The near infrared (nIR)/optical counterparts of low mass X-ray binaries (LMXBs) are often observationally dim and reside in high source density fields which make their identification problematic; however, without such a counterpart identification we are unable to investigate many of the properties of LMXB systems. Here, in the context of a larger identification campaign, we examine the fields of four LMXB systems near the Galactic centre, in a bid to identify nIR/optical counterparts to the previously detected X-ray point sources. We obtain nIR/optical images of the fields with the ESO - New Technology Telescope and apply standard photometric and astrometric calibrations; these data are supplemented by Spitzer-GLIMPSE catalog data. On the basis of positional coincidence with the arcsecond accurate X-ray positions, we identify unambiguous counterpart candidates for XTE J1637-498, IGR J17379-3747, IGR J17585-3057 and GX 9+1. We propose tentative nIR counterparts of four LMXBs which require further investigation to confirm their associations to the X-ray sources.
Neutron stars are strongly magnetized rotating compact objects. Therefore they also produce huge electric fields accelerating particles to ultra-relativistic energies. The simplest magnetic topology is a dipole traditionally located at the stellar centre. In this paper, we reinvestigate the consequences of an off-centred rotating magnetic dipole, showing accurate magnetic field line geometries, the associated spin-down luminosity as well as the corresponding electromagnetic kick and torque imprinted to the neutron star. Results are obtained by time dependent numerical simulations of Maxwell eq…
The presence of some X-ray sources in the Galactic Centre region which show variability, but do not show outbursts in over a decade of monitoring has been used to argue for the presence of a large population of stellar mass black holes in this region. A core element of the arguments that these objects are accreting black holes is the claim that neutron stars (NSs) in low mass X-ray binaries (LMXBs) do not have long transient recurrence times. We demonstrate in this paper that about half of the known transient LMXBs with clear signatures for NS primaries have recurrence times in excess of a dec…
We present near-infrared and optical imaging of fifteen candidate black hole X-ray binaries. In addition to quiescent observations for all sources, we also observed two of these sources (IGR J17451-3022 and XTE J1818-245) in outburst. We detect the quiescent counterpart for twelve out of fifteen sources, and for the remaining three we report limiting magnitudes. The magnitudes of the detected counterparts range between $K_s$ = 17.59 and $K_s$ = 22.29 mag. We provide (limits on) the absolute magnitudes and finding charts of all sources. Of these twelve detections in quiescence, seven represent …
Very faint X-ray transients (VFXTs) are a group of X-ray binaries with low luminosities, the peak X-ray luminosities during their outbursts being only 10$^{34}$--10$^{36}$ erg\,s$^{-1}$. Using the $γ$-ray data obtained with the Large Area Telescope (LAT) onboard {\it Fermi Gamma-Ray Space Telescope}, we investigate their possible nature of containing rotation-powered pulsars, or more specifically being transitional millisecond pulsars (MSPs). Among more than 40 known VFXTs, we select 12 neutron star systems. We analyze the LAT data for the fields of the 12 VFXTs in 0.2--300 GeV energy range, b…
Seventeen years of hard X-ray observations with the instruments of the INTEGRAL observatory, with a focus on the Milky Way and in particular on the Galactic Centre region, have provided a unique database for exploration of the Galactic population of low-mass X-ray binaries (LMXBs). Our understanding of the diverse energetic phenomena associated with accretion of matter onto neutron stars and black holes has greatly improved. We review the large variety of INTEGRAL based results related to LMXBs. In particular, we discuss the spatial distribution of LMXBs over the Galaxy and their X-ray luminos…
Precise and accurate measurements of distances to Galactic X-ray binaries (XRBs) reduce uncertainties in the determination of XRB physical parameters. We have cross-matched the XRB catalogues of Liu et al. (2006, 2007) to the results of Gaia Data Release 2. We identify 86 X-ray binaries with a Gaia candidate counterpart, of which 32 are low-mass X-ray binaries (LMXBs) and 54 are high-mass X-ray binaries (HMXBs). Distances to Gaia candidate counterparts are, on average, consistent with those measured by Hipparcos and radio parallaxes. When compared to distances measured by Gaia candidate counte…
Black hole-neutron star (BHNS) binaries are amongst promising candidates for the joint detection of electromagnetic (EM) signals with gravitational waves (GWs) and are expected to be detected in the near future. Here we study the effect of the BHNS binary parameters on the merger ejecta properties and associated EM signals. We estimate the remnant disk and unbound ejecta masses for BH mass and spin distributions motivated from the observations of transient low-mass X-ray binaries (LMXBs) and specific NS equation of state (EoS). The amount of r-process elements synthesised in BHNS mergers is es…
We discuss the properties of stellar mass black hole (BH) mergers induced by tidal encounters with a massive BH at galactic centres or potentially in dense star clusters. The tidal disruption of stellar binaries by a massive BH is known to produce hypervelocity stars. However, such a tidal encounter does not always lead to the break-up of binaries. Since surviving binaries tend to become hard and eccentric, this process can produce BH mergers in principle. For initially circular binaries, we show that the gravitational wave (GW) merger times become shorter by a factor of more than $10^{2}$ ($1…
Pulsars (PSRs) orbiting intermediate or supermassive black holes at the centre of galaxies and globular clusters are known as Extreme Mass Ratio Binaries (EMRBs) and have been identified as precision probes of strong-field GR. For appropriate orbital parameters, some of these systems may also emit gravitational radiation in a `burst-like' pattern. The observation of this burst radiation in conjunction with the electromagnetic radio timing signal would allow for multimessenger astronomy in strong-field gravitational regimes. In this work we investigate gravitational radiation from these PSR-EMR…
We investigated for a possible connection between the types of X-ray binaries (XRBs) and the properties of compact star clusters in the nearby galaxy NGC 628. Using {\it Chandra} archival data covering the years 2001-2018, 75 X-ray sources were detected within the field of view of observations. A total of 69 XRBs, one of which is an ultraluminous X-ray source (ULX), were found to be in the luminosity range of 3$\times10^{36}\leq L_{X}$ $\leq $ 2$\times10^{39}$ erg s$^{-1}$. We identified the optical counterpart(s) of 15 of the 42 XRBs that coincide with the {\it HST} field of view via improved…
The detection of a pulsar (PSR) in a tight, relativistic orbit around a supermassive or intermediate mass black hole - such as those in the Galactic centre or in the centre of Globular clusters - would allow for precision tests of general relativity (GR) in the strong-field, non-linear regime. We present a framework for calculating the theoretical time-frequency signal from a PSR in such an Extreme Mass Ratio Binary (EMRB). This framework is entirely relativistic with no weak-field approximations and so able to account for all higher-order strong-field gravitational effects, relativistic spin …
In analogy with spontaneous magnetization of ferromagnets below the Curie temperature, a neutron star (NS), with a compactness above a certain critical value, may undergo spontaneous scalarization and exhibit an interior nontrivial scalar configuration. Consequently, the exterior space-time is changed, and an external scalar field appears, which subsequently triggers a scalarization of its companion. The dynamical interplay produces a gravitational scalar counterpart of tensor gravitational waves. In this paper, we resort to scalar-tensor theory and demonstrate that the gravitational scalar co…
We used archival data from the \emph{Chandra X-ray Observatory} (\emph{Chandra}) and the \emph{Hubble Space Telescope}, to identify 334 candidate X-ray binary (XRB) systems and their potential optical counterparts in the interacting galaxy pair NGC 5194/5195 (M51). We present the catalog and data analysis of X-ray and optical properties for those sources, from the deep $892$ ks \emph{Chandra} observations, along with the magnitudes of candidate optical sources as measured in the $8.16$ ks \emph{HST} observations. The X-ray luminosity function of the X-ray sources above a few times $10^{36}\, {…
We study the impact of gas accretion on the orbital evolution of black-hole binaries initially at large separation in the band of the planned Laser Interferometer Space Antenna (LISA). We focus on two sources: (i)~stellar-origin black-hole binaries~(SOBHBs) that can migrate from the LISA band to the band of ground-based gravitational-wave observatories within weeks/months; and (ii) intermediate-mass black-hole binaries~(IMBHBs) in the LISA band only. Because of the large number of observable gravitational-wave cycles, the phase evolution of these systems needs to be modeled to great accuracy t…
The recent advanced LIGO/Virgo detections of gravitational waves (GWs) from stellar binary black hole (BBH) mergers, in particular GW190521, which is potentially associated with a quasar, have stimulated renewed interest in active galactic nuclei (AGNs) as factories of merging BBHs. Compact objects evolving from massive stars are unavoidably enshrouded by a massive envelope to form accretion-modified stars (AMSs) in the dense gaseous environment of a supermassive black hole (SMBH) accretion disk. We show that most AMSs form binaries due to gravitational interaction with each other during radia…
We propose a novel scenario for possible electromagnetic (EM) emission by compact binary mergers in the accretion disks of active galactic nuclei (AGNs). Nuclear star clusters in AGNs are a plausible formation site of compact-stellar binaries (CSBs) whose coalescences can be detected through gravitational waves (GWs). We investigate the accretion onto and outflows from CSBs embedded in AGN disks. We show that these outflows are likely to create outflow "cavities" in the AGN disks before the binaries merge, which makes EM or neutrino counterparts much less common than would otherwise be expecte…
High-mass X-ray binaries (HMXBs) are a particular class of high-energy sources that require multi-wavelength observational efforts to be properly characterised. New identifications and the refinement of previous measurements are regularly published in the literature by independent teams of researchers and might, when they are collected in a catalogue, offer a tool for facilitating further studies of HMXBs. We update previous instances of HMXB catalogues in the Galaxy and provide the community easy access to the most complete set of observables on Galactic HMXBs. In addition to the fixed versio…
In the next decade, the Laser Interferometer Space Antenna (LISA) will detect the coalescence of massive black hole binaries (MBHBs) in the range $[10^4, 10^8] \, \rm M_{\odot}$, up to $z\sim10$. Their gravitational wave (GW) signal is expected to be accompanied by an electromagnetic counterpart (EMcp), generated by the gas accreting on the binary or on the remnant BH. In this work, we present the number and characteristics (such as redshift and mass distribution, apparent magnitudes or fluxes) of EMcps detectable jointly by LISA and some representative EM telescopes. We combine state-of-the-a…
Multiwavelength search for counterparts of supersoft X-ray sources in M31
我们在哈勃空间望远镜（HST）的“全色哈勃仙女座宝库”（PHAT）档案图像和测光目录中搜索了M31中7个超软X射线源（SSS）的光学/UV/IR对应物。三个SSS是瞬态的，其他四个是持久性的来源。PHAT提供了机会，以确定SSS托管非常大的白矮星，可能爆炸的Ia型超新星在单一的简并双星，与典型的共生星，高质量的近距离双星，或系统的光度发光吸积盘的星等和颜色指数。我们发现的证据表明，瞬态SSS是经典的或经常性的新星，我们确定的两个可能的对应物可能是共生双星进行质量转移在一个非常高的速度。在其中一个持久源r3-8的误差圈内有一颗候选的吸积白矮星双星。在M31，r2-12中研究最充分的SSS的空间误差圆中，没有红巨星或AGB恒星在光学和紫外波段足够明亮，成为共生系统，承载吸积和氢燃烧的白矮星。该SSS具有周期为217.7 s的X射线通量的已知调制，并且我们测量了其导数的上限，0.82 x 10（-11）。这个极限可以与轨道周期为几小时的双星中高速吸积的白矮星的自转周期相一致。然而，没有发光的对应物具有典型的吸积盘由热的中心源照射的颜色指数。采用半经验关系，盘光学光度的上限意味着白矮星双星的轨道周期的上限只有169分钟。
Ground-based optical photometry of the counterparts of High-Mass X-ray Binaries (HMXBs) has revealed the presence of periodic modulations on timescales of ~0.3-0.5 d. More recent space-based observations Corot and TESS of OB and Be stars have shown that pulsations caused by p and g modes are common in early type stars. We have therefore undertaken a systematic search for variability in the optical counterparts of 23 HMXBs (mostly neutron star systems, but including one black hole, Cyg X-1) using TESS data primarily in 2 min cadence mode. After removing the orbital period modulation in four sys…
The next two decades are expected to open the door to the first coincident detections of electromagnetic (EM) and gravitational wave (GW) signatures associated with massive black hole (MBH) binaries heading for coalescence. These detections will launch a new era of multimessenger astrophysics by expanding this growing field to the low-frequency GW regime and will provide an unprecedented understanding of the evolution of MBHs and galaxies. They will also constitute fundamentally new probes of cosmology and would enable unique tests of gravity. The aim of this Living Review is to provide an int…
Roche lobe overflow from a donor star onto a black hole or neutron star binary companion can evolve to a phase of unstable runaway mass-transfer, lasting as short as hundreds of orbits ($\lesssim 10^{2}$ yr for a giant donor), and eventually culminating in a common envelope event. The highly super-Eddington accretion rates achieved during this brief phase ($\dot{M} \gtrsim 10^{5}\dot{M}_{\rm Edd})$ are accompanied by intense mass-loss in disk winds, analogous but even more extreme than ultra-luminous X-ray (ULX) sources in the nearby universe. Also in analogy with observed ULX, this expanding …
The gravitational-wave signal from the merger of two neutron stars cannot be easily differentiated from the signal produced by a comparable-mass mixed binary of a neutron star and a black hole. Indeed, both binary types can account for the gravitational-wave signal GW170817 even if its electromagnetic counterpart emission is taken into account. We propose a method that {requires neither information from the post-inspiral phase of the binary nor an electromagnetic counterpart} to identify mixed binaries of neutron stars merging with low-mass black holes using gravitational-waves alone. This met…
