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Observations of a Correlated Gamma-Ray and Optical Flare for BL Lacertae

S. D. BloomNAS/NRC Resident Research AssociateD. L. BertschNASA Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Code 661, Greenbelt, MD 20771R. C. HartmanNASA Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Code 661, Greenbelt, MD 20771P. SreekumarNASA Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Code 661, Greenbelt, MD 20771D. J. ThompsonNASA Goddard Space Flight Center, Laboratory for High Energy Astrophysics, Code 661, Greenbelt, MD 20771T. J. BalonekDepartment of Physics and Astronomy, Colgate University, Hamilton, NY 13346-1398Eli BeckermanDepartment of Physics and Astronomy, Colgate University, Hamilton, NY 13346-1398Scott DavisDepartment of Physics and Astronomy, Colgate University, Hamilton, NY 13346-1398Kathryn WhitmanDepartment of Physics and Astronomy, Colgate University, Hamilton, NY 13346-1398H. R. MillerDepartment of Physics and Astronomy, Georgia State University, Atlanta, GA 30303A. D. NairDepartment of Physics and Astronomy, Georgia State University, Atlanta, GA 30303Lewis C. RobertsDepartment of Physics and Astronomy, Georgia State University, Atlanta, GA 30303G. TostiCattedra di Astrofisica, Universitá di Perugia, via A. Pascoli, I-06100 Perugia, ItalyE. MassaroR. NesciM. MaesanoF. MontagniMiran JangDepartment of Astronomy and Space Science, Kyung Hee University, Yongin, Kyungki-Do, 449-701, KoreaH. BockM. DietrichM. HerterK. OtterbeinM. PfeifferT. SeitzS. Wagner

1997en

ABI

Annotatsiya

BL Lacertae was detected by the EGRET instrument on CGRO at the 10.2 σ level with an average flux of 171 ± 42 × 10 −8 photons cm −2 s −1 at energies&gt; 100 MeV during the optical outburst of 1997 July. This flux is more than 4 times the previously highest level. Within the July 15-22 observation there was a dramatic factor of 2.5 increase in the gamma-ray flux on July 18.75–19.08, apparently preceding by several hours a brief optical flare. The gamma-ray flux decreased to its previous level within 8 hrs and the optical flux decreased to its prior level in less than 2 hrs. The gamma-ray photon spectral index of 1.68 ±0.12 indicates that the spectrum during the 7-day observation was harder than the previous detection. Subject headings: Gamma Rays: observations — galaxies: active — BL Lacertae

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DOI: 10.1086/311035

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