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 ORCID: https://orcid.org/0000-0001-6789-6196, 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:	21 Oct 2022 09:19
URI:	https://orca.cardiff.ac.uk/id/eprint/36006

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