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Swift/BAT hard X-ray monitoring: A New Outburst of Black Hole Transient H1743-322

ATel #8751; Jie Lin, Wenfei Yu, Zhen Yan, Hui Zhang (SHAO) and Wenda Zhang (MPA)
on 28 Feb 2016; 16:16 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Wenfei Yu (wenfei@shao.ac.cn)

Subjects: X-ray, Black Hole, Transient

Referred to by ATel #: 8800, 8849, 9726, 10751

H 1743-322 is one of the a few black hole transients which undergo frequent outbursts in the past decade. From December 2009 to June 2015, it has turned into outbursts for at least eight times (ATEL #2364, #2774, #3277, #3842, #4418, #5241, #6474, and #7607), and its outbursts take place rather regularly with recurrence time of about 7-8 months.

Recent Swift/BAT monitoring in the 15-50 keV band indicates that from MJD 57442 to MJD 57446, its 15-50 keV X-ray flux as seen from Swift/BAT has increased from 0.009+/-0.004 Crab to 0.056+/-0.008 Crab. At the same time, MAXI detects similar a hard X-ray flux level in the 10-20 keV band at around 0.05 Crab, while the soft X-ray flux below 10 keV is only marginally detected. This suggests that the source has a rather hard X-ray spectrum. The hardness ratio between the hard band (15-50 keV) and the soft band (2-10 keV) band and increasing hard X-ray flux indicate that H 1743-322 is in the hard state during the rising phase of its current outburst. Usually during the rising phase of its outbursts, the source shows strong X-ray low frequency QPOs (e.g., C-type BH QPOs). If the source will transit to the intermediate state and the soft state later during the outburst, we should detect episodic jets in the radio band as well. Multi-wavelength observations towards the understanding of its QPOs and jet emission are encouraged.