Scanning Modulation Collimator Research Articles

Position and Variability of 2A 1704+241

ABSTRACTWe present results of analyses of observations of the X‐ray source 2A 1704+241 with the ROSAT Position Sensitive Proportional Counter (PSPC) and the High Resolution Imager (HRI). The source 2A 1704+241 was first associated with the M giant star HD 154791 based on observations with the HEAO 1 scanning modulation collimator and the Einstein IPC and analysis of a spectrum of HD 154791 obtained with the International Ultraviolet Explorer. This identification was unusual because there are few bright X‐ray binaries associated with an M giant star. We observed 2A 1704+241 with the PSPC and the HRI in order to determine more accurately the position of the X‐ray source and in order to study the previously seen 900 s variability in the Einstein data. Based on the previous identification and determination of the position of MS 1703.7+2417, an active galactic nucleus in the field, and the position of three previously unreported X‐ray sources that we have associated with stars in the USNO‐A2.0 catalog, we have greatly reduced the X‐ray positional error of 2A 1704+241. HD 154791 remains the prime candidate as the optical counterpart of the X‐ray source. While the 50% modulation in the X‐ray flux seen by the Einstein IPC is apparent in the ROSAT data, it appears to be at a slightly different frequency.

Changes in the Long‐Term Intensity Variations in Cygnus X‐2 and LMC X‐3

We report the detection of changes in the long-term intensity variations in two X-ray binaries, Cyg X-2 and LMC X-3. In this work, we have used the long-term light curves obtained with the All-Sky Monitors (ASMs) of the Rossi X-Ray Timing Explorer (RXTE), Ginga, Ariel 5, and Vela 5B and the scanning modulation collimator of HEAO 1. It is found that in the light curves of both the sources, obtained with these instruments at various times over the last 30 years, more than one periodic or quasi-periodic component is always present. The multiple prominent peaks in the periodograms have frequencies unrelated to each other. In Cyg X-2, RXTE-ASM data show strong peaks at 40.4 and 68.8 days, and Ginga-ASM data show strong peaks at 53.7 and 61.3 days. Multiple peaks are also observed in LMC X-3. The various strong peaks in the periodograms of LMC X-3 appear at 104, 169, and 216 days (observed with RXTE-ASM) and 105, 214, and 328 days (observed with Ginga-ASM). The present results, when compared with the earlier observations of periodicities in these two systems, demonstrate the absence of any stable long period. The 78 day periodicity detected earlier in Cyg X-2 was probably due to the short time base in the RXTE data that were used, and the periodicity of 198 days in LMC X-3 was due to a relatively short duration of observation with HEAO 1.

Two X-ray-selected BL Lacertae objects observed with the HEAO 1 scanning modulation collimator

Two 16th magnitude BL Lac objects, H1101 - 232 and H1426 + 428, have been discovered. Each is a persistent and relatively bright X-ray source. A 2.7 percent linear polarization is measured in the optical emission or H101 - 232. The X-ray identification of H1426 + 428 is confirmed in an Exosat observation. The X-ray spectrum is well-modeled by a power law with an energy index of 1.19. Both BL Lac objects exhibit high f(x)/f(opt) ratios and they show a distinct resemblance to other X-ray selected BL Lac objects. The host galaxies are about 18th mag with angular diameters of about 20 arcsec and each may be the dominant member of a cluster of galaxies. Additional wide-slit spectroscopy reveals faint absorption features with redshifts of 0.129 for H1426 + 428 and 0.186 for H1101 - 232. The implied X-ray and optical luminosities exceed 10 to the 45th ergs/s for both BL Lac nuclei, assuming isotropic emission.

A scanning modulation collimator observation of the high-energy X-ray source in the Crab Nebula

Two-dimensional maps of the 22-64 keV emission from the Crab Nebula with an angular resolution of 15 arcsec has been synthesized. The maps are generated by application of a maximum entropy method operating on a series of one-dimensional scans obtained with a balloon-borne modulation collimator telescope. The two-dimensional size, shape and orientation of the hard X-ray nebula relative to the pulsar have been measured for the first time. The implications of these results for models of electron transport in the Crab are discussed, and the geometry of the observed X-ray nebula is related to other features of the Crab Nebula system.

Discovery of three new RS Canum Venaticorum-like counterparts to HEAO I X-ray sources

The identification of three high-latitude HEAO I Scanning Modulation Collimator X-ray sources with the chromospherically active RS CVn-like stars HD 113816, HD 146413, and HD 39576 is reported. Optical observations, including coude spectroscopy and broad-band and narrow band photoelectric photometry are presented. The Ca II emission strength of all three stars shows that they are chromospherically active. HD 146413 and HD 39576 exhibit variable X-ray emission in the 1-13 keV energy range, while HD 113816 is a softer and steadier source. The level of X-ray flux detected from these three stars is some one to two orders of magnitude higher than predicted empirically from the Ca II emission fluxes. It is proposed that this emission results from flarelike activity.

A VLA survey of unidentified HEAO-1 X-ray sources

view Abstract Citations (7) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A VLA survey of unidentified HEAO-1 X-ray sources. Schmelz, J. T. ; Feigelson, E. D. ; Schwartz, D. A. Abstract The authors have employed a new technique to uncover candidates for unidentified bright X-ray sources where traditional methods have proved unsuccessful. The C configuration VLA was used at 20 cm to search for 47 unidentified sources detected in the HEAO-1 all-sky X-ray survey. Approximate pointing positions were obtained by superimposing the large error boxes from the NRL experiment and the grid of small diamonds from the Scanning Modulation Collimator. Radio maps of the 30arcmin primary beam were made and 238 radio sources (with flux densities as small as 1 - 3 mJy) were detected in or near the diamond-shaped error boxes. A search was made for the associated optical objects on POSS prints, and tentative classifications of the resulting radio/optical candidates were made. The candidate X-ray identifications include five possible RS CVn systems, three active galactic nuclei, three galaxy or cluster sources, and two X-ray binaries. Publication: The Astronomical Journal Pub Date: September 1986 DOI: 10.1086/114188 Bibcode: 1986AJ.....92..585S Keywords: Astronomical Spectroscopy; Radio Astronomy; Spaceborne Astronomy; X Ray Sources; Active Galactic Nuclei; Binary Stars; Bl Lacertae Objects; Cataclysmic Variables; Centimeter Waves; Heao 1; Seyfert Galaxies; Visible Spectrum; Astrophysics full text sources ADS | data products SIMBAD (47) NED (4)

The discovery of eight bright active galactic nuclei observed with the HEAO 1 scanning modulation collimator

The eight 14th- and 15th-magnitude active galactic nuclei (AGNs) considered include one QSO and seven type 1 Seyferts; all were discovered in the course of a systematic program for the identification of the fainter X-ray sources of the HEAO 1 survey. While the X-ray and optical luminosities, and many of the optical emission features of the AGNs resemble other bright Seyfert 1s nearby, three of the galaxies exhibit very strong Fe II emission, and two show very weak forbidden line spectra. Photometric magnitudes and selected emission line intensities are given for each of the AGNs.

Identification of two hard X-ray emitting Be stars using the HEAO 1 scanning modulation collimator

view Abstract Citations (27) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Identification of two hard X-ray emitting Be stars using the HEAO 1 scanning modulation collimator. Steiner, J. E. ; Ferrara, A. ; Garcia, M. ; Patterson, J. ; Schwartz, D. A. ; Warwick, R. S. ; Watson, M. G. ; McClintock, J. E. Abstract Using precise positions from the HEAO 1 Scanning Modulation Collimator experiment, two hard X-ray sources, 4U 0728 - 25 = 3A 0726 - 260 and 4U 2206 + 54 = 3A 2206 + 543, are identified with early-type stars. In both cases broad (10 A FWHM) H-alpha emission is detected. The UBV colors suggest that the optical counterparts are main-sequence B0-B2 stars at 2-6 kpc, implying a mean X-ray luminosity of order 10 to the 35th ergs/sq cm s (2-10 keV). The X-ray emission in both cases is highly variable, and it is suggested that they belong to the class of X-ray emitting Be stars, containing a neutron star in a widely separated binary system. Publication: The Astrophysical Journal Pub Date: May 1984 DOI: 10.1086/162042 Bibcode: 1984ApJ...280..688S Keywords: B Stars; Variable Stars; X Ray Sources; X Ray Stars; Collimators; Heao 1; Stellar Spectra; Astrophysics full text sources ADS | data products SIMBAD (2)

Evidence for a Black Hole in LMC X-3

The best X-ray position (Einstein Observatory HRI - Giacconi et al 1979) for LMC X-3 confirms its identification with the early type star first suggested by Warren and Penfold (1975). Our spectroscopic observations obtained with the CTIO 4–m telescope show the WP star is a slightly reddened B3 V star with mV ≈ 16.9. Large radial velocity variations (Δv ≈ 500 km s−1) reveal an orbital period of 1.7049 days. From the orbital elements (Table 1) one can determine the mass function f(M) = (Mx sin i)3/(Mopt + Mx)2 = 2.3 M⊙, which shows without any assumptions about the mass of the optical star, the orbital inclination, or the mass ratio the unseen X-ray object has a mass >2.3 M⊙. Detailed analysis of the HEAO–1 scanning modulation collimator X-ray data shows that the system does not eclipse, implying that the orbital inclination is ≤ 65°. Assuming the B star mass lies between 4 and 8 M⊙ (an average mass for a normal B3 V star would be about 6–7 M⊙), the mass of the unseen companion must lie between 7 and 13 M⊙ (see Fig. 4a - Hutchings, this volume). Smaller inclinations of course give even higher masses. An important point is that the unseen star must have a mass larger than that of the B star, and thus if it were any kind of normal star it should be easily seen in the spectrum. Thus the X-ray emitting object is a very good candidate for a black hole.

Identification and properties of the M giant/X-ray system HD 154791 = 2A 1704+241

The Aerial V X-ray source 2A 1704+241 (= 4U 1700+24 = 3A 1703+241) is identified with the M3 II star HD 154791. The identification is based on a precise X-ray position determined by the HEAO 1 scanning modulation collimator and the Einstein Observatory imaging proportional counter, together with a spectrum measured by the International Ultraviolet Explorer. The ultraviolet spectrum shows strong emission of C IV 1550 A, N v 1238 A, and Mg II 2800 A, which is very unusual among M giants. This is the first X-ray detection of an M giant which has a completely normal optical spectrum. The X-ray luminosity reaches three orders of magnitude above the mean upper limit for the coronal X-ray flux from M giants. Although there is no direct evidence for a binary system, since radial velocity variations have not been observed, it is shown that a plausible neutron star binary model can be constructed.

H0323 + 022 - A puzzling high-latitude X-ray/optical/radio source

view Abstract Citations (52) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS H 0323+022 : a puzzling high-latitude X-ray/optical/radio source. Doxsey, R. ; Bradt, H. ; McClintock, J. ; Petro, L. ; Remillard, R. ; Ricker, G. ; Schwartz, D. ; Wood, K. Abstract A flaring X-ray source, H0323+022, has been located at high galactic latitude (b = -42°) with the scanning modulation collimator on HEAO 1 and identified with a V = 16.5 ultraviolet-excess object. The counterpart has been observed on two occasions to have zero redshift absorption lines characteristic of an F or G star in the range 3800-7300 Å, but on at least five other occasions, these features have been absent. The object also has a large infrared flux indicating a multicomponent source. Observations with the Einstein Observatory indicate that the X-ray source has two components, a steady, soft component and a variable, hard component which exhibited a pronounced 60 s dip as well as flaring activity on time scales down to 6 hours. The source has also been detected at 5 GHz with a flux density of 41 ± 1 mJy by Feigelson, Giommi, and Maccacaro. Publication: The Astrophysical Journal Pub Date: January 1983 DOI: 10.1086/183941 Bibcode: 1983ApJ...264L..43D Keywords: Radio Sources (Astronomy); Spaceborne Astronomy; Ubv Spectra; Visible Spectrum; X Ray Sources; Absorption Spectra; Collimators; Heao 1; Infrared Astronomy; Radiant Flux Density; Stellar Spectrophotometry; Ultraviolet Astronomy; Astrophysics full text sources ADS | data products SIMBAD (1) NED (1)

The Ophiuchus cluster - A bright X-ray cluster of galaxies at low galactic latitude

The discovery of an extended X-ray source identified with a cluster of galaxies at low galactic latitude is reported. The source, designated the Ophiuchus cluster, was detected near 4U 1708-23 with the HEAO 1 Scanning Modulation Collimator, and identified with the cluster on the basis of extended X-ray size and positional coincidence on the ESO/SRC (J) plate of the region. An X-ray flux density in the region 2-10 keV of approximately 25 microJ was measured, along with an X-ray luminosity of 1.6 x 10 to the 45th ergs/sec and an X-ray core radius of approximately 4 arcmin (0.2 Mpc) for an assumed isothermal sphere surface brightness distribution. The X-ray spectrum in the range 2-10 keV obtained with the HEAO 1 A-2 instrument is well fit by a thermal bremsstrahlung model with kT = 8 keV and a 6.7-keV iron line of equivalent width 450 eV. The steep-spectrum radio source MSH 17-203 also appears to be associated with the cluster, which is the closest and brightest representative of the class of X-ray clusters with a dominant central galaxy.

The optical identification of H2252 - 035 with a cataclysmic variable

An improved position is presented for the X-ray source H2252-033 using the Ariel V Sky Survey Instrument, and precise positioning using the Scanning Modulation Collimator on HEAO-1. The source is identified optically with a 13th magnitude emission-line object, which is probably a white dwarf binary with a well formed accretion disk, with similarities to the dwarf novae (e.g., SS Cyg) at minimum.

Unidentified galactic X-ray sources positioned with the HEAO-1 scanning modulation collimator

Observations made with the HEAO-1 scanning modulation collimator are used to determine the positions of 16 unidentified X-ray sources at low galactic latitudes. Positions were obtained to within 10-30 arcsec in one dimension from two four-grid collimator observations made at six-month intervals. Positions determined in addition for eight sources identified with optical objects verify the method employed. Of the unidentified sources, the positional uncertainties of ten are reduced by factors of two to eight, the precise X-ray positions (within 10 arcsec) obtained by lunar occultation experiments are confirmed for three and multiple precise positions (within 20 arcsec) which reduce the previous location uncertainties by factors of greater than 100 are obtained for the remaining three.

Optical identification of 4U1907 + 09 using the HEAO-1 scanning modulation collimator position

The paper reports an optical identification of 4U1907 + 09 with a m(v) = 16.4 stellar object in the location determined by the scanning modulation collimator experiment on the first High Energy Astronomy Observatory (HEAO-1). The identification is based on the presence of very strong and broad H-alpha emission. The optical data constrain the distance to be 2-13 kpc, and this gives a range of uncertainty to the typical 2-10 keV luminosity of (1 x 10 to the 35th to 3 x 10 to the 36th) erg/s. The X-ray spectrum and variability is reported, and consideration is given to the hypothesis that the object is an OB supergiant, although its faintness in the blue makes precise spectral classification impossible. It is suggested that this system is an example of a luminous, massive primary emitting a stellar wind which is accreted on the compact object.

Erratum - a 6-MONTH X-Ray Survey of the Large Magellanic Cloud with the HEAO-1 Scanning Modulation Collimator

Erratum - a 6-MONTH X-Ray Survey of the Large Magellanic Cloud with the HEAO-1 Scanning Modulation Collimator

Study of the structure of the TYCHO SNR with the HEAO 1 scanning modulation collimator experiment

The Tycho SNR was observed with the scanning modulation collimator experiment on board the HEAO 1 satellite. A soft extended source was detected. The extended X-ray source is best fitted with a thin spherical shell model of approximately 3.8 arc minute radius. The presence of a brighter, less extended structure in the western side of the remnant is suggested by our data.

Seyfert Type 1 galaxies observed with the HEAO 1 scanning modulation collimator

The paper deals with the detection of 16 X-ray sources (1.5 to 13.5 keV) during pointed observations with the HEAO 1 satellite of 19 Seyfert Type 1 (Sy 1) galaxies. For 15 sources, the Sy 1 galaxy nucleus, previously proposed as the X-ray source counterpart, lies within one of the 1 to 5 square arcmin uncertainty regions determined with the HEAO 1 modulation collimator experiment.

Recent X-Ray Observations of Seyferts and Emission-Line Galaxies

It has been just a few years since Type 1 Seyferts were established as a class of X-ray sources with luminosities in the range 1042 - 1045 ergs s-1 by Elvis et al. (1978) using data from the sky survey instrument on Ariel V, and by Tananbaum et al. (1978) using data from UHURU.The average error-box sizes for X-ray sources identified with Type 1 Seyferts in the 2A catalog (Cooke et al. 1978) is ˜ 0.4 sq. degrees, and ˜ 1.0 sq. degrees for those in the 4U catalog (Forman et al. 1978). Improvement in these positions has been made over the past two years by the modulation collimators on board the satellites SAS-3 and HEAO-1. In particular, the HEAO-1 scanning modulation collimator has been used to position a total of 20 X-ray sources, confirming the identification in each case, with the possible exception of Mkn 279 (Dower et al. 1979, Griffiths et al. 1979a). Of the 37 X-ray sources which were discovered prior to the launch of the Einstein Observatory and which have been associated with Type 1 Seyferts, 21 have been positioned to ˜ 1 arc minute, representing an improvement by factors of ˜ 20 to 100 over the previous 2A and 4U error box sizes. Some examples of the error boxes and identifications confirmed with the HEAO-1 scanning modulation collimator are shown in figs. 1 and 2. In fig. 1 both NGC 7213 (Philips 1979) and MCG - 2 - 58 - 22 (Ward et al. 1978) were discovered to be Seyferts by optical spectroscopy of candidate objects in the error regions of the corresponding X-ray sources. NGC 7213 is a Seyfert nucleus in a galaxy of Type SO (Philips 1979). In fig. 2, NGC 931 was likewise discovered to be a Seyfert as a result of its X-ray emission (Ward and Wilson 1978).

Optical and X-ray properties of the newly discovered BL Lacertae object PKS 2155-304 /= H2155-304/

The soft X-ray source H 2155-304 has been precisely located with the HEAO 1 scanning modulation collimator, and identified with an object of bolometric magnitude approximately 14. The linear polarization, variability, spectrum, and diffuse image of the optical flux, together with the positional coincidence of the radio source PKS 2155-304, indicate that this object is a new member of the BL Lacertae class. Its characteristics are compared with those of other X-ray-emitting BL Lacertae objects, particularly Mrk 421.