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  • 1
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    Moderate Geomagnetic Storms: Interplanetary Origins and Coupling Functions (ISEE3 Data) (1996)
    In:  CASI
    Details
    Publication Date: 2018-06-27
    Description: Geomagnetic storms are related to the ring current intensification, which is driven by energy injection primarily during energetic solar wind-magnetosphere coupling due to reconnection at the magnetopause. This work identified the interplanetary origins of moderate geomagnetic storms (-100nT is less or equal to Dst(sub peak) is less than or equal to -50 nT) and analyzed the coupling processes during the storm main phase at solar maximum (1978-1979).
    Keywords: Astrophysics
    Type: Proceedings of the Fourth Brazilian Meeting on Plasma Physics and the Sixth Brazilian Plasma Astrophysics Workshop; 146-149
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  • 2
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    Note on the gauge symmetries of unimodular gravity (2016)
    American Physical Society (APS)
    Details
    Publication Date: 2016-07-01
    Description: Author(s): Enrique Álvarez, Sergio González-Martín, and Carmelo P. Martín The symmetries of unimodular gravity are clarified somewhat. [Phys. Rev. D 93, 123018] Published Thu Jun 30, 2016
    Keywords: Astrophysics
    Print ISSN: 0556-2821
    Electronic ISSN: 1089-4918
    Topics: Physics
    Published by American Physical Society (APS)
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  • 3
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    Constructing a cosmological model-independent Hubble diagram of type Ia supernovae with cosmic chronometers (2016)
    American Physical Society (APS)
    Details
    Publication Date: 2016-02-23
    Description: Author(s): Zhengxiang Li, J. E. Gonzalez, Hongwei Yu, Zong-Hong Zhu, and J. S. Alcaniz We apply two methods, i.e., the Gaussian processes and the nonparametric smoothing procedure, to reconstruct the Hubble parameter H ( z ) as a function of redshift from 15 measurements of the expansion rate obtained from age estimates of passively evolving galaxies. These reconstructions enable us to d… [Phys. Rev. D 93, 043014] Published Mon Feb 22, 2016
    Keywords: Astrophysics
    Print ISSN: 0556-2821
    Electronic ISSN: 1089-4918
    Topics: Physics
    Published by American Physical Society (APS)
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  • 4
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    Dirac quasinormal modes of Chern-Simons and BTZ black holes with torsion (2014)
    American Physical Society (APS)
    Details
    Publication Date: 2014-01-09
    Description: Author(s): Ramón Bécar, P. A. González, and Y. Vásquez We study Chern-Simons black holes in d dimensions and we calculate analytically the quasinormal modes of fermionic perturbations. Also, we consider as background the five-dimensional Chern-Simons black hole with torsion and the BTZ black hole with torsion. We have found that the quasinormal modes de... [Phys. Rev. D 89, 023001] Published Wed Jan 08, 2014
    Keywords: Astrophysics
    Print ISSN: 0556-2821
    Electronic ISSN: 1089-4918
    Topics: Physics
    Published by American Physical Society (APS)
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  • 5
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    Fast Molecular Outflows in Luminous Galaxy Mergers: Evidence for Quasar Feedback from Herschel (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We report the results from a systematic search for molecular (OH 119 micron) outflows with Herschel/PACS in a sample of 43 nearby (z 〈 0.3) galaxy mergers, mostly ultraluminous infrared galaxies (ULIRGs) and QSOs. We find that the character of the OH feature (strength of the absorption relative to the emission) correlates with that of the 9.7 micron silicate feature, a measure of obscuration in ULIRGs. Unambiguous evidence for molecular outflows, based on the detection of OH absorption profiles with median velocities more blueshifted than50 km/s, is seen in 26 (70%) of the 37 OH-detected targets, suggesting a wide-angle (approx. 145 deg.) outflow geometry. Conversely, unambiguous evidence for molecular inflows, based on the detection of OH absorption profiles with median velocities more redshifted than +50 km/s is seen in only four objects, suggesting a planar or filamentary geometry for the inflowing gas. Terminal outflow velocities of approx. 1000 km/s are measured in several objects, but median outflow velocities are typically approx.200 km/s1. While the outflow velocities show no statistically significant dependence on the star formation rate, they are distinctly more blueshifted among systems with large active galactic nucleus (AGN) fractions and luminosities [log (L(sub AGN)/L(sub solar)) =〉 11.8 +/- 0.3]. The quasars in these systems play a dominant role in driving the molecular outflows. However, the most AGN dominated systems, where OH is seen purely in emission, show relatively modest OH line widths, despite their large AGN luminosities, perhaps indicating that molecular outflows subside once the quasar has cleared a path through the obscuring material.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN12514 , The Astrophysical Journal (ISSN 0004-637X); 776; 1; 27
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  • 6
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    Spectrum and Morphology of the Two Brightest Milagro Sources in the Cygnus Region: MGRO J2019+37 and MGRO J2031+41 (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The Cygnus region is a very bright and complex portion of the TeV sky, host to unidentified sources and a diffuse excess with respect to conventional cosmic-ray propagation models. Two of the brightest TeV sources, MGRO J2019+37 and MGRO J2031+41, are analyzed using Milagro data with a new technique, and their emission is tested under two different spectral assumptions: a power law and a power law with an exponential cutoff. The new analysis technique is based on an energy estimator that uses the fraction of photomultiplier tubes in the observatory that detect the extensive air shower. The photon spectrum is measured in the range 1-100 TeV using the last three years of Milagro data (2005-2008), with the detector in its final configuration. An F-test indicates that MGRO J2019+37 is better fit by a power law with an exponential cutoff than by a simple power law. The best-fitting parameters for the power law with exponential cutoff model are a normalization at 10 TeV of 7(sup +5 sub 2) 10(exp 10)/ s /sq m/ TeV, a spectral index of 2.0(sup +0.5 sub -10), and a cutoff energy of 29(sup +50 sub 16) TeV. MGRO J2031+41 shows no evidence of a cutoff. The best-fitting parameters for a power law are a normalization of 2.1(sup +0.6 sub 0.6) 10(exp 10)/ s/sq m/ TeV and a spectral index of 3.22(sup +0.23 sub 0.18. The overall flux is subject to a approx.. 30% systematic uncertainty. The systematic uncertainty on the power-law indices is approx. 0.1. Both uncertainties have been verified with cosmic-ray data. A comparison with previous results from TeV J2032+4130, MGRO J2031+41, and MGRO J2019+37 is also presented.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN9514 , The Astrophysical Journal; 753; 2; 159
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  • 7
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    Milagro Limits and HAWC Sensitivity for the Rate-Density of Evaporating Primordial Black Holes (2014)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Primordial Black Holes (PBHs) are gravitationally collapsed objects that may have been created by density fluctuations in the early universe and could have arbitrarily small masses down to the Planck scale. Hawking showed that due to quantum effects, a black hole has a temperature inversely proportional to its mass and will emit all species of fundamental particles thermally. PBHs with initial masses of approx.5.0 x 10(exp 14) g should be expiring in the present epoch with bursts of high-energy particles, including gamma radiation in the GeV-TeV energy range. The Milagro high energy observatory, which operated from 2000 to 2008, is sensitive to the high end of the PBH evaporation gamma-ray spectrum. Due to its large field-of-view, more than 90% duty cycle and sensitivity up to 100 TeV gamma rays, the Milagro observatory is well suited to perform a search for PBH bursts. Based on a search on the Milagro data, we report new PBH burst rate density upper limits over a range of PBH observation times. In addition, we report the sensitivity of the Milagro successor, the High Altitude Water Cherenkov (HAWC) observatory, to PBH evaporation events.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN34614 , Astroparticle Physics (ISSN 0927-6505); 64; 4-12
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  • 8
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    Weak Lensing Results of the Merging Cluster A1758 (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: Here we present the weak lensing results of A1758, which is known to have four cluster members undergoing two separate mergers, A1758N and A1758S. Weak lensing results of A1758N agree with previous weak lensing results of clusters lE0657-558 (Bullet cluster) and MACS J0025.4-1222, whose X-ray gas components were found to be largely separated from their clusters' gravitational potentials. A1758N has a geometry that is different from previously published mergers in that one of its X-ray peaks overlays the corresponding gravitational potential and the other X-ray peak is well separated from its cluster's gravitational potential.
    Keywords: Astrophysics
    Type: GSFC.ABS.5269.2011
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  • 9
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    The Nanograv Nine-Year Data Set: Measurement and Analysis of Variations in Dispersion Measures (2017)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We analyze dispersion measure(DM) variations of 37 millisecond pulsars in the nine-year North American Nanohertz Observatory for Gravitational Waves (NANOGrav) data release and constrain the sources of these variations. DM variations can result from a changing distance between Earth and the pulsar, inhomogeneities in the interstellar medium, and solar effects. Variations are significant for nearly all pulsars, with characteristic timescales comparable to or even shorter than the average spacing between observations. Five pulsars have periodic annual variations, 14 pulsars have monotonically increasing or decreasing trends, and 14 pulsars show both effects. Of the four pulsars with linear trends that have line-of-sight velocity measurements, three are consistent with a changing distance and require an overdensity of free electrons local to the pulsar. Several pulsars show correlations between DM excesses and lines of sight that pass close to the Sun. Mapping of the DM variations as a function of the pulsar trajectory can identify localized interstellar medium features and, in one case, an upper limit to the size of the dispersing region of 4 au. Four pulsars show roughly Kolmogorov structure functions (SFs), and another four show SFs less steep than Kolmogorov. One pulsar has too large an uncertainty to allow comparisons. We discuss explanations for apparent departures from a Kolmogorov-like spectrum, and we show that the presence of other trends and localized features or gradients in the interstellar medium is the most likely cause.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN45943 , The Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 841; 2; 125
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  • 10
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    Testing the Universality of the Stellar IMF with Chandra and HST (2017)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The stellar initial mass function (IMF), which is often assumed to be universal across unresolved stellar populations, has recently been suggested to be bottom-heavy for massive ellipticals. In these galaxies, the prevalence of gravity-sensitive absorption lines (e.g., Na I and Ca II) in their near-IR spectra implies an excess of low-mass (m 〈 or approx. = 0.5 Stellar Mass) stars over that expected from a canonical IMF observed in low-mass ellipticals. A direct extrapolation of such a bottom-heavy IMF to high stellar masses (m 〉 or approx. = 8 Stellar Mass) would lead to a corresponding deficit of neutron stars and black holes, and therefore of low-mass X-ray binaries (LMXBs), per unit near-IR luminosity in these galaxies. Peacock et al. searched for evidence of this trend and found that the observed number of LMXBs per unit K-band luminosity (N/LK) was nearly constant. We extend this work using new and archival Chandra X-ray Observatory and Hubble Space Telescope observations of seven low-mass ellipticals where N/LK is expected to be the largest and compare these data with a variety of IMF models to test which are consistent with the observed N/LK. We reproduce the result of Peacock et al., strengthening the constraint that the slope of the IMF at m 〉 or approx. = 8 Stellar Mass must be consistent with a Kroupa-like IMF. We construct an IMF model that is a linear combination of a Milky Way-like IMF and a broken power-law IMF, with a steep slope (alpha1 = 3.84) for stars 〈 0.5 Stellar Mass (as suggested by near-IR indices), and that flattens out (alpha2 = 2.14) for stars 〉 0.5 Stellar Mass, and discuss its wider ramifications and limitations.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN45844 , The Astrophysical Journal (ISSN 2041-8205) (e-ISSN 2041-8213); 835; 2; 183
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