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Optical and NIR observations of GRO J1655-40

ATel #418; Michelle Buxton, Charles Bailyn, Dipankar Maitra (Yale University)
on 21 Feb 2005; 19:09 UT
Credential Certification: Michelle Buxton (buxton@astro.yale.edu)

Subjects: Infra-Red, Optical, Binary, Black Hole, Transient

Referred to by ATel #: 419, 487, 608

In response to the recent report of renewed activity in GRO J1655-40 (ATEL #414), we have obtained B, V, I, J and K-band images using the ANDICAM instrument on the SMARTS 1.3m telescope at CTIO. On UT Feb 21.3-21.4 we measure the following magnitudes: B = 18.5, V = 17.0, I = 14.9, J = 13.4, K = 12.4. In comparison to the average quiescent magnitudes (Greene, Bailyn & Orosz 2001, ApJ, 554, 1290), we find the following differences in magnitude: dB = 0.3, dV = 0.2, dI = 0.2, dJ = 0.5, dK = 0.9. Our dJ agrees with that of Torres et al. (ATEL #417). The B and V mags are within the amplitudes of the quiescent ellipsoidal variations, the I mag is just above. The J and K mags, however, are well outside the ellipsoidal variations. Hence, we confirm that GRO J1655-40 is entering a new active phase. The strong IR rise suggests that we may be in the early stages of an outburst like that of 1997, when Orosz et al. (1997, ApJ, 478, L83) noted a rise in the red bands that preceded the rise in the bluer bands. This might also be an IR flare like that described by Buxton & Bailyn (2004, ApJ, 615, 880) in 4U 1543-47. Multiwavelength observations, particularly radio, would be very desirable. We will be monitoring this object on a daily basis with SMARTS.