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  • 1
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    Paleogenomics of echinoderms (2006)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2006-11-11
    Description: Paleogenomics propels the meaning of genomic studies back through hundreds of millions of years of deep time. Now that the genome of the echinoid Strongylocentrotus purpuratus is sequenced, the operation of its genes can be interpreted in light of the well-understood echinoderm fossil record. Characters that first appear in Early Cambrian forms are still characteristic of echinoderms today. Key genes for one of these characters, the biomineralized tissue stereom, can be identified in the S. purpuratus genome and are likely to be the same genes that were involved with stereom formation in the earliest echinoderms some 520 million years ago.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Bottjer, David J -- Davidson, Eric H -- Peterson, Kevin J -- Cameron, R Andrew -- RR-15044/RR/NCRR NIH HHS/ -- New York, N.Y. -- Science. 2006 Nov 10;314(5801):956-60.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089-0740, USA. dbottjer@usc.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17095693" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Calcification, Physiologic/genetics ; Calcium Carbonate/analysis ; Echinodermata/*genetics/physiology ; *Fossils ; *Genes ; *Genomics ; Lectins, C-Type/chemistry/genetics/physiology ; Phylogeny ; Protein Structure, Tertiary ; Proteins/chemistry/genetics/physiology ; Strongylocentrotus purpuratus/chemistry/classification/*genetics/physiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    Fermi LAT Search for Dark Matter in Gamma-Ray Lines and the Inclusive Photon Spectrum (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Dark matter particle annihilation or decay can produce monochromatic gamma-ray lines and contribute to the diffuse gamma-ray background. Flux upper limits are presented for gamma-ray spectral lines from 7 to 200 GeV and for the diffuse gamma-ray background from 4.8 GeV to 264 GeV obtained from two years of Fermi Large Area Telescope data integrated over most of the sky. We give cross section upper limits and decay lifetime lower limits for dark matter models that produce gamma-ray lines or contribute to the diffuse spectrum, including models proposed as explanations of the PAMELA and Fermi cosmic-ray data.
    Keywords: Astronomy
    Type: GSFC-E-DAA-TN6618
    Format: application/pdf
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  • 3
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    Fermi Detection of Gamma-Ray Emission from the M2 Soft X-Ray Flare on 2010 June 12 (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: The GOES M2-class solar flare, SOL2010-06-12T00:57, was modest in many respects yet exhibited remarkable acceleration of energetic particles. The flare produced an approximately 50 s impulsive burst of hard X- and gamma-ray emission up to at least 400 MeV observed by the Fermi GBM and LAT experiments. The remarkably similar hard X-ray and high-energy gamma-ray time profiles suggest that most of the particles were accelerated to energies greater than or equal to 300 MeV with a delay of approximately 10 s from mildly relativistic electrons, but some reached these energies in as little as approximately 3 s. The gamma-ray line fluence from this flare was about ten times higher than that typically observed from this modest GOES class of X-ray flare. There is no evidence for time-extended greater than 100 MeV emission as has been found for other flares with high-energy gamma rays.
    Keywords: Astronomy
    Type: GSFC.JA.5878.2012 , GSFC.JA.7277.2012
    Format: application/pdf
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  • 4
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    Fermi Large Area Telescope Observations of the Supernova Remnant GS.7-0.1 (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: We present a detailed analysis of the GeV gamma-ray emission toward the supernova remnant (SNR) G8.7-0.1 with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. An investigation of the relationship among G8.7-0.l and the TeV unidentified source HESS J1804-216 provides us with an important clue on diffusion process of cosmic rays if particle acceleration operates in the SNR. The GeV gamma-ray emission is extended with most of the emission in positional coincidence with the SNR G8.7-0.l and a lesser part located outside the western boundary of G8.7-0.l. The region of the gamma-ray emission overlaps spatially-connected molecular clouds, implying a physical connection for the gamma-ray structure. The total gamma-ray spectrum measured with LAT from 200 MeV-100 GeV can be described by a broken power-law function with a break of 2.4 +/- 0.6 (stat) +/- 1.2 (sys) GeV, and photon indices of 2.10 +/- 0.06 (stat) +/- 0.10 (sys) below the break and 2.70 +/- 0.12 (stat) +/- 0.l4 (sys) above the break. Given the spatial association among the gamma rays, the radio emission of G8.7-0.1, and the molecular clouds, the decay of 1IoS produced by particles accelerated in the SNR and hitting the molecular clouds naturally explains the GeV gamma-ray spectrum. We also find that the GeV morphology is not well represented by the TeV emission from HESS J1804-216 and that the spectrum in the GeV band is not consistent with the extrapolation of the TeV gamma-ray spectrum. The spectral index of the TeV emission is consistent with the particle spectral index predicted by a theory that assumes energy-dependent diffusion of particles accelerated in an SNR. We discuss the possibility that the TeV spectrum originates from the interaction of particles accelerated in G8.7-0.1 with molecular clouds, and we constrain the diffusion coefficient of the particles.
    Keywords: Astronomy
    Type: GSFC.JA.5424.2011
    Format: application/pdf
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  • 5
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    PSR J2021+4026 in the Gamma Cygni Region: The First Variable Gamma-Ray Pulsar Seen by the Fermi LAT (2013)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Long-term monitoring of PSR J2021+4026 in the heart of the Cygnus region with the Fermi Large Area Telescope unveiled a sudden decrease in flux above 100 MeV over a timescale shorter than a week. The "jump" was near MJD 55850 (2011 October 16), with the flux decreasing from (8.33 plus or minus 0.08)10(exp 10) erg cm(exp 2) s(exp 1) to (6.86 plus or minus 0.13) 10 (exp 1)0 erg cm (exp 2) s(exp 1). Simultaneously, the frequency spindown rate increased from (7.8 plus or minus 0.1) 10(exp 13) Hz s(exp 1) to (8.1 plus or minus 0.1) 10(exp 1)3 Hz s(exp 1). Significant (greater than 5 sigma) changes in the pulse profile and marginal (less than 3 sigma) changes in the emission spectrum occurred at the same time. There is also evidence for a small, steady flux increase over the 3 yr preceding MJD 55850. This is the first observation at gamma-ray energies of mode changes and intermittent behavior, observed at radio wavelengths for other pulsars. We argue that the change in pulsed gamma-ray emission is due to a change in emission beaming and we speculate that it is precipitated by a shift in the magnetic field structure, leading to a change of either effective magnetic inclination or effective current.
    Keywords: Astronomy
    Type: GSFC-E-DAA-TN15968 , The Astrophysical Journal Letters (ISSN 0004-637X) (e-ISSN 1538-4357); 777; 1; L2
    Format: text
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