Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session G17: NICER: First Results |
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Sponsoring Units: DAP Chair: Julie McEnery, NASA/GSFC Room: B234-235 |
Sunday, April 15, 2018 8:30AM - 9:06AM |
G17.00001: A NICER View: Astrophysics and Exploration from the International Space Station Invited Speaker: Zaven Arzoumanian Neutron stars are extraordinary in nearly every way. They are made of the densest stuff in the universe, their gravity is immense, and they are the most powerful magnets known. Some sweep narrow beams of radiation through space as they spin, often as fast as blender blades, appearing to flash with unrivaled regularity like cosmic timepieces. Launched in June 2017, NASA's dual-purpose Neutron star Interior Composition Explorer (NICER) mission aims to answer longstanding questions about the physics and astrophysics of neutron stars, with a telescope on the International Space Station designed to investigate their X-ray emissions and time their pulsations precisely. The mission's second purpose is a first-ever demonstration of autonomous spacecraft navigation using neutron stars as beacons in a ``Galactic Positioning System." This presentation provides an overview of the NICER mission, its SEXTANT navigation demonstration, and the insights that NICER is delivering about the physics of neutron stars, black holes, and the high-energy processes that they drive. [Preview Abstract] |
Sunday, April 15, 2018 9:06AM - 9:18AM |
G17.00002: Towards Neutron Star Radius and Mass Determinations Using NICER Sharon Morsink Determining the masses and radii of neutron stars is important, not only for understanding the astronomical properties of these stars, but also for understanding the physical properties of the cold dense matter within them. The NICER mission will measure the masses and radii of several rotation-powered pulsars by fitting pulse waveform models to observations of the soft X-ray waveforms produced by the rotation of hot spots located near their magnetic polar caps. In this talk I will describe how these measurements will be made, the results we expect, and how these results will be used to constrain the properties of cold dense matter. [Preview Abstract] |
Sunday, April 15, 2018 9:18AM - 9:30AM |
G17.00003: Mapping the Radii Around Neutron Stars with NICER Renee Ludlam Relativistic disk lines provide a valuable tool to determine magnetic field strengths, extent of boundary layers, and even place a limit on the radii of neutron stars. With the sensitivity and low energy bandpass of NICER, we have the opportunity to search for low energy relativistic features down to 0.25 keV that are free from pile-up distortions. One neutron star low-mass X-ray binary that has previously shown strong disk line features is Serpens X-1. Moreover, the source has a low absorption column along the line of sight making it a perfect target to search for multiple emission lines that have the potential to provide improved constraints on neutron star radii. I will present early NICER results on the first detection of Fe L in the persistent emission from Serpens X-1 and the implications for the accretion and star itself. [Preview Abstract] |
Sunday, April 15, 2018 9:30AM - 9:42AM |
G17.00004: Spectral-Timing of Aquila X-1 Peter Bult Accretion discs around neutron stars are bright in X-rays. This emission has long been known to vary with energy, revealing the material composition of the disc. But also to vary the with a multitude of periods, revealing geometric structures in the disc. Understanding how, exactly, these spectral and temporal signatures couple is crucial for understanding the dynamics of the accretion process through extremely curved space-time. Providing excellent spectral and timing capabilities, NICER is well suited for this task.\\ \\ Using NICER observations of Aquila X-1 we find, for the first time in a neutron star system, that instabilities in the accretion disc have a two-component spectrum, with the low energy variability driving leading the correlated signals at higher energies. This contribution presents these new results, and their implications for the accretion process in neutron star and black hole systems. [Preview Abstract] |
Sunday, April 15, 2018 9:42AM - 9:54AM |
G17.00005: NICER monitoring of magnetar 4U 0142+61 during outburst Melania Nynka Magnetars make up an extraordinary subcategory of neutron stars. While canonical neutron stars or pulsars power their emission rotationally through the loss of angular momentum, magnetars are dominated by the evolution of ultra strong magnetic fields. NICER is well-suited to study the unusual and variable behavior of magnetars which includes large X-ray outbursts, flares, and glitches in timing properties that can be used to probe their extreme environments.\\ \\ Shortly after the launch of NICER magnetar 4U 0142+61 rapidly brightened in X-ray and was quickly observed by the newly-commissioned observatory. With a subsequent 4-month monitoring program NICER was able to observe the evolution of the spectrum, pulse profile, and timing properties of the magnetar as it slowly transitioned back to its quiescent state. We present the findings from this campaign and discuss the implications for the structure and physical processes that govern magnetars and their magnetospheres. [Preview Abstract] |
Sunday, April 15, 2018 9:54AM - 10:06AM |
G17.00006: A Persistent Disk Wind in GRS 1915+105 with NICER Joey Neilsen As a result of their small sizes and deep gravitational potentials, accreting stellar mass black holes can vary on timescales as short as milliseconds, even as they launch relativistic jets and ionized winds, outshine stars by orders of magnitude, and provide testbeds for General Relativity. As such, they are excellent targets for NICER's sensitive X-ray capabilities. One such source, the bright, erratic black hole GRS 1915+105, has long been a target for studies of these accretion/ejection processes. In this talk, I will present our analysis of 39 NICER observations of GRS 1915+105 over five months, focusing on Fe XXVI Lyman alpha absorption lines present in the vast majority of our spectra. I will discuss how these signatures of a well-known ionized wind depend on the broad properties of the X-ray lightcurve: intensity, spectral shape, and variability. Our results are consistent with an average wind column density that is fairly steady over weeks or months but may vary rapidly with the source on timescales of seconds. The dependence of the wind absorption on spectral shape echoes known behavior of disk winds in outbursts of Galactic black holes; these results clearly indicate that NICER will be a powerful tool for studying black hole winds in the future. [Preview Abstract] |
Sunday, April 15, 2018 10:06AM - 10:18AM |
G17.00007: NICER's Nicer Responses to Alerts of Giant Stellar Flares Kenji Hamaguchi The Sun occasionally erupts magnetic reconnection X-ray flares, the largest ones of which can cause geomagnetic storms. The Sun is believed to have produced much stronger flares in early ages, which could have affected formation of pre-organic molecules and/or early life on Earth. Such giant X-ray flares, or “superflares”, have been spotted occasionally from active stars in the solar neighborhood such as dMe and RS CVn stars with the all-sky X-ray monitor MAXI onboard the International Space Station (ISS). However, MAXI can provide only limited X-ray information owing to its small photon collecting power and high background.\\ \\ The NICER observatory onboard ISS has large photon collecting power as well as rapid repointing capability, enabling detailed follow-up of these X-ray flares within a fraction of a day of the MAXI triggers. Since its launch in June 2017, NICER has observed four giant X-ray flares on the active binary systems, GT Muscae, UX Ari, sigma Gem and HR 1099 in response to their detections by MAXI. It collected 300-900 X-ray photons per second from each flare, arguably the highest signal-to-noise X-ray data for stellar flares obtained to date. Their light curves are smooth on both short and long timescales, while their spectra clearly show emission lines from multiple elements. [Preview Abstract] |
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