Abstract
We present simultaneous, multi-wavelength observations of the Small Magellanic Cloud Be/XRB IGR J01217-7257 (=SXP 2.16) during outbursts in 2014, 2015 and 2016. We also present the results of RXTE observations of the Small Magellanic Cloud during which the source was initially discovered with a periodicity of 2.1652$\pm$0.0001 seconds which we associate with the spin period of the neutron star. A systematic temporal analysis of long term Swift/BAT data reveals a periodic signal of 82.5$\pm$0.7 days, in contrast with a similar analysis of long base line OGLE I-band light curves which reveals an 83.67$\pm$0.05 days also found in this work. Interpreting the longer X-ray periodicity as indicative of binary motion of the neutron star, we find that outbursts detected by INTEGRAL and Swift between 2014 and 2016 are consistent with Type I outbursts seen in Be/XRBs, occurring around periastron. Comparing these outbursts with the OGLE data, we see a clear correlation between outburst occurrence and increasing I-band flux. A periodic analysis of subdivisions of OGLE data reveals three epochs during which short periodicities of $\sim$1 day are significantly detected which we suggest are non-radial pulsations (NRPs) of the companion star. These seasons immediately precede those exhibiting clear outburst behaviour, supporting the suggested association between the NRPs, decretion disk growth and the onset of Type I outbursts.
Highlights
Be/X-ray binaries (BeXRBs) are a subclass of high mass Xray binaries (HXMBs) comprising a significant fraction of Galactic X-ray binaries (Liu et al 2006)
We present multi-wavelength observations of the Small Magellanic Cloud Be/XRB, IGR J01217−7257, known as SXP 2.16, during three outburst epochs as well as the original RXTE discovery data for the first time
Detected on 2003 January 05 during RXTE scans of the Small Magellanic Cloud (SMC) with a periodicity of 2.1562 s, the source was not subsequently detected for 11 years until January 2014 when it was detected by INTEGRAL
Summary
Be/X-ray binaries (BeXRBs) are a subclass of high mass Xray binaries (HXMBs) comprising a significant fraction of Galactic X-ray binaries (Liu et al 2006). It has been found that the Small Magellanic Cloud (SMC) hosts a population of HMXBs comparable to our Galaxy. All but one of the known SMC HMXBs are BeXRBs, making the SMC a rich target for monitoring these sources, as they provide a population at known distance (62 kpc, Haschke et al 2012) and low Galactic obscuration. The SMC has been regularly monitored by INTEGRAL as part of a Large Programme. Over the course of an observation period (one year), the SMC was be observed for a total of ∼1 Ms This programme has had major success in the discovery and classification of new X-ray binaries in the SMC (Coe et al 2010; McBride et al 2010; Coe et al 2015b)
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