The neutron star transient 4U 1608-52 has left the hard state
ATel #5094; Wenda Zhang and Wenfei Yu (Shanghai Astronomical Observatory)
on 31 May 2013; 05:51 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 SXT 4U 1608-52 has started an outburst starting from around 2013 May 27 UT (MJD 56439) as indicated by BAT monitoring in 15-50 keV around 2013 May 27 UT (MJD 56439) and MAXI monitoring in all 3 bands on 2013 May 29 UT (MJD 56441; also see MAXI mail alert).
On 2013 May 28 UT (MJD 56440), the BAT/15-50 keV intensity was 0.031+/-0.005 Crab and the MAXI/2-10 keV intensity was 0.022+/-0.004 Crab. On 2013 May 29 UT (MJD 56441), the BAT/15-50 keV intensity increased slightly to 0.037+/-0.007 Crab, while the MAXI/2-10 keV intensity was 0.141+/-0.021 Crab, increased by a factor of ~7. The BAT/15-50 to MAXI/2-10 keV hardness ratio was 1.45+/-0.36 on MJD 56440 and 0.26+/-0.06 on MJD 56441. According to Yu & Yan 2009, ApJ, 701, 1940 and our results from MAXI and BAT for 4U 1608-52, this harness ratio is outside the peak of the hardness distribution corresponding to the hard state. Hence we conclude that 4U 1608-522 has left the hard state since MJD 56441.
