A Faint, Steep-Spectrum Burst from the Radio Transient GCRT J1745-3009

GCRT J1745-3009 is a transient bursting radio source located in the directionof the Galactic center. It was discovered in a 330 MHz VLA observation from2002 September 30--October 1 and subsequently rediscovered in a 330 MHz GMRTobservation from 2003 September 28 by Hyman et al. Here we report a new radiodetection of the source in 330 MHz GMRT data taken on 2004 March 20. Theobserved properties of the single burst detected differ significantly fromthose measured previously, suggesting that GCRT J1745-3009 was detected in anew physical state. The 2004 flux density was ~0.05 Jy, ~10x weaker than thesingle 2003 burst and ~30x weaker than the five bursts detected in 2002. Wederive a very steep spectral index, alpha = -13.5 +/- 3.0, across the bandpass,a new result previously not detectable due to limitations in the analysis ofthe 2002 and 2003 observations. Also, the burst was detected for only ~2 min.,in contrast to the 10 min. duration observed in the earlier bursts. Due tosparse sampling, only the single burst was detected in 2004, as in the 2003epoch, and we cannot rule out additional undetected bursts that may haveoccurred with the same ~77 min. periodicity observed in 2002 or with adifferent periodicity. Considering our total time on source throughout both ourarchival and active monitoring campaigns, we estimate the source exhibitsdetectable bursting activity ~7% of the time.Comment: 11 pages including 2 figures; submitted to ApJ Letter