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Highly radio-loud quasars (HRLQs; log  R > 2.5) at z ≳ 4 show apparent enhanced X-ray emission compared to matched HRLQs at lower redshifts, perhaps due to a redshift-dependent fractional contribution to the X-ray luminosity from inverse-Compton scattering of cosmic microwave background photons (IC/CMB). Using new Chandra observations and archival X-ray data, we investigate this phenomenon with an optically flux-limited sample of 41 HRLQs at z  = 4–5.5 all with sensitive X-ray coverage, the largest sample utilized to date by a wide margin. X-ray enhancements are assessed using X-ray-to-optical flux ratios and spectral energy distributions. We confirm the presence of X-ray enhancements at a 4.9–5.3σ significance level, finding that the median factor of enhancement is ≈1.8 at our sample median redshift of z ≈ 4.4. Under a fractional IC/CMB model, the expected enhancement at lower redshifts is modest; e.g. ≈4 per cent at z ≈ 1.5. We also investigate a sample of seven radio-loud quasars (RLQs; log  R > 1) at even higher redshifts of z  = 5.6–6.8, using new and archival X-ray data. These RLQs also show evidence for X-ray enhancements by a median factor of ≈2.7 at a 3.7–4.9σ significance level. The X-ray spectral and other properties of these z  = 5.6–6.8 RLQs, however, pose challenges for a straightforward fractional IC/CMB interpretation of their enhancements. [ABSTRACT FROM AUTHOR]

Observations of the high-mass gamma-ray binary LS 2883/PSR B1259–63 with the Chandra X-ray Observatory during the 2011–2014 and 2014–2017 binary cycles have shown X-ray-emitting clumps, presumably ejected from the binary during periastron passages. These clumps traveled at projected velocities of ∼0.1 c and have shown evidence of being accelerated. The clumps also evolved in shape, size, and flux. We monitored this binary with Chandra during the 2017–2021 binary cycle to search for additional X-ray-emitting ejections. While we find evidence of extended emission in two of the six observations, it is unlike the clumps observed in the previous three binary cycles. More specifically, the extended emission is not well localized, and no bright clump is observed moving away from the binary. It is still unclear what caused the lack of X-ray-emitting clump in this orbital cycle, but it may be due to changes in the decretion disk of the Be star. [ABSTRACT FROM AUTHOR]

We study the four-dimensional relationships between magnetic activity, rotation, mass, and age for solar-type stars in the age range 5–25 Myr. This is the late-pre-main-sequence (l-PMS) evolutionary phase when rapid changes in a star's interior may lead to changes in the magnetic dynamo mechanisms. We carefully derive rotational periods and spot sizes for 471 members of several l-PMS open clusters using photometric light curves from the Zwicky Transient Facility. Magnetic activity was measured in our previous Chandra-based study, and additional rotational data were obtained from other work. Several results emerge. Mass-dependent evolution of rotation through the l-PMS phase agrees with astrophysical models of stellar angular momentum changes, although the data suggest a subpopulation of stars with slower initial rotations than commonly assumed. There is a hint of the onset of unsaturated tachoclinal dependency of X-ray activity on rotation, as reported by Argiroffi et al., but this result is not confidently confirmed. Both X-ray luminosity and starspot area decrease approximately as t −1 for solar-mass stars, suggesting that spot magnetic fields are roughly constant and l-PMS stars follow the universal solar-scaling law between the X-ray luminosity and surface magnetic flux. Assuming convective dynamos are dominant, theoretical magnetic fluxes fail to reveal the universal law for l-PMS stars that enter late Henyey tracks. Altogether we emerge with a few lines of evidence suggesting that the transition from the turbulent to solar-type dynamo occurs at the later stages of l-PMS evolution as stars approach the zero-age main sequence. [ABSTRACT FROM AUTHOR]

We report strong and rapid X-ray variability found from the super-Eddington accreting quasar SDSS J081456.10+532533.5 at z = 0.1197. It has a black hole mass of 2.7 × 107 M ⊙ and a dimensionless accretion rate of ≈4 measured from reverberation-mapping observations. It showed weak X-ray emission in the 2021 February Chandra observation, with the 2 keV flux density being 9.6 − 4.6 + 11.6 times lower compared to an archival Swift observation. The 2 keV flux density is also 11.7 − 6.3 + 9.6 times weaker compared to the expectation from its optical/UV emission. In a follow-up XMM-Newton observation 32 days later, the 2 keV flux density increased by a factor of 5.3 − 2.4 + 6.4 , and the spectra are best described by a power law modified with partial-covering absorption; the absorption-corrected intrinsic continuum is at a nominal flux level. Nearly simultaneous optical spectra reveal no variability, and there is only mild long-term optical/infrared variability from archival data (with a maximum variability amplitude of ≈50%). We interpret the X-ray variability with an obscuration scenario, where the intrinsic X-ray continuum does not vary but the absorber has a variable column density and covering factor along the line of sight. The absorber is likely the small-scale clumpy accretion wind that has been proposed to be responsible for similar X-ray variability in other super-Eddington accreting quasars. [ABSTRACT FROM AUTHOR]

We report results for a complete sample of 10 luminous radio-quiet quasars with large C iv equivalent widths (EW ≥ 150 Ă...). For 8/10 we performed Chandra snapshot observations. We find that, in addition to the enhanced C iv line EW, their He ii and Mg ii lines are enhanced, but the C iii ] line is not. Their X-ray emission is substantially stronger than expected from their ultraviolet luminosity. Additionally, these large C iv EW quasars show small C iv blueshifts and possibly low Eddington ratios, suggesting that they are “extreme low Eigenvector 1 (EV1)” quasars. The mean excess He ii EW is well matched by radiation pressure compression (RPC) photoionization models, with the harder α ox ionizing spectrum. However, these results do not reproduce well the enhancement pattern of the C iv, Mg ii, and C iii ] EWs, or the observed high C iv /Mg ii ratio. RPC calculations indicate that the C iv /Mg ii line ratio is an effective metallicity indicator, and models with subsolar-metallicity gas and a hard ionizing continuum reproduce well the enhancement pattern of all four ultraviolet lines. We find that the C iv /Mg ii line ratio in quasars is generally correlated with the excess X-ray emission. Extremely high EV1 quasars are characterized by high metallicity and suppressed X-ray emission. The underlying mechanism relating gas metallicity and X-ray emission is not clear but may be related to radiation-pressure-driven disk winds, which are enhanced at high metallicity, and consequent mass loading reducing coronal X-ray emission. [ABSTRACT FROM AUTHOR]

Dust-obscured galaxies (DOGs) with extreme infrared luminosities may represent a key phase in the co-evolution of galaxies and supermassive black holes. We select 12 DOGs at 0.3 ≲ z ≲ 1.0 with broad Mg  ii or H β emission lines and investigate their X-ray properties utilizing snapshot observations (∼3 ks per source) with Chandra. By assuming that the broad lines are broadened due to virial motions of broad-line regions, we find that our sources generally have high Eddington ratios (λEdd). Our sources generally have moderate intrinsic X-ray luminosities (L X ≲ 1045 erg s−1), which are similar to those of other DOGs, but are more obscured. They also present moderate outflows and intense starbursts. Based on these findings, we conclude that high-λEdd DOGs are closer to the peaks of both host-galaxy and black hole growth compared to other DOGs, and that (active galactic nucleus) AGN feedback has not swept away their reservoirs of gas. However, we cannot fully rule out the possibility that the broad lines are broadened by outflows, at least for some sources. We investigate the relations among L X, AGN rest-frame 6  μ m monochromatic luminosity, and AGN bolometric luminosity, and find the relations are consistent with the expected ones. [ABSTRACT FROM AUTHOR]

We report the discovery of a probable dwarf galaxy colliding with NGC 1232. This collision is visible only in the X-ray spectral band, and it is creating a region of shocked gas with a temperature of 5.8 MK covering an impact area 7.25 kpc in diameter. The X-ray luminosity is 3.7 × 1038 erg s-1. The long lifetime of this gas against radiative and adiabatic cooling should permit the use of the luminous afterglow from such collisions to be used as a way of estimating their importance in galaxy evolution. [ABSTRACT FROM AUTHOR]

ABSTRACT Rich young stellar clusters produce H ii regions whose expansion into the nearby molecular cloud is thought to trigger the formation of new stars. However, the importance of this mode of star formation is uncertain. This investigation seeks to quantify triggered star formation (TSF) in IC 1396A (aka the Elephant Trunk Nebula), a bright-rimmed cloud (BRC) on the periphery of the nearby giant H ii region IC 1396 produced by the Trumpler 37 cluster. X-ray selection of young stars from Chandra X-ray Observatory data is combined with existing optical and infrared surveys to give a more complete census of the TSF population. Over 250 young stars in and around IC 1396A are identified; this doubles the previously known population. A spatio-temporal gradient of stars from the IC 1396A cloud towards the primary ionizing star HD 206267 is found. We argue that the TSF mechanism in IC 1396A is a radiation-driven implosion process persisting over several million years. Analysis of the X-ray luminosity and initial mass functions indicates that >140 stars down to 0.1 M⊙ were formed by TSF. Considering other BRCs in the IC 1396 H ii region, we estimate the TSF contribution for the entire H ii region exceeds 14-25 per cent today, and may be higher over the lifetime of the H ii region. Such triggering on the periphery of H ii regions may be a significant mode of star formation in the Galaxy. [ABSTRACT FROM AUTHOR]

We report the discovery of 12 new fossil groups (FGs) of galaxies, systems dominated by a single giant elliptical galaxy and cluster-scale gravitational potential, but lacking the population of bright galaxies typically seen in galaxy clusters. These FGs, selected from the maxBCG optical cluster catalog, were detected in snapshot observations with the Chandra X-ray Observatory. We detail the highly successful selection method, with an 80% success rate in identifying 12 FGs from our target sample of 15 candidates. For 11 of the systems, we determine the X-ray luminosity, temperature, and hydrostatic mass, which do not deviate significantly from expectations for normal systems, spanning a range typical of rich groups and poor clusters of galaxies. A small number of detected FGs are morphologically irregular, possibly due to past mergers, interaction of the intra-group medium with a central active galactic nucleus (AGN), or superposition of multiple massive halos. Two-thirds of the X-ray-detected FGs exhibit X-ray emission associated with the central brightest cluster galaxy (BCG), although we are unable to distinguish between AGN and extended thermal galaxy emission using the current data. This sample representing a large increase in the number of known FGs, will be invaluable for future planned observations to determine FG temperature, gas density, metal abundance, and mass distributions, and to compare to normal (non-fossil) systems. Finally, the presence of a population of galaxy-poor systems may bias mass function determinations that measure richness from galaxy counts. When used to constrain power spectrum normalization and Ωm, these biased mass functions may in turn bias these results. [ABSTRACT FROM AUTHOR]

LS 5039 is a high-mass binary with a period of 4 days, containing a compact object and an O-star, one of the few high-mass binaries detected in γ-rays. Our Chandra Advanced CCD Imaging Spectrometer observation of LS 5039 provided a high-significance (≈10σ) detection of extended emission clearly visible for up to I' from the point source. The spectrum of this emission can be described by an absorbed power-law model with photon index Γ = 1.9 ± 0.3, somewhat softer than the point-source spectrum Γ = 1.44 ± 0.07, with the same absorption, NH = (6.4 ± 0.6) × 1021 cm-2. The observed 0.5-8 keV flux of the extended emission is ...8.8 × 10-14 erg s-1cm-2 or 5% of the point-source flux; the latter is a factor of ~2 lower than the lowest flux detected so far. Fainter extended emission with comparable flux and a softer (Γ ≈ 3) spectrum is detected at even greater radii (up to 2'). Two possible interpretations of the extended emission are a dust scattering halo and a synchrotron nebula powered by energetic particles escaping the binary. We discuss both of these scenarios and favor the nebula interpretation, although some dust contribution is possible. We have also found transient sources located within a narrow stripe south of LS 5039. We discuss the likelihood of these sources to be related to LS 5039. [ABSTRACT FROM AUTHOR]