The neutron star system 4U 1608-52 has returned to the hard state
ATel #5135; Wenda Zhang and Wenfei Yu (Shanghai Astronomical Observatory)
on 16 Jun 2013; 20:16 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Wenfei Yu (wenfei@shao.ac.cn)
Subjects: X-ray, Binary, Neutron Star, Transient
The neutron star LMXB 4U 1608-52 has started an outburst from around 2013 May 27 UT (MJD 56439, Atel #5094) and was in the high soft state since 2013 May 29 UT (MJD 56441) by its BAT(15-50 keV)/MAXI(2-10 keV) hardness ratio, according to the harness distribution (see, e.g., Yu & Yan 2009).
The BAT/15-50 keV intensity started to increase on 2013 Jun 13 UT (MJD 56456). It was 0.01+/-0.01 Crab on 2013 Jun 12 UT (MJD 56455), then increased to 0.04+/-0.01 Crab on 2013 Jun 13 UT (MJD 56456), 0.06+/-0.01 crab on 2013 Jun 14 UT (MJD 56457) and 0.08+/-0.00 crab on 2013 Jun 15 UT (MJD 56458). On the other hand, the MAXI/2-10 keV intensity has been declining since 2013 Jun 01 UT (MJD 57444). Overall the BAT(15-50 keV)/MAXI(2-10) keV hardness ratio has been increasing since MJD 56456, from 0.29+/-0.09 on MJD 56456 to 1.13+/-0.08 on MJD 56458. The later value on MJD 56458 belongs to the hard state hardness range. We therefore conclude that the source just entered the hard state. Continuous monitoring of the source in ratio and X-ray are encouraged.
We thank MAXI and Swift teams for providing timely X-ray monitoring of the transient.
