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Renewed activity from GX 399-4

ATel #1954; Martin Still, Catherine Brocksopp (UCL-MSSL), Piergiorgio Casella (Amsterdam)
on 9 Mar 2009; 18:30 UT
Credential Certification: Martin Still (mds@mssl.ucl.ac.uk)

Subjects: Optical, Ultra-Violet, X-ray, Binary, Black Hole, Transient, Variables

Referred to by ATel #: 1962, 2270

Further to the alert by Markwardt et al. (ATel #1945), the Swift-BAT scaled map transient analysis and the RXTE Galactic bulge scans indicate that GX 339-4 is entering another epoch of activity. Within the RXTE-PCA energy band the source has attained its brightest state since the 2007 major outburst. Monitoring over the coming weeks will reveal whether this source continues to brighten towards a major outburst or undergoes one of its more common minor high state episodes.

Swift observed GX 339-4 on March 7, 2009 14:52-15:11 UT. The XRT finds a source with episodes of constant 1.8e-10 erg/s/cm2 0.3-10 keV flux with occasional 50s timescale flares, reaching a maximum flux of 2.6e-9 erg/s/cm2. The spectrum can be fit with a (7 +/- 2)e21 cm-2 absorbed powerlaw of spectral index 1.5 +/- 0.1 and, while caution is required with this rapidly varying source, an additional 110 +/- 10 eV thermal component can be added with a statistical improvement to the fit at the 4.3 sigma significance level, contributing 5% to the total absorbed flux.

Despite the direction of GX 339-4 towards the Galactic center GX 339-4 is bright in the UV bands. Current Swift-UVOT UV and optical magnitudes are uvw2 = 19.10 +/- 0.18, uvm2 > 18.14 (3 sigma upper limit), uvw1 = 18.26 +/- 0.13, u = 17.45 +/- 0.09, b = 17.24 +/- 0.05, v = 16.53 +/- 0.07.

A Swift monitoring campaign for GX 339-4 has been triggered.

Scaled Map Transient Analysis for GX 339-4 (H. Krimm)