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  • 11
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    High-Energy X-rays from J174545.5-285829, the Cannonball: a Candidate Pulsar Wind Nebula Associated with Sgr a East (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We report the unambiguous detection of non-thermal X-ray emission up to 30 keV from the Cannonball, a few arcsecond long diffuse X-ray feature near the Galactic Center, using the NuSTAR X-ray observatory. The Cannonball is a high-velocity (v(proj) approximately 500 km s(exp 1)) pulsar candidate with a cometary pulsar wind nebula (PWN) located approximately 2' north-east from Sgr A*, just outside the radio shell of the supernova remnant Sagittarius A (Sgr A) East. Its non-thermal X-ray spectrum, measured up to 30 keV, is well characterized by a Gamma is approximately 1.6 power law, typical of a PWN, and has an X-ray luminosity of L(3-30 keV) = 1.3 10(exp 34) erg s(exp 1). The spectral and spatial results derived from X-ray and radio data strongly suggest a runaway neutron star born in the Sgr A East supernova event. We do not find any pulsed signal from the Cannonball. The NuSTAR observations allow us to deduce the PWN magnetic field and show that it is consistent with the lower limit obtained from radio observations.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN16070 , The Astrophysical Journal; 778; 2; L31
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  • 12
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    NuSTAR Discovery of a Cyclotron Line in KS 1947+300 (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We present a spectral analysis of three simultaneous Nuclear Spectroscopy Telescope Array and Swift/XRT observations of the transient Be-neutron star binary KS 1947+300 taken during its outburst in 2013/2014. These broadband observations were supported by Swift/XRTmonitoring snapshots every three days, which we use to study the evolution of the spectrum over the outburst.We find strong changes of the power-law photon index, which shows a weak trend of softening with increasing X-ray flux. The neutron star shows very strong pulsations with a period of P [almost equal to] 18.8 s. The 0.8-79 keV broadband spectrum can be described by a power law with an exponential cutoff and a blackbody component at low energies. During the second observation we detect a cyclotron resonant scattering feature at 12.5 keV, which is absent in the phase-averaged spectra of observations 1 and 3. Pulse phase-resolved spectroscopy reveals that the strength of the feature changes strongly with pulse phase and is most prominent during the broad minimum of the pulse profile. At the same phases the line also becomes visible in the first and third observation at the same energy. This discovery implies that KS 1947+300 has a magnetic field strength of B [almost equal to] 1.1 1012(1 + z) G, which is at the lower end of known cyclotron line sources.
    Keywords: Astronomy
    Type: GSFC-E-DAA-TN16207 , GSFC-E-DAA-TN21840 , Astrophysical Journal Letters; 784; 2; L40
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  • 13
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    NuStar and Swift Observations of the Fast Rotating Magnetized White Dwarf AE Aquarii (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: AE Aquarii is a cataclysmic variable with the fastest known rotating magnetized white dwarf (P(sub spin) = 33.08 s). Compared to many intermediate polars, AE Aquarii shows a soft X-ray spectrum with a very low luminosity (LX (is) approximately 10(exp 31) erg per second). We have analyzed overlapping observations of this system with the NuSTAR and the Swift X-ray observatories in 2012 September. We find the 0.5-30 keV spectra to be well fitted by either an optically thin thermal plasma model with three temperatures of 0.75(+0.18 / 0.45), 2.29(+0.96 / 0.82), and 9.33 (+6.07 / 2.18) keV, or an optically thin thermal plasma model with two temperatures of 1.00 (+0.34 / 0.23) and 4.64 (+1.58 / 0.84) keV plus a power-law component with photon index of 2.50 (+0.17 / 0.23). The pulse profile in the 3-20 keV band is broad and approximately sinusoidal, with a pulsed fraction of 16.6% +/- 2.3%. We do not find any evidence for a previously reported sharp feature in the pulse profile.
    Keywords: Astrophysics; Astronomy
    Type: GSFC-E-DAA-TN16195 , The Astrophysical Journal; 782; 1; 3
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  • 14
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    The Disk Wind in the Rapidly Spinning Stellar-mass Black Hole 4U 1630-472 Observed with NuSTAR (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We present an analysis of a short NuSTAR observation of the stellar-mass black hole and low-mass X-ray binary 4U 1630472. Reflection from the inner accretion disk is clearly detected for the first time in this source, owing to the sensitivity of NuSTAR. With fits to the reflection spectrum, we find evidence for a rapidly spinning black hole, a = 0.985(+0.005/0.014) (1 sigma statistical errors). However, archival data show that the source has relatively low radio luminosity. Recently claimed relationships between jet power and black hole spin would predict either a lower spin or a higher peak radio luminosity. We also report the clear detection of an absorption feature at 7.03 +/- 0.03 keV, likely signaling a disk wind. If this line arises in dense, moderately ionized gas (log xi = 3.6(+0.2/0.3) and is dominated by He-like Fe xxv, the wind has a velocity of v/c = 0.043(+0.002/0.007) (12900(+600/2100) km s(exp 1)). If the line is instead associated with a more highly ionized gas (log xi = 6.1(+0.7/0.6)), and is dominated by Fe xxvi, evidence of a blueshift is only marginal, after taking systematic errors into account. Our analysis suggests the ionized wind may be launched within 200-1100 Rg, and may be magnetically driven.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN16161 , The Astrophysical Journal; 784; 1; L2
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  • 15
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    NuSTAR J163433-4738.7: A Fast X-Ray Transient in the Galactic Plane (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: During hard X-ray observations of the Norma spiral arm region by the Nuclear Spectroscopic Telescope Array (NuSTAR) in 2013 February, a new transient source, NuSTAR J163433-4738.7, was detected at a significance level of 8sigma in the 3-10 keV bandpass. The source is consistent with having a constant NuSTAR count rate over a period of 40 ks and is also detected simultaneously by Swift at lower significance. The source is not significantly detected by NuSTAR, Swift, or Chandra in the days before or weeks after the discovery of the transient, indicating that the strong X-ray activity lasted between approx. 0.5 and 1.5 days. Near-infrared imaging observations were carried out before and after the X-ray activity, but we are not able to identify the counterpart. The combined NuSTAR and Swift energy spectrum is consistent with a power law with a photon index of Gamma = 4.1(+1.5/1.0) (90% confidence errors), a blackbody with kT = 1.2+/-0.3 keV, or a Bremsstrahlung model with kT = 3.0(+2.1/1.2) keV. The reduced-2 values for the three models are not significantly different, ranging from 1.23 to 1.44 for 8 degrees of freedom. The spectrum is strongly absorbed with NH = (2.8(+2.3/1.4) 10(exp23) cm(exp2), (9(+15 /7) ) 10(exp22) cm(exp2), and (1.7(+1.7/0.9)) 10(exp23) cm(exp2), for the power-law, blackbody, and Bremsstrahlung models, respectively. Although the high column density could be due to material local to the source, it is consistent with absorption from interstellar material along the line of sight at a distance of 11 kpc, which would indicate an X-ray luminosity greater than 10(exp34) erg s(exp1). Although we do not reach a definitive determination of the nature of NuSTAR J163433-4738.7, we suggest that it may be an unusually bright active binary or a magnetar.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN21804 , The Astrophysical Journal; 785; 1; 4
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  • 16
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    NuSTAR Observations of the Magnetar 1E 2259+586 (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We report on new broad band spectral and temporal observations of the magnetar 1E 2259+586, which is located in the supernova remnant CTB 109. Our data were obtained simultaneously with the Nuclear Spectroscopic Telescope Array (NuSTAR) and Swift, and cover the energy range from 0.5-79 keV. We present pulse profiles in various energy bands and compare them to previous RXTE results. The NuSTAR data show pulsations above 20 keV for the first time and we report evidence that one of the pulses in the double-peaked pulse profile shifts position with energy. The pulsed fraction of the magnetar is shown to increase strongly with energy. Our spectral analysis reveals that the soft X-ray spectrum is well characterized by an absorbed double blackbody or blackbody plus power-law model in agreement with previous reports. Our new hard X-ray data, however, suggest that an additional component, such as a power law, is needed to describe the NuSTAR and Swift spectrum. We also fit the data with the recently developed coronal outflow model by Beloborodov for hard X-ray emission from magnetars. The outflow from a ring on the magnetar surface is statistically preferred over outflow from a polar cap.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN21706 , The Astrophysical Journal; 789; 1; 75
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  • 17
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    Evidence of Significant Energy Input in the Late Phase of A Solar Flare from NuSTAR X-Ray Observations (2017)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We present observations of the occulted active region AR 12222 during the third Nuclear Spectroscopic Telescope ARray (NuSTAR) solar campaign on 2014 December 11, with concurrent Solar Dynamics Observatory (SDO)/ AIA and FOXSI-2 sounding rocket observations. The active region produced a medium-size solar flare 1 day before the observations, at approximately 18 UT on 2014 December 10, with the post-flare loops still visible at the time of NuSTAR observations. The time evolution of the source emission in the SDO/AIA 335 channel reveals the characteristics of an extreme-ultraviolet late-phase event, caused by the continuous formation of new post-flare loops that arch higher and higher in the solar corona. The spectral fitting of NuSTAR observations yields an isothermal source, with temperature 3.8-4.6 MK, emission measure (0.3-1.8) 1046 cm3, and density estimated at (2.5-6.0) 108 cm3. The observed AIA fluxes are consistent with the derived NuSTAR temperature range, favoring temperature values in the range of 4.0-4.3 MK. By examining the post-flare loops' cooling times and energy content, we estimate that at least 12 sets of post-flare loops were formed and subsequently cooled between the onset of the flare and NuSTAR observations, with their total thermal energy content an order of magnitude larger than the energy content at flare peak time. This indicates that the standard approach of using only the flare peak time to derive the total thermal energy content of a flare can lead to a large underestimation of its value.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN43950 , The Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 835; 1; 6
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  • 18
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    The Distribution of Radioactive Ti-44 in Cassiopeia A (2016)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The distribution of elements produced in the innermost layers of a supernova explosion is a key diagnostic for studying the collapse of massive stars. Here we present the results of a 2.4 Ms NuSTAR observing campaign aimed at studying the supernova remnant Cassiopeia A (Cas A). We perform spatially resolved spectroscopic analysis of the Ti-44 ejecta, which we use to determine the Doppler shift and thus the three-dimensional (3D) velocities of the Ti-44 ejecta. We find an initial Ti-44 mass of (1.54 +/- 0.21) x 10(exp. -4) Solar Mass, which has a present-day average momentum direction of 340 degrees +/- 15 degrees projected onto the plane of the sky (measured clockwise from celestial North) and is tilted by 58 degrees +/- 20 degrees into the plane of the sky away from the observer, roughly opposite to the inferred direction of motion of the central compact object. We find some Ti-44 ejecta that are clearly interior to the reverse shock and some that are clearly exterior to it. Where we observe Ti-44 ejecta exterior to the reverse shock we also see shock-heated iron; however, there are regions where we see iron but do not observe Ti-44. This suggests that the local conditions of the supernova shock during explosive nucleosynthesis varied enough to suppress the production of Ti-44 by at least a factor of two in some regions, even in regions that are assumed to be the result of processes like Alpha-rich freezeout that should produce both iron and titanium.
    Keywords: Statistics and Probability; Astrophysics
    Type: GSFC-E-DAA-TN43949 , The Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 834; 1; 19
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  • 19
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    THE NuSTAR Hard X-Ray Survey of the Norma Arm Region (2017)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We present a catalog of hard X-ray sources in a square-degree region surveyed by the Nuclear Spectroscopic Telescope Array (NuSTAR) in the direction of the Norma spiral arm. This survey has a total exposure time of 1.7 Ms, and the typical and maximum exposure depths are 50 ks and 1 Ms, respectively. In the area of deepest coverage, sensitivity limits of 5 x 10(exp -14) and 4 x 10(exp -14) ergs/s/sq cm in the 3-10 and 10-20 keV bands, respectively, are reached. Twenty-eight sources are firmly detected, and 10 are detected with low significance; 8 of the 38 sources are expected to be active galactic nuclei. The three brightest sources were previously identified as a low-mass X-ray binary, high-mass X-ray binary, and pulsar wind nebula. Based on their X-ray properties and multiwavelength counterparts, we identify the likely nature of the other sources as two colliding wind binaries, three pulsar wind nebulae, a black hole binary, and a plurality of cataclysmic variables (CVs). The CV candidates in the Norma region have plasma temperatures of approx. 10-20 keV, consistent with the Galactic ridge X-ray emission spectrum but lower than the temperatures of CVs near the Galactic center. This temperature difference may indicate that the Norma region has a lower fraction of intermediate polars relative to other types of CVs compared to the Galactic center. The NuSTAR logN-logS distribution in the 10-20keV band is consistent with the distribution measured by Chandra at 2-10 keV if the average source spectrum is assumed to be a thermal model with kT approx. =15 keV, as observed for the CV candidates.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN44064 , The Astrophysical Journal Supplement Series (ISSN 0067-0049) (e-ISSN 1538-4365); 229; 2; 33
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  • 20
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    Getting NuSTAR on Target: Predicting Mast Motion (2017)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Nuclear Spectroscopic Telescope Array (NuSTAR) is the first focusing high energy (3-79 keV) X-ray observatory operating for four years from low Earth orbit. The X-ray detector arrays are located on the spacecraft bus with the optics modules mounted on a flexible mast of 10.14m length. The motion of the telescope optical axis on the detectors during each observation is measured by a laser metrology system and matches the pre-launch predictions of the thermal flexing of the mast as the spacecraft enters and exits the Earths shadow each orbit. However, an additional motion of the telescope field of view was discovered during observatory commissioning that is associated with the spacecraft attitude control system and an additional flexing of the mast correlated with the Solar aspect angle for the observation. We present the methodology developed to predict where any particular target coordinate will fall on the NuSTAR detectors based on the Solar aspect angle at the scheduled time of an observation. This may be applicable to future observatories that employ optics deployed on extendable masts. The automation of the prediction system has greatly improved observatory operations efficiency and the reliability of observation planning.
    Keywords: Astrophysics; Statistics and Probability
    Type: GSFC-E-DAA-TN41251 , SPIE Proceedings (ISSN 0277-786X) (e-ISSN 1996-756X); 9910; 99100Z|Observatory Operations: Strategies, Processes, and Systems VI; Jun 27, 2016 - Jul 01, 2016; Edinburgh; United Kingdom
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