2003IAUC.8258....1C

A. Clocchiatti and D. Minitti, Pontificia Universidad Catolica de Chile, on behalf of the SuperMACHO project (involving also C. Aguilera, A. Becker, K. Cook, R. Covarrubias, S. Hawley, R. Hiriart, S. Keller, A. Miceli, G. Miknaitis, S. Nikolaev, K. Olsen, J. Prieto, G. Proctor, A. Rest, B. Schmidt, C. Smith, C. Stubbs, N. Suntzeff, and D. Welch), report the discovery of a highly unusual outburst of a quasistellar object (QSO) at z = 2.87. The object, located at R.A. = 5h13m03s.94, Decl. = -70o22'50".5 (equinox 2000.0), had a quiescent broadband magnitude of VR approximately 22.2. Multiple broadband-VR-filter images taken at the Blanco 4-m telescope at Cerro Tololo reveal no significant change in brightness from the beginning of observations in 2001 Sept. until 2003 Sept. 27 UT, around the date that it began to brighten linearly in flux with time. By Dec. 15, it had brightened by a factor of 15 and has reached VR = 19.4 with no evidence of a change in trend. Identified as a SuperMACHO microlensing candidate, follow-up spectroscopy (456-s exposure) was obtained at the Magellan II (Clay) 6.5-m telescope (+ LDSS2 spectrograph with medium-blue grism) on Dec. 3.8. The spectrum reveals several prominent QSO lines with strong P-Cyg profiles, indicative of an ejection velocity of 1600 km/s; identified features include H (Lyman-alpha), N V, C IV 154.9-nm, Si IV 139.3-nm, O IV, and [C III] 191.0-nm. The high redshift, extreme current luminosity, evidence of outflow (from P-Cyg line profiles), and continued brightening suggest that this is an object worthy of intense monitoring.