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Start of OIR reflare in GX 339-4

ATel #468; Michelle Buxton, Charles Bailyn (Yale University)
on 22 Apr 2005; 16:53 UT
Credential Certification: Michelle Buxton (buxton@astro.yale.edu)

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

Observations of GX 339-4 taken with the SMARTS 1.3m telescope at CTIO show that it has increased significantly at infrared wavelengths, indicating the beginning of an optical/infrared (OIR) reflare. The change in magnitudes between MJD 53476.3 and MJD 53482.3 are as follows: dV = 0.4, dI = 0.5, dJ = 0.8, dH = 1.0. We have observed this OIR reflare phenomenon during the 2002/2003 outburst of GX 339-4 (Buxton et al., in prep.) and in 4U 1543-47 (Buxton & Bailyn, 2004, ApJ, 615, 880) and XTE J1550-564 (Jain et al., 2001, ApJ, 554, L181). In each case, the reflares appeared after a transition into the low-hard state. Hence, these OIR reflares seem to be a common occurrence in BH LMXBs after transitioning into the low-hard state, as GX 339-4 did very recently (ATEL #455). It is widely believed that this X-ray state is associated with the presence of steady radio jets (Fender, Belloni & Gallo, 2004, MNRAS, 355, 1105). Therefore, these OIR reflares may be associated with synchrotron emission from a jet. We strongly encourage observers to monitor GX 339-4 at all wavelengths, particularly radio at more than one frequency, during this OIR reflare period. For our V- and J-band lightcurves see http://www.astro.yale.edu/buxton/smarts/light_curves/gx339.html.