Conveners
A NICER view of extreme gravity from the International Space Station: Monday block 1
- Zaven Arzoumanian (NASA Goddard Space Flight Center)
- Guglielmo Mastroserio (Università degli Studi di Milano)
A NICER view of extreme gravity from the International Space Station: Monday block 2
- Zaven Arzoumanian (NASA Goddard Space Flight Center)
- Guglielmo Mastroserio (Università degli Studi di Milano)
Description
Strong gravity is the driver of some of the most energetic phenomena in the universe, which are also copious producers of X-rays. Imprinted on this radiation — in its brightness fluctuations and time-dependent energy spectra — are keys to our understanding of physical extremes: ultra-dense matter and exceptionally powerful electromagnetic fields, in addition to dynamic gravitational environments. NASA’s Neutron Star Interior Composition Explorer (NICER), a telescope on the International Space Station, provides the combination of capabilities in soft X-rays that is needed to probe extraordinary cosmic processes and to address high-priority questions in time-domain and multi-messenger astrophysics. Following a brief overview of the mission, this session will cover some key NICER results and their physical implications for the structure of neutron stars, accretion as a probe of black holes, gravitational waves from supermassive black-hole binaries and rapidly spinning pulsars, and the recently discovered "quasi-periodic eruption" phenomenon, which may represent the first electromagnetic evidence for extreme-mass-ratio inspiral events highly anticipated by the future LISA gravitational-wave observatory.
The dense interiors of neutron stars provide a window to the nature of cold matter at densities above nuclear that complements precision laboratory nuclear experiments. The uncertain physics at high density leads to a range of possible equations of state (EOS). Since each potential EOS allows a different neutron star mass and radius curve, observations of many neutron star masses and radii...
Type-I X-ray bursts are powered by the unstable thermonuclear burning of accreted hydrogen and helium material on the surface of a neutron star (NS) in low-mass X-ray binary systems. They typically last for tens to hundreds of seconds, depending on the fuel composition. Among the observed bursts, approximately 20% of them are powerful enough to lift the NS photosphere tens to hundreds of...
Pulsars are promising sources of gravitational waves (GWs). While asymmetric mass distributions will produce continuos GWs, sudden relocations of small fractions of the internal neutron superfluid could produce transient GW emission. Such rearrangements are believed to be responsible for rapid accelerations in rotation, known as glitches, which have been observed in hundreds of pulsars. The...
We present the strategy, analysis, and results of our four-year timing program of RX J0806.4-4123 with NICER. RX J0806.4-4123 belongs to the group of radio-quiet X-ray thermal isolated neutron stars (XTINSs) that are located between the rotation-powered pulsars and the magnetars in the P-Pdot diagram. The slowly rotating XTINSs constitute a key population to learn about the structure, physics...
Black holes are among the most challenging objects to study in the universe since nothing can escape from their event horizon. Fortunately, these objects leave traces by imposing their extreme gravitational pull on the surrounding matter as it falls into the black hole. Spectral-timing analysis has become very popular for studying accreting black holes and inferring the geometrical structure...
The Galactic X-ray black hole candidate GRS 1915+105 exhibits high-frequency quasi-periodic oscillations (HFQPOs) at ~ 67 Hz only during the radio-quiet 'softer' variability classes. We have studied the long-term X-ray variability from 1996 to 2017 using observations from RXTE, AstroSat, NuSTAR and NICER. AstroSat observations reveal the first detection of a soft-lag for higher energy photons...
Supermassive black hole binaries (SMBHBs) represent the latest stage in the hierarchical growth of massive galaxies through major mergers. In these systems, accretion onto the black holes is expected to form two individual accretion disks around each black hole, fed by a larger circumbinary disk. Consequently, the X-ray and UV emission from these systems is expected to vary regularly, with...
A new subclass of transients spatially coincident with centers of galaxies have been uncovered in the past few years. One of the leading hypothesis for these repeaters is that they could be driven by objects orbiting massive black holes. I will give an overview of how NICER's large effective area and excellent maneuverability have been instrumental in making these discoveries.
