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  • 1
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    Characteristics of the persistent emission of SGR 1806-20 (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Earlier, using the X-ray satellite ASCA, we had identified the soft gamma-ray burst repeater (SGR) 1806-20 with a persistent X-ray source, AX 1805.7-2025 which is located close to the center of the radio supernova remnant G10.0-0.3. A burst seen by Burst and Transient Source Experiment (BATSE) was shown to be centered on G10.0-0.3. Here we report detailed temporal and spectral analysis of the persistent source. We find that AX 1805.7-2025 is a very compact source, size less than 30 sec in diameter, with a power-law spectrum. The count rate from AX 1805.7-2025 is steady on timescales of minutes, days, and 1 week. Most supernova remnants have extended X-ray emission ascribed to shocked gas. We set an upper limit to an extended X-ray emission both in continuum and line emission. We conclude that an isolated neutron star, most likely a pulsar, powers the radio remnant G10.0-0.3. Finally, we note that the persistent spectrum appears to be less absorbed than the burst spectrum.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 436; 1; p. L23-L25
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  • 2
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    A 110-ms pulsar, with negative period derivative, in the globular cluster M15 (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The discovery of a 110-ms pulsar, PSR2127+11, in the globular cluster M15, is reported. The results of nine months of timing measurements place the new pulsar about 2 arcsec from the center of the cluster, and indicate that it is not a member of a close binary system. The measured negative value of the period derivative is probably the result of the pulsar being bodily accelerated in our direction by the gravitational field of the collapsed core of M15. This apparently overwhelms a positive contribution to the period derivative due to magnetic braking. Although the pulsar has an unexpectedly long period, it is argued that it belongs to the class of 'recycled' pulsars, which have been spun up by accretion in a binary system. The subsequent loss of the pulsar's companion is probably due to disruption of the system by close encounters with other stars.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 337; 531-533
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  • 3
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    Diffraction limited infrared images of the binary star T Tauri (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: High-resolution images of T Tau and its infrared companion have been reconstructed from near- and midinfrared data collected at the Hale 5-m telescope. The near-infrared (1-5 microns) results were obtained by 2D speckle imaging and the midinfrared (10-20 microns) results were derived from shift-and-add procedures applied to slit scans. The spectral energy distributions of the separated components were constructed from 1- to 20-micron data collected in less than half a year (September 1990 to January 1991). The spectral energy distribution of the optical component (T Tau N) is interpreted as containing two distinct constituents, a photosphere and a surrounding disk of circumstellar material. Measurements at a number of infrared wavelengths over the period December 1985 to January 1991 show a 2-mag color-independent change in the brightness of the infrared component (T Tau S). It is proposed that this may have been caused by an increase in accretion onto T Tau S and model the spectral energy distribution of T Tau S as being dominated by an accretion disk.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 102; 2066-207
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  • 4
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    The Z-dependence of the Spin Temperature of HI (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: Results relating to the following aspects of hydrogen clouds are presented: (1) the vertical distribution of cold H T clouds; (2) possible systematic warming of H T clouds at high absolute values of z; (3) possible increase of the fraction of warm intercloud medium H T with high absolute values of z; and (4) the effect of optical depth on previous H T emission surveys.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 269-273
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  • 5
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    ROSAT observations of six millisecond pulsars (1994)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We present ROSAT observations toward six known millisecond radio pulsars. These observations yielded upper limits to the X-ray flux in the ROSAT band (0.1-2.4 keV) for five pulsars and a possible association of an X-ray source with PSR B1821-24, in the globular cluster M28. At the 99.9% confidence level, the source is pulsed at the expected radio pulsar frequency. We compare our results with predicted X-ray luminosities by Seward & Wang Oegelman. The X-ray luminosities of PSRs B1257+12 and J0437-4715, millisecond pulsars with similar periods and spin-down rates, are found to differ by more than a factor of 25. X-ray emission from radio pulsars has been ascribed to a thermal component arising from a surface hot spot and a power-law magnetospheric component (Halpern & Ruderman). In the context of this model and these observations, we argue that the orientation of the magnetic and rotation axes with respect to the line of sight is very different for PSR J0437-4715 compared to PSR B1257+12. Finally, we suggest that the beaming factor for X-ray emission is independent of the pulsar period, unlike that for radio emission; if so, most millisecond pulsars are visible in the radio but no at X-ray energies.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 436; 2; p. L153-L156
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  • 6
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    The magnetic fields, ages, and original spin periods of millisecond pulsars (1994)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Accurate determination of the spin-down rates of millisecond pulsars requires consideration of the apparent acceleration of the pulsars due to their high transverse velocities. We show that for several nearby pulsars the neglect of this effect leads to substantial errors in inferred pulsar ages and magnetic fields. Two important ramifications follow. (1) The intrinsic magnetic field strengths of all millisecond pulsars lie below 5 x 10(exp 8) G, strengthening an earlier suggestion of a 'gap' between the magnetic field strengths of millisecond pulsars and of high-mass binary pulsars such as PSR B1913+16, which are thought to have been formed by mass transfer in low-mass and high-mass X-ray binaries, respectively. This result suggests that the magnetic field strengths of recycled pulsars are related to their formation and evolution in binary systems. (2) The corrected characteristic ages of several millisecond pulsars appear to be greater than the age of the Galactic disk. We reconcile this apparent paradox by suggesting that some millisecond pulsars were born with periods close to their current periods. This conclusion has important implications for the interpretation of the cooling ages of white dwarf companions, the birthrate discrepancy between millisecond pulsars and their X-ray binary progenitors, and the possible existence of a class of weakly magnetized (B much less than 10(exp 8)G), rapidly rotating neutron stars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 (ISSN 0004-637X); 421; p. L15-L18
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  • 7
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    Stellar black holes in globular clusters (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The recent discovery of large populations of millisec pulsars associated with neutron stars in globular clusters indicates that several hundred stellar black holes of about 10 solar masses each can form within a typical cluster. While, in clusters of high central density, the rapid dynamical evolution of the black-hole population leads to an ejection of nearly all holes on a short timescale, systems of intermediate density may involve a normal star's capture by one of the surviving holes to form a low-mass X-ray binary. One or more such binaries may be found in the globular clusters surrounding our galaxy.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 364; 6436; p. 421-423.
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  • 8
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    X-ray detection of the eclipsing millisecond pulsar PSR1957+20 (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: X-ray emission has been detected from the binary millisecond pulsar system PSR1957+20 using the Rosat satellite. The observations show that less than 20 percent of the pulsars's spindown luminosity can be carried away by electrons and positrons with Lorentz factor gamma about 10 exp 5, and less than 5 percent by electrons and positrons with gamma about 10 exp 8. Neither of these fluxes can provide the penetrating flux required to heat the companion's photosphere. These observations and those by Fruchter et al. (1992) represent the first direct diagnostics of the relativistic wind from a weakly magnetized pulsar and suggest that the wind differs substantially from that of the more highly magnetized Crab pulsar.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 359; 6393; p. 300-302.
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  • 9
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    An association between a long-period pulsar and an old supernova remnant (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: A possible association between pulsar 2334 + 61, with a relatively long period of 0.5 s, and G114.3 + 0.3, a fairly old SNR is reported. The flat spectral index of -0.36 +/- 0.03 and large fractional polariazation suggest that the radio emission is powered by the pulsar. If so, the pulsar must have been born with a relatively short period of less than 100 ms. As the SNR is not particularly unusual morphologically, there might be many more such SNRs containing pulsars that are not beamed towards us.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 362; 6416; p. 135-137.
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  • 10
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    Identification of the nebula G70.7 + 1.2 as a bow shock powered by a pulsar/Be-star binary (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: New data are presented here that firmly establish the nonthermal nature of the radio emission from the enigmatic radio and optical nebula G70.7 + 1.2. H-alpha and forbidden O I Fabry-Perot observations are used to argue that the extended optical emission from the nebula arises from a bow shock powered by a mass-losing luminous star moving supersonically through dense gas. The strong nonthermal radio emission from the object is then explained as the shocked relativistic wind from a pulsar, which is proposed here as a companion to the Be star. The coincidence of the optical and radio emission requires the pulsar and stellar winds to be mixed together. The system has a large overall velocity of about 60 km/s which is inexplicable in all other models but which is typical of binary pulsars.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 360; 6400; p. 139-141.
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