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Abstract We present ground-based optical transmission spectroscopy of the low-density hot Jupiter WASP-88b covering the wavelength range 4413 − 8333 Å with the FORS2 spectrograph on the Very Large Telescope. The FORS2 white light curves exhibit a significant time-correlated noise which we model using a Gaussian Process and remove as a wavelength-independent component from the spectroscopic light curves. We analyse complementary photometric observations from the Transiting Exoplanet Survey Satellite and refine the system properties and ephemeris. We find a featureless transmission spectrum with increased absorption towards shorter wavelengths. We perform an atmospheric retrieval analysis with the aura code, finding tentative evidence for haze in the upper atmospheric layers and a lower likelihood for a dense cloud deck. Whilst our retrieval analysis results point toward clouds and hazes, further evidence is needed to definitively reject a clear-sky scenario.

SMC X-2 exhibits X-ray outburst behaviour that makes it one of the most luminous X-ray sources in the Small Magellanic Cloud. In the last decade it has undergone two such massive outbursts – in 2015 and 2022. The first outburst is well reported in the literature, but the 2022 event has yet to be fully described and discussed. That is the goal of this paper. In particular, the post-peak characteristics of the two events are compared. This reveals clear similarities in decay profiles, believed to be related to different accretion mechanisms occurring at different times as the outbursts evolve. The H α emission line indicates that the Be disc undergoes complex structural variability, with evidence of warping as a result of its interaction with the neutron star. The detailed observations reported here will be important for modelling such interactions in this kind of binary systems. [ABSTRACT FROM AUTHOR]

Here, we present the results of our multiwavelength campaign aimed at classifying Swift J170800−402551.8 as part of the Swift Deep Galactic Plane Survey (DGPS). We utilized Target of Opportunity (ToO) observations with the Neil Gehrels Swift Observatory, Chandra X-ray Observatory , Neutron star Interior Composition Explorer (NICER), X-ray Multi-Mirror Mission (XMM–Newton), Nuclear Spectroscopic Telescope Array (NuSTAR), and the Southern African Large Telescope (SALT), as well as multiwavelength archival observations from Gaia , VST Photometric Hα Survey, and VISTA Variables in the Via Lactea. The source displays a periodicity of 784 s in our XMM–Newton observation. The X-ray spectrum (XMM–Newton and NuSTAR) can be described by thermal bremsstrahlung radiation with a temperature of kT ≈ 30 keV. The phase-folded X-ray light curve displays a double-peaked, energy-dependent pulse profile. We used Chandra to precisely localize the source, allowing us to identify and study the multiwavelength counterpart. Spectroscopy with SALT identified a Balmer H α line, and potential He  i lines, from the optical counterpart. The faintness of the counterpart (r ≈ 21 AB mag) favours a low-mass donor star. Based on these criteria, we classify Swift J170800−402551.8 as a candidate intermediate polar cataclysmic variable, where the spin period of the white dwarf is 784 s. [ABSTRACT FROM AUTHOR]

We present the Living Swift- XRT Point Source (LSXPS) catalogue and real-time transient detector. This system allows us for the first time to carry out low-latency searches for new transient X-ray events fainter than those available to the current generation of wide-field imagers, and report their detection in near real time. Previously, such events could only be found in delayed searches, e.g. of archival data; our low-latency analysis now enables rapid and ongoing follow-up of these events, enabling the probing of time-scales previously inaccessible. The LSXPS is, uniquely among X-ray catalogues, updated in near real time, making this the first up-to-date record of the point sources detected by a sensitive X-ray telescope: the Swift X-ray Telescope. The associated upper limit calculator likewise makes use of all available data allowing contemporary upper limits to be rapidly produced on demand. These facilities, which enable the low-latency transient system, are also fully available to the community, providing a powerful resource for time-domain and multimessenger astrophysics. [ABSTRACT FROM AUTHOR]

On 2021 August 8, the recurrent nova RS Ophiuchi (RS Oph) erupted again, after an interval of 15.5 yr. Regular monitoring by the Neil Gehrels Swift Observatory began promptly, on August 9.9 (0.37 d after the optical peak), and continued until the source passed behind the Sun at the start of November, 86 d later. Observations then restarted on day 197, once RS Oph emerged from the Sun constraint. This makes RS Oph the first Galactic recurrent nova to have been monitored by Swift throughout two eruptions. Here we investigate the extensive X-ray data sets between 2006 and 2021, as well as the more limited data collected by the European X-ray Observatory Satellite (EXOSAT) in 1985. The hard X-rays arising from shock interactions between the nova ejecta and red giant wind are similar following the last two eruptions. In contrast, the early supersoft source (SSS) in 2021 was both less variable and significantly fainter than in 2006. However, 0.3–1 keV light curves from 2021 reveal a 35 s quasi-periodic oscillation consistent in frequency with the 2006 data. The Swift X-ray spectra from 2021 are featureless, with the soft emission typically being well parametrized by a simple blackbody, while the 2006 spectra showed much stronger evidence for superimposed ionized absorption edges. Considering the data after day 60 following each eruption, during the supersoft phase the 2021 spectra are hotter, with smaller effective radii and lower wind absorption, leading to an apparently reduced bolometric luminosity. We explore possible explanations for the gross differences in observed SSS behaviour between the 2006 and 2021 outbursts. [ABSTRACT FROM AUTHOR]

The radiative counterpart of the supermassive black hole at the Galactic Centre, Sagittarius A*, displays flaring emission in the X-ray band atop a steady, quiescent level. Flares are also observed in the near-infrared band. The physical process producing the flares is not fully understood and it is unclear if the flaring rate varies, although some recent works suggest it has reached unprecedented variability in recent years. Using over a decade of regular X-ray monitoring of Neil Gehrels Swift Observatory, we studied the variations in count rate of Sgr A* on time-scales of years. We decomposed the X-ray emission into quiescent and flaring emission, modelled as a constant and power-law process, respectively. We found that the complete, multiyear data set cannot be described by a stationary distribution of flare fluxes, while individual years follow this model better. In three of the ten studied years, the data is consistent with a purely Poissonian quiescent distribution, while for 5 yr, only an upper limit of the flare flux distribution parameter could be determined. We find that these possible changes cannot be explained fully by the different number of observations per year. Combined, these results are instead consistent with a changing flaring rate of Sgr A*, appearing more active between 2006–2007 and 2017–2019, than between 2008–2012. Finally, we discuss this result in the context of flare models and the passing of gaseous objects, and discuss the extra statistical steps taken, for instance, to deal with the background in the Swift observations. [ABSTRACT FROM AUTHOR]

Very faint X-ray transients (VFXTs) are X-ray transients with peak X-ray luminosities (LX) of L |$_X \lesssim 10^{36}$|  erg s−1, which are not well understood. We carried out a survey of 16 deg2 of the Galactic Bulge with the Swift Observatory, using short (60 s) exposures, and returning every 2 weeks for 19 epochs in 2017–18 (with a gap from 2017 November to 2018 February, when the Bulge was in sun-constraint). Our main goal was to detect and study VFXT behaviour in the Galactic Bulge across various classes of X-ray sources. In this work, we explain the observing strategy of the survey, compare our results with the expected number of source detections per class, and discuss the constraints from our survey on the Galactic VFXT population. We detected 91 X-ray sources, 25 of which have clearly varied by a factor of at least 10. In total, 45 of these X-ray sources have known counterparts: 17 chromospherically active stars, 12 X-ray binaries, 5 cataclysmic variables (and 4 candidates), 3 symbiotic systems, 2 radio pulsars, 1 active galactic nuclei, and a young star cluster. The other 46 are of previously undetermined nature. We utilize X-ray hardness ratios, searches for optical/infrared counterparts in published catalogues, and flux ratios from quiescence to outburst to constrain the nature of the unknown sources. Of these 46, 7 are newly discovered hard transients, which are likely VFXT X-ray binaries. Furthermore, we find strong new evidence for a symbiotic nature of four sources in our full sample, and new evidence for accretion power in six X-ray sources with optical counterparts. Our findings indicate that a large subset of VXFTs is likely made up of symbiotic systems. [ABSTRACT FROM AUTHOR]

We report on the discovery of a new, transient ultraluminous X-ray source (ULX) in the galaxy NGC 7090. This new ULX, which we refer to as NGC 7090 ULX3, was discovered via monitoring with Swift during 2019–2020, and to date has exhibited a peak luminosity of L X ∼ 6 × 1039 erg s−1. Archival searches show that, prior to its recent transition into the ULX regime, ULX3 appeared to exhibit a fairly stable luminosity of L X ∼ 1038 erg s−1. Such strong long-time-scale variability may be reminiscent of the small population of known ULX pulsars, although deep follow-up observations with XMM–Newton and NuSTAR do not reveal any robust X-ray pulsation signals. Pulsations similar to those seen from known ULX pulsars cannot be completely excluded, however, as the limit on the pulsed fraction of any signal that remains undetected in these data is ≲20 per cent. The broad-band spectrum from these observations is well modelled with a simple thin disc model, consistent with sub-Eddington accretion, which may instead imply a moderately large black hole accretor (M BH ∼ 40 M⊙). Similarly, though, more complex models consistent with the super-Eddington spectra seen in other ULXs (and the known ULX pulsars) cannot be excluded given the limited signal-to-noise ratio of the available broad-band data. The nature of the accretor powering this new ULX therefore remains uncertain. [ABSTRACT FROM AUTHOR]

Motivated by the recent discoveries that six ultraluminous X-ray sources (ULXs) are powered by highly super-Eddington X-ray pulsars, we searched for additional pulsating ULX (PULX) candidates by identifying sources that exhibit long-term flux variability of at least an order of magnitude (a common feature seen in the six known PULXs, which may potentially be related to transitions to the propeller regime). Expanding on previous studies, we used the available fluxes from XMM–Newton, Swift , and Chandra , along with carefully computed upper limits in cases of a non-detection, to construct long-term light curves for a sample of 296 ULXs selected from the XMM–Newton archive. Among these 296, we find 25 sources showing flux variability larger than a factor of 10, of which 17 show some evidence for (or are at least consistent with) exhibiting bimodal flux distributions, as would be expected for sources undergoing propeller transitions. These sources are excellent candidates for continued monitoring programs to further test for this behaviour. There are three sources in our final sample with fluxes similar to NGC 5907 ULX1, currently the faintest known PULX, which would also be good targets for deeper observations with current facilities to search for pulsations. For the rest of the PULX candidates identified here, the next generation of X-ray telescopes (such as Athena) may be required to determine their nature owing to their lower peak fluxes. [ABSTRACT FROM AUTHOR]

We report the discovery of a planet - OGLE-2014-BLG-0676Lb- via gravitational microlensing. Observations for the lensing event were made by the following groups: Microlensing Observations in Astrophysics; Optical Gravitational Lensing Experiment; Wise Observatory; RoboNET/Las Cumbres Observatory Global Telescope; Microlensing Network for the Detection of Small Terrestrial Exoplanets; and μ-FUN. All analyses of the light-curve data favour a lens system comprising a planetary mass orbiting a host star. The most-favoured binary lens model has a mass ratio between the two lens masses of (4.78 ± 0.13) × 10-3. Subject to some important assumptions, a Bayesian probability density analysis suggests the lens system comprises a 3.09+1.02 -1.12 MJ planet orbiting a 0.62+0.20 -0.22 M☉ host star at a deprojected orbital separation of 4.40+2.16 -1.46 au. The distance to the lens system is 2.22+0.96 -0.83 kpc. Planet OGLE- 2014-BLG-0676Lb provides additional data to the growing number of cool planets discovered using gravitational microlensing against which planetary formation theories may be tested. Most of the light in the baseline of this event is expected to come from the lens and thus high-resolution imaging observations could confirm our planetary model interpretation. [ABSTRACT FROM AUTHOR]

We report on the detection of a bright, short, structured X-ray burst coming from the supernova remnant RCW 103 on 2016 June 22 caught by the Swift/Burst Alert Telescope (BAT) monitor, and on the follow-up campaign made with Swift/X-ray Telescope, Swift/UV/Optical Telescope, and the optical/near-infrared (NIR) Gamma-Ray burst Optical and Near-infrared Detector. The characteristics of this flash, such as duration and spectral shape, are consistent with typical short bursts observed from soft gamma repeaters. The BAT error circle at 68 per cent confidence range encloses the point-like X-ray source at the centre of the nebula, 1E 161348-5055. Its nature has been long debated due to a periodicity of 6.67 h in X-rays, which could indicate either an extremely slow pulsating neutron star, or the orbital period of a very compact X-ray binary system. We found that 20 min before the BAT trigger, the soft X-ray emission of 1E 161348-5055 was a factor of ~100 higher than measured 2 yr earlier, indicating that an outburst had already started. By comparing the spectral and timing characteristics of the source in the 2 yr before the outburst and after the BAT event, we find that, besides a change in luminosity and spectral shape, also the 6.67 h pulsed profile has significantly changed with a clear phase shift with respect to its low-flux profile. The UV/optical/NIR observations did not reveal any counterpart at the position of 1E 161348-5055. Based on these findings, we associate the BAT burst with 1E 161348-5055, we classify it as a magnetar, and pinpoint the 6.67 h periodicity as the magnetar spin period. [ABSTRACT FROM AUTHOR]