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Chandra observations of the nearby candidate Lyman continuum (LyC) emitting galaxy Tol 0440-381 show brightening of an X-ray source by at least a factor of 4 to a luminosity of |$1.6 \times 10^{40} \rm \, erg \, s^{-1}$| over 3.8 d. The X-ray emission likely arises from either a low-luminosity active galactic nucleus or an ultraluminous X-ray source. The properties of the X-ray source are similar to those found in Haro 11 and Tololo 1247-232, the only other LyC emitting galaxies that have been resolved in X-rays. All three galaxies host luminous, variable, and hard-spectrum X-ray sources that are likely accretion-powered. Accretion on to compact objects produces powerful outflows and ionizing radiation that could help enable LyC escape. [ABSTRACT FROM AUTHOR]

X-ray binaries may have helped reionize the early Universe by enabling Lyman continuum escape. We analysed a set of eight local galaxies that are potential Lyman leaking galaxies, identified by a blue colour and weak emission lines, using Chandra X-ray observations. Five of the galaxies feature X-ray sources, while three galaxies are not significantly detected in X-rays. X-ray luminosities were found for the galaxies and X-ray sources. Four of the galaxies have elevated X-ray luminosity versus what would be expected based on star formation rate and metallicity. The presence of detected X-ray sources within the galaxies is found to correlate with the ratio of the star formation rate estimated from the near-ultraviolet flux to that estimated from the infrared. This implies reduced obscuration due to dust in the galaxies with X-ray sources. These results support the idea that X-ray binaries may be an important part of the process of reionziation. [ABSTRACT FROM AUTHOR]

Chandra observations of the nearby, Lyman-continuum (LyC) emitting galaxy Tol 1247-232 resolve the X-ray emission and show that it is dominated by a point-like source with a hard spectrum (Γ = 1.6 ± 0.5) and a high luminosity [(9 ± 2) × 1040 erg s-1]. Comparison with an earlier XMM-Newton observation shows flux variation of a factor of 2. Hence, the X-ray emission likely arises from an accreting X-ray source: a low-luminosity active galactic nucleus or one or a few X-ray binaries. The Chandra X-ray source is similar to the point-like, hard spectrum (- = 1.2 ± 0.2), high-luminosity (1041 erg s-1) source seen in Haro 11, which is the only other confirmed LyC-emitting galaxy that has been resolved in X-rays. We discuss the possibility that accreting X-ray sources contribute to LyC escape. [ABSTRACT FROM AUTHOR]

The source of energetic photons that heated and reionized the early Universe remains uncertain. Early galaxies had low metallicity and recent population synthesis calculations suggest that the number and luminosity of high-mass X-ray binaries are enhanced in star-forming galaxies with low metallicity, offering a potentially important and previously overlooked source of heating and reionization. Lyman break analogue (LBA) galaxies are local galaxies that strongly resemble the high-redshift, star-forming Lyman Break Galaxies and have been suggested as local analogues to these metal-deficient galaxies found in the early Universe. We studied a sample of ten LBAs in order to measure the relation between star formation rate and X-ray luminosity. We found that for LBAs with metallicities in the range 12 + log10(O/H) = 8.15 - 8.80, the LX -SFR relation was log10(LX/SFR[erg s-1 M-1⊙ yr])=39.85(±0.10) in the 0.5 - 8 keV band with a dispersion of σ = 0.25 dex. This is an enhancement of nearly a factor of 2 in the L0.5 - 8keV-SFR relation relative to results for nearby, near-solar metallicity galaxies. The enhancement is significant at the 98.2% level (2.4σ). Our enhanced LX/SFR relation is consistent with the metallicity-dependent predicted value from population synthesis models. We discuss the possibility of a LX-SFR-Metallicity plane for star-forming galaxies. These results are important to our understanding of reionization and the formation of early galaxies. [ABSTRACT FROM AUTHOR]

Late-type non-starburst galaxies have been shown to contain X-ray emitting objects, some being ultraluminous X-ray sources. We report on XMM-Newton observations of 11 nearby, late-type galaxies previously observed with the Hubble Space Telescope (HST) in order to find such objects. We found 18 X-ray sources in or near the optical extent of the galaxies, most being point-like. If associated with the corresponding galaxies, the source luminosities range from 2 ? 1037 erg s-1 to 6 ? 1039 erg s-1. We found one ultraluminous X-ray source, which is in the galaxy IC 5052, and one source coincident with the galaxy IC 4662 with a blackbody temperature of 0.166 ± 0.015 keV that could be a quasi-soft source or a quiescent neutron star X-ray binary in the Milky Way. One X-ray source, XMMU J205206.0-691316, is extended and coincident with a galaxy cluster visible on an HST image. The X-ray spectrum of the cluster reveals a redshift of z = 0.25 ± 0.02 and a temperature of 3.6±0.4 keV. The redshiftwas mainly determined by a cluster of Fe XXIV lines between the observed energy range 0.8 - 1.0 keV. [ABSTRACT FROM AUTHOR]

We examine the X-ray spectra of VII Zw 403, a nearby low-metallicity blue compact dwarf (BCD) galaxy. The galaxy has been observed to contain an X-ray source, likely a high-mass X-ray binary (HMXB), with a luminosity of 1.3-23 × 1038 erg s-1 in the 0.3-8 keV energy range. A new Suzaku observation shows a transition to a luminosity of 1.7 × 1040 erg s-1 [0.3-8 keV], higher by a factor of 7-130. The spectra from the high-flux state are hard, best described by a disc plus Comptonization model, and exhibit curvature at energies above 5 keV. This is consistent with many high-quality ultraluminous X-ray source spectra which have been interpreted as stellar mass black holes accreting at super-Eddington rates. However, this lies in contrast to another HMXB in a low-metallicity BCD, I Zw 18, that exhibits a soft spectrum at high flux, similar to Galactic black hole binaries and has been interpreted as a possible intermediate-mass black hole. Determining the spectral properties of HMXBs in BCDs has important implications for models of the Epoch of Reionization. It is thought that the main component of X-ray heating in the early Universe was dominated by HMXBs within the first galaxies. Early galaxies were small, metal-deficient, star-forming galaxies with large HI mass fractions - properties shared by local BCDs we see today. Understanding the spectral evolution of HMXBs in early Universe analogue galaxies, such as BCDs, is an important step in estimating their contribution to the heating of the intergalactic medium during the Epoch of Reionization. The strong contrast between the properties of the only two spectroscopically studied HMXBs within BCDs motivates further study on larger samples of HMXBs in low-metallicity environments in order to properly estimate the X-ray heating in the early Universe. [ABSTRACT FROM AUTHOR]

We observed the Ultraluminous X-ray Source (ULX) IC 342 X-1 simultaneously in X-ray and radio with Chandra and the JVLA to investigate previously reported unresolved radio emission coincident with the ULX. The Chandra data reveal a spectrum that is much softer than observed previously and is well modelled by a thermal accretion disc spectrum. No significant radio emission above the rms noise level was observed within the region of the ULX, consistent with the interpretation as a thermal state though other states cannot be entirely ruled out with the current data. We estimate the mass of the black hole using the modelled inner disc temperature to be $30 \,\mathrm{M_{{\odot }}} \lesssim M\sqrt{\mathrm{cos}i}\lesssim 200 \,\mathrm{M_{{\odot }}}$ based on a Shakura–Sunyaev disc model. Through a study of the hardness and high-energy curvature of available X-ray observations, we find that the accretion state of X-1 is not determined by luminosity alone. [ABSTRACT FROM PUBLISHER]

We obtained three epochs of simultaneous Hubble Space Telescope (HST)/Wide Field Camera 3 and Chandra observations of the ultraluminous X-ray source (ULX) NGC 5408 X-1. The counterpart of the X-ray source is seen in all HST filters, from the UV through the near-IR (NIR), and for the first time, we resolve the optical nebula around the ULX. We identified a small OB association near the ULX that may be the birthplace of the system. The stellar association is young, ~5 Myr, contains massive stars up to 40 M⊙, and is thus similar to associations seen near other ULXs, albeit younger. The UV/optical/NIR spectral energy distribution (SED) of the ULX counterpart is consistent with that of a B0I supergiant star. We are also able to fit the whole SED from the X-rays to the NIR with an irradiated disk model. The three epochs of data show only marginal variability and thus, we cannot firmly conclude on the nature of the optical emission. [ABSTRACT FROM AUTHOR]

Holmberg IX X-1 is an archetypal ultraluminous X-ray source (ULX). Here we study the properties of the optical counterpart and of its stellar environment using optical data from SUBARU/Faint Object Camera and Spectrograph, GEMINI/GMOS-N and Hubble Space Telescope (HS7)/Advanced Camera for Surveys, as well as simultaneous Chandra X-ray data. The V ~ 22.6 spectroscopically identified optical counterpart is part of a loose cluster with an age ≲20 Myr. Consequently, the mass upper limit on individual stars in the association is about 20 M.... The counterpart is more luminous than the other stars of the association, suggesting a non-negligible optical contribution from the accretion disk. An observed UV excess also points to non-stellar light similar to X-ray active low-mass X-ray binaries. A broad HeII λ686 emission line identified in the optical spectrum of the ULX further suggests optical light from X-ray reprocessing in the accretion disk. Using stellar evolutionary tracks, we have constrained the mass of the counterpart to be ≳10 M..., even if the accretion disk contributes significantly to the optical luminosity. Comparison of the photometric properties of the counterpart with binary models show that the donor may be more massive, ≳25 M..., with the ULX system likely undergoing case AB mass transfer. Finally, the counterpart exhibits photometric variability of 0.14 mag between two HST observations separated by 50 days which could be due to ellipsoidal variations and/or disk reprocessing of variable X-ray emission. [ABSTRACT FROM AUTHOR]

We report on an X-ray polarimetric observation of the high-mass X-ray binary LMC X-1 in the high/soft state, obtained by the Imaging X-ray Polarimetry Explorer (IXPE) in 2022 October. The measured polarization is below the minimum detectable polarization of 1.1 per cent (at the 99 per cent confidence level). Simultaneously, the source was observed with the Neutron Star Interior Composition Explorer (NICER), Nuclear Spectroscopic Telescope Array (NuSTAR), and Spectrum-Rontgen-Gamma (SRG)/Astronomical Roentgen Telescope – X-ray Concentrator (ART-XC) instruments, which enabled spectral decomposition into a dominant thermal component and a Comptonized one. The low 2–8 keV polarization of the source did not allow for strong constraints on the black hole spin and inclination of the accretion disc. However, if the orbital inclination of about 36° is assumed, then the upper limit is consistent with predictions for pure thermal emission from geometrically thin and optically thick discs. Assuming the polarization degree of the Comptonization component to be 0, 4, or 10 per cent, and oriented perpendicular to the polarization of the disc emission (in turn assumed to be perpendicular to the large-scale ionization cone orientation detected in the optical band), an upper limit to the polarization of the disc emission of 1.0, 0.9, or 0.9 per cent, respectively, is found (at the 99 per cent confidence level). [ABSTRACT FROM AUTHOR]

NGC 1313 X-2 is one of the few known pulsating ultraluminous X-ray sources (PULXs), and so is thought to contain a neutron star that accretes at highly super-Eddington rates. However, the physics of this accretion remains to be determined. Here, we report the results of two simultaneous XMM–Newton and HST observations of this PULX taken to observe two distinct X-ray behaviours as defined from its Swift light curve. We find that the X-ray spectrum of the PULX is best described by the hard ultraluminous regime during the observation taken in the lower flux, lower variability amplitude behaviour; its spectrum changes to a broadened disc during the higher flux, higher variability amplitude epoch. However, we see no accompanying changes in the optical/UV fluxes, with the only difference being a reduction in flux in the near-infrared (NIR) as the X-ray flux increased. We attempt to fit irradiation models to explain the UV/optical/IR fluxes but they fail to provide meaningful constraints. Instead, a physical model for the system leads us to conclude that the optical light is dominated by a companion O/B star, albeit with an IR excess that may be indicative of a jet. We discuss how these results may be consistent with the precession of the inner regions of the accretion disc leading to changes in the observed X-ray properties, but not the optical, and whether we should expect to observe reprocessed emission from ULXs. [ABSTRACT FROM AUTHOR]

We present the results of a spectroscopic study of the Fe Kα emission of the persistent neutron-Star atoll low-mass X-ray binary and type TX-ray burster GX 3+1 with the EPIC-PN on board XMM-Newton. The source shows a flux modulation over several years and we observed it during its fainter phase, which corresponds to an X-ray luminosity of Lx -∼ 1037 erg s-1. When fitted with a two-component model, the X-ray spectrum shows broad residuals at -6-7 keV that can be ascribed to an iron K,, fluorescence line, in addition, lower energy features are observed at ∼ 3.3 key, ∼ 3.9 keV and might originate from Ar XVIII and Ca XIX. The broad iron line feature is well fitted with a relativistically smeared profile. This result is robust against possible systematics caused by instrumental pile-up effects. Assuming that the line is produced by reflection from the inner accretion disk, we infer an inner disk radius of ∼25Rg and a disk inclination of 35° < i< 44° [ABSTRACT FROM AUTHOR]

We report on observations of the X-ray pulsar IGR J16320−4751 (also known as AX J1631.9−4752) performed simultaneously with International Gamma-Ray Astrophysics Laboratory ( INTEGRAL) and XMM–Newton. We refine the source position and identify the most likely infrared counterpart. Our simultaneous coverage allows us to confirm the presence of X-ray pulsations at ∼1300 s, that we detect above 20 keV with INTEGRAL for the first time. The pulse fraction is consistent with being constant with energy, which is compatible with a model of polar accretion by a pulsar. We study the spectral properties of IGR J16320−4751 during two major periods occurring during the simultaneous coverage with both satellites, namely a flare and a non-flare period. We detect the presence of a narrow 6.4 keV iron line in both periods. The presence of such a feature is typical of supergiant wind accretors such as Vela X-1 or GX 301−2. We inspect the spectral variations with respect to the pulse phase during the non-flare period, and show that the pulse is solely due to variations of the X-ray flux emitted by the source and not due to variations of the spectral parameters. Our results are therefore compatible with the source being a pulsar in a High Mass X-ray Binary. We detect a soft excess appearing in the spectra as a blackbody with a temperature of ∼0.07 keV. We discuss the origin of the X-ray emission in IGR J16320−4751: while the hard X-rays are likely the result of Compton emission produced in the close vicinity of the pulsar, based on energy argument we suggest that the soft excess is likely the emission by a collisionally energized cloud in which the compact object is embedded. [ABSTRACT FROM AUTHOR]

We present an in-depth study of the large scale, western jet of the microquasar XTEJ1550-564, based on X-ray and radio observations performed in 2002-2003. The jet is spatially resolved in both observing windows. The X-ray jet is expanding in time along the axis of the jet's propagation: we observe the formation of a tail (~2.25 arcsec), which appears to extend backwards with an apparent velocity ~-0.10c. The origin of this feature is discussed in the framework of scenarios of energy dissipation. A single power law adequately describes the broad-band spectra, supporting a synchrotron origin of the X-ray emission. However, a spectral break at ≈1015 Hz is necessary in coincidence with a re-flare at 8.64 GHz in 2002 September. This finding may be indicative of emission from newly accelerated lowenergy particles. The first detection of the jet is in 2001 February (F8.64 GHz =0.25±0.09 mJy) in the flux rising phase. A phase of stable emission is followed by a rapid decay (tdecay =167±5 d). The decay at radio frequencies is significantly shorter than in X-rays (tdecay = 338 ± 14 d). We detected a high fraction (up to ~9 per cent) of linearly polarized radiation at 4.8 and 8.6 GHz. The orientation of the electric vector is consistent with the picture of a shockcompressed magnetic field, and there are hints of variations on month-time-scales, possibly connected with the evolution of the jet structure. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper we report on Expanded Very Large Array radio and Chandra and Swift X-ray observations of the outburst decay of the transient black hole candidate MAXI J1659-152 in 2011. We discuss the distance to the source taking the high inclination into account and conclude that the source distance is probably 6 ± 2 kpc. The lowest observed flux corresponds to a luminosity of erg s−1. This, together with the orbital period of 2.4 h reported in the literature, suggests that the quiescent X-ray luminosity is higher than predicted on the basis of the orbital period-quiescent X-ray luminosity relationship. It is more in line with that expected for a neutron star, although the outburst spectral and timing properties reported in the literature strongly suggest that MAXI J1659-152 harbours a black hole. This conclusion is subject to confirmation of the lowest observed flux as the quiescent flux. The relation between the accretion and ejection mechanisms can be studied using the observed correlation between the radio and X-ray luminosities as these evolve over an outburst. We determine the behaviour of MAXI J1659-152 in the radio-X-ray diagram at low X-ray luminosities using the observations reported in this paper and at high X-ray luminosities using values reported in the literature. At high X-ray luminosities, the source lies closer to the sources that follow a correlation index steeper than 0.6-0.7. However, when compared to other sources that follow a steeper correlation index, the X-ray luminosity in MAXI J1659-152 is also lower. The latter can potentially be explained by the high inclination of MAXI J1659-152 if the X-ray emission comes from close to the source and the radio emission is originating in a more extended region. However, it is probable that the source was not in the canonical low-hard state during these radio observations and this may affect the behaviour of the source as well. At intermediate X-ray luminosities, the source makes the transition from the radio underluminous sources in the direction of the relation traced by the 'standard' correlation similar to what has been reported for H 1743−322 in the literature. However, MAXI J1659-152 remains underluminous with respect to this 'standard' correlation. [ABSTRACT FROM AUTHOR]

ABSTRACT We present optical, X-ray and radio observations of the black hole transient (BHT) XTE J1752−223 towards and in quiescence. Optical photometry shows that the quiescent magnitude of XTE J1752−223 is fainter than 24.4 mag in the i′ band. A comparison with measurements of the source during its 2009-2010 outburst shows that the outburst amplitude is more than 8 mag in the i′ band. Known X-ray properties of the source combined with the faintness of the quiescence optical counterpart and the large outburst optical amplitude point towards a short orbital-period system ( Porb≲ 6.8 h) with an M type (or later) mass donor, at a distance of 3.5 ≲ d≲ 8 kpc. Simultaneous X-ray and radio data were collected with Chandra and the Expanded Very Large Array (EVLA), allowing constraints to be placed on the quiescent X-ray and radio flux of XTE J1752−223. Furthermore, using data covering the final stage of the outburst decay, we investigated the low-luminosity end of the X-ray-radio correlation for this source and compared it with other BHTs. We found that XTE J1752−223 adds to the number of outliers with respect to the 'standard' X-ray-radio luminosity relation. Furthermore, XTE J1752−223 is the second source, after the BHT H1743−322, that shows a transition from the region of the outliers towards the 'standard' correlation at low luminosity. Finally, we report on a faint, variable X-ray source we discovered with Chandra at an angular distance of ∼2.9 arcsec to XTE J1752−223 and at a position angle consistent with that of the radio jets previously observed from the BHT. We discuss the possibility that we detected X-ray emission associated with a jet from XTE J1752−223. [ABSTRACT FROM AUTHOR]

We present optical, X-ray and radio observations of the black hole transient (BHT) XTE J1752−223 towards and in quiescence. Optical photometry shows that the quiescent magnitude of XTE J1752−223 is fainter than 24.4 mag in the i′ band. A comparison with measurements of the source during its 2009–2010 outburst shows that the outburst amplitude is more than 8 mag in the i′ band. Known X-ray properties of the source combined with the faintness of the quiescence optical counterpart and the large outburst optical amplitude point towards a short orbital-period system (Porb≲ 6.8 h) with an M type (or later) mass donor, at a distance of 3.5 ≲d≲ 8 kpc. Simultaneous X-ray and radio data were collected with Chandra and the Expanded Very Large Array (EVLA), allowing constraints to be placed on the quiescent X-ray and radio flux of XTE J1752−223. Furthermore, using data covering the final stage of the outburst decay, we investigated the low-luminosity end of the X-ray–radio correlation for this source and compared it with other BHTs. We found that XTE J1752−223 adds to the number of outliers with respect to the ‘standard’ X-ray–radio luminosity relation. Furthermore, XTE J1752−223 is the second source, after the BHT H1743−322, that shows a transition from the region of the outliers towards the ‘standard’ correlation at low luminosity. Finally, we report on a faint, variable X-ray source we discovered with Chandra at an angular distance of ∼2.9 arcsec to XTE J1752−223 and at a position angle consistent with that of the radio jets previously observed from the BHT. We discuss the possibility that we detected X-ray emission associated with a jet from XTE J1752−223. [ABSTRACT FROM AUTHOR]

ABSTRACT Ultraluminous X-ray sources (ULXs) are interesting systems as they can host intermediate-mass black holes. Alternatively, ULXs can represent stellar mass black holes accreting at super-Eddington rates. Recently, spectral curvature or breaks at energies above a few keV have been detected in high-quality ULX spectra. These spectral features have been taken as evidence against the intermediate-mass black hole case. In this paper, we report on a new XMM-Newton observation of the ULX Holmberg II X-1 that also shows a clear spectral break at approximately 4 keV. This observation was performed during a low-luminosity state of the system and by comparing these new data to a high-luminosity state XMM-Newton observation, we can conclude that the spectral break energy increases with luminosity. This behaviour is different from a ULX in the Holmberg IX galaxy, where an opposite trend between the luminosity and the spectral break energy has been claimed. We discuss mechanisms that could explain this complex behaviour. [ABSTRACT FROM AUTHOR]

We have performed the first sensitive X-ray observation of the low-mass X-ray binary (LMXB) SAX J1750.8 -2900 in quiescence with XMM-Newton. The spectrum was fit to both a classical blackbody model, and a non-magnetized, pure hydrogen neutron star (NS) atmosphere model. A power-law component was added to these models, but we found that it was not required by the fits. The distance to SAX J1750.8-2900 is known to be D = 6.79 kpc from a previous analysis of photospheric radius expansion bursts. This distance implies a bolometric luminosity (as given by the NS atmosphere model) of (1.05 ±0.12) x 1034 (D/6.79 kpc)² erg s-1, which is the highest known luminosity for a NS LMXB in quiescence. One simple explanation for this surprising result could be that the crust and core of the NS were not in thermal equilibrium during the observation. We argue that this was likely not the case, and that the core temperature of the NS in SAX J1750.8-2900 is unusually high. [ABSTRACT FROM AUTHOR]

We report on the discovery by the Swift Gamma-Ray Burst Explorer of the black hole (BH) candidate Swift J1539.2-6227 and the subsequent course of an outburst beginning in 2008 November and lasting at least seven months. The source was discovered during normal observations with the Swift Burst Alert Telescope on 2008 November 25. An extended observing campaign with the Rossi X-Ray Timing Explorer and Swift provided near-daily coverage over 176 days, giving us a good opportunity to track the evolution of spectral and timing parameters with fine temporal resolution through a series of spectral states. The source was first detected in a hard state during which strong low-frequency quasi-periodic oscillations (QPOs) were detected. The QPOs persisted for about 35 days and a signature of the transition from the hard- to soft-intermediate states was seen in the timing data. The source entered a short-lived thermal state about 40 days after the start of the outburst. There were variations in spectral hardness as the source flux declined and returned to a hard state at the end of the outburst. The progression of spectral states and the nature of the timing features provide strong evidence that Swift J1539.2-6227 is a candidate BH in a low-mass X-ray binary system. [ABSTRACT FROM AUTHOR]

In this paper, we report on radio (Very Large Array and Austrialian Telescope Compact Array) and X-ray ( RXTE, Chandra and Swift) observations of the outburst decay of the transient black hole candidate H 1743-322 in early 2008. We find that the X-ray light curve followed an exponential decay, levelling off towards its quiescent level. The exponential decay time-scale is 4 days and the quiescent flux corresponds to a luminosity of erg s−1. This together with the relation between quiescent X-ray luminosity and orbital period reported in the literature suggests that H 1743-322 has an orbital period longer than ≈10 h. Both the radio and X-ray light curve show evidence for flares. The radio–X-ray correlation can be well described by a power-law with index 0.18. This is much lower than the index of 0.6–0.7 found for the decay of several black hole transients before. The radio spectral index measured during one of the radio flares while the source is in the low–hard state is , which indicates that the radio emission is optically thin. This is unlike what has been found before in black hole sources in the low–hard state. We attribute the radio flares and the low index for the radio–X-ray correlation to the presence of shocks downstream the jet flow, triggered by ejection events earlier in the outburst. We find no evidence for a change in X-ray power-law spectral index during the decay, although the relatively high extinction of limits the detected number of soft photons and thus the accuracy of the spectral fits. [ABSTRACT FROM AUTHOR]