NICER / ISS Science Nugget
for November 28, 2019

NICER discovers 9.29 sec pulsations in RX J0209.6-7427

On 21 November, 2019, JAXA's ISS payload MAXI detected transient X-ray emission in the direction of the Small Magellanic Cloud (SMC) and called it MAXI J0206-749. A follow-up observation by NASA's Swift observatory determined that the source was, in fact, the previously known X-ray emitter RX J0209.6-7427, last seen by the European ROSAT mission in 1993.

Following up on the MAXI and Swift observations, NICER quickly discovered that RX J0209.6 is pulsating with a period of 9.29 seconds. The NICER and MAXI teams jointly published this result as an Astronomers Telegram (Iwakiri et al., ATel #13309); the folded pulse profile is shown in the accompanying figure. NICER's initial detection of the overall source count rate was approximately 77 counts per second. It has been steadily rising and NICER is now conducting simultaneous observations of the source with NASA's NuSTAR (high-energy X-ray) observatory.

Available evidence suggests that RX J0209.6 is a high mass X-ray binary. It is only the second known to lie within the Magellanic Bridge that connects the Small and Large Magellanic Clouds. Over the next few weeks, we hope to determine the binary's orbital parameters.

Pulse profile for RX J0209.6-7427, a candidate HMXB

Figure: The phase-folded X-ray light curve of RX J0209.6-7427 as measured by NICER. (T. Strohmayer, NASA GSFC)

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