COMPTEL observations of the quasar PKS 0528+134 during the first 3.5 years of the CGRO mission

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dc.creatorCollmar, W.
dc.creatorBennett, K.
dc.creatorBloemen, H.
dc.creatorBlom, J. J.
dc.creatorHermsen, W.
dc.creatorLichti, G.
dc.creatorPohl, M.
dc.creatorRyan, J.
dc.creatorSchoenfelder, V.
dc.creatorStacy, J. G.
dc.creatorSteinle, H.
dc.creatorWilliams, O. R.
dc.date1997-11-18
dc.date.accessioned2026-07-07T02:25:09Z
dc.date.available2026-07-07T02:25:09Z
dc.descriptionThe COMPTEL observations of the blazar-type quasar PKS 0528+134 in the energy range 0.75 MeV to 30 MeV carried out between April 1991 and September 1994 have been analyzed. During the first two years PKS 0528+134 was most significantly detected at energies above 3 MeV. During the last year there is only evidence for the quasar at energies below 3 MeV indicating a spectral change. The time-averaged COMPTEL energy spectrum between 0.75 MeV and 30 MeV is well represented by a power-law shape. Spectra collected from different observational periods reveal different power-law shapes: a hard state during flaring observations reported by EGRET, and a soft state otherwise. The combined simultaneous EGRET and COMPTEL spectra indicate these two spectral states as well. During low intensisty gamma-ray phases no spectral break is obvious from the combined COMPTEL and EGRET measurements. For the gamma-ray flaring phases however, the combined COMPTEL and EGRET data require a spectral bending at MeV-energies. By fitting broken power-law functions the best-fit values for the break in photon index range between 0.6 and 1.7, and for the break energy between ~5 MeV and ~20 MeV. Because the flux values measured by COMPTEL below 3 MeV in both states are roughly equal, the observations would be consistent with an additional spectral component showing up during gamma-ray flaring phases of PKS 0528+134. Such a component could be introduced by e.g. a high-energy electron-positron population with a low-energy cutoff in their bulk Lorentz factor distribution. The multiwavelength spectrum of PKS 0528+134 for gamma-ray flaring phases shows that the major energy release across the entire electro-magnetic spectrum is measured at MeV-energies.
dc.description10 pages, 8 postscript figures, latex, to appear in: A&A 328, 33 (1997)
dc.identifierhttps://arxiv.org/abs/astro-ph/9711198
dc.identifierhttp://arxiv.org/abs/astro-ph/9711198
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/11819
dc.subjectAstrophysics
dc.titleCOMPTEL observations of the quasar PKS 0528+134 during the first 3.5 years of the CGRO mission
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