The Transient 1a1118-61 Outburst Observed With Suzaku
Abstract
We present the first broadband (1-80) keV spectra of the hard X-ray Be/HMXB transient 1A1118-61 during its third ever observed outburst in 2009 January. We used Suzaku to observe 1A1118-61 during its peak (2-10 keV flux of 100 mCrab) and 2 weeks later when the flux decreased to 20 mCrab.
We report on the first detection of a possible broad cyclotron resonance scattering feature at 55 keV during both observations, indicating a magnetic field strength of 4.7 TeraGauss, a very high and with A0535+26 one of the highest observed strength. A Fe K alpha line is clearly visible in both observations. In the peak, one also observes an Fe K beta line; the ratio of the line strengths indidcates an origin in cold/neutral material. The continuum power law index hardens significantly between peak and off-peak, similar to outbursts observed in other transient HMXBs which burst more frequently, i.e. A0535+26. We determine the pulse period using Suzaku and RXTE monitoring data and we present the first phase resolved analysis of this source. Alhough similarities with other X-ray transients can be seen, the reason for the long periods between outbursts is still not understood, but a presumably low accretion rate is one possible explanation.- Publication:
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AAS/High Energy Astrophysics Division #11
- Pub Date:
- March 2010
- Bibcode:
- 2010HEAD...11.4225S