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A gamma-ray flare in NRAO 190

McGlynn, Thomas A., Hartman, Robert C., Bloom, Steven D., Aller, Margo, Aller, Hugh, Filippenko, Alexei V., Barth, Aaron J., Gear, Walter Kieran, Marscher, Alan P., Mattox, John R., Reich, W., Robson, E. I., Schramm, Jochen, Stevens, J. A., Terasranta, H., Tornikoski, M., Vestrand, W. Thomas, Wagner, Stefan and Heines, Anke 1997. A gamma-ray flare in NRAO 190. Astrophysical Journal 481 (2) , pp. 625-632. 10.1086/304068

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Abstract

We describe observations of the quasi-stellar object (QSO) NRAO 190 during a gamma-ray flare from 1994 August 9 to 1994 August 29. This QSO was serendipitously detected by the EGRET instrument on the Compton Gamma Ray Observatory in a gamma-ray flare with a luminosity at least 10 times that of its quiescent state. Optical, radio, and microwave data were obtained during or near the gamma-ray observations. The historical behavior of this object places it in the category of bright, flat-spectrum radio sources with strong optical variability that appear to form the largest class of non-Galactic high-energy gamma-ray sources. During the gamma-ray flare the source is observed with l(E > 100 MeV) = 8.4 ± 1.2 × 10-7 photons s-1 cm-2. A single power-law model gives a best-fit photon index of γ = -1.83 ± 0.14. Little evidence for major radio variability is seen during the flare or immediately afterward, although there is some increase in the 10-100 GHz flux over the next several months. There may be a slight hardening of the radio spectrum. In the optical region there are significant fluctuations on timescales of 1 day or less, although the overall optical luminosity is within the range of previous measurements. Optical observations a few weeks after the gamma-ray observations show a drop of about 60% and reduced variability. A contemporary optical spectrum shows that the source may be slightly harder than seen in a previously published spectrum. Radio monitoring of the source over the year subsequent to the flare has shown a very substantial drop in the flux at many frequencies.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Uncontrolled Keywords: gamma rays: observations; quasars: individual (NRAO 190)
Publisher: Institute of Physics Science
ISSN: 0004-637X
Last Modified: 04 Jun 2017 04:17
URI: http://orca.cf.ac.uk/id/eprint/36006

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