Accretion of matter onto black holes is universally associated with strong radiative feedback 1 and powerful outflows 2 . In particular, black hole transients 3 show outflows whose properties 4 are strongly coupled to those of the accretion flow. This includes X-ray winds of ionized material, expelled from the accretion disc encircling the black hole, and collimated radio jets 5,6 . Very recently, a distinct optical variability pattern has been reported in the transient black hole transient V404 Cyg, and interpreted as disrupted mass flow into the inner regions of its large accretion disc 7 . Here, we report on the discovery of a sustained outer accretion disc wind in V404 Cyg, which is unlike any seen previously. We find that the outflowing wind is neutral, has a large covering factor, expands at 1% of the speed of light and triggers a nebular phase once accretion sharply drops and the ejecta become optically thin. The large expelled mass (> l0 -8 M ¤ ) indicates that the outburst was prematurely ended when a sizeable fraction of the outer disc was depleted by the wind, detaching the inner regions from the rest of the disc. The luminous, but brief, accretion phases shown by transients with large accretion discs 2 imply that this outflow is most likely a new fundamental ingredient regulating mass accretion onto black holes.The X-ray binary V404 Cyg (GS 2023+338) is a confirmed stellar-mass BH 8 with a precisely determined distance of 2.4 kpc 9 . Following 25 years of quiescence, the Swift mission detected renewed activity on Jun 15, 2015 10 , initiating a 2-week period of intensely violently variable emission across all wavelengths 11,12 . Our high signal-to-noise GTC optical spectra covering the entire X-ray/radio active phase (~15 days) show that, contemporaneously with radio jet emission, continuous ejections of neutral material at ~0.01c are present from low-level accretion phases (<1% of the Eddington luminosity; L EDD ) to the Xray peak (Methods; Fig. 1, ED Fig. 1). These are observed in hydrogen (Balmer) and helium (He I) emission lines as deep P-Cyg profiles throughout the outburst 13 , and extremely broad wings once the Xray and radio fluxes decay. P-Cyg profiles result from resonant scattering in an expanding outflow with a spherical geometry or at least sustaining a large solid angle 14, 15 (Methods). Among a dozen transitions showing this feature, the deepest are seen in the He I-5876 emission line, which is used as a reference for this study (see ED Fig. 2.).The strongest P-Cyg profiles are witnessed during days 1 to 6 (Fig. 1 and Fig. 2 for the evolution of the profiles during day 2; Methods), when the X-ray luminosity is typically 10 3 times fainter than the ~L EDD flares displayed later in the outburst 7,11 (ED Fig.1). Blue-shifted absorptions are as deep as 30% below the continuum level and we measure terminal velocities in the range V T =1,500 -3,000 km s -1 (Fig. 1, Fig 2, ED Fig 2; ED Fig. 3). Symmetric red-shifted (i.e. positive velocity) outflow emission, completely detached from the accre...

We present new medium resolution, optical long-slit spectra of a sample of 6 UV/optical and 17 X-ray selected tidal disruption event candidate host galaxies. We measure emission line ratios from the optical spectra, finding that the large majority of hosts are quiescent galaxies, while those displaying emission lines are generally consistent with star-formation dominated environments; only 3 sources show clear evidence of nuclear activity. We measure bulge velocity dispersions using absorption lines and infer host black hole (BH) masses using the M -σ relation. While the optical and X-ray host BH masses are statistically consistent with coming from the same parent population, the optical host M BH distribution has a visible peak near M BH ∼ 10 6 M , whereas the X-ray host distribution appears flat in M BH . We find a subset of X-ray selected candidates that are hosted in galaxies significantly less luminous (M g ∼ -16) and less massive (stellar mass ∼ 10 8.5−9 M ) than those of optical events. Using statistical tests we find suggestive evidence that, in terms of black hole mass, stellar mass and absolute magnitude, the hard X-ray hosts differ from the UV/optical and soft Xray samples. Similar to individual studies, we find that the size of the emission region for the soft X-ray sample is much smaller than the optical emission region, consistent with a compact accretion disk. We find that the typical Eddington ratio of the soft X-ray emission is ∼ 0.01, as opposed to the optical events which have L BB ∼ L Edd . The latter seems artificial if the radiation is produced by self-intersection shocks, and instead suggests a connection to the SMBH.

The Fermi Large Area Telescope gamma-ray source 3FGL J2039.6−5618 contains a periodic optical and X-ray source that was predicted to be a “redback” millisecond pulsar (MSP) binary system. However, the conclusive identification required the detection of pulsations from the putative MSP. To better constrain the orbital parameters for a directed search for gamma-ray pulsations, we obtained new optical light curves in 2017 and 2018, which revealed long-term variability from the companion star. The resulting orbital parameter constraints were used to perform a targeted gamma-ray pulsation search using the Einstein@Home distributed volunteer computing system. This search discovered pulsations with a period of 2.65 ms, confirming the source as a binary MSP now known as PSR J2039−5617. Optical light curve modelling is complicated, and likely biased, by asymmetric heating on the companion star and long-term variability, but we find an inclination i ≳ 60 ○, for a low pulsar mass between 1.1 M⊙ &lt; Mpsr &lt; 1.6 M⊙, and a companion mass of 0.15–0.22 M⊙, confirming the redback classification. Timing the gamma-ray pulsations also revealed significant variability in the orbital period, which we find to be consistent with quadrupole moment variations in the companion star, suggestive of convective activity. We also find that the pulsed flux is modulated at the orbital period, potentially due to inverse Compton scattering between high-energy leptons in the pulsar wind and the companion star’s optical photon field.

Abstract We report the results of optical follow-up observations of 29 gravitational-wave triggers during the first half of the LIGO-Virgo Collaboration (LVC) O3 run with the Gravitational-wave Optical Transient Observer (GOTO) in its prototype 4-telescope configuration (GOTO-4). While no viable electromagnetic counterpart candidate was identified, we estimate our 3D (volumetric) coverage using test light curves of on- and off-axis gamma-ray bursts and kilonovae. In cases where the source region was observable immediately, GOTO-4 was able to respond to a GW alert in less than a minute. The average time of first observation was 8.79 hours after receiving an alert (9.90 hours after trigger). A mean of 732.3 square degrees were tiled per event, representing on average 45.3 per cent of the LVC probability map, or 70.3 per cent of the observable probability. This coverage will further improve as the facility scales up alongside the localisation performance of the evolving gravitational-wave detector network. Even in its 4-telescope prototype configuration, GOTO is capable of detecting AT2017gfo-like kilonovae beyond 200 Mpc in favourable observing conditions. We cannot currently place meaningful electromagnetic limits on the population of distant ($\hat{D}_L = 1.3$ Gpc) binary black hole mergers because our test models are too faint to recover at this distance. However, as GOTO is upgraded towards its full 32-telescope, 2 node (La Palma & Australia) configuration, it is expected to be sufficiently sensitive to cover the predicted O4 binary neutron star merger volume, and will be able to respond to both northern and southern triggers.