We report on simultaneous radio and X-ray observations of the radio-emitting magnetar 1E1547.0-5408 on 2009 January 25 and February 3, with the 64-m Parkes radio telescope and the Chandra and XMM-Newton X-ray observatories. The magnetar was observed in a period of intense X-ray bursting activity and enhanced X-ray emission. We report here on the detection of two radio bursts from 1E1547.0-5408, reminiscent of Fast Radio Bursts (FRBs). One of the radio bursts was anticipated by ~1s (about half a rotation period of the pulsar) by a bright SGR-like X-ray burst, resulting in a F_radio/F_X ~ 10^-9. Radio pulsations were not detected during the observation showing the FRB-like radio bursts, while they were detected in the previous radio observation. We also found that the two radio bursts are neither aligned with the latter radio pulsations nor with the peak of the X-ray pulse profile (phase shift of ~0.2). Comparing the luminosity of these FRB-like bursts and those reported from SGR1935+2154, we find that the wide range in radio efficiency and/or luminosity of magnetar bursts in the Galaxy may bridge the gap between ordinary pulsar radio bursts and the extragalactic FRB phenomenon.

We discovered 2.8 s pulsations in the X-ray emission of the ultraluminous X-ray source (ULX) M51 ULX-7 within the UNSEeN project, which was designed to hunt for new pulsating ULXs (PULXs) with XMM–Newton. The pulse shape is sinusoidal and large variations of its amplitude were observed even within single exposures (pulsed fraction from less than 5% to 20%). M51 ULX-7 is a variable source, generally observed at an X-ray luminosity between 10 and 10 erg s−1, located in the outskirts of the spiral galaxy M51a at a distance of 8.6 Mpc. According to our analysis, the X-ray pulsar orbits in a 2-d binary with a projected semi-major axis aX sin i ' 28 lt-s. For a neutron star (NS) of 1.4M , this implies a lower limit on the companion mass of 8M , placing the system hosting M51 ULX-7 in the high-mass X-ray binary class. The barycentric pulse period decreased by'0.4 ms in the 31 d spanned by our May–June 2018 observations, corresponding to a spinup rate Ṗ ' −1.5 × 10−10 s s−1. In an archival 2005 XMM–Newton exposure, we measured a spin period of ∼3.3 s, indicating a secular spin-up of Ṗsec ' −10−9 s s−1, a value in the range of other known PULXs. Our findings suggest that the system consists of an OB giant and a moderately magnetic (dipole field component in the range 10 G . Bdip . 10 G) accreting NS with weakly beamed emission (1/12 . b . 1/4).

Ultraluminous X-ray sources (ULXs) are a class of accreting compact objects with X-ray luminosities above 10(39) erg s(-1). The ULX population counts several hundred objects but only a fraction are well studied. Here we present a detailed analysis of all ULXs hosted in the galaxy NGC 7456. It was observed in X-rays only once in the past (in 2005) by XMM-Newton. but the observation was short and strongly affected by high background. In 2018, we obtained a new, deeper (similar to 90 ks) XMM-Newton observation that allowed us to perform a detailed characterization of the ULXs hosted in the galaxy. ULX-1 and ULX-2, the two brightest objects (L-X similar to 6-10 x 10(39) erg s(-1)), have spectra that can be described by a model with two thermal components, as often found in ULXs. ULX-1 also shows one order of magnitude in flux variability on short-term timescales (hundreds to thousands of kiloseconds). The other sources (ULX-3 and ULX-4) show flux changes of at least an order of magnitude, and these objects may be candidate transient ULXs, although longer X-ray monitoring or further studies are required to ascribe them to the ULX population. In addition, we found a previously undetected source that might be a new candidate ULX (labeled as ULX-5), with a luminosity of similar to 10(39) erg s(-1) and hard power-law spectral shape, whose nature is still unclear and for which a background active galactic nucleus cannot be excluded. We discuss the properties of all the ULXs in NGC 7456 within the framework of super-Eddington accretion onto stellar-mass compact objects. Although no pulsations were detected, we cannot exclude that the sources host neutron stars.

Among hard X-ray Galactic sources detected in the Swift and INTEGRAL surveys, those discovered as accreting white dwarf binaries have suprisingly boosted in number in the recent years. The majority are identified as magnetic Cataclysmic Variables of the Intermediate Polar type, suggesting this subclass as an important constituent of the Galactic population of X-ray sources. We here review and discuss the X-ray emission properties of newly discovered sources in the framework of an identification programme with the XMM-Newton satellite that increased the sample of this subclass by a factor of two.

Disc instability models predict that for X-ray binaries in quiescence, there should be a brightening of the optical flux prior to an X-ray outburst. Tracking the X-ray variations of X-ray binaries in quiescence is generally not possible, so optical monitoring provides the best means to measure the mass accretion rate variability between outbursts, and to identify the beginning stages of new outbursts. With our regular Faulkes Telescope/Las Cumbres Observatory (LCO) monitoring we are routinely detecting the optical rise of new X-ray binary outbursts before they are detected by X-ray all-sky monitors. We present examples of detections of an optical rise in X-ray binaries prior to X-ray detection. We also present initial optical monitoring of the new black hole transient MAXI J1820+070 (ASASSN-18ey) with the Faulkes, LCO telescopes and Al Sadeem Observatory in Abu Dhabi, UAE. Finally, we introduce our new real-time data analysis pipeline, the 'X-ray Binary New Early Warning System (XB-NEWS)' which aims to detect and announce new X-ray binary outbursts within a day of first optical detection. This will allow us to trigger X-ray and multi-wavelength campaigns during the very early stages of outbursts, to constrain the outburst triggering mechanism.

We present optical, UV and X-ray monitoring of the short orbital period black hole X-ray binary candidate Swift J1753.5-0127, focusing on the final stages of its 12$-$year long outburst that started in 2005. From September 2016 onward, the source started to fade and within three months, the optical flux almost reached the quiescent level. Soon after that, using a new proposed rebrightening classification method we recorded a mini-outburst and a reflare in the optical light curves, peaking in February (V$\rm\sim$17.0) and May (V$\rm\sim$17.9) 2017, respectively. Remarkably, the mini-outburst has a peak flux consistent with the extrapolation of the slow decay before the fading phase preceding it. The following reflare was fainter and shorter. We found from optical colors that the temperature of the outer disk was $\sim 11$,000 K when the source started to fade rapidly. According to the disk instability model, this is close to the critical temperature when a cooling wave is expected to form in the disk, shutting down the outburst. The optical color could be a useful tool to predict decay rates in some X-ray transients. We notice that all X-ray binaries that show mini-outbursts following a main outburst are short orbital period systems ($<$ 7 h). In analogy with another class of short period binaries showing similar mini-outbursts, the cataclysmic variables of the RZ LMi type, we suggest mini-outbursts could occur if there is a hot inner disk at the end of the outburst decay.

In 2003, the magnetar XTE J1810-197 started an outburst that lasted until early 2007. In the following 11 years, the source stayed in a quiescent/low activity phase. XTE J1810-197 is one of the closest magnetars, hence its X-ray properties can be studied in detail even in quiescence and an extended monitoring has been carried out to study its long term timing and spectral evolution. Here, we report the results of new X-ray observations, taken between September 2017 and April 2018, with XMM-Newton, Chandra and Nicer. We derived a phase-connected timing solution yielding a frequency derivative of -9.26(6)x10^-14 Hz s-1. This value is consistent with that measured between 2009 and 2011, indicating that the pulsar spin-down rate remained quite stable during the long quiescent period. A spectral analysis of all the X-ray observations taken between 2009 and 2018 does not reveal significant spectral and/or flux variability. The spectrum of XTE J1810-197 can be described by the sum of two thermal components with temperatures of 0.15 and 0.3 keV, plus a power law component with photon index 0.6. We also found evidence for an absorption line at ~1.2 keV and width of 0.1 keV. Thanks to the long exposure time of the summed XMM-Newton observations, we could also carry out a phase-resolved spectral analysis for this source in quiescence. This showed that the flux modulation can be mainly ascribed to the the warmer of the two thermal components, whose flux varies by ~45 per cent along the pulse phase.

Among hard X-ray galactic sources detected by INTEGRAL and Swift surveys, those discovered as accreting white dwarfs have surprisingly boosted in number, representing 20% of the galactic sample. The majority are identified as magnetic cataclysmic variabiles of the intermediate polar type suggesting this subclass as an important constituent of galactic population of X-ray sources. In this conference-proceeding, we review the X-ray emission properties as observed with our ongoing XMM-Newton programme of newly discovered INTEGRAL and/or Swift sources that enlarged almost by a factor of two, identifying cataclysmic variabiles commonalities and outliers.

In this White Paper we present the potential of the Enhanced X-ray Timing and Polarimetry (eXTP) mission for determining the nature of dense matter; neutron star cores host an extreme density regime which cannot be replicated in a terrestrial laboratory. The tightest statistical constraints on the dense matter equation of state will come from pulse profile modelling of accretion-powered pulsars, burst oscillation sources, and rotation-powered pulsars. Additional constraints will derive from spin measurements, burst spectra, and properties of the accretion flows in the vicinity of the neutron star. Under development by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is expected to be launched in the mid 2020s.

In this paper we present the science potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies of strongly magnetized objects. We will focus on the physics and astrophysics of strongly magnetized objects, namely magnetars, accreting X-ray pulsars, and rotation powered pulsars. We also discuss the science potential of eXTP for QED studies. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is expected to be launched in the mid 2020s.

Optical and X-ray observations suggested that the 9.38 h binary, SWIFT J0746.3- 1608 could be a Cataclysmic Variable of the magnetic or nova-like type, or a low mass X-ray binary. Its optical, UV, and X-ray light curves are strongly variable over years. We report on a recent XMM-Newton observation (28 April 2018), when the source had recovered from a deep low state that likely begun mid-late 2011. We detect for the first time a signal at about 38 min that we interpret as the rotation of the accreting white dwarf primary. Its amplitude decreases with increasing energy, indicating localised photoelectric absorption from cold material. The X-ray spectrum shows optically thin thermal emission with excess at the iron complex, absorbed by a dense medium partially covering the X-ray source. Based on these features, we propose that SWIFT J0746.3-1608 is a magnetic CV of the Intermediate Polar (IP) type. The long-term light curves at different wavelengths show high and low states, a rare phenomenon in the IP subclass and observed so far in only three other systems. The long orbital period, the peculiar long term variability, and its proposed magnetic nature, makes SWIFT J0746.3-1608 an interesting evolutionary test case.

To confirm the nature of the donor star in the ultracompact X-ray binary candidate 47 Tuc X9, we obtained optical spectra (3000-10 000 angstrom) with the Hubble Space Telescope / Space Telescope Imaging Spectrograph. We find no strong emission or absorption features in the spectrum of X9. In particular, we place 3 sigma upper limits on the H alpha and He II lambda 4686 emission line equivalent widths -EWH alpha less than or similar to 14 angstrom and -EWHe II less than or similar to 9 angstrom, respectively. This is much lower than seen for typical X-ray binaries at a similar X-ray luminosity (which, for L2-10 keV approximate to 10(33)-10(34) erg s(-1) is typically -EWH alpha similar to 50 angstrom). This supports our previous suggestion, by Bahramian et al., of an H-poor donor in X9. We perform timing analysis on archival far-ultraviolet, V-and I-band data to search for periodicities. In the optical bands, we recover the 7-d superorbital period initially discovered in X-rays, but we do not recover the orbital period. In the far-ultraviolet, we find evidence for a 27.2 min period (shorter than the 28.2 min period seen in X-rays). We find that either a neutron star or black hole could explain the observed properties of X9. We also perform binary evolution calculations, showing that the formation of an initial black hole/He-star binary early in the life of a globular cluster could evolve into a present-day system such as X9 (should the compact object in this system indeed be a black hole) via mass-transfer driven by gravitational wave radiation.

IGR J14257-6117 is an unclassified source in the hard X-ray catalogues. Optical follow-ups suggest it could be a Cataclysmic Variable (CV) of the magnetic type. We present the first high signal-to-noise (S/N) X-ray observation performed by XMM-Newlon at 0.3-10 keV, complemented with 10-80 keV coverage by Swift/BAT, aimed at revealing the source nature. We detected for the first time a fast periodic variability at 509.5 s and a longer periodic variability at 4.05 h, ascribed to the white dwarf (WD) spin and binary orbital periods, respectively. These unambiguously identify IGR J14257-6117 as a magnetic CV of the intermediate polar (IP) type. The energy-resolved light curves at both periods reveal amplitudes decreasing with increasing energy, with the orbital modulation reaching similar to 100 per cent in the softest band. The energy spectrum shows optically thin thermal emission with an excess at the iron complex, absorbed by two dense media (N-H similar to 10(22 - 23), cm(-2),) partially covering the X-ray source. These are likely localized in the magnetically confined accretion flow above the WD surface and at the disc rim, producing the energy-dependent spin and orbital variabilities, respectively. IGR J14257-6117 joins the group of strongest orbitally modulated IPs now counting four systems. Drawing similarities with low-mass X-ray binaries displaying orbital dips, these IPs should be seen at large orbital inclinations allowing azimuthally extended absorbing material fixed in the binary frame to intercept the line of sight. For IGRJ14257-6117, we estimate 50 degrees less than or similar to i less than or similar to 70 degrees. Whether also the mass accretion rate plays a role in the large orbital modulations in IPs cannot be established with the present data.

We present six years of optical monitoring of the black hole (BH) candidate X-ray binary Swift J1357.2–0933, during and since its discovery outburst in 2011. On these long timescales, the quiescent light curve is dominated by high amplitude, short-term (seconds–days) variability spanning ∼2 mag, with an increasing trend of the mean flux from 2012 to 2017 that is steeper than in any other X-ray binary found to date (0.17 mag yr −1 ). We detected the initial optical rise of the 2017 outburst of Swift J1357.2–0933, and we report that the outburst began between 2017 April 1 and 6. Such a steep optical flux rise preceding an outburst is expected according to disk instability models, but the high amplitude variability in quiescence is not. Previous studies have shown that the quiescent spectral, polarimetric, and rapid variability properties of Swift J1357.2–0933 are consistent with synchrotron emission from a weak compact jet. We find that a variable optical/infrared spectrum is responsible for the brightening: a steep, red spectrum before and soon after the 2011 outburst evolves to a brighter, flatter spectrum since 2013. The evolving spectrum appears to be due to the jet spectral break shifting from the infrared in 2012 to the optical in 2013, then back to the infrared by 2016–2017 while the optical remains relatively bright. Swift J1357.2–0933 is a valuable source to study BH jet physics at very low accretion rates and is possibly the only quiescent source in which the optical jet properties can be regularly monitored.

We present timing and spectral analysis of a sample of seven hard X-ray selected Cataclysmic Variable candidates based on simultaneous X-ray and optical observations collected with XMM-Newton , complemented with Swift/BAT and INTEGRAL/IBIS hard X-ray data and ground-based optical photometry. For six sources, X-ray pulsations are detected for the first time in the range $\rm \sim296-6098\,s$, identifying them as members of the magnetic class. Swift J0927.7-6945, Swift J0958.0-4208, Swift J1701.3-4304, Swift J2113.5+5422, and possibly PBC J0801.2-4625, are Intermediate Polars (IPs), while Swift J0706.8+0325 is a short (1.7 h) orbital period Polar, the 11$^{\rm th}$ hard X-ray selected identified so far. X-ray orbital modulation is also observed in Swift J0927.7-6945 (5.2 h) and Swift J2113.5+5422 (4.1 h). Swift J1701.3-4304 is discovered as the longest orbital period (12.8 h) deep eclipsing IP. The spectra of the magnetic systems reveal optically thin multi-temperature emission between 0.2 and 60 keV. Energy dependent spin pulses and the orbital modulation in Swift J0927.7-6945 and Swift J2113.5+5422 are due to intervening local high density absorbing material ($\rm N_H\sim10^{22-23}\,cm^{-2}$). In Swift J0958.0-4208 and Swift J1701.3-4304, a soft X-ray blackbody (kT$\sim$50 and $\sim$80 eV) is detected, adding them to the growing group of "soft" IPs. White dwarf masses are determined in the range $\rm \sim0.58-1.18\,M_{\odot}$, indicating massive accreting primaries in five of them. Most sources accrete at rates lower than the expected secular value for their orbital period. Formerly proposed as a long-period (9.4 h) novalike CV, Swift J0746.3-1608 shows peculiar spectrum and light curves suggesting either an atypical low-luminosity CV or a low mass X-ray binary.

The candidate black hole X-ray binary Swift J1753.5-0127 faded to quiescence in 2016 November, after a prolonged outburst that was discovered in 2005. Nearly three months later the system displayed renewed activity that lasted through 2017 July. Here, we present radio and X-ray monitoring over 3 months of the renewed activity to study the coupling between the jet and the inner regions of the disk/jet system. Our observations cover low X-ray luminosities that have not historically been well-sampled (Lx 2e33 - 1e36 erg/s; 1-10 keV), including time periods when the system was both brightening and fading. At these low luminosities Swift J1753.5-0127 occupies a parameter space in the radio/X-ray luminosity plane that is comparable to "canonical" systems (e.g., GX 339-4), regardless of whether the system was brightening or fading, even though during its >11-year outburst Swift J1753.5-0127 emitted less radio emission from its jet than expected. We discuss implications for the existence of a single radio/X-ray luminosity correlation for black hole X-ray binaries at the lowest luminosities (Lx < 1e35 erg/s), and we compare to supermassive black holes. Our campaign includes the lowest luminosity quasi-simultaneous radio/X-ray detection to date for a black hole X-ray binary during its rise out of quiescence, thanks to early notification from optical monitoring combined with fast responses from sensitive multiwavelength facilities.

We present the results of our analysis of new optical, ultraviolet (UV) and X-ray observations of a highly variable source $-$ AX J1549.8$-$5416. Both the detection of several fast rise, exponential decay outbursts in the optical light curve and the lack of He II emission lines in the optical spectra suggest AX J1549.8$-$5416 is a cataclysmic variable of the dwarf nova (DN) type. The multiwavelength analysis of three mini-outbursts and one normal outburst represent one of the most complete multiwavelength studies of a DN and help to refine the relationship between the X-ray, UV and optical emission in this system. We find that the UV emission is delayed with respect to the optical by $1.0-5.4$ days during the rising phase of the outburst. The X-ray emission is suppressed during the peak of the optical outburst and recovers during the end of the outburst. From our analysis of archival Swift, Chandra and XMM-Newton observations of AX J1549.8$-$5416, we estimate this DN has a high duty cycle ($\sim50\%$), suggesting a quiescent X-ray luminosity larger than $10^{32}$ erg/s. We also find the X-ray and UV flux are roughly anti-correlated. Furthermore, we find that, at low X-ray fluxes, the X-ray spectrum is well described by a single temperature thermal plasma model, while at high X-ray fluxes, an isobaric cooling flow model also works. We find that the maximum temperature of the plasma in quiescence is significantly higher than that in outburst.

We present six years of optical monitoring of the black hole (BH) candidate X-ray binary Swift J1357.2–0933, during and since its discovery outburst in 2011. On these long timescales, the quiescent light curve is dominated by high amplitude, short-term (seconds–days) variability spanning ∼ 2 mag, with an increasing trend of the mean flux from 2012 to 2017 that is steeper than in any other X-ray binary found to date (0.17 mag yr). We detected the initial optical rise of the 2017 outburst of Swift J1357.2–0933, and we report that the outburst began between 2017 April 1 and 6. Such a steep optical flux rise preceding an outburst is expected according to disk instability models, but the high amplitude variability in quiescence is not. Previous studies have shown that the quiescent spectral, polarimetric, and rapid variability properties of Swift J1357.2–0933 are consistent with synchrotron emission from a weak compact jet. We find that a variable optical/infrared spectrum is responsible for the brightening: a steep, red spectrum before and soon after the 2011 outburst evolves to a brighter, flatter spectrum since 2013. The evolving spectrum appears to be due to the jet spectral break shifting from the infrared in 2012 to the optical in 2013, then back to the infrared by 2016–2017 while the optical remains relatively bright. Swift J1357.2–0933 is a valuable source to study BH jet physics at very low accretion rates and is possibly the only quiescent source in which the optical jet properties can be regularly monitored.

Context. Based on XMM-Newton X-ray observations IGR J19552+0044 appears to be either a pre-polar or an asynchronous polar.