Engineering topics

Halpern, J. P.

Publications and source records attributed to Halpern, J. P..

31 records · Page 2

NASA NTRS1987

A hard X-ray source in the nearest molecular cloud

The previous unidentified hard X-ray source H 0253 + 193 is coincident with Lynds 1457, a dark nebula at high galactic latitude (l = 159 deg, b = -34 deg). The Einstein IPC position coincides with the peak in the CO map obtained by Hobbs, Blitz, and Magnani (1986). Using interstellar Na I absorption, these authors determined a distance to the cloud of 65 pc, making this the nearest known molecular cloud. The X-ray source can be explained as an embedded T Tauri star with a 2-10 keV luminosity of 1 x 10 to the 31st erg/s.

Halpern, J. P.↗

NASA NTRS1986

X-ray emission lines from three Galactic bulge sources

X-ray spectroscopic observations obtained with the Einstein objective grating spectrometer (OGS) and monitor proportional counter (MPC) instruments of three Galactic bulge sources, the globular cluster burst source 1820-30, the burster Serpens X-1, and the GX 9+9 are presented. Joint spectral fits to the OGS and MPC data are consistent for all three sources with either a thermal bremsstrahlung model with temperature ranging from 6 to 10 keV or with a two-component blackbody model, where one component may be associated with the neutron star and one with the accretion disk. The spectra of Serpens X-1 and 1820-30 harden with increases in intensity. The implications of the results for recent models of low-mass X-ray binaries are discussed.

Vrtilek, S. D.↗

NASA NTRS1986

NGC 6212 - An X-ray-selected active elliptical galaxy

Optical and X-ray data on the elliptical galaxy NGC 6212 are reported. The X-ray flux varies by a factor of four on a time scale of months. The optical spectrum shows broad Balmer emission lines and narrow forbidden lines which are typical of low-luminosity X-ray selected Seyfert galaxies. The continuum is predominantly stellar, with no evidence for a nonthermal contribution. Narrow emission lines extend at least 11 kpc from the nucleus and are used to derive a rotation curve. The X-ray variability and relatively weak radio emission of NGC 6212 are not unusual for Seyfert galaxies.

Halpern, J. P.↗

NASA NTRS1986

1E 1415.6+2557 - An X-ray-selected BL Lacertae object in a luminous galaxy

The identification of a fifth serendipitous Einstein source with a new BL Lac object in a very luminous galaxy is reported. The resolved component is well fitted by an exponential disk with scale length 18 kpc and absolute magnitude of roughly -24.2. A redshift of 0.237 is derived from stellar absorption features. No emission lines are seen in the 3200-9000 A wavelength range. Decomposition of the optical spectrum into a standard galaxy plus a power law yields a spectral index of 0.5 + or - 0.5, significantly flatter than in the average BL Lac object. Linear polarization of the nonstellar component is about 6 percent in the 4500-7000 A wavelength range. The X-ray flux in the 0.3-3.5 keV band is 1.16 x 10 to the -11th ergs/sq cm/s, corresponding to a luminosity of 3.5 x 10 to the 45th ergs/s . The radio flux density is 85.6 mJy at 20 cm and 54.5 mJy at 6 cm.

Halpern, J. P.↗

NASA NTRS1986

Detection of forbidden Ni II lambda 7378 in six Seyfert galaxies

A line due to Ni 2 7378 in the Seyfert galaxies NGC 1068, 2110, 3227, 4151, 5506, and Arp 102 B was detected. The average Ni abundance is about 2 times solar, which is 5 times less than in the filaments of the Crab Nebula. This argues for nucleosynthetic processing in the latter. The Ni 2 line is spatially resolved in NGC 1068, and shows at least a factor of 4 enhancement in the Ni abundance away from the nucleus. The off-nuclear abundance of Ni in NGC 1068 approaches that of the Crab, which strongly suggests that type supernovae enriched the off-nuclear gas clouds.

Halpern, J. P.↗

NASA NTRS1985

Temporal and spectral study of a newly discovered spiking phenomenon in the pre-eclipse and anomalous dip states of Hercules X-1

A new phenomenon has been detected in observations of Hercules X-1 at times consistent with the preeclipse and anomalous dips. The X-ray intensity does not drop for the duration of the dip but is punctuated by short spikes that appear to repeat with a period of approximately 108 minutes. Spectral fits during the on-state, the spike-state, and the low-state suggest a single, constant intrinsic source spectrum which becomes partially covered by an absorbing medium during the spike and low states. All three states can be fitted with the same flat power law between 1 and 20 keV with an absorber of varying covering fraction. Since the morphology and spectrum of the spikes are similar during both the preeclipse and the anomalous dips, and the possible 108 minute period is seen in both states, there is for the first time strong support for a common origin for the preeclipse and anomalous dips.

Vrtilek, S. D.↗

NASA NTRS1985

Observations of the Geminga optical candidate

The present spectroscopy and photometry for the proposed optical counterpart of the X-ray source IE 0630 + 178, which is also a candidate for identification with the gamma-ray source 'Geminga', yields a spectrum that is featureless at the current S/N ratio and resists classification. The properties of the X-ray and optical objects, and the statistical circumstances of the identification process, do not support the association of optical, X-ray, and gamma-ray sources. The uniqueness of the X-ray source nevertheless suggests that its X-rays are thermal emission from the surface of a neutron star whose optical counterpart is an undetected blue star of B magnitude approximately 26.

Halpern, J. P.↗

NASA NTRS1985

X-ray spectrum and variability of 3C 120

The X-ray luminosity of 3C 120 is variable by a factor of 2.5 on time scales of days to months. The spectral slope of the 2-10 keV X-rays changes systematically in the sense that the higher intensity states are steeper. Simple power laws fitted to the data are consistent with an energy index alpha of 0.51 + or - 0.13 at minimum intensity and 0.83 + or - 0.03 at maximum, with a continuous variation in between. A more complicated spectral shape cannot be ruled out, but changes in absorbing column density alone cannot explain the data. The results are interpreted in terms of beamed synchrotron emission from a relativistic jet, a model which has been invoked previously for the spectra of BL Lac objects. The spectral variability is in marked contrast to the behavior of 3C 273, another superluminal source in which the X-ray spectral index is constant to a high degree of accuracy despite variability in time scales and amplitudes which are quite similar to those of 3C 120. The difference may be due to the degree of beaming of the respective core components. Another model which is consistent with the data involves thermal emission from isothermal shocks in a hot (approximately 10 to the 8th K) medium. Thermal Compton and spherical accretion X-ray source models do not reproduce the correct behavior of alpha versus flux.

Halpern, J. P.↗

NASA NTRS1985

Detection of Ni 2 lambda 7378 in six Seyfert galaxies

A line due to Ni 2 7378 in the Seyfert galaxies NGC 1068, 2110, 3227, 4151, 5506, and Arp 102 B was detected. The average Ni abundance is about 2 times solar, which is 5 times less than in the filaments of the Crab Nebula. This argues for nucleosynthetic processing in the latter. The Ni 2 line is spatially revolved in NGC 1068, and shows at least a factor of 4 enhancement in the Ni abundance away from the nucleus. The off-nuclear abundance of Ni in NGC 1068 approaches that of the Crab, which strongly suggests that type supernovae enriched the off-nuclear gas clouds.

Halpern, J. P.↗

NASA NTRS1984

1300 + 361 A,B is not a gravitational lens

Spectroscopic observations toward 1300 + 361 B obtained at 320-940 nm using a double spectrograph with CCD detectors on the 5-m Hale telescope (resolution about 7 A at 470-940 nm and 10-12 A at 320-470 nm on April 4-5, 1984, are reported. Two objects with magnitude 20 and spectral characteristics resembling those of an interacting pair of metal-poor H II regions at redshift 0.107 are observed, separated by about 10.6 arcsec and with a velocity difference of less than 80 km/s. It is considered unlikely that these objects form a gravitational-lens system. The ratio of the dereddened flux of the 5007-A forbidden line of O III to that of H-beta is found to be 5.03 for 1300 + 361 A and 3.67 for 1300 + 361 B; the difference is attributed to the presence of star-forming regions in the interacting system.

Halpern, J. P.↗

NASA NTRS1984

NGC 7213 - A key to the nature of liners?

New optical spectra of the nearby S0 galaxy NGC 7213 are analyzed. The observations are described and a brief overview of the spectrum is given. The subtraction of the stellar component is presented, and the measurement of various emission lines is discussed in detail. Important physical parameters are derived, including those pertaining to atomic data, line widths, physical conditions, geometry and kinematics, the Balmer decrement, and ultraviolet emission lines. The Seyfert characteristics of NGC 7213 are reviewed, and the galaxy's shock features are reconciled with photoionization models. The presented arguments may apply to classical liners as well. Theoretical models that can help explain the relationships discovered among the emission lines are examined.

Filippenko, A. V.↗

NASA NTRS1984

The nonstellar continuum of the Seyfert galaxy NGC 7213

The optical continuum of the nearby Seyfert galaxy NGC 7213 is decomposed into stellar and nonstellar components, and the spectrum at X-ray energies is derived from observations made with the Monitor Proportional Counter and the Imaging Proportional Counter aboard the Einstein Observatory. These results are used to obtain conclusions about the galaxy's column density and spectral index, covering fraction and visual extinction, and thermal emission. Ultraviolet, infrared, and radio observations published elsewhere are then combined with the new data to produce the overall continuum.

Halpern, J. P.↗

NASA NTRS1984

Variable X-ray absorption in the QSO MR 2251 - 178

The monitoring proportional counter of the Einstein Observatory has been used to observe the QSO MR 2251 - 178 on two occasions, approximately 1 year apart, in the 2-10 keV range. Evidence is found for an increase in the absorbing column density by a large factor over the 1 year interval. Simultaneous measurements with the high resolution imager are used to further constrain the soft X-ray flux and to show that the highly absorbed spectrum must have excess emission below 1 keV. A model is presented in which photoionization by the X-ray continuum ionizes a cloud or shell of material, so that the emergent spectrum is transparent below the K-edge of O VII at 739 eV, but is highly absorbed above this energy.

Halpern, J. P.↗