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Palomar Gattini-IR (PGIR) is a wide-field, synoptic infrared time domain survey covering ≈15,000 sq. deg. of the accessible sky at ≈1–3 night cadence to a depth of J≈ 13.0 and ≈14.9 Vega mag in and outside the Galactic plane, respectively. Here, we present the first data release of J-band light curves of Two Micron All Sky Survey (2MASS) sources within the survey footprint covering approximately the first four years of operations. We describe the construction of the source catalog based on 2MASS point sources, followed by exposure filtering criteria and forced PSF photometry. The catalog contains light curves of ≈286 million unique sources with 2MASS magnitudes of J< 15.5 mag, with a total of ≈50 billion photometric measurements and ≈20 billion individual source detections at signal-to-noise-ratio > 3. We demonstrate the photometric fidelity of the catalog by (i) quantifying the magnitude-dependent accuracy and uncertainty of the photometry with respect to 2MASS and (ii) comparing against forced PGIR aperture photometry for known variable sources. We present simple filtering criteria for selecting reliable photometric measurements as well as example Pythonnotebooks for users. This catalog is one of the largest compilation of nightly cadence, synoptic infrared light curves to date, comparable to those in the largest optical surveys, providing a stepping stone to upcoming infrared surveys in the coming decade.

Long Period Variables (LPVs) are stars with periods of several hundred days, representing the late, dust-enshrouded phase of stellar evolution in low to intermediate mass stars. In this paper, we present a catalog of 154,755 LPVs using near-IR lightcurves from the Palomar Gattini-IR (PGIR) survey. PGIR has been surveying the entire accessible northern sky (δ> −28°) in the J-band at a cadence of 2–3 days since 2018 September, and has produced J-band lightcurves for more than 60 million sources. We used a gradient-boosted decision tree classifier trained on a comprehensive feature set extracted from PGIR lightcurves to search for LPVs in this data set. We developed a parallelized and optimized code to extract features at a rate of ∼0.1 s per lightcurve. Our model can successfully distinguish LPVs from other stars with a true positive rate of 95%. Cross-matching with known LPVs, we find 70,369 (∼46%) new LPVs in our catalog.

We present results from a systematic infrared (IR) census of R Coronae Borealis (RCB) stars in the Milky Way, using data from the Palomar Gattini IR (PGIR) survey. RCB stars are dusty, erratic variable stars presumably formed from the merger of a He-core and a CO-core white dwarf (WD). PGIR is a 30 cm J-band telescope with a 25 deg2camera that surveys 18,000 deg2of the northern sky (δ> −28°) at a cadence of 2 days. Using PGIR J-band lightcurves for ∼60 million stars together with mid-IR colors from WISE, we selected a sample of 530 candidate RCB stars. We obtained near-IR spectra for these candidates and identified 53 RCB stars in our sample. Accounting for our selection criteria, we find that there are a total of ≈350−100+150RCB stars in the Milky Way. Assuming typical RCB lifetimes, this corresponds to an RCB formation rate of 0.8–5 × 10−3yr−1, consistent with observational and theoretical estimates of the He-CO WD merger rate. We searched for quasi-periodic pulsations in the PGIR lightcurves of RCB stars and present pulsation periods for 16 RCB stars. We also examined high-cadenced TESS lightcurves for RCB and the chemically similar, but dustless hydrogen-deficient carbon (dLHdC) stars. We find that dLHdC stars show variations on timescales shorter than RCB stars, suggesting that they may have lower masses than RCB stars. Finally, we identified 3 new spectroscopically confirmed and 12 candidate Galactic DY Per type stars—believed to be colder cousins of RCB star—doubling the sample of Galactic DY Per type stars.

All stellar-mass black holes have hitherto been identified by X-rays emitted from gas that is accreting onto the black hole from a companion star. These systems are all binaries with a black-hole mass that is less than 30 times that of the Sun1–4. Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star–black-hole binaries5,6. When the black hole is not accreting gas, it can be found through radial-velocity measurements of the motion of the companion star. Here we report radial-velocity measurements taken over two years of the Galactic B-type star, LB-1. We find that the motion of the B star and an accompanying Hα emission line require the presence of a dark companion with a mass of 68−13+11solar masses, which can only be a black hole. The long orbital period of 78.9 days shows that this is a wide binary system. Gravitational-wave experiments have detected black holes of similar mass, but the formation of such massive ones in a high-metallicity environment would be extremely challenging within current stellar evolution theories.

Powerful relativistic jets are one of the main ways in which accreting black holes provide kinetic feedback to their surroundings. Jets launched from or redirected by the accretion flow that powers them are expected to be affected by the dynamics of the flow, which for accreting stellar-mass black holes has shown evidence for precession1due to frame-dragging effects that occur when the black-hole spin axis is misaligned with the orbital plane of its companion star2. Recently, theoretical simulations have suggested that the jets can exert an additional torque on the accretion flow3, although the interplay between the dynamics of the accretion flow and the launching of the jets is not yet understood. Here we report a rapidly changing jet orientation—on a time scale of minutes to hours—in the black-hole X-ray binary V404 Cygni, detected with very-long-baseline interferometry during the peak of its 2015 outburst. We show that this changing jet orientation can be modelled as the Lense–Thirring precession of a vertically extended slim disk that arises from the super-Eddington accretion rate4. Our findings suggest that the dynamics of the precessing inner accretion disk could play a role in either directly launching or redirecting the jets within the inner few hundred gravitational radii. Similar dynamics should be expected in any strongly accreting black hole whose spin is misaligned with the inflowing gas, both affecting the observational characteristics of the jets and distributing the black-hole feedback more uniformly over the surrounding environment5,6. The relativistic jets associated with the black-hole X-ray binary system V404 Cygni change their orientation on time scales of minutes to hours, implying that the direction of the jets is being affected by the dynamics of the surrounding accretion flow that powers them.

Maps of low-inclination nearby galaxies in Sloan Digitized Sky Survey u - g, g - r, and r - i colors are used to determine whether ultraluminous X-ray sources (ULXs) are predominantly associated with star-forming regions of their host galaxies. An empirical selection criterion is derived from colors of H II regions in M 81 and M 101 that differentiates between the young, blue stellar component and the older disk and bulge population. This criterion is applied to a sample of 58 galaxies of Hubble type S0 and later and verified through an application of Fisher's linear discriminant analysis. It is found that 60% (49%) of ULXs in optically bright environments are within regions blueward of their host galaxy's H II regions compared to only 27% (0%) of a control sample according to the empirical (Fisher) criterion. This is an excess of 3s above the 32% (27%) expected if the ULXs were randomly distributed within their galactic hosts. This indicates a ULX preference for young, [?]10 Myr, OB associations. However, none of the ULX environments have the morphology and optical brightness suggestive of a massive young super-star cluster though several are in extended or crowded star-forming (blue) environments that may contain clusters unresolved by Sloan imaging. Ten of the 12 ULX candidates with estimated X-ray luminosities in excess of 3 x 1039 erg s-1 are equally divided among the group of ULX environments redward of H II regions and the group of optically faint regions. This likely indicates that the brightest ULXs turn on at a time somewhat later than typical of H II regions; say 10-20 Myr after star formation has ended. This would be consistent with the onset of an accretion phase as the donor star ascends the giant branch if the donor is an [?]20 M star.

We have studied the X-ray nuclear activity of 187 nearby (distance less than 15 Mpc) galaxies observed with Chandra/ACIS. We found that 86 of them have a pointlike X-ray core, consistent with an accreting black hole (BH). We argue that the majority of them are nuclear BHs, rather than X-ray binaries. The fraction of galaxies with an X-ray-detected nuclear BH is higher ([?]60%) for ellipticals and early type spirals (E to Sb), and lower ([?]30%) for late-type spirals (Sc to Sm). There is no preferential association of X-ray cores with the presence of a large-scale bar; in fact, strongly barred galaxies appear to have slightly lower detection fraction and luminosity for their nuclear X-ray sources, compared with nonbarred or weakly barred galaxies of similar Hubble types. The cumulative luminosity distribution of the nuclear sources in the 0.3-8 keV band is a power law with slope [?] -0.5, from [?]2 x 1038 erg s-1 to [?]1042 erg s-1. The Eddington ratio is lower for ellipticals (L X/L Edd [?] 10-8) and higher for late-type spirals (up to L X/L Edd [?] 10-4), but in all cases, the accretion rate is low enough to be in the radiatively inefficient regime. The intrinsic absorbing column density is generally low, especially for the less luminous sources: there appear to be no Type 2 nuclear BHs at luminosities [?]1039 erg s-1. The lack of a dusty torus or of other sources of intrinsic absorption (e.g., an optically thick disk wind) may be directly related to the lack of a standard accretion disk around those faint nuclear BHs. The fraction of obscured sources increases with the nuclear BH luminosity: two-thirds of the sources with L X > 1040 erg s-1 have a fitted column density greater than 1022 cm-2. This is in contrast to the declining trend of the obscured fraction with increasing luminosities, observed in more luminous active galactic nuclei and quasars.

We have re-examined the most luminous X-ray sources in the starburst galaxy NGC 4631, using XMM-Newton, Chandra, and ROSAT data. The most interesting source is a highly variable supersoft ultraluminous X-ray source (ULX). We suggest that its bolometric luminosity [?] a few 1039 erg s-1 in the high/supersoft state: this is an order of magnitude lower than estimated in previous studies, thus reducing the need for extreme or exotic scenarios. Moreover, we find that this source was in a noncanonical low/soft (kT [?] 0.1-0.3 keV) state during the Chandra observation. By comparing the high and low state, we argue that the spectral properties may not be consistent with the expected behavior of an accreting intermediate-mass black hole. We suggest that recurrent super-Eddington outbursts with photospheric expansion from a massive white dwarf (M wd [?] 1.3 M ), powered by nonsteady nuclear burning, may be a viable possibility, in alternative to the previously proposed scenario of a super-Eddington outflow from an accreting stellar-mass black hole. The long-term average accretion rate required for nuclear burning to power such white-dwarf outbursts in this source and perhaps in other supersoft ULXs is [?](5-10) x 10-6 M yr-1: this is comparable to the thermal-timescale mass transfer rate invoked to explain the most luminous hard-spectrum ULXs (powered by black hole accretion). The other four most luminous X-ray sources in NGC 4631 (three of which can be classified as ULXs) appear to be typical accreting black holes, in four different spectral states: high/soft, convex-spectrum, power-law with soft excess, and simple power-law. None of them require masses [?]50 M .

A thorough search for ultraluminous X-ray source candidates within the Local Volume is made. The search spatially matches potential ULXs detected in X-ray images or cataloged in the literature with galaxies tabulated in the Catalog of Neighboring Galaxies compiled by Karachentsev et al. The specific ULX frequency (occurrence rate per unit galaxy mass) is found to be a decreasing function of host galaxy mass for host masses above ~108.5 M. There is too little mass in galaxies below this point to determine whether this trend continues to lower galaxy mass. No ULXs have yet been detected in lower mass galaxies. Systematic differences between dwarf and giant galaxies that may explain an abundance of ULXs in dwarf galaxies and what they may imply about the nature of ULXs are discussed.

We have studied the X-ray emission from four historical Type II supernovae (the newly recovered 1941C in NGC 4136 and 1959D in NGC 7331; and 1968D and 1980K in NGC 6946), using Chandra ACIS-S imaging. In particular, the first three are the oldest ever found in the X-ray band, and provide constraints on the properties of the stellar wind and circumstellar matter encountered by the expanding shock at more advanced stages in the transition toward the remnant phase. We estimate emitted luminosities [?] 5 x 1037 erg s[?]1 for SN 1941C, ~a few x 1037 erg s[?]1 for SN 1959D, [?] 2 x 1038 erg s[?]1 for SN 1968D, and [?] 4 x 1037 erg s[?]1 for SN 1980K, in the 0.3-8 keV band. X-ray spectral fits to SN 1968D suggest the presence of a harder component, possibly a power law with photon index [?]2, contributing [?]1037 erg s[?]1 in the 2-10 keV band. We speculate that it may be evidence of nonthermal emission from a Crab-like young pulsar.

We report the discovery of an X-ray source coincident with the nuclear star cluster at the dynamical center of the nearby late-type spiral galaxy NGC 2403. The X-ray luminosity of this source varies from below detection levels, ~1035 erg s-1 in the 0.5-8.0 keV band to 7 x 1038 erg s-1 on timescales between observations of <2 months. The X-ray spectrum is well fit by an accretion disk model consisting of multiple blackbody components and corresponding physically to a compact object mass of [?]5 M. No pulsations nor aperiodic behavior is evident in its X-ray light curve on the short timescales of the individual observations. The X-ray properties of the source are more similar to those of the nuclear source X-8 in M33, believed to be a low-mass X-ray binary, then to those of the low-luminosity active galactic nucleus (AGN) in NGC 4395. The brightness of the nuclear star cluster, MI ~ -11.8 mag, is typical of clusters in late-type spirals but its effective radius, re ~ 12 pc, is several times larger than average indicating a relatively relaxed cluster and a low probability of a central massive object. Estimating from its observed colors and brightness, the cluster has a mass of [?]106.5 M and an age of ~1.4 Gyr.

We report the discovery with XMM-Newton of quasi-periodic variability in the 0.2-10 keV X-ray flux from the ULX NGC 5408 X-1. The average power spectrum of all EPIC-pn data reveals a strong 20 mHz QPO with an average amplitude (rms) of 9% and a coherence Q [?] n0/s [?] 6. In a 33 ks time interval when the 20 mHz QPO is strongest we also find evidence for a second QPO peak at 15 mHz, the first indication of a close pair of QPOs in a ULX source. The frequency ratio of this QPO pair is inconsistent with 3 : 2 at the 3 s level but is consistent with a 4 : 3 ratio. A power-law noise component with slope near 1.5 is also present below 0.1 Hz with evidence for a break to a flatter slope at about 3 mHz. The source shows substantial broadband variability, with a total amplitude (rms) of about 30% in the 0.1-100 mHz frequency band. The power spectrum of hard X-ray photons (>2 keV) shows a ``classic'' flat-topped continuum breaking to a power law with index 1.5-2. Both the break and 20 mHz QPO are detected in the hard band, and the 20 mHz QPO is essentially at the break. The QPO is both strong and narrow in this band, having an amplitude (rms) of 15%, and Q [?] 25. Both the timing and spectral properties of NGC 5408 X-1 are strikingly reminiscent of Galactic black holes at high inferred accretion rates, but with its characteristic frequencies (QPO and break frequencies) scaled down by a factor of 10-100. We discuss the implications of these findings for the object's mass.

The nearby SB(r)b galaxy NGC 3351 (M95) displays an ~600 pc diameter star-forming circumnuclear ring fueled by gas accreted through a stellar bar. The X-ray emission from this region is composed of numerous pointlike sources embedded in hot (kT = 0.5 +- 0.1 keV), nonuniform diffuse gas. Most of the pointlike sources are likely themselves concentrated regions of hot gas. The morphology of the X-ray emission is similar to, but not identical with, UV and Ha hot spots in the circumnuclear ring. The emission morphology can be understood if star formation is occurring through a series of instantaneous starbursts at various locations around the ring and the UV, Ha, and X-ray emission trace successively later stages in the evolution of the underlying stellar populations. X-ray emission extends at least 500 pc beyond the circumnuclear ring. This emission is interpreted as the result of gas outflow from the star-forming ring into the disk and halo of NGC 3351. There is evidence that the outflow is confined by cold ambient gas near the plane of the galaxy but that flow out of the plane is not restricted. The nucleus of the galaxy lacks both large amounts of hot gas and any pointlike source above an estimated X-ray luminosity of 1037 ergs s-1 in the 0.5-8.0 keV band. This luminosity is orders of magnitude too low to account for the observed nuclear Ha luminosity, 3.5 x 1038 ergs s-1, by X-ray photoionization.

We have obtained optical spectra of the soft X-ray transient GRO J1655-40 during different X-ray spectral states (quiescence, high-soft, and hard outburst) between 1994 August and 1997 June. Characteristic features observed during the 1996-1997 high-soft state were: (1) broad absorption lines at Ha and Hb, probably formed in the inner disk; (2) double-peaked He II l4686 emission lines, formed in a temperature-inversion layer on the disk surface, created by the soft X-ray irradiation; and (3) double-peaked Ha emission, with a strength associated with the hard X-ray flux, suggesting that it was probably emitted from deeper layers than He II l4686. The He II l4686 line profile appeared approximately symmetric, as we would expect from a disk surface with an axisymmetric emissivity function. The Balmer emission, on the other hand, appeared to come only from a double-armed region on the disk, possibly the locations of tidal density waves or spiral shocks. The observed rotational velocities of all the double-peaked lines suggest that the disk was extended slightly beyond its tidal radius. Three classes of lines were identified in the spectra taken in 1994 August-September, during a period of low X-ray activity between two strong X-ray flares: broad absorption, broad (flat-topped) emission, and narrow emission. We have found that the narrow (single-peaked or double-peaked) emission lines cannot be explained by a conventional thin accretion disk model. We propose that the system was in a transient state, in which the accretion disk might have had an extended optically thin cocoon and significant matter outflow, which would also explain the systematic blueshift of the narrow emission lines and the flat-topped profiles of the broad emission lines. After the onset of a hard X-ray flare the disk signatures disappeared, and strong single-peaked Ha and Paschen emission was detected, suggesting that the cocoon became opaque to optical radiation. High-ionization lines disappeared or weakened. Two weeks after the end of the flare, the cocoon appeared to be once again optically thin.

AbstractWe conducted spectroscopic and photometric observations of the optical companion of the X-ray transient RX J0117·6–7330 in the Small Magellanic Cloud, during a quiescent state. The primary star is identified as a B0·5 IIIe with a mass M*= (18 ± 2)M? and bolometric magnitude Mbol= –7·4 ± 0·2. The main spectral features are strong Ha emission, Hß and H? emission cores with absorption wings, and narrow He I and O II absorption lines. Equivalent widths and full widths at half maximum of the main lines are listed. The average systemic velocity over our observing run is vr= (184 ± 4) km s-1; measurements over a longer period of time are needed to determine the binary period and the Kvelocity of the primary. We determine a projected rotational velocity vsin i= (145 ± 10) km s-1for the Be star; if we assume a true rotational velocity at the equator v= (400 ± 50) km s-1, we deduce that the inclination angle of the system is i= (21 ± 3) deg.

In this paper we investigate the effects of a large-scale magnetic field (with open field lines) on the structure of an advective accretion disk. We find self-similar solutions to the MHD equations describing the disk/magnetic field system; these equations reduce to the case studied by Narayan & Yi (1994) in the absence of an external, macroscopic magnetic field. Our main assumptions are the existence of a hot, tenuous corona above and below the disk, and the presence of a wind starting from the base of the corona and centrifugally accelerated along the field lines up to the Alfven surface. The wind appears to be the most efficient mechanism for extracting angular momentum from the inflowing gas, even when the mass lost in the wind is negligible with respect to the mass accreted; other notable effects of the interplay between the disk structure and the magnetic field with its associated wind include a bending of the field lines toward the surface of the disk (dragging of the field by the accreting matter), a squeezing effect (the disk scale height is reduced because of a magnetic pressure gradient), an increased radial infall velocity (consequence of the quicker loss of angular momentum), and a decrease of the gas temperature in the disk. We can equivalently describe the loss of angular momentum in the wind by introducing an effective viscosity parameter aeff, which can become greater than 1 regardless of the true viscosity parameter a.

Palomar Gattini-IR is a new wide-field, near-infrared (NIR) robotic time domain survey operating at Palomar Observatory. Using a 30 cm telescope mounted with a H2RG detector, Gattini-IR achieves a field of view (FOV) of 25 sq. deg. with a pixel scale of 8.?7 in J-band. Here, we describe the system design, survey operations, data processing system and on-sky performance of Palomar Gattini-IR. As a part of the nominal survey, Gattini-IR scans ?7500 square degrees of the sky every night to a median 5?depth of 15.7 AB mag outside the Galactic plane. The survey covers ?15,000 square degrees of the sky visible from Palomar with a median cadence of 2 days. A real-time data processing system produces stacked science images from dithered raw images taken on sky, together with point-spread function (PSF)-fit source catalogs and transient candidates identified from subtractions within a median delay of ?4 hr from the time of observation. The calibrated data products achieve an astrometric accuracy (rms) of ?0.?7 with respect to GaiaDR2 for sources with signal-to-noise ratio > 10, and better than ?0.?35 for sources brighter than ?12 Vega mag. The photometric accuracy (rms) achieved in the PSF-fit source catalogs is better than ?3% for sources brighter than ?12 Vega mag and fainter than the saturation magnitude of ?8.5 Vega mag, as calibrated against the Two Micron All Sky Survey catalog. The detection efficiency of transient candidates injected into the images is better than 90% for sources brighter than the 5?limiting magnitude. The photometric recovery precision of injected sources is 3% for sources brighter than 13 mag, and the astrometric recovery rms is ?0.?9. Reference images generated by stacking several field visits achieve depths of ?16.5 AB mag over 60% of the sky, while it is limited by confusion in the Galactic plane. With a FOV ?40× larger than any other existing NIR imaging instrument, Gattini-IR is probing the reddest and dustiest transients in the local universe such as dust obscured supernovae in nearby galaxies, novae behind large columns of extinction within the galaxy, reddened microlensing events in the Galactic plane and variability from cool and dust obscured stars. We present results from transients and variables identified since the start of the commissioning period.

Recent XMM-Newton and Chandra observations have revealed that Jupiter's X-ray emission comprises both, thermal and non-thermal spectral components. While the emission from the low-latitude planetary disk has the properties of scattered solar X-rays, with a thermal spectrum and typical coronal emission lines, the auroral soft (≪ 2 keV) X-rays are thought to be produced by ion charge exchange; very recently, a higher energy auroral component has been revealed by XMM-Newton: this is attributed to energetic electron bremsstrahlung, is dominant above 2 keV, and is variable, displaying both thermal and non-thermal characteristics. The disk and soft X-ray auroral components are separated spectroscopically in the high resolution data provided by the XMM-Newton Reflection Grating Spectrometer. Our results on the morphology, dynamics and energetics of the aurorae support current models developed to explain Jupiter's complex magnetosphere.