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

We present the calibration of the Nuclear Spectroscopic Telescope Array (NuSTAR) X-ray satellite. We used the Crab as the primary effective area calibrator and constructed a piece-wise linear spline function to modify the vignetting response. The achieved residuals for all off-axis angles and energies, compared to the assumed spectrum, are typically better than ±2% up to 40 keV and 5-10 % above due to limited counting statistics. An empirical adjustment to the theoretical 2D point spread function (PSF) was found using several strong point sources, and no increase of the PSF half power diameter (HPD) has been observed since the beginning of the mission. We report on the detector gain calibration, good to 60 eV for all grades, and discuss the timing capabilities of the observatory, which has an absolute timing of ± 3 ms. Finally we present cross-calibration results from two campaigns between all the major concurrent X-ray observatories (Chandra, Swift, Suzaku and XMM-Newton), conducted in 2012 and 2013 on the sources 3C 273 and PKS 2155-304, and show that the differences in measured flux is within ∼10% for all instruments with respect to NuSTAR. Subject headings: space vehicles: instruments -X-rays: individual (3C 273) -X-rays: individual (PKS 2155-304)

Asymmetry is required by most numerical simulations of stellar core-collapse explosions, but the form it takes differs significantly among models. The spatial distribution of radioactive (44)Ti, synthesized in an exploding star near the boundary between material falling back onto the collapsing core and that ejected into the surrounding medium, directly probes the explosion asymmetries. Cassiopeia A is a young, nearby, core-collapse remnant from which (44)Ti emission has previously been detected but not imaged. Asymmetries in the explosion have been indirectly inferred from a high ratio of observed (44)Ti emission to estimated (56)Ni emission, from optical light echoes, and from jet-like features seen in the X-ray and optical ejecta. Here we report spatial maps and spectral properties of the (44)Ti in Cassiopeia A. This may explain the unexpected lack of correlation between the (44)Ti and iron X-ray emission, the latter being visible only in shock-heated material. The observed spatial distribution rules out symmetric explosions even with a high level of convective mixing, as well as highly asymmetric bipolar explosions resulting from a fast-rotating progenitor. Instead, these observations provide strong evidence for the development of low-mode convective instabilities in core-collapse supernovae.

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.

Stellar metals shine toward our eyes only Taking a different look at a familiar star may still yield surprises. Boggs et al. trained the x-ray vision of the NuSTAR observatory on the well-studied supernova 1987A. Core-collapse explosions such as SN 1987A produce a titanium isotope, 44 Ti, whose radioactive decay yields hard x-ray emission lines. All the emission associated with 44Ti appears to be from material moving toward us, with none moving away. This implies that the explosion was not symmetric. These findings help to explain the mechanics of SN 1987A and of core-collapse supernovae in general. Science , this issue p. 670

We present the X-ray timing and spectral evolution of the Galactic Center magnetar SGR J1745−2900 for the first ∼4 months post-discovery using data obtained with the Nuclear Spectroscopic Telescope Array (NuSTAR) and Swift observatories. Our timing analysis reveals a large increase in the magnetar spindown rate by a factor of 2.60 ±0.07 over our data span. We further show that the change in spin evolution was likely coincident with a bright X-ray burst observed

We report NuSTAR observations of the millisecond pulsar -low mass X-ray binary (LMXB) transition system PSR J1023+0038 from June and October 2013, before and after the formation of an accretion disk around the neutron star. Between June 10-12, a few days to two weeks before the radio disappearance of the pulsar, the 3-79 keV X-ray spectrum was well fit by a simple power law with a photon index of Γ = 1.17 +0.08 −0.07 (at 90 % confidence) with a 3-79 keV luminosity of 7.4±0.4×10 32 erg s −1 . Significant orbital modulation was observed with a modulation fraction of 36±10 %. During the October 19-21 observation, the spectrum is described by a softer power law (Γ = 1.66 +0.06 −0.05 ) with an average luminosity of 5.8 ± 0.2 × 10 33 erg s −1 and a peak luminosity of ≈ 1.2 × 10 34 erg s −1 observed during a flare. No significant orbital modulation was detected. The spectral observations are consistent with previous and current multi-wavelength observations and show the hard X-ray power law extending to 79 keV without a spectral break. Sharp edged, flat bottomed 'dips' are observed with widths between 30-1000 s and ingress and egress time-scales of 30-60 s. No change in hardness ratio was observed during the dips. Consecutive dip separations are log-normal in distribution with a typical separation of approximately 400 s. These dips are distinct from dipping activity observed in LMXBs. We compare and contrast these dips to observations of dips and state changes in the similar transition systems PSR J1824−2452I and XSS J1227.0−4859 and discuss possible interpretations based on the transitions in the inner disk.

We present broadband (3 -78 keV) NuSTAR X-ray imaging and spectroscopy of the Crab nebula and pulsar. We show that while the phase-averaged and spatially integrated nebula + pulsar spectrum is a power-law in this energy band, spatially resolved spectroscopy of the nebula finds a break at ∼9 keV in the spectral photon index of the torus structure with a steepening characterized by ∆Γ ∼ 0.25. We also confirm a previously reported steepening in the pulsed spectrum, and quantify it with a broken power-law with break energy at ∼12 keV and ∆Γ ∼ 0.27. We present spectral maps of the inner 100 of the remnant and measure the size of the nebula as a function of energy in seven bands. These results find that the rate of shrinkage with energy of the torus size can be fitted by a power-law with an index of γ = 0.094 ± 0.018, consistent with the predictions of Kennel and Coroniti (1984). The change in size is more rapid in the NW direction, coinciding with the counter-jet where we find the index to be a factor of two larger. NuSTAR observed the Crab during the latter part of a γ-ray flare, but found no increase in flux in the 3 -78 keV energy band.