The X-ray spectrum of 3C 273
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Worrall, D. M.↗
Engineering topics
Serlemitsos, P. J.
Publications and source records attributed to Serlemitsos, P. J..
A change in the X-ray spectrum of Markarian 421
HEAO 1 A-2 experiment observations of the BL Lacertae object Mrk 421 in May 1978 show a marked spectral change from the OSO 8 observations of May 1977. The source was not detected above 10 keV in May 1978. The 2-10 keV spectrum could be well fitted by a power law with an energy slope of 2.2 to 4.2; thermal bremsstrahlung models with T less than 20 million are also acceptable. There was no indication of any low-energy turnover, so that the inferred column density is less than 7 x 10 to the 21st H atoms per sq cm. The total flux is consistent with an extrapolation of the UV data from IUE, but the slope is not consistent with the UV slope. Possible models for the origin of the spectral transition are discussed.
Mushotzky, R. F.↗
HEAO-1 spectra of X-ray emitting Seyfert 1 galaxies
The A-2 experiment on HEAO-1 determined spectral parameters for seven Seyfert 1 galaxies: NGC3783, NGC4151, NGC5548, NGC6814, MK509, MCG8-11-11, and ES0141-G55. The X-ray spectra above 5 keV can be well fit by power laws of energy index alpha between .3 and 1.0 and, with the exception of MK509, by a high temperature (kt 15 keV) thermal bremsstrahlung spectrum. The column densities, with the exception of NGC4151, are less than 5 x 10 to the 22nd power at/sq cm with only the low luminosity objects having measurable columns. Galaxy ES0141-G55 showed a strong soft X-ray excess in March 1978 similar to that seen in the BL lac object MK421. Variability on a six month time scale was exhibited by MCG8-11-11, NGC3783, and possibly NGC6814. Various correlations between optical and X-ray properties are discussed. Using the typical Seyfert 1 spectrum their contribution to the diffuse X-ray background above five keV is computed.
Mushotzky, R. F.↗
HEAO 1 observations of the X-ray pulsar 4U 1626-67
Results are reported for an observation of the 7-s pulsar 4U 1626-67 with the A-2 experiment on HEAO 1. The phase-averaged X-ray spectrum between 0.7 and 60 keV is complex, as are the constituent spectra, which change radically as a function of pulse phase. Included in this spectral change is the sudden appearance and subsequent decay of a continuum or emission feature with a mean energy of 19 keV, which contains about one-half the power in this spectral range. Pulse-timing results include a new determination of the pulse period and a factor of 8 reduction in the upper limit for the light travel time for orbital periods between 1 and 7 hours. These findings are discussed and compared with the general nature of pulsar spectra.
Pravdo, S. H.↗
Observations of the transient X-ray source 4U 0115+63
Results are presented for HEAO A-2 pointed observations and Ariel 5 A11-Sky Monitor observations of the X-ray transient 4U 0115 + 63. The transient source pulses with a period of 3.6136 s + or - 0.0004 s, has a hard spectrum typical of an X-ray binary pulsar, and has a broad iron line emission feature. A discussion of the transient behavior is given, and inferences are made concerning the nature of the X-ray source based on the pointed data.
Rose, L. A.↗
The diffuse X-ray background spectrum from 3 to 50keV
The spectrum of the extragalactic diffuse X-ray background was measured with the GSFC cosmic X-ray experiment on HEAO-1 for regions of the sky away from known point sources and more than 20 deg from the galactic plane. A total exposure of 80 sq m-sec-sr is available at present. Free-free emission from an optically thin plasma of 40 plus or minus 5 keV provides an excellent description of the observed spectrum from 3 to 50 keV. This spectral shape is confirmed by measurements from 5 separate layers of three independent detectors. With an estimated absolute precision of about 10 percent, the intensity of the emission at 10 keV is 3.2 keV/keV-sq cm-sec-sr, a value consistent with the average of previously reported spectra. No other spectral features, such as iron line emission, are evident. This spectrum is not typical of known extragalactic objects. A uniform hot intergalactic medium of approximately 36 percent of the closure density of the universe would produce such a flux, although non-uniform models indicating less total matter are probably more realistic.
Marshall, F. E.↗
New hard X-ray sources observed with HEAO A-2
A search for new hard X-ray sources using data from the first complete view of the sky with the HEAO A-2 experiment has discovered 47 new sources, detected seven sources recently discovered with other experiments, and significantly reduced the size of the error boxes for six previously known sources. Intensities and error boxes are given for each of these sources; identifications are suggested when an error box contains an object similar to known X-ray sources. The new identifications consist of seven type 1 Seyfert galaxies, including two whose Seyfert characteristics were discovered as a result of their location in an X-ray error box; one intermediate Seyfert galaxy; three Abell clusters; five N galaxies; two bursting radio sources; and an additional three nearby galaxies with bright nuclei and narrow emission lines.
Marshall, F. E.↗
X-ray observations of H1908+050 /=SS 433/
The X-ray source H1908+050 (=4U 1908+05 = A1909+04) was observed for three 6 day periods in 1977 and 1978 with the HEAO A-2 experiment. Because of the positional error box and variability of the source, the unusual emission-line object and variable radio source SS 433 has been suggested as the optical counterpart. The X-ray luminosity of the source varied by a factor of about 2 on a time scale of 6 months, and the spectrum of the object is consistent with either a power law of photon index of 2.1 or with 14.3 KeV thermal bremsstrahlung emission with an about 575 eV equivalent-width iron line. These X-ray characteristics argue against the source being extragalactic, but do not uniquely identify the type of source. The measurements are consistent with emission from a white dwarf with 100 million gauss magnetic field, but are also similar to the X-ray emission sometimes seen from Cir X-1. A search has been made for X-ray emission from similar radio sources, but no new X-ray sources were detected. A previously known source, A1850+00, is a possible counterpart for one of these radio sources.
Marshall, F. E.↗
X-ray line emission from Capella
X-ray emission line components from Mg, Si, S and Fe were unambiguously detected from Capella with the Solid-State Spectrometer onboard the Einstein Observatory. The X-ray spectrum is inconsistent with an isothermal corona, and requires components between 6,000,000 K and at least 24,000,000 K for an adequate fit. An inhomogeneous corona in which the X-ray emitting plasma is confined to magnetically-contained loops appears to be reconcilable with all of the experimental evidence.
Holt, S. S.↗
The Einstein /HEAO 2/ X-ray Observatory
The Einstein (HEAO 2) X-ray Observatory, launched in 1978, includes a fully imaging focusing X-ray telescope with an angular resolution of a few arc sec, a field of view of up to one deg, and a sensitivity several hundred times greater than previously available in any X-ray astronomy experiment. A high-resolution imager, an imaging proportional counter, a focal plane crystal spectrometer, and a monitor proportional counter are among the principal instruments on board the Einstein X-ray Observatory. About 20% of the total effective observing time in the first year of the X-ray astronomy experiment has been reserved for guest observers.
Giacconi, R.↗
Long-term studies with the Ariel 5 ASM. 2: The strong Cygnus sources
The three bright 3-6 keV X-ray sources in Cygnus are examined for regular temporal variability with a 1300-day record from the Ariel 5 All Sky Monitor. The only periods consistently observed are 5.6 days for Cyg X-1, 11.23 days for Cyg X-2, and 4.8 hours for Cyg X-3.
Holt, S. S.↗
The X-ray spectrum of 3C 273
An X-ray spectral measurement of the quasar 3C 273 with the HEAO-A2 experiment in June/July 1978 is reported. The best power law fit to the photon flux over the range 2-60 keV gives a slope of 1.41 + or - 0.02. However, structure is observed, indicating a slope of 1.52 between 2 keV and 9 keV and a slight flattening between 9 keV and 30 keV. Observations with the same experiment in December 1977 and OSO-8 in June 1976 allows confirmation of 40% intensity variability on the time scale of months, although within limits provided by the poorer statistical quality of the additional data no spectral change is discerned. Absorption from the source is found to be low, with the 1978 data yielding a 90% confidence upper limit to the hydrogen column density of 4.5 x 10 to the 21st power atoms/sq cm.
Worrall, D. M.↗
A change in the X-ray spectrum of MK 421
HEAO-1 experiment A-2 observations of the BL Lac object MK421 in May 1978 show a marked spectral change from the OSO-8 observations of May 1977. The source was not detected above 10 keV in May 1978. The 2-10 keV spectrum could be well fit by a power law of energy slope 2.2 is less than or minus 4.2; thermal bremsstrahlung models with T less than 2 X 10 to the 7th power deg K are also acceptable. There was no indication of any low energy turnover, so that the inferred column density N sub H is less than 7 X 10 to the 21st power at/sq cm. The total flux is consistent with an extrapolation of the UV data from IUE, but the slope is not consistent with the UV slope. Possible models for the origin of the spectral transition are discussed.
Mushotzky, R. F.↗
X-ray observations of H1908+050 (=SS433?)
The X-ray source H1908+50 (=4U1908+05=A1909+4) was observed for three 6 day periods in 1977 and 1978 with the HEAO A-2 experiment. The unusual emission line object and variable radio source SS433 was suggested as the optical counterpart. The X-ray of the source varied by a factor of about 2 on a time scale of 6 months, and the spectrum of the object is consistent with either a power law of photon index of 2.1 or with 14.3 keV thermal bremsstrahlung emission with about 575 eV equivalent width iron line. These X-ray characteristics argue against the source being extragalactic. The measurements are consistent with emission from a white dwarf, but are also similar to the X-ray emission sometimes seen from Cir X-1. A search was made for X-ray emission from similar radio sources.
Marshall, F. E.↗
HEAO 1 observations of the X-ray pulsar 4U1626-67
Results of an observation of the 7-s pulsar 4U1626-67 with the A2 experiments on HEAO 1 are reported. The phase-averaged X-ray spectra which change radically as a function of pulse phase. Included in this spectral change is the sudden appearance and subsequent decay of a continuum or emission feature with a mean energy of 19 keV which contains about 1/2 the power in this spectral range. Pulse timing results include a new determination of the pulse period and a factor 8 reduction in the upper limit for the light travel time for orbital periods between 1 and 7 hours. The findings for this system are discussed and compared with the general nature of pulsar spectra.
Pravdo, S. H.↗
Observations of the transient X-ray source 4U0115+63
Results of HEAO-2 pointed observations and Ariel 5 All Sky Monitor observations of the X-ray transient 4U0115+63 are presented. The transient source pulses with a period of 3.6136 s + or - .0004 s, has a hard spectrum typical of an X-ray binary pulsar, and has a broad iron line emission feature. A discussion of the transient behavior is given and inferences are made concerning the nature of the X-ray source based on the pointed data.
Rose, L. A.↗
OSO 8 X-ray spectra of clusters of galaxies. II - Discussion
An observational description of X-ray clusters of galaxies is given based on OSO 8 X-ray results for spatially integrated spectra of 20 such clusters and various correlations obtained from these results. It is found from a correlation between temperature and velocity dispersion that the X-ray core radius should be less than the galaxy core radius or, alternatively, that the polytropic index is about 1.1 for most of the 20 clusters. Analysis of a correlation between temperature and emission integral yields evidence that more massive clusters accumulate a larger fraction of their mass as intracluster gas. Galaxy densities and optical morphology, as they correlate with X-ray properties, are reexamined for indications as to how mass injection by galaxies affects the density structure of the gas. The physical arguments used to derive iron abundances from observed equivalent widths of iron line features in X-ray spectra are critically evaluated, and the associated uncertainties in abundances derived in this manner are estimated to be quite large.
Smith, B. W.↗
X-ray spectra of X Persei
The GSFC cosmic X-ray spectroscopy experiment on OSO 8 observed X Per for 20 days during two observations in 1976 February and 1977 February. The spectrum of X Per varies in phase with its 13.9 minute period, hardening significantly at X-ray minimum. Unlike other X-ray binary pulsar spectra, those of X Per do not exhibit iron line emission or strong absorption features. Our data show no evidence for a 22 hour periodicity in the X-ray intensity of X Per. These results indicate that the X-ray emission from X Per may be originating from a neutron star in a low-density region far from the optically identified Be star.
Becker, R. H.↗