLMXBs with the cataclysmic variables (CVs) in the cluster confirms that overall the qLMXBs have larger X-ray to optical flux ratios. Based on their optical/NUV colours, we conclude that the accretion discs in the qLMXBs are less prominent than in CVs. This makes the ratio of X-ray flux to excess blue-optical flux a powerful discriminator between CVs and qLMXBs.

Radio imaging of gravitationally lensed radio-quiet quasars

Abstract We present 6-GHz Very Large Array radio images of 70 gravitational lens systems at 300-mas resolution, in which the source is an optically-selected quasar, and nearly all of which have two lensed images. We find that about in half of the systems (40/70, with 33/70 secure), one or more lensed images are detected down to our detection limit of 20 $\mu$Jy beam−1, similar to previous investigations and reinforcing the conclusion that typical optically-selected quasars have intrinsic GHz radio flux densities of a few $\mu$Jy (∼1023 W Hz−1) at redshifts of 1–2. In addition, for ten cases it is likely that the lensing galaxies are detected in the radio. Available detections of, and limits on the far-infrared luminosities from the literature, suggest that nearly all of the sample lie on the radio-FIR correlation typical of star-forming galaxies, and that their radio luminosities are at least compatible with the radio emission being produced by star formation processes. One object, WISE2329−1258, has an extra radio component that is not present in optical images, and is difficult to explain using simple lens models. In-band spectral indices, where these can be determined, are generally moderately steep and consistent with synchrotron processes either from star-formation/supernovae or AGN. Comparison of the A/B image flux ratios at radio and optical wavelengths suggests a 10 per cent level contribution from finite source effects or optical extinction to the optical flux ratios, together with sporadic larger discrepancies that are likely to be due to optical microlensing.

Revisiting X-Ray-bright Optically Normal Galaxies with the Chandra Source Catalog

X-ray bright optically normal galaxies (XBONGs) are galaxies with X-ray luminosities consistent with those of active galactic nuclei (AGNs) but no evidence of AGN optical emission lines. Crossmatching the Chandra Source Catalog version 2 with the Sloan Digital Sky Survey sample of spectroscopically classified galaxies, we have identified 817 XBONG candidates with L X > 1042 erg s−1 and X-ray to optical flux ratio F XO > 0.1. Comparisons with Wide-field Infrared Survey Explorer colors and near-IR, optical, UV, and radio luminosities show that the loci of XBONGs are in-between those of control samples of normal galaxies and quasars and are consistent with low-luminosity quasars. We find that 43% of the XBONG sample have X-ray colors suggesting N H > 1022 cm−2, double the fraction in the QSO sample, suggesting that a large fraction of XBONG are highly obscured AGNs. However, ∼50% of the XBONGs are not obscured and have X-ray colors harder than those of normal galaxies. Some of these XBONGs have spatially extended X-ray emission. These characteristics suggest that they may be unidentified galaxy groups and clusters. Using the X-ray luminosity functions of QSOs, galaxies, groups and clusters, we estimate the approximate fraction of extended XBONGs to be <20%. We also assess the approximate fraction of XBONGs whose AGN signatures are diluted by stellar light of host galaxies to be ∼30%, based on their redshift and deviation from the extrapolation of the QSO L X–L r relation.

The nature of the X-ray sources in dwarf galaxies in nearby clusters from the KIWICS

ABSTRACT We present a deep search for and analysis of X-ray sources in a sample of dwarf galaxies (Mr &amp;lt; −15.5 mag) located within twelve galaxy clusters from the Kapteyn IAC WHT Enhanced Area Velocity Explores Isaac Newton Telescope Cluster Survey of photometric observations in the r and g using the Wide Field Camera at the 2.5-m Isaac Newton telescope. We first investigated the optical data, identified 2720 dwarf galaxies in all fields and determined their characteristics; namely, their colours, effective radii, and stellar masses. We then searched the Chandra data archive for X-ray counterparts of optically detected dwarf galaxies. We found a total of 20 X-ray emitting dwarf galaxies, with X-ray flux ranging from 1.7 × 10−15 to 4.1 × 10−14 erg cm−2 s−1 and X-ray luminosities varying from 2 × 1039 to 5.4 × 1041 erg s−1. Our results indicate that the X-ray luminosity of the sources in our sample is larger than the Eddington luminosity limit for a typical neutron star, even at the lowest observed levels. This leads us to conclude that the sources emitting X-rays in our sample are likely black holes. Additionally, we have employed a scaling relation between black hole and stellar mass to estimate the masses of the black holes in our sample, and have determined a range of black hole masses from 4.6 × 104 to 1.5 × 106 M⊙. Finally, we find a trend between X-ray to optical flux ratio and X-ray flux. We discuss the implications of our findings and highlight the importance of X-ray observations in studying the properties of dwarf galaxies.

Varstrometry selected radio-loud candidates of dual and off-nucleus quasars at sub-kpc scales

ABSTRACT Dual super massive black holes (SMBHs) at sub-kpc to kpc scales, the product of galaxy mergers, are progenitors of eventually coalescing binary SMBHs. If both or one of the dual SMBHs are accreting, they may appear as dual AGNs or off-nucleus AGNs. Studying such systems is essential to learn the dynamical evolution of binary SMBHs as well as the process of galaxy merging. Recently a novel astrometry-based method named varstrometry has been put forward to search for dual SMBHs at high redshift, as the unsynchronized flux variability of dual AGNs (or off-nucleus AGNs) will cause astrometric jitters detectable by Gaia without spatially resolving them. Based on Gaia varstrometry, we select a rare sample of five radio loud quasars with clear Gaia astrometric jitters. With e-MERLIN observations, we have revealed a single compact radio source for each of them. Remarkably all but one exhibit clear Gaia-radio offsets of ∼9–60 mas. The observed Gaia jitters appear consistent with the expected values. These detected Gaia-radio offsets suggest these candidate dual SMBHs may have projected separations as small as ∼0.01–0.1 arcsec (∼0.1 kpc, depending on the optical flux ratio of two SMBHs). Meanwhile, this work highlights the remarkably high efficiency of Gaia varstrometry selection of jittering sources.

The Physical Conditions of Emission-line Galaxies at Cosmic Dawn from JWST/NIRSpec Spectroscopy in the SMACS 0723 Early Release Observations

We present rest-frame optical emission-line flux ratio measurements for five z > 5 galaxies observed by the James Webb Space Telescope Near-Infared Spectrograph (NIRSpec) in the SMACS 0723 Early Release Observations. We add several quality-control and post-processing steps to the NIRSpec pipeline reduction products in order to ensure reliable relative flux calibration of emission lines that are closely separated in wavelength, despite the uncertain absolute spectrophotometry of the current version of the reductions. Compared to z ∼ 3 galaxies in the literature, the z > 5 galaxies have similar [O iii]λ5008/Hβ ratios, similar [O iii]λ4364/Hγ ratios, and higher (∼0.5 dex) [Ne III]λ3870/[O II]λ3728 ratios. We compare the observations to MAPPINGS V photoionization models and find that the measured [Ne III]λ3870/[O II]λ3728, [O iii]λ4364/Hγ, and [O iii]λ5008/Hβ emission-line ratios are consistent with an interstellar medium (ISM) that has very high ionization (, units of cm s−1), low metallicity (Z/Z ⊙ ≲ 0.2), and very high pressure (, units of cm−3). The combination of [O iii]λ4364/Hγ and [O iii]λ(4960 + 5008)/Hβ line ratios indicate very high electron temperatures of , further implying metallicities of Z/Z ⊙ ≲ 0.2 with the application of low-redshift calibrations for “T e -based” metallicities. These observations represent a tantalizing new view of the physical conditions of the ISM in galaxies at cosmic dawn.

SUPER VII. morphology and kinematics of H α emission in AGN host galaxies at cosmic noon using SINFONI

ABSTRACTWe present spatially resolved H α properties of 21 type 1 AGN host galaxies at z ∼ 2 derived from the SUPER survey. These targets were observed with the adaptive optics capabilities of the SINFONI spectrograph, a near-infrared integral field spectrograph, that provided a median spatial resolution of 0.3 arcsec (∼2 kpc). We model the H α emission line profile in each pixel to investigate whether it traces gas in the narrow line region or if it is associated with star formation. To do this, we first investigate the presence of resolved H α emission after subtracting the AGN PSF. We find extended H α emission in 16 out of the 21 type 1 AGN host galaxies (76 per cent). Based on the BPT diagnostics, optical line flux ratios and line widths (FWHM), we show that the H α emission in five galaxies is ionized by the AGN (30 per cent), in four galaxies by star formation (25 per cent) and for the rest (45 per cent), the ionization source is unconstrained. Two galaxies show extended H α FWHM &amp;gt;600 km s−1, which is interpreted as a part of an AGN-driven outflow. Morphological and kinematic maps of H α emission in targets with sufficient signal-to-noise ratio suggest the presence of rotationally supported discs in six galaxies and possible presence of companions in four galaxies. In two galaxies, we find an anticorrelation between the locations of extended H α emission and [O iii]-based ionized outflows, indicating possible negative feedback at play. However, in the majority of galaxies, we do not find evidence of outflows impacting H α-based star formation.

The optically elusive, changing-look active nucleus in NGC 4156

We report on the changing-look nature of the active galactic nucleus (AGN) in the galaxy NGC 4156, which was serendipitously discovered thanks to data acquired in 2019 at the Telescopio Nazionale Galileo (TNG) during a student observing programme. Previous optical spectra had never shown any signatures of broad-line emission, and evidence of the AGN had come only from X-ray observations, given the optical narrow-line flux ratios made it unfeasible to unambiguously denote it as a Seyfert galaxy. Our 2019 TNG data unexpectedly revealed the appearance of broad-line components in both the Hα and Hβ profiles, along with a rise of the continuum, thus implying a changing-look AGN transitioning from a type 2 (no broad-line emission) towards a (nearly) type 1. The broad-line emission has then been confirmed by our 2022 follow-up observations, whereas the rising continuum is no longer been detected, which hints at a further evolution backwards to a (nearly) type 2. The presence of broad-line components also allowed us to obtain the first single-epoch estimate of the black hole mass (log(MBH/M⊙)∼8.1) in this source. The observed spectral variability might be the result of a change in the accretion activity of NGC 4156, although variable absorption cannot be completely excluded.

Catalog of X-Ray Detected Be Stars (XDBS)

We present a catalog of X-ray Detected Be Stars (XDBS) with 161 Be stars from the Be Star Spectra (BeSS) database having X-ray counterparts in the Chandra Source Catalog v2.0, XMM-Newton 4XMM-DR11 Catalog, or Swift 2SXPS Catalog. The multi-wavelength catalog includes accurate optical positions, X-ray properties (fluxes, photon indices and hardness ratios), optical, near-infrared and infrared photometry, source classifications (when available), and other properties including proper motions, effective temperatures, X-ray to optical flux ratios as well. We also provide a convenient https://home.gwu.edu/~kargaltsev/XDBS/graphical user interface which allows for easy visualization of the catalog content.

Average bolometric corrections and optical to X-ray flux measurements as a function of accretion rate for X-ray binaries

ABSTRACT In this paper, we use an RXTE library of spectral models from 10 black hole and 9 pulsar X-ray binaries, as well as model spectra available in the literature from 13 extra-galactic ultra-luminous X-ray sources (ULXs). We compute average bolometric corrections (BC = Lband/Lbol) for our sample as a function of different accretion rates. We notice the same behaviour between black hole and pulsar BCs only when ULX pulsars are included. These measurements provide a picture of the energetics of the accretion flow for an X-ray binary based solely on its observed luminosity in a given band. Moreover, it can be a powerful tool in X-ray binary population synthesis models. Furthermore, we calculate the X-ray (2–10 keV) to optical (V band) flux ratios originating from the disc/corona at different Eddington ratios for the black hole X-ray binaries in our sample. This provides a metric of the maximum contribution of the disc to the optical emission of a binary system and better constraints on its nature (donor type, etc.). We find that the optical to X-ray flux ratio shows very little variation as a function of accretion rate, but testing for different disc geometry scenarios we find that the optical contribution of the disc increases as the p value decreases [T(r) ∼ r−p]. Moreover, observational data are in agreement with a thicker disc scenario (p &amp;lt; 0.65), which could also possibly explain the lack of observed high-inclination systems.

The ROSAT Raster survey in the north ecliptic pole field

The north ecliptic pole (NEP) is an important region for extragalactic surveys. Deep and wide contiguous surveys are being performed by several space observatories, most currently with the eROSITA telescope. Several more are planned for the near future. We analyse all the ROSAT pointed and survey observations in a region of 40 deg2 around the NEP, restricting the ROSAT field of view to the inner 30′ radius. We obtain an X-ray catalogue of 805 sources with 0.5−2 keV fluxes &gt; 2.9 × 10−15 erg cm−2 s−1, about a factor of three deeper than the ROSAT All-Sky Survey in this field. The sensitivity and angular resolution of our data are comparable to the eROSITA All-Sky Survey expectations. The 50% position error radius of the sample of X-ray sources is ∼10″. We use HEROES optical and near-infrared imaging photometry from the Subaru and Canada/France/Hawaii telescopes together with GALEX, SDSS, Pan-STARRS, and WISE catalogues, as well as images from a new deep and wide Spitzer survey in the field to statistically identify the X-ray sources and to calculate photometric redshifts for the candidate counterparts. In particular, we utilize mid-infrared (mid-IR) colours to identify active galactic nucleus (AGN) X-ray counterparts. Despite the relatively large error circles and often faint counterparts, together with confusion issues and systematic errors, we obtain a rather reliable catalogue of 766 high-quality optical counterparts, corresponding redshifts and optical classifications. The quality of the dataset is sufficient to look at ensemble properties of X-ray source classes. In particular we find a new population of luminous absorbed X-ray AGN at large redshifts, identified through their mid-IR colours. This populous group of AGN was not recognized in previous X-ray surveys, but could be identified in our work due to the unique combination of survey solid angle, X-ray sensitivity, and quality of the multi-wavelength photometry. We also use the WISE and Spitzer photometry to identify a sample of 185 AGN selected purely through their mid-IR colours, most of which are not detected by ROSAT. Their redshifts and upper limits to X-ray luminosity and X-ray–to–optical flux ratios are even higher than for the new class of X-ray selected luminous type 2 AGN (AGN2); they are probably a natural extension of this sample. This unique dataset is important as a reference sample for future deep surveys in the NEP region, in particular for eROSITA and also for Euclid and SPHEREX. We predict that most of the absorbed distant AGN should be readily picked up by eROSITA, but they require sensitive mid-IR imaging to be recognized as optical counterparts.

A multiwavelength study of the dual nuclei in Mrk 212

ABSTRACT We present radio observations of the galaxy merger remnant Mrk 212 with the Karl G. Jansky Very Large Array (VLA) and the upgraded Giant Meter Radio Telescope (uGMRT). Mrk 212 has two previously known radio sources associated with the two optical nuclei, S1 and S2, with a projected separation of ∼6 kpc, making it a dual active galactic nuclei (AGN) candidate. Our new 15-GHz VLA observations reveal that S1 is a double radio source centred around the optical nucleus; its total extent is ∼750 pc its average 1.4−8.5 GHz spectral index is −0.81 ± 0.06. S1 therefore resembles a compact symmetric object. The 15-GHz VLA image identifies the radio source at S2 to be a compact core. Our radio observations therefore strongly support the presence of a dual AGN in Mrk 212. The optical emission line flux ratios obtained from the Himalayan Chandra Telescope (HCT) observations however, show that S1 and S2 both fall in the AGN + star formation (SF) region of the Baldwin, Philips and Terlevich (BPT) diagram. Weak AGN lying in the SF or AGN + SF intermediate regions in the BPT diagram have indeed been reported in the literature; our sources clearly fall in the same category. We find an extended radio structure in our newly reduced 8.5-GHz-VLA data, that is offset by ∼1 arcsec from the optical nucleus S2. New deep FUV and NUV observations with the Ultraviolet Imaging Telescope aboard AstroSat reveal SF knots around S2 as well as kpc-scale tidal tails; the SF knots around S2 coincide with the extended radio structure detected at 8.5 GHz. The radio spectral indices are consistent with SF. Any possible association with the AGN in S2 is unclear at this stage.

A Catalog of 406 AGNs in MaNGA: A Connection between Radio-mode AGNs and Star Formation Quenching

Abstract Accurate active galactic nucleus (AGN) identifications and spatially resolved host galaxy properties are a powerful combination for studies of the role of AGNs and AGN feedback in the coevolution of galaxies and their central supermassive black holes. Here, we present robust identifications of 406 AGNs in the first 6261 galaxies observed by the integral field spectroscopy survey Mapping Nearby Galaxies at Apache Point Observatory. Instead of using optical line flux ratios, which can be difficult to interpret in light of the effects of shocks and metallicity, we identify the AGNs via mid-infrared Wide-field Infrared Survey Explorer colors, Swift/BAT ultrahard X-ray detections, NVSS and FIRST radio observations, and broad emission lines in SDSS spectra. We subdivide the AGNs into radio-quiet and radio-mode AGNs, and examine the correlations of the AGN classes with host galaxy star formation rates and stellar populations. When compared to the radio-quiet AGN host galaxies, we find that the radio-mode AGN host galaxies are preferentially elliptical, lie further beneath the star-forming main sequence (with lower star formation rates at fixed galaxy mass), have older stellar populations, and have more negative stellar age gradients with galactocentric distance (indicating inside-out quenching of star formation). These results establish a connection between radio-mode AGNs and the suppression of star formation.

X-ray activity from different types of stars

X-ray emission is an important indicator of stellar activity. In this paper, we study stellar X-ray activity using the XMM-Newton and LAMOST data for different types of stars. We provide a sample including 1259 X-ray-emitting stars, of which 1090 have accurate stellar parameter estimations. Our sample size is much larger than those used in previous works. We find a bimodal distribution of the X-ray to optical flux ratio (log(fX/fV)) for G and K stars. We interpret that this bimodality is due to two subpopulations with different coronal heating rates. Furthermore, using the full widths at half maxima calculated from Hα and Hβ lines, we show that these stars in the inactive peaks have smaller rotational velocities. This is consistent with the magnetic dynamo theory that presumes stars with low rotational velocities have low levels of stellar activity. We also examine the correlation between log(fX/fV) and luminosity of the excess emission in the Hα line, and find a tight relation between the coronal and chromospheric activity indicators.

V902 Monocerotis: A likely disc-accreting intermediate polar

Aims. We aim to confirm whether the eclipsing cataclysmic variable (CV) V902 Mon is an intermediate polar (IP), to characterise its X-ray spectrum and flux, and to refine its orbital ephemeris and spin period. Methods. We performed spectrographic observations of V902 Mon in 2016 with the 2.2 m Calar Alto telescope, and X-ray photometry and spectroscopy with XMM-Newton in October 2017. This data was supplemented by several years of AAVSO visual photometry. Results. We confirmed V902 Mon as an IP based on detecting the spin period, which has a value of 2208 s, at multiple epochs. Spectroscopy of the donor star and Gaia parallax yield a distance of 3.5−0.9+1.3 kpc, suggesting an X-ray luminosity one or two orders of magnitude lower than the 1033 erg s−1 typical of previously known IPs. The X-ray to optical flux ratio is also very low. The inclination of the system is more than 79°, and is most likely a value of around 82°. We have refined the eclipse ephemeris, stable over 14 000 cycles. The Hα line is present throughout the orbital cycle and is clearly present during eclipse, suggesting an origin distant from the white dwarf, and shows radial velocity variations at the orbital period. The amplitude and overall recessional velocity seem inconsistent with an origin in the disc. The XMM-Newton observation reveals a partially absorbed plasma model typical of magnetic CVs, that has a fluorescent iron line at 6.4 keV showing a large equivalent width of 1.4 keV. Conclusions. V902 Mon is an IP, and probably a member of the hypothesized X-ray underluminous class of IPs. It is likely to be a disc accretor, although the radial velocity behaviour of the Hα line remains puzzling. The large equivalent width of the fluorescent iron line, the small FX/Fopt ratio, and the only marginal detection of X-ray eclipses suggests that the X-ray emission arises from scattering.

Parameterizations of Chromospheric Condensations in dG and dMe Model Flare Atmospheres

Abstract The origin of the near-ultraviolet and optical continuum radiation in flares is critical for understanding particle acceleration and impulsive heating in stellar atmospheres. Radiative-hydrodynamic (RHD) simulations in 1D have shown that high energy deposition rates from electron beams produce two flaring layers at T ∼ 104 K that develop in the chromosphere: a cooling condensation (downflowing compression) and heated non-moving (stationary) flare layers just below the condensation. These atmospheres reproduce several observed phenomena in flare spectra, such as the red-wing asymmetry of the emission lines in solar flares and a small Balmer jump ratio in M dwarf flares. The high beam flux simulations are computationally expensive in 1D, and the (human) timescales for completing NLTE models with adaptive grids in 3D will likely be unwieldy for some time to come. We have developed a prescription for predicting the approximate evolved states, continuum optical depth, and emergent continuum flux spectra of RHD model flare atmospheres. These approximate prescriptions are based on an important atmospheric parameter: the column mass ( ) at which hydrogen becomes nearly completely ionized at the depths that are approximately in steady state with the electron beam heating. Using this new modeling approach, we find that high energy flux density (&gt;F11) electron beams are needed to reproduce the brightest observed continuum intensity in IRIS data of the 2014 March 29 X1 solar flare, and that variation in from 0.001 to 0.02 g cm−2 reproduces most of the observed range of the optical continuum flux ratios at the peak of M dwarf flares.

Shocks and Spatially Offset Active Galactic Nuclei Produce Velocity Offsets in Emission Lines

Abstract While 2% of active galactic nuclei (AGNs) exhibit narrow emission lines with line-of-sight velocities that are significantly offset from the velocity of the host galaxy’s stars, the nature of these velocity offsets is unknown. We investigate this question with Chandra/ACIS and Hubble Space Telescope/Wide Field Camera 3 observations of seven velocity-offset AGNs at ; all seven galaxies have a central AGN, but a peak in emission that is spatially offset by &lt;kpc from the host galaxy’s stellar centroid. These spatial offsets are responsible for the observed velocity offsets and are due to shocks, either from AGN outflows (in four galaxies) or gas inflowing along a bar (in three galaxies). We compare our results with a velocity-offset AGN whose velocity offset originates from a spatially offset AGN in a galaxy merger. The optical line flux ratios of the offset AGN are consistent with pure photoionization, while the optical line flux ratios of our sample are consistent with contributions from photoionization and shocks. We conclude that these optical line flux ratios could be efficient for separating velocity-offset AGNs into subgroups of offset AGNs—which are important for studies of AGN fueling in galaxy mergers—and central AGNs with shocks, where the outflows are biased toward the most energetic outflows that are the strongest drivers of feedback.

Spectroscopic classification of X-ray sources in the Galactic Bulge Survey

We present the classification of 26 optical counterparts to X-ray sources discovered in the Galactic Bulge Survey. We use (time-resolved) photometric and spectroscopic observations to classify the X-ray sources based on their multiwavelength properties. We find a variety of source classes, spanning different phases of stellar/binary evolution. We classify CX21 as a quiescent cataclysmic variable (CV) below the period gap, and CX118 as a high accretion rate (nova-like) CV. CXB12 displays excess UV emission, and could contain a compact object with a giant star companion, making it a candidate symbiotic binary or quiescent low-mass X-ray binary (although other scenarios cannot be ruled out). CXB34 is a magnetic CV (polar) that shows photometric evidence for a change in accretion state. The magnetic classification is based on the detection of X-ray pulsations with a period of 81 ± 2 min. CXB42 is identified as a young stellar object, namely a weak-lined T Tauri star exhibiting (to date unexplained) UX Ori-like photometric variability. The optical spectrum of CXB43 contains two (resolved) unidentified double-peaked emission lines. No known scenario, such as an active galactic nucleus or symbiotic binary, can easily explain its characteristics. We additionally classify 20 objects as likely active stars based on optical spectroscopy, their X-ray to optical flux ratios and photometric variability. In four cases we identify the sources as binary stars.

An X-ray/SDSS sample

Multi-phase fast, massive outflows have been postulated to play a crucial role in galaxy evolution. The aim of this work is to constrain the nature and the fraction of outflowing gas in AGNs, as well as the nuclear conditions possibly at the origin of such phenomena. We present a large spectroscopic sample of X-ray detected SDSS AGNs at z <0.8. X-ray and optical flux ratio diagnostics are used to select the sample. Physical and kinematic characterisation are derived re-analysing optical (and X-ray) spectra. We derive the incidence of ionised (~40%) and atomic (< 1%) outflows covering a wide range of AGN bolometric luminosity, from 10^42 to 10^46 erg/s. We also derive bolometric luminosities and X-ray bolometric corrections to test whether the presence of outflows is associated with an X-ray loudness, as suggested by our recent results obtained studying high-z QSOs. We study the relations between the outflow velocity inferred from [O III] kinematic analysis and different AGN power tracers, such as black hole mass (M_BH), [O III] and X-ray luminosity. We show a well defined positive trend between outflow velocity and L_X, for the first time over a range of 5 order of magnitudes. Overall, we find that in the QSO-luminosity regime and at M_BH>10^8 Msun the fraction of AGNs with outflows becomes >50%. Finally, we discuss our results about X-ray bolometric corrections and outflow incidence in cold and ionised phases in the context of an evolutionary sequence allowing two distinct stages for the feedback phase: an initial stage characterized by X-ray/optical obscured AGNs in which the atomic gas is still present in the ISM and the outflow processes involve all the gas components, and a later stage associated with unobscured AGNs, which line of sight has been cleaned and the cold components have been heated or exhausted.

Efficiency of Synchrotron Radiation from Rotation-powered Pulsars

Abstract Synchrotron radiation is widely considered to be the origin of the pulsed non-thermal emissions from rotation-powered pulsars in optical and X-ray bands. In this paper, we study the synchrotron radiation emitted by the created electron and positron pairs in the pulsar magnetosphere to constrain the energy conversion efficiency from the Poynting flux to the particle energy flux. We model two pair creation processes, two-photon collision, which efficiently works in young γ-ray pulsars (≲106 year), and magnetic pair creation, which is the dominant process to supply pairs in old pulsars (≳106 year). Using the analytical model, we derive the maximum synchrotron luminosity as a function of the energy conversion efficiency. From the comparison with observations, we find that the energy conversion efficiency to the accelerated particles should be an order of unity in the magnetosphere, even though we make a number of the optimistic assumptions to enlarge the synchrotron luminosity. In order to explain the luminosity of the non-thermal X-ray/optical emission from pulsars with low spin-down luminosity L sd ≲ 1034 erg s−1, non-dipole magnetic field components should be dominant at the emission region. For the γ-ray pulsars with L sd ≲ 1035 erg s−1, observed γ-ray to X-ray and optical flux ratios are much higher than the flux ratio between curvature and the synchrotron radiations. We discuss some possibilities such as the coexistence of multiple accelerators in the magnetosphere as suggested from the recent numerical simulation results. The obtained maximum luminosity would be useful to select observational targets in X-ray and optical bands.