1,022 research outputs found
Initial measurements of black hole spin in GX 339-4 from Suzaku spectroscopy
We report on a deep Suzaku observation of the stellar-mass black hole GX 339-4 in outburst. A clear, strong, relativistically shaped iron emission line from the inner accretion disk is observed. The broadband disk reflection spectrum revealed is one of the most sensitive yet obtained from an accreting black hole. We fit the Suzaku spectra with a physically motivated disk reflection model, blurred by a new relativistic line function in which the black hole spin parameter is a variable. This procedure yielded a black hole spin parameter of a p. Joint modeling of these Suzaku spectra and prior XMM-Newton spectra obtained in two different 0.89 +/- 0.04 outburst phases yields a spin parameter of a = 0.93 +/- 0.01. The degree of consistency between these results suggests that disk reflection models allow for spin measurements that are not strongly biased by scattering effects. We suggest that the best value of the black hole spin parameter is a = 0.93 +/- 0.01 (statistical) +/- 0.04 (systematic). Although preliminary, these results represent the first direct measurement of nonzero spin in a stellar-mass black hole using relativistic line modeling
The Parsec-scale Structure, Kinematics, and Polarization of Radio-Loud Narrow-Line Seyfert 1 Galaxies
Several narrow-line Seyfert 1 galaxies (NLS1s) have now been detected in
gamma rays, providing firm evidence that at least some of this class of active
galactic nuclei (AGN) produce relativistic jets. The presence of jets in NLS1s
is surprising, as these sources are typified by comparatively small black hole
masses and near- or super-Eddington accretion rates. This challenges the
current understanding of the conditions necessary for jet production. Comparing
the properties of the jets in NLS1s with those in more familiar jetted systems
is thus essential to improve jet production models. We present early results
from our campaign to monitor the kinematics and polarization of the
parsec-scale jets in a sample of 15 NLS1s through multifrequency observations
with the Very Long Baseline Array. These observations are complemented by
fast-cadence 15 GHz monitoring with the Owens Valley Radio Observatory 40m
telescope and optical spectroscopic monitoring with with the 2m class telescope
at the Guillermo Haro Astrophysics Observatory in Cananea, Mexico.Comment: 4 pages, 1 figure. To appear in the Proceedings of the IAU Symposium
No. 313: "Extragalactic jets from every angle," Galapagos, Ecuador, 15-19
September 2014, F. Massaro, C. C. Cheung, E. Lopez, and A. Siemiginowska
(Eds.), Cambridge University Pres
Direct Distance Measurements to Superluminal Radio Sources
We present a new technique for directly measuring the distances to
superluminal radio sources. By comparing the observed proper motions of
components in a parsec scale radio jet to their measured Doppler factors, we
can deduce the distance to the radio source independent of the standard rungs
in the cosmological distance ladder. This technique requires that the jet angle
to the line of sight and the ratio of pattern to flow velocities are
sufficiently constrained. We evaluate a number of possibilities for
constraining these parameters and demonstrate the technique on a well defined
component in the parsec scale jet of the quasar 3C279 (z = 0.536). We find an
angular size distance to 3C279 of greater than 1.8 (+0.5,-0.3) n^{1/8} Gpc,
where n is the ratio of the energy density in the magnetic field to the energy
density in the radiating particles in that jet component. For an Einstein-de
Sitter Universe, this measurement would constrain the Hubble constant to be H <
65 n^{-1/8} km/s/Mpc at the two sigma level. Similar measurements on higher
redshift sources may help discriminate between cosmological models.Comment: 18 pages, 8 figures, to be published in The Astrophysical Journa
Doping dependence and anisotropy of minority electron mobility in molecular beam epitaxy-grown p type GaInP
The article of record as published may be found at http://dx.doi.org/10.1063/1.4902316Direct imaging of minority electron transport via the spatially resolved recombination luminescence signature has been used to determine carrier diffusion lengths in GaInP as a function of doping. Minority electron mobility values are determined by performing time resolved photoluminescence measurements of carrier lifetime on the same samples. Values at 300 K vary from~2000 to 400 cm2/V s and decrease with increasing doping. Anisotropic diffusion lengths and strongly polarized photoluminescence are observed, resulting from lateral composition modulation along the [110] direction. We report anisotropic mobility values associated with carrier transport parallel and perpendicular to the modulation direction.USDOEAC05-06OR23100DEAC36-08GO28308This work was supported at the Naval Postgraduate School in part by National Science Foundation Grant No. DMR-0804527 and in part by the NPS Energy Academic Group with funding from the Navy Energy Coordination Office. T.C. acknowledges support from the Department of Energy, Office of Science Graduate Fellowship Program (DOE SCGF), made possible in part by the American Recovery and Reinvestment Act of 2009, administered by ORISE-ORAU under Control No. DE-AC05-06OR23100. TRPL work at NREL was supported by the Department of Energy Office of Science, Basic Energy Sciences under DEAC36-08GO28308
Morphological analysis on the coherence of kHz QPOs
We take the recently published data of twin kHz quasi-period oscillations
(QPOs) in neutron star (NS) lowmass X-ray binaries (LMXBs) as the samples, and
investigate the morphology of the samples, which focuses on the quality factor,
peak frequency of kHz QPOs, and try to infer their physical mechanism. We
notice that: (1) The quality factors of upper kHz QPOs are low (2 ~ 20 in
general) and increase with the kHz QPO peak frequencies for both Z and Atoll
sources. (2) The distribution of quality factor versus frequency for the lower
kHz QPOs are quite different between Z and Atoll sources. For most Z source
samples, the quality factors of lower kHz QPOs are low (usually lower than 15)
and rise steadily with the peak frequencies except for Sco X-1, which drop
abruptly at the frequency of about 750 Hz. While for most Atoll sources, the
quality factors of lower kHz QPOs are very high (from 2 to 200) and usually
have a rising part, a maximum and an abrupt drop. (3) There are three Atoll
sources (4U 1728-34, 4U 1636-53 and 4U 1608-52) of displaying very high quality
factors for lower kHz QPOs. These three sources have been detected with the
spin frequencies and sidebands, in which the source with higher spin frequency
presents higher quality factor of lower kHz QPOs and lower difference between
sideband frequency and lower kHz QPO frequency.Comment: 8 pages, 8 figures, publishe
Continued Neutron Star Crust Cooling of the 11 Hz X-Ray Pulsar in Terzan 5: A Challenge to Heating and Cooling Models?
The transient neutron star low-mass X-ray binary and 11 Hz X-ray pulsar IGR
J17480-2446 in the globular cluster Terzan 5 exhibited an 11-week accretion
outburst in 2010. Chandra observations performed within five months after the
end of the outburst revealed evidence that the crust of the neutron star became
substantially heated during the accretion episode and was subsequently cooling
in quiescence. This provides the rare opportunity to probe the structure and
composition of the crust. Here, we report on new Chandra observations of Terzan
5 that extend the monitoring to ~2.2 yr into quiescence. We find that the
thermal flux and neutron star temperature have continued to decrease, but
remain significantly above the values that were measured before the 2010
accretion phase. This suggests that the crust has not thermally relaxed yet,
and may continue to cool. Such behavior is difficult to explain within our
current understanding of heating and cooling of transiently accreting neutron
stars. Alternatively, the quiescent emission may have settled at a higher
observed equilibrium level (for the same interior temperature), in which case
the neutron star crust may have fully cooled.Comment: Accepted to ApJ without revision. Updated references and fixed few
typos to match published version. 7 pages, 3 figures, 3 table
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