The neutron star LMXB transient 4U 1608-52 is evolving towards the hard state
ATel #5990; Wenda Zhang and Wenfei Yu (Shanghai Astronomical Observatory)
on 20 Mar 2014; 13:33 UT
Credential Certification: Wenfei Yu (wenfei@shao.ac.cn)
Subjects: X-ray, Binary, Transient
The neutron star LMXB transient 4U 1608-52 has started an outburst since 2014-01-16 UT (MJD 56673) when it soon entered into the soft state as seen in its hardness ratio between the BAT (15-50 keV) and MAXI (2-10 keV) intensities in Crab units, according to the distributions of the hardness ratio of the hard state and/or the soft state (see Yu & Yan 2009, ApJ, 701, 1940).
The MAXI 2-10 keV intensity has started a quick decline since March 17 (MJD 56733) from 0.19+-0.01 Crab to 0.09+/-0.02 Crab on March 19 (MJD 56735). On the other hand, the BAT 15-50 keV intensity started to increase from 0.02+/-0.00 Crab on March 17 (MJD 56733) to 0.04+/-0.00 Crab on March 18 (MJD 56734) and March 19 (MJD 56735). As a result, the hardness ratio between the BAT 15-50 keV intensity (in Crab unit) and MAXI 2-10 keV intensity (in Crab unit) has increased from 0.09+/-0.02 on MJD 56732 to 0.46+/-0.12 on MJD 56735.
We therefore concluded that the source has left the soft state and is evolving towards the hard state. Continuous multi-wavelength monitoring of the source during the spectral state transition to the hard state, which would detect jet activities, is encouraged. We thank MAXI and Swift teams for providing X-ray monitoring data of the source.
