Th. Boller

Publications (7)12.05 Total impact

• Article: An X-Ray-Luminous, Dwarf Seyfert Companion of Markarian 273

  X.-Y. Xia, Th. Boller, H. Wu, Z.-G. Deng, Y. Gao, Z.-L. Zou, S. Mao, and G. Börner
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  ABSTRACT: We report the discovery of the brightest X-ray source hosted by a faint (MB=-16) dwarf galaxy in the immediate vicinity of the ultraluminous IRAS merging galaxy Markarian 273. The dwarf galaxy, 13 away from Mrk 273, is at the tip of a faint northeast plume of Mrk 273. Its spectrum exhibits strong [O III], Hα, and [N II] emission lines, which establish the redshift of the dwarf galaxy, z=0.0376, the same as that of Mrk 273. The emission-line ratios are typical of Seyfert galaxies. The X-ray emission is consistent with a pointlike source coincident with the center of the dwarf galaxy. The intrinsic X-ray luminosity, 6.3×1041 ergs s−1, in the 0.1-2.4 keV energy range, is about 7 times larger than the B-band luminosity. The X-ray spectrum of the source can be fitted with a power law. All the evidence is consistent with the source being a Seyfert galaxy. Out of ~10 faint objects in the same field, only one is detected by ROSAT, and its ratio of soft X-ray to optical luminosity is as high as those for BL Lacertae objects and few active galactic nuclei (AGNs). If there is a population of such dwarf AGNs hidden as companions of major merger galaxies (such as Mrk 273), they may contribute to the luminosity function of AGNs and the cosmic X-ray background at the faint end.
  The Astrophysical Journal 01/2009; 496(1):L9. · 6.02 Impact Factor
• Source

  Available from: arxiv.org

  Article: Chandra Observations of MRK 273: Unveiling the Central AGN and the Extended Hot Gas Halo

  X. Y. Xia, S. J. Xue, S Mao, Th. Boller, Z. G. Deng, H Wu
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  ABSTRACT: We report X-ray observations of the field containing the ultraluminous IRAS galaxy Mrk~273 Using the ACIS-S3 instrument on board Chandra. The high resolution X-ray image, for the first time, reveals a compact hard X-ray nucleus in Mrk~273. Its X-ray energy distribution is well described by a heavily obscured power-law spectrum plus a narrow $\Feka$ emission line at 6.4 keV. The neutral hydrogen column density is about $4\times10^{23}\cm^{-2}$, implying an absorption -corrected X-ray luminosity (0.1--10 keV) for the nucleus of $\Lx\approx 6.5\times 10^{43} \ergs$. There are also bright soft X-ray clumps and diffuse soft X-ray emissions surrounding the central hard X-ray nucleus within the $10\arcsec$ of the nuclear region. Its spectrum can be fitted by a MEKAL thermal model with temperature of about 0.8 keV and high metallicity ($Z\sim 1.5Z_\odot$) plus emission lines from $\alpha$ elements and ions. Further outside the central region, the Chandra observations reveal a very extended hot gas halo with a projected diameter of about $108 \kpc\times 68 \kpc$ and soft X-ray luminosity of $\Lx\approx 1.9\times 10^{41} \ergs$. The temperature of the hot gas is about 0.62 keV with a low metallicity ($Z \sim 0.1 Z_\odot$). We discuss the nature of the AGN in Mrk~273 and the implications of our results on the origin of X-ray halos in elliptical galaxies. We also discuss the properties of Mrk~273x, a background AGN in the Mrk~273 field. The AGN has an X-ray luminosity of $\Lx \approx 2.43\times 10^{44}\ergs$ in the 0.5-10 keV band. Its X-ray properties resemble those of Seyfert 1 galaxies while its optical properties are similar to Seyfert 2 galaxies. Such mixed classifications may be a challenge for the unification scheme of AGNs. Comment: 23 pages, 11 figures. ApJ accepted, minor revised version
  07/2001;
• Source

  Available from: arxiv.org

  Article: Soft X-ray Properties of ULIRGs Based on a Large and Complete Sample

  X. Y. Xia, Th. Boller, Z. G. Deng, G. Borner
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  ABSTRACT: We report on the results of the cross-correlation of a sample of 903 Ultraluminous IRAS galaxies (ULIRGs) with the ROSAT-All Sky Survey Bright Source Catalogue and the ROSAT archived pointing observations. The sample of ULIRGs has been compiled from the PSCz redshift survey. In total, 35 ULIRGs are securely detected by the ROSAT All-Sky Survey and pointing observations, five of which are blazars. The statistical properties of these sources in the soft X-ray band are determined and compared with their properties in other wavebands. We find that the ratio of the soft X-ray to the far-infrared flux spans about 5 orders of magnitude and reaches values of about unity. This ratio is a good indicator of the main energy source of ULIRGs. Those with soft X-ray to far-infrared flux exceeding 0.01 are probably powered by accretion onto central supermassive black holes while those with ratios smaller than 0.001 are probably caused by starbursts or other heating processes, or are Compton thick sources. Some ULIRGs have energy contributions from both. This ratio is low for most ULIRGs and hyperluminous infrared galaxies, which explains their low detection rate by ROSAT and ASCA. We also find that some ULIRGs have a similar soft X-ray luminosity vs. temperature relation to that for groups of galaxies and elliptical galaxies, suggesting a common origin of these systems. Our study also reveals a correlation between the hardness ratio and the soft X-ray luminosity for Seyfert 1s/QSOs.
  04/2001;
• Source

  Available from: Shude Mao

  Article: Ultraluminous IRAS galaxy 10026+4347

  X. Y. Xia, Shude Mao, H Wu, Z Zheng, Th. Boller, Z. G. Deng, Z. -L. Zou
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  ABSTRACT: We study optical and X-ray properties of the ultraluminous IRAS galaxy 10026+4347. This galaxy is a narrow-line QSO with very strong FeII emission. Three optical spectra were taken over two years. The full widths at half maximum (FWHMs) of the emission lines are constant whereas the third spectrum seems to show a continuum change. Intermediate-band photometry also shows a small (0.1 mag) but significant decrease in flux. HST WFPC2 images suggest that this object is a post-merger galaxy. The source is X-ray luminous (L_x ~ 10^45 erg/s) with a very soft X-ray spectrum (photon index ~ 3.2) The X-ray luminosity exhibits variabilities of a factor of ~8 over four years and a factor of two within two days. During these X-ray flux changes, the X-ray spectral shapes are consistent with no variation. All the optical and X-ray properties resemble those of narrow-line Seyfert 1 galaxies, except that the FWHM of Hbeta is about 2500 km/s, larger than that for most NLS1s. We discuss the implications of our results on models of NLS1s.
  12/1998;
• Article: An X-Ray Luminous, Dwarf Seyfert Companion of Markarian 273 (ApJ, 496, L9 [1998])

  X.-Y. Xia, Th. Boller, H. Wu, Z.-G. Deng, Y. Gao, Z.-L. Zou, S. Mao, G. Börner
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  ABSTRACT: In the Letter ``An X-Ray Luminous, Dwarf Seyfert Companion of Markarian 273'' by X.-Y. Xia, Th. Boller, H. Wu, Z.-G. Deng, Y. Gao, Z.-L. Zou, S. Mao, and G. Börner (ApJ, 496, L9 [1998]), an observational error occurred that invalidates some of our conclusions. Since Mrk 273x was essentially invisible (B~21) in our acqusition image, in order to position the slit on the faint Mrk 273x, a slit rotation had to be applied. Unfortunately, the amount of rotation was applied incorrectly. As a result, the spectrum obtained (shown in Fig. 2) was not for the intended target, Mrk 273x, but for an object very close to, but northeast of, Mrk 273. A new spectrum of Mrk 273x indicates that Mrk 273x is at redshift 0.458, not at 0.0378 as quoted in the Letter. The larger redshift implies that both the optical and X-ray luminosity have to be revised upward by a factor of ~170. Mrk 273x is therefore not a dwarf galaxy optically. The X-ray properties of Mrk 273x remain the same except that its soft X-ray luminosity now reaches ~10^44 ergs s^-1 for H_0=50 km s^-1 Mpc^-1. The new observations will be presented in a subsequent paper (X.-Y. Xia et al., in preparation [1998]) in order to make corrections and shed further insights on the objects in the Mrk 273 field.
  The Astrophysical Journal 10/1998; 507:L99-L99. · 6.02 Impact Factor
• Source

  Available from: Yu Gao

  Article: An X-ray Luminous, Dwarf Seyfert Companion of Mrk 273

  X. Y. Xia, Th. Boller, H Wu, Z. G. Deng, Y Gao, Z. -L. Zou, Shude Mao, G. Borner
  [show abstract] [hide abstract]
  ABSTRACT: We report the discovery of the brightest X-ray source hosted by a faint (M_B=-16) dwarf galaxy in the immediate vicinity of the ultraluminous IRAS merging galaxy Mrk 273. The dwarf galaxy, 1.3 arcmin away from Mrk 273, is at the tip of a faint northeast plume of Mrk 273. Its spectrum exhibits strong [OIII], Halpha, [NII] emission lines, which establish the redshift of the dwarf galaxy, $z=0.0376$, the same as that of Mrk 273. The emission line ratios are typical of Seyfert galaxies. The X-ray emission is consistent with a point-like source coincident with the center of the dwarf galaxy. The intrinsic X-ray luminosity, 6.3x10^{41} ergs, in the 0.1--2.4 keV energy range, is about seven times larger than the B band luminosity. The X-ray spectrum of the source can be fit with a power-law. All the evidence is consistent with the source being a Seyfert galaxy. It is mysterious why out of $\sim 10$ faint objects in the same field only one is detected by ROSAT and its ratio of soft X-ray to optical luminosity is as high as those for BL Lac objects and few active galactic nuclei (AGNs). If there is a population of such dwarf AGNs hidden as companions of major merger galaxies (such as Mrk 273), they may contribute to the luminosity function of AGNs and the cosmic X-ray background at the faint end. Comment: 15 pages, 2 figures, ApJ Letters, in press
  01/1998;
• Source

  Available from: articles.adsabs.harvard.edu

  Article: An Ultraluminous IRAS Galaxy with an Extremely Soft X-Ray Spectrum

  X. Y. Xia, Th. Boller, Z. G. Deng
  113:434.