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From: starrfie@hydro.la.asu.edu (Sumner Starrfield) Subject: [active_stars agn Be bright cv extragalactic lmxb novae] Repeating Gamma Ray Bur (fwd) Date: Tue, 5 Oct 93 13:27:35 MST Forwarded message: >From robinson@astro.psu.edu Tue Oct 5 12:36:09 1993 Date: Tue, 5 Oct 93 15:20:07 EDT Message-ID: <vsnet-history1598@hoge.baba.hajime.jp> To: mwex@astro.astro.psu.edu Subject: [active_stars agn Be bright cv extragalactic lmxb novae] Repeating Gamma Ray Bur From: "Craig Robinson" <robinson@astro.psu.edu> Reply-To: "Craig Robinson" <robinson@astro.psu.edu> Sender: robinson@astro.psu.edu [Posted to: the MultiWaveLink targets of opportunity mailing list] The Compton Gamma Ray Observatory reports that the soft gamma ray repeater known as SGR1806-20 is again active. This prolific repeating source, one of only three gamma ray burst sources know to repeat, was observed to burst around 110 times over the period from 1978 to 1986 with over half of these bursts occurring in a period of two weeks. We are sending this message to notify observers of this fortunate opportunity to search for the counterpart to this gamma ray source at other wavelengths. The identification of optical counterparts to gamma ray bursts sources has been controversial and consists primarily of searches using archival plates or observations looking for quiescent counterparts. The re-activation of SGR1806-20 has provided observers the best chance to successfully perform pointed observations of a gamma ray burst event. The fact that this source repeated was not previously known until the end of the observations of its bursts in 1986. Knowledge of the temporal behavior and/or spectral characteristics of these bursts at optical (and other) wavelengths may provide the additional constraints necessary to identify the physical nature of these objects. While soft gamma ray bursts could represent a different physical class of objects than classical bursts, the origin of either class is still not resolved. Information of the error "box" for SGR1806-20 may be found in Atteia et al. (1987, ApJ 320, L105 [see Figure 3]) and is included here: Ellipse Center: R.A. (1950) = 18 h 05 m 38 s , Dec (1950) = -20 d 26' 40" Ellipse Major axis length = 2.06 degrees (primarily in declination) Ellipse Minor axis length = 0.074 degrees Total Surface area = 430 arcmin^2. It is suggested that observers monitor this region for burst events or for perhaps the identification of the counterpart to SGR1806-20 now that it is active. We were recently informed that the ASCA (X-ray satellite) team is planning a target of opportunity observation of the error region for over 80 ksec starting at 16:30 UT on October 9th. Observers unfamiliar with gamma ray bursts are directed to the review by Higdon & Lingenfelter (1990, Ann. Rev. 28, 401), the conference proceedings entitled Gamma-ray Bursts (Ho, Epstein & Fenimore 1992), and more recent papers in Ap.J. and elsewhere. -Craig Robinson (robinson@astro.psu.edu) Penn. State University
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