The X-ray structure and spectrum of NGC 6251
1993; IOP Publishing; Volume: 412; Linguagem: Inglês
10.1086/172944
ISSN1538-4357
Autores Tópico(s)Stellar, planetary, and galactic studies
Resumoview Abstract Citations (85) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The X-Ray Structure and Spectrum of NGC 6251 Birkinshaw, M. ; Worrall, D. M. Abstract NGC 6251 has been observed in low-energy X-rays with the Position Sensitive Proportional Counter on board ROSAT. No X-ray emission is seen from the 4.5' long radio jet of this galaxy, suggesting that the electron spectrum is cut off for electron energies greater than E_max_~10^12^ eV, but a bright X-ray source is coincident with the center of the galaxy. Most of the counts in this source are in a component of small angular size, FWHM < 4", corresponding to a linear size less than 3 kpc, although there is evidence for the presence of a low surface brightness halo with FWHM ~3'. If this halo is thermal bremsstrahlung of gas near NGC 6251, this gas cannot confine the arcminute-scale radio jet by simple (static) gas pressure. The spectrum of the X-ray core source in NGC 6251 is a bad match to a single-component thermal model and, when fitted by a simple power-law model, requires the presence of an absorbing column far in excess of the Galactic or intrinsic columns. The nuclear spectrum can be well fitted by a composite model with two (or more) different components: a plausible decomposition consists of a flat-spectrum (energy index α_X_ ~0.27) power-law component from a mini-active galactic nucleus (AGN) plus an 0.5 keV thermal component. The power-law spectral index is close to the high- frequency radio spectral index of the VLBI core, supporting a synchro- self-Compton model for this component of the X-ray emission. The temperature of the thermal component is characteristic of the temperatures of gas found in other elliptical galaxies, and the gas must be in a cooling flow. The infall of material into the nucleus is sufficiently rapid to power the mini-AGN component, if the mass of the central black hole exceeds 5 x 10^4^ M_sun_. Unification schemes that relate BL Lac objects and radio galaxies (e.g., Padovani & Urry 1990) require a component of unbeamed X-ray emission: it is possible that the type of thermal gas that we find in NGC 6251 may produce the necessary unbeamed X-ray component. Publication: The Astrophysical Journal Pub Date: August 1993 DOI: 10.1086/172944 Bibcode: 1993ApJ...412..568B Keywords: Astronomical Spectroscopy; Galactic Nuclei; Radio Jets (Astronomy); X Ray Sources; Emission Spectra; Galactic Radiation; Proportional Counters; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 6251; GALAXIES: JETS; GALAXIES: NUCLEI; RADIATION MECHANISMS: MISCELLANEOUS; X-RAYS: GALAXIES full text sources ADS | data products SIMBAD (7) NED (1) HEASARC (1)
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