NICER / ISS Science Nugget
for October 24, 2019

NICER discovers pulsations from new transient Swift J1845.7-0037

During the week of October 12th, when NICER was powered down due to ELC power issues, we received a Target of Opportunity (TOO) request to observe a new transient found by JAXA's MAXI payload (also on the ISS). NASA's Swift observatory produced a better localization of the new target, which is now called Swift J1845.7-0037.

As soon as power was restored to NICER on Oct 19th, NICER conducted a series of observations of this new transient. NICER found that it is a pulsar with a period of 207.4 seconds (see figure).

NICER light curves for the newly discovered pulsar Swift J1845.7-0037

Figure: NICER light curves, folded on the 207.4 sec period, of Swift J1845.7-0037 in several X-ray energy ranges. Figure by G. Jaisawal of the Technical University of Denmark.

NICER continues to monitor Swift J1845.7-0037 to better understand the characteristics of this newly found pulsar.

Initial analysis suggests that this is a Be X-ray Binary (BeXRB). BeXRBs are a class of high-mass X-ray binaries that consist of a Be star and a neutron star. The neutron star is usually in a wide, highly elliptical orbit around the Be star. The Be stellar wind forms a disk confined to a plane often different from the orbital plane of the neutron star. When the neutron star passes through the Be disk, it accretes a large amount of gas in a short time which produces a large outburst of radiation.

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