The Nuclear Spectroscopic Telescope Array (NuSTAR) mission, launched on 2012 June 13, is the first focusing high-energy X-ray telescope in orbit. NuSTAR operates in the band from 3 to 79 keV, extending the sensitivity of focusing far beyond the ∼10 keV high-energy cutoff achieved by all previous X-ray satellites. The inherently low background associated with concentrating the X-ray light enables NuSTAR to probe the hard X-ray sky with a more than 100-fold improvement in sensitivity over the collimated or coded mask instruments that have operated in this bandpass. Using its unprecedented combination of sensitivity and spatial and spectral resolution, NuSTAR will pursue five primary scientific objectives: (1) probe obscured active galactic nucleus (AGN) activity out to the

Ultraluminous X-ray sources (ULX) are off-nuclear point sources in nearby galaxies whose X-ray luminosity exceeds the theoretical maximum for spherical

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We present the first systematic analysis of the X-ray variability of Sgr A * during the Chandra Xray Observatory's 2012 Sgr A * X-ray Visionary Project (XVP). With 38 High Energy Transmission Grating Spectrometer (HETGS) observations spaced an average of 7 days apart, this unprecedented campaign enables detailed study of the X-ray emission from this supermassive black hole at high spatial, spectral and timing resolution. In 3 Ms of observations, we detect 39 X-ray flares from Sgr A * , lasting from a few hundred seconds to approximately 8 ks, and ranging in 2 − 10 keV luminosity from ∼ 10 34 erg s −1 to 2 × 10 35 erg s −1 . Despite tentative evidence for a gap in the distribution of flare peak count rates, there is no evidence for X-ray color differences between faint and bright flares. Our preliminary X-ray flare luminosity distribution dN/dL is consistent with a power law with index −1.9 +0.3 −0.4 ; this is similar to some estimates of Sgr A * 's NIR flux distribution. The observed flares contribute one-third of the total X-ray output of Sgr A * during the campaign, and as much as 10% of the quiescent X-ray emission could be comprised of weak, undetected flares, which may also contribute high-frequency variability. We argue that flares may be the only source of X-ray emission from the inner accretion flow.

We report on the formation and evolution of two large-scale, synchrotron-

Black holes in binary systems execute patterns of outburst activity where two characteristic X-ray states are associated with different behaviours observed at radio wavelengths. The hard state is associated with radio emission indicative of a continuously replenished, collimated, relativistic jet, whereas the soft state is rarely associated with radio emission, and never continuously, implying the absence of a quasi-steady jet. Here we report radio observations of the black hole transient MAXI J1820+070 during its 2018 outburst. As the black hole transitioned from the hard to soft state we observed an isolated radio flare, which, using high angular resolution radio observations, we connect with the launch of bi-polar relativistic ejecta. This flare occurs as the radio emission of the core jet is suppressed by a factor of over 800. We monitor the evolution of the ejecta over 200 days and to a maximum separation of 10 , during which period it remains detectable due to in-situ particle acceleration. Using simultaneous radio observations sensitive to different angular scales we calculate an accurate estimate of energy content of the approaching ejection. This energy estimate is far larger than that derived from state transition radio flare, suggesting a systematic underestimate of jet energetics.Black hole X-ray binary (BHXRB) systems consist of a stellar-mass black hole accreting material via Roche lobe overflow from a main sequence companion star. X-ray observations of such systems, which probe their accretion flow, have revealed the existence of two primary accretion states, termed hard and soft 1,2 . In the hard state the X-ray spectrum is non-thermal, and thought to be dominated by emission from an inner accretion disk corona. In the soft state coronal emission is suppressed, and the X-ray spectrum is well described by thermal emission from the accretion disk 4 itself. Contemporaneous radio observations, which probe the jets, show that the accretion state of a BHXRB system determines the form of the outflows it produces 1-5 . During the hard state radio emission is from a flat spectrum, collimated, compact (solar-system scale) jet 6,7 which is quenched in the soft state [8][9][10][11] . The most dramatic outburst behaviour occurs as sources transition from the hard to the soft accretion state. During the transition, as the core jet quenches, systems exhibit short timescale (of the order hours) radio flaring superposed on the decaying core jet flux 1 . These flares have been associated with the ejection of discrete (apparently no longer connected spatially to the black hole) knots of material, which can be observed to move (sometimes apparently superluminally) away from the black hole, reaching separations tens of thousands times farther than that of the core jet 12 . The mechanism(s) causing the launch of these ejections, as well as the radio flaring, are not well understood. Jets and ejections represent two of the primary channels through which galactic black holes return matter and energy into their surroundin...

We have discovered at x-ray and radio wavelengths large-scale moving jets from the microquasar XTE J1550−564. Plasma ejected from near the black hole traveled at relativistic velocities for at least four years. We present direct evidence for gradual deceleration in a relativistic jet. The broadband spectrum of the jets is consistent with synchrotron emission from high energy (up to 10 TeV) particles accelerated in shock waves formed within the relativistic ejecta or by the interaction of the jets with the interstellar medium.

We report the discovery of 3.76-s pulsations from a new burst source near Sgr A* observed by the NuSTAR Observatory. The strong signal from SGR J1745−29 presents a complex pulse profile modulated with pulsed fraction 27 ± 3% in the 3 − 10 keV band. Two observations spaced 9 days apart yield a spin-down rate ofṖ = (6.5 ± 1.4) × 10 −12 . This implies a magnetic field B = 1.6 × 10 14 G, spin-down powerĖ= 5 × 10 33 erg s −1 , and characteristic age P/2Ṗ = 9 × 10 3 yr, for the rotating dipole model. However, the currentṖ may be erratic, especially during outburst. The flux and modulation remained steady during the observations and the 3 − 79 keV spectrum is well fitted by a combined blackbody plus power-law model with temperature k T BB = 0.96 ± 0.02 keV and photon index Γ = 1.5 ± 0.4. The neutral hydrogen column density (N H ∼ 1.4 × 10 23 cm −2 ) measured by NuSTAR and Swift suggests that SGR J1745−29 is located at or near the Galactic Center. The lack of an X-ray counterpart in the published Chandra survey catalog sets a quiescent 2 − 8 keV luminosity limit of L x < ∼ 10 32 erg s −1 . The bursting, timing, and spectral properties indicate a transient magnetar undergoing an outburst with 2 − 79 keV luminosity up to 3.5 × 10 35 erg s −1 for a distance of 8 kpc. SGR J1745−29 joins a growing subclass of transient magnetars, indicating that many magnetars in quiescence remain undetected in the X-ray band or have been detected as high-B radio pulsars. The peculiar location of SGR J1745−29 has important implications for the formation and dynamics of neutron stars in the Galactic Center region.