NICER / ISS Science Nugget
for April 6, 2023
Rip Van Winkle Binary Awakens
Dr. J. Coley (Howard Univ.) and collaborators this week posted an Astronomer's Telegram reporting preliminary NICER results (Figure 1) stemming from observations made in response to an alert provided by JAXA's MAXI payload on March 30. The MAXI team notified the community that the X-ray binary system known as 4U 0115+63 was in outburst for the first time in 27 years. 4U 0115 consists of a neutron star interacting with a massive companion star, in a 2.1 day binary orbit. The neutron star draws matter from its companion, with the flow channeled by the neutron star's strong magnetic field onto its magnetic polar caps. The polar caps are heated by the infalling material, and their glow in X-rays reveals the neutron star's rotation period (3.6 seconds; Figure 2) and its evolution through the outburst. The system's overall X-ray brightness, including a contribution from the hot accretion flow itself, continues to rise as of this writing. NICER's timely publication of its early results as a Telegram has encouraged additional prompt multi-wavelength followup observations with other facilities.
Figure:
Left: Rising NICER X-ray "light curve" Ñ the rate of photon detections in 16-second time bins Ñ of the binary system 4U 0115+63, in its ongoing historic outburst.
Right: A close-up, finely sampled in time, of the last measurement shown in Figure 1. Narrow peaks at 3.6 second intervals are evident, single pulses tracking the rotation period of the neutron star in 4U 0115.
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