IXO Science with Planned Future Missions
Briefly reviews: 5 missions in progress (Astro-H, NuSTAR, Spektrum R-G, Astrosat) and 2 missions under study (NICER, LOFT)
Wilson-Hodge, Colleen A.↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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X-ray Pulsar Navigation Algorithms and Testbed for SEXTANT
The Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) is a NASA funded technologydemonstration. SEXTANT will, for the first time, demonstrate real-time, on-board X-ray Pulsar-based Navigation (XNAV), a significant milestone in the quest to establish a GPS-like navigation capability available throughout our Solar System and beyond. This paper describes the basic design of the SEXTANT system with a focus on core models and algorithms, and the design and continued development of the GSFC X-ray Navigation Laboratory Testbed (GXLT) with its dynamic pulsar emulation capability. We also present early results from GXLT modeling of the combined NICER X-ray timing instrument hardware and SEXTANT flight software algorithms.
Pulsar Navigation↗
SEXTANT - Station Explorer for X-Ray Timing and Navigation Technology
The Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) is a NASA funded technology- demonstration. SEXTANT will, for the first time, demonstrate real-time, on-board X-ray Pulsar-based Navigation (XNAV), a significant milestone in the quest to establish a GPS-like navigation capability available throughout our Solar System and beyond. This paper describes the basic design of the SEXTANT system with a focus on core models and algorithms, and the design and continued development of the GSFC X-ray Navigation Laboratory Testbed (GXLT) with its dynamic pulsar emulation capability. We also present early results from GXLT modeling of the combined NICER X-ray timing instrument hardware and SEXTANT flight software algorithms.
X-rays↗
Station Explorer for X-Ray Timing and Navigation Technology (SEXTANT)
The Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) is a NASA funded technology- demonstration. SEXTANT will, for the first time, demonstrate real-time, on-board X-ray Pulsar-based Navigation (XNAV), a significant milestone in the quest to establish a GPS-like navigation capability available throughout our Solar System and beyond. This paper describes the basic design of the SEXTANT system with a focus on core models and algorithms, and the design and continued development of the GSFC X-ray Navigation Laboratory Testbed (GXLT) with its dynamic pulsar emulation capability. We also present early results from GXLT modeling of the combined NICER X-ray timing instrument hardware and SEXTANT flight software algorithms.
Timing↗
Goddard's Astrophysics Science Divsion Annual Report 2014
The Astrophysics Science Division (ASD, Code 660) is one of the world's largest and most diverse astronomical organizations. Space flight missions are conceived, built and launched to observe the entire range of the electromagnetic spectrum, from gamma rays to centimeter waves. In addition, experiments are flown to gather data on high-energy cosmic rays, and plans are being made to detect gravitational radiation from space-borne missions. To enable these missions, we have vigorous programs of instrument and detector development. Division scientists also carry out preparatory theoretical work and subsequent data analysis and modeling. In addition to space flight missions, we have a vibrant suborbital program with numerous sounding rocket and balloon payloads in development or operation. The ASD is organized into five labs: the Astroparticle Physics Lab, the X-ray Astrophysics Lab, the Gravitational Astrophysics Lab, the Observational Cosmology Lab, and the Exoplanets and Stellar Astrophysics Lab. The High Energy Astrophysics Science Archive Research Center (HEASARC) is an Office at the Division level. Approximately 400 scientists and engineers work in ASD. Of these, 80 are civil servant scientists, while the rest are resident university-based scientists, contractors, postdoctoral fellows, graduate students, and administrative staff. We currently operate the Swift Explorer mission and the Fermi Gamma-ray Space Telescope. In addition, we provide data archiving and operational support for the XMM mission (jointly with ESA) and the Suzaku mission (with JAXA). We are also a partner with Caltech on the NuSTAR mission. The Hubble Space Telescope Project is headquartered at Goddard, and ASD provides Project Scientists to oversee operations at the Space Telescope Science Institute. Projects in development include the Neutron Interior Composition Explorer (NICER) mission, an X-ray timing experiment for the International Space Station; the Transiting Exoplanet Sky Survey (TESS) Explorer mission, in collaboration with MIT (Ricker, PI); the Soft X-ray Spectrometer (SXS) for the Astro-H mission in collaboration with JAXA, and the James Webb Space Telescope (JWST). The Wide-Field Infrared Survey Telescope (WFIRST), the highest ranked mission in the 2010 decadal survey, is in a pre-phase A study, and we are supplying study scientists for that mission.
Caltech on the NuSTAR mission↗
The NuSTAR View of the Non-Thermal Emission from PSR J0437-4715
We present a hard X-ray Nuclear Spectroscopic Telescope Array (NuSTAR) observation of PSR J0437-4715, the nearest millisecond pulsar. The known pulsations at the apparent pulse period approximately 5.76 ms are observed with a significance of 3.7sigma, at energies up to 20 keV above which the NuSTAR background dominates. We measure a photon index gamma = 1.50 +/- 0.25(90 per cent confidence) for the power-law fit to the non-thermal emission. It had been shown that spectral models with two or three thermal components fit the XMM-Newton spectrum of PSR J0437-4715, depending on the slope of the power-law component, and the amount of absorption of soft X-rays. The new constraint on the high-energy emission provided by NuSTAR removes ambiguities regarding the thermal components of the emission below 3 keV. We performed a simultaneous spectral analysis of the XMM-Newton and NuSTAR data to confirm that three thermal components and a power law are required to fit the 0.3-20 keV emission of PSR J0437-4715. Adding a ROSAT-PSPC spectrum further confirmed this result and allowed us to better constrain the temperatures of the three thermal components. A phase resolved analysis of the NuSTAR data revealed no significant change in the photon index of the high-energy emission. This NuSTAR observation provides further impetus for future observations with the NICER mission (Neutron Star Interior Composition Explorer) whose sensitivity will provide much stricter constraints on the equation of state of nuclear matter by combining model fits to the pulsars phase-folded light curve with the pulsars well-defined mass and distance from radio timing observations.
stars; neutro↗
Autonomous Navigation Above the GNSS Constellations and Beyond: GPS Navigation for the Magnetospheric Multiscale Mission and SEXTANT Pulsar Navigation Demonstration
This talk will describe two first-of-their-kind technology demonstrations attached to ongoing NASA science missions, both of which aim to extend the range of autonomous spacecraft navigation far from the Earth. First, we will describe the onboard GPS navigation system for the Magnetospheric Multiscale (MMS) mission which is currently operating in elliptic orbits reaching nearly halfway to the Moon. The MMS navigation system is a key outgrowth of a larger effort at NASA Goddard Space Flight Center to advance high-altitude Global Navigation Satellite System (GNSS) navigation on multiple fronts, including developing Global Positioning System receivers and onboard navigation software, running simulation studies, and leading efforts to characterize and protect signals at high-altitude in the so-called GNSS Space-Service Volume (SSV). In the second part of the talk, we will describe the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) mission that aims to make the first in-space demonstration of X-ray pulsar navigation (XNAV). SEXTANT is attached to the NASA astrophysics mission Neutron-star Interior Composition ExploreR (NICER) whose International Space Station mounted X-ray telescope is investigating the fundamental physics of extremes in gravity, material density, and electromagnetic fields found in neutron stars, and whose instrument provides a nearly ideal navigation sensor for XNAV.
Winternitz, Luke↗
SEXTANT X-Ray Pulsar Navigation Demonstration: Additional On-Orbit Results
The Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) is a technology demonstration enhancement to the Neutron-star Interior Composition Explorer (NICER) mission, a NASA Astrophysics Explorer Mission of Opportunity to the International Space Station, launched in June of 2017. In late 2017, SEXTANT successfully completed a first demonstration of in-space and autonomous X-ray pulsar navigation (XNAV). This form of navigation relies on processing faint signals from millisecond pulsars-rapidly rotating neutron stars that appear to pulsate in the X-ray band-and could potentially provide a GPS-like navigation capability applicable throughout the solar-system and beyond. In this work, we briefly review prior SEXTANT results and then present new results focusing on: making use of the high- flux but rotationally unstable Crab pulsar, and using XNAV to estimate position, velocity, and time in the presence of an imperfect local clock.
Navigation↗
Predicted Performance of an X-Ray Navigation System for Future Deep Space and Lunar Missions
In November 2017, the NASA Goddard Space Flight Center (GSFC) Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) experiment successfully demonstrated the feasibility of X-ray Pulsar Navigation (XNAV) as part of the Neutron Star Interior Composition Explorer (NICER) mission, which is an X-ray Astrophysics Mission of Opportunity currently operating onboard the International Space Station (ISS). XNAV provides a GPS-like absolute autonomous navigation and timing capability available anywhere in the Solar System and beyond. While the most significant benefits of XNAV are expected to come in support of very deep-space missions, the absolute autonomous navigation and timing capability also has utility for inner Solar System missions where increased autonomy or backup navigation and timing services are required, e.g., address loss of communication scenarios.The NASA commitment to develop a Gateway to support exploration of the Moon and eventually Mars, as well as current and future robotic missions such as James Webb Space Telescope (JWST), New Horizons, and much more, certainly will tax the existing ground based infrastructure in terms of availability. There- fore, an extended look at the feasibility and potential performance of XNAV for comparable missions is warranted. In this paper, we briefly review the XNAV concept and present case studies of its utility and performance for a Gateway orbit, Sun-Earth libration orbit, and a deep space transit trajectory.
Getchius, Joel↗
The Changing Changing-Look AGN 1ES 1927+654
We report on X-ray follow-up observations of the March 2018 nuclear transient event AT2018zf (ASASSN-18el) from an ongoing campaign that includes XMM-Newton, NuSTAR, Swift, and high cadence (daily-to-weekly) NICER observations. The event was associated with the Seyfert galaxy 1ES 1927+654, a "True Type-2" that, nevertheless, showed an X-ray spectrum typical of an unobscured Type 1 AGN. Optical monitoring revealed the emergence of broad Balmer emission lines following the outburst, suggesting a transition from a Type 2 to a Type 1 AGN on timescales consistent with the light-travel time between the central black hole and the broad line region. The optical outburst was followed by a dramatic shift in the X-ray spectrum as the hard X-ray luminosity of the corona plunged by >2 orders of magnitude and the spectrum became dominated by a 10^6 K thermal component. The subsequent X-ray evolution of 1ES 1927+654 includes an additional two-order of magnitude decline in overall luminosity, followed by an extended period of quiescence, and re-brightening to levels that make it the brightest AGN currently in the X-ray sky. Throughout its evolution, the source has displayed X-ray flux variability of factors of several on timescales less than hour, and of ~100 on timescales less than a day. The X-ray spectrum varies along a consistent luminosity-dependent track, wherein increases in flux are accompanied by a spectral hardening. We seem to be witnessing the onset of an instability in the pre-existing AGN disc and corona, followed by a still-continuing re-emergence of the corona. If the initial transient is identified as the tidal disruption of a star, it is possible that this was the instigator of this unique behavior.
Loewenstein, M.↗
Timing the Pulsations of The Accreting Millisecond Pulsar SAX J1808.4-3658 During Its 2019 Outburst
In this paper we present a coherent timing analysis of the 401 Hz pulsations of the accreting millisecond X-ray pulsar SAX J1808.4-3658 during its 2019 outburst. Using observations collected with the Neutron Star Interior Composition Explorer (NICER), we establish the pulsar spin frequency and orbital phase during its latest epoch. We find that the 2019 outburst shows a pronounced evolution in pulse phase over the course of the outburst. These phase shifts are found to correlate with the source flux, and are interpreted in terms of hot-spot drift on the stellar surface, driven by changes in the mass accretion rate. Additionally, we find that the long-term evolution of the pulsar spin frequency shows evidence for a modulation at the Earth's orbital period, enabling pulsar timing based astrometry of this accreting millisecond pulsar.
Peter Bult↗
A strongly changing accretion morphology during the outburst decay of the neutron star x-ray binary 4U 1608-52
It is commonly assumed that the properties and geometry of the accretion flow in transient low-mass X-ray binaries (LMXBs) significantly change when the X-ray luminosity decays below ∼10−2 of the Eddington limit (LEdd). However, there are few observational cases where the evolution of the accretion flow is tracked in a single X-ray binary over a wide dynamic range. In this work, we use NuSTAR and NICER observations obtained during the 2018 accretion outburst of the neutron star LMXB 4U 1608−52, to study changes in the reflection spectrum. We find that the broad Fe–Kα line and Compton hump, clearly seen during the peak of the outburst when the X-ray luminosity is ∼1037 erg s−1 (∼0.05 LEdd), disappear during the decay of the outburst when the source luminosity drops to ∼4.5 × 1035 erg s−1 (∼0.002 LEdd). We show that this non-detection of the reflection features cannot be explained by the lower signal-to-noise ratio at lower flux, but is instead caused by physical changes in the accretion flow. Simulating synthetic NuSTAR observations on a grid of inner disc radius, disc ionization, and reflection fraction, we find that the disappearance of the reflection features can be explained by either increased disc ionization (log ξ 4.1) or a much decreased reflection fraction. A changing disc truncation alone, however, cannot account for the lack of reprocessed Fe–Kα emission. The required increase in ionization parameter could occur if the inner accretion flow evaporates from a thin disc into a geometrically thicker flow, such as the commonly assumed formation of a radiatively inefficient accretion flow at lower mass accretion rates.
J. van den Eijnden↗
The RS CVn Type star GT Mus Shows Most Energetic X-ray Flares Throughout the 2010s
We report that the RS CVn-type star GT Mus (HR4492, HD101379+HD101380) was the most active star in the X-ray sky in the last decade in terms of the scale of recurrent energetic flares. We detected eleven flares from GT Mus in eight years of observations with MAXI (Monitor of All-sky X-ray Image)from 2009 August to 2017 August. The detected flare peak luminosities were 1–4×1033erg s−1in the2.0–20.0 keV band for its distance of 109.6 pc. The durations of the flares ranged from 1–4 days. The flare energies are calculated to be 1–8×1038erg, which are at the upper end of the observed stellar flare. We carried out X-ray follow-up observations for one of the eleven flares with NICER (Neutron star Interior Composition Explorer) on 2017 July 18 and found that the flare cooled quasi-statically. On the basis of a quasi-static cooling model, the flare loop length is derived to be 4×1012cm (or60R). The electron density is derived to be1×1010cm−3, which is consistent with the typical value of solar and stellar flares (1010−11cm−3).
Ryo Sasaki↗
The Soft State of the Black Hole Transient Source MAXI J1820+070: Emission from the Edge of the Plunge Region?
The Galactic black hole X-ray binary MAXI J1820+070 had a bright outburst in 2018 when it became the second brightest X-ray source in the sky. It was too bright for X-ray CCD instruments such as XMM–Newton and Chandra, but was well observed by photon counting instruments such as Neutron star Inner Composition Explorer (NICER) and Nuclear Spectroscopic Telescope Array (NuSTAR). We report here on the discovery of an excess emission component during the soft state. It is best modelled with a blackbody spectrum in addition to the regular disc emission, modelled as either diskbb or kerrbb. Its temperature varies from about 0.9 to 1.1 keV, which is about 30–80 per cent higher than the inner disc temperature of diskbb. Its flux varies between 4 and 12 per cent of the disc flux. Simulations of magnetized accretion discs have predicted the possibility of excess emission associated with a non-zero torque at the innermost stable circular orbit (ISCO) about the black hole, which, from other NuSTAR studies, lies at about 5 gravitational radii or about 60 km (for a black hole, mass is 8Msun). In this case, the emitting region at the ISCO has a width varying between 1.3 and 4.6 km and would encompass the start of the plunge region where matter begins to fall freely into the black hole.
A C Fabian↗
The Lowest-frequency Fast Radio Bursts: Sardinia Radio Telescope Detection of the Periodic FRB 180916 at 328 MHz
We report on the lowest-frequency detection to date of three bursts from the fast radio burst FRB 180916.J0158+65, observed at 328 MHz with the Sardinia Radio Telescope (SRT). The SRT observed the periodic repeater FRB 180916.J0158+65 for five days from 2020 February 20 to 24 during a time interval of active radio bursting, and detected the three bursts during the first hour of observations; no more bursts were detected during the remaining ∼30 hr. Simultaneous SRT observations at 1548 MHz did not detect any bursts. Burst fluences are in the range 37 to 13 Jy ms. No relevant scattering is observed for these bursts. We also present the results of the multiwavelength campaign we performed on FRB 180916.J0158+65, during the five days of the active window. Simultaneously with the SRT observations, others with different time spans were performed with the Northern Cross at 408 MHz, with XMM-Newton, NICER, INTEGRAL, AGILE, and with the TNG and two optical telescopes in Asiago, which are equipped with fast photometers. XMM-Newton obtained data simultaneously with the three bursts detected by the SRT, and determined a luminosity upper limit in the 0.3–10 keV energy range of ∼10(exp 45) erg/s for the burst emission. AGILE obtained data simultaneously with the first burst and determined a fluence upper limit in the MeV range for millisecond timescales of 10(exp -8) erg/sq.cm. Our results show that absorption from the circumburst medium does not significantly affect the emission from FRB 180916.J0158+65, thus limiting the possible presence of a superluminous supernova around the source, and indicate that a cutoff for the bursting mechanism, if present, must be at lower frequencies. Our multi-wavelength campaign sensitively constrains the broadband emission from FRB 180916.J0158+65, and provides the best limits so far for the electromagnetic response to the radio bursting of this remarkable source of fast radio bursts.
M. Pilia↗
NGC 300 ULX1: Spin Evolution, Super-Eddington Accretion, and Outflows
NGC300 ULX1 is an ultraluminous X-ray pulsar, showing an unprecedented spin evolution, from about 126 s to less than 20 s in only 4 yr, consistent with steady mass accretion rate. Following its discovery we have been monitoring the system with Swift and NICER to further study its properties. We found that even though the observed flux of the system dropped by a factor of >~20, the spin-up rate remained almost constant. A possible explanation is that the decrease in the observed flux is a result of increased absorption of obscuring material due to outflows or a precessing accretion disc.
G Vasilopoulos↗
Timing of the Accreting Millisecond Pulsar IGR J17591-2342: Evidence of Spin-down during Accretion
We report on the phase-coherent timing analysis of the accreting millisecond X-ray pulsar IGR J17591–2342, using Neutron Star Interior Composition Explorer (NICER) data taken during the outburst of the source between 2018 August 15 and 2018 October 17. We obtain an updated orbital solution of the binary system. We investigate the evolution of the neutron star spin frequency during the outburst, reporting a refined estimate of the spin frequency and the first estimate of the spin frequency derivative ( ˙ν ∼ −7 × 10−14 Hz s−1), confirmed independently from the modelling of the fundamental frequency and its first harmonic. We further investigate the evolution of the X-ray pulse phases adopting a physical model that accounts for the accretion material torque as well as the magnetic threading of the accretion disc in regions where the Keplerian velocity is slower than the magnetosphere velocity. From this analysis we estimate the neutron star magnetic field Beq = 2.8(3) × 108 G. Finally, we investigate the pulse profile dependence on energy finding that the observed behaviour of the pulse fractional amplitude and lags as a function of energy is compatible with the down-scattering of hard X-ray photons in the disc or the neutron star surface.
A Sanna↗
A Real-time View of Orbital Evolution in HM Cancri
HM Cancri is a double-degenerate binary with the shortest orbital period presently known. The 5.36 minute period is seen as a large amplitude, soft X-ray modulation, likely resulting from a hot-spot produced by direct impact accretion. With such a7short orbital period it is expected to have a gravitational wave luminosity comparable8to or larger than that in the X-ray, and its orbital frequency is known to be increasing9at a rate consistent with the expected loss of angular momentum due to gravitational radiation. We use recent Neutron Star Interior Composition Explorer(NICER) observations to extend its long-term X-ray timing baseline to almost 20 yr. Phase coherent timing of these new data combined with existing Chandra data demonstrates conclusively that the rate of orbital frequency increase is slowing, and we measure a non-zero f0=8.95 ± 1.4 x 1027 Hz s2, to our knowledge the first such measurement of its kind for any compact astrophysical binary. With the simultaneous high precision measurement of f0= 3.557 ± 0.005 x 1016 Hz s1, we estimate that the system17will reach its maximum orbital frequency of fmax 3.1172091 mHz in 1,260 ± 200 yr, indicating that the system is close to its epoch of maximum orbital frequency. Assuming mass transfer is conservative, the measurement of f<0 implies that the20accretion rate from the donor is growing, with 5.4 x 1010<M2<4.0 x 1010 M⊙yr2. Further quantitative comparisons with theoretical models should enable more precise inferences regarding its current evolutionary state.
White dwarfs↗