NICER / ISS Science Nugget
for July 2, 2020

A long-duration X-ray burst from IGR J17062-6143

At 4:15 a.m. Eastern on June 22nd, 2020, the MAXI/GSC nova alert system was triggered by a bright X-ray burst from the neutron-star system IGR J17062-6143. After receiving this information from the ISS MAXI team, NICER's observing plan was updated and the payload slewed to this target, collecting our first view only 3 hours after the MAXI trigger.

The NICER light curve (see figure 1) indicates that we caught the tail end of an approximately 5-hour-long thermonuclear X-ray burst. Such long-duration X-ray bursts are rare events, and have been detected from this source only twice before (in 2012 and 2015).

Due to the human intervention that is needed for NICER to follow up on MAXI triggers, the brightest phases of this long-duration burst went unobserved. In the future, this reaction time may be reduced to minutes, as we work to fully automate Target-of-Opportunity follow-up using a laptop onboard ISS.

Light curve for IGR J17062-6143 showing tail end of recent outburst

Figure 1: The number of X-rays per second detected by NICER as a function of time is shown for the recent MAXI triggered observation of the neutron star system IGR J17062-6143. MAXI detected the source bursting about 3 hours earlier with a flux much higher. NICER caught the tail of this burst and followed its evolution back to a quiescent state.

Continuing observations of IGR J17062 over the following week have shown that the source brightness fell below its historical level recorded by NICER for this neutron star. Over the course of several days, the flux then gradually increased back to its historical level. While analysis of these data is still ongoing, a possible explanation for this dip in flux may lie in the interaction between the X-ray burst and the neutron star accretion environment (see figure 2). The massive thermonuclear burst likely blasted the accretion disk around the neutron star with X-rays. This irradiation may have been strong enough to obliterate the inner regions of the disk, so that the dip and subsequent recovery of the flux reflect the emptying and gradual re-filling of the accretion disk.

Artist impression of a neutron star system like IGR J17072-6143

Figure 2: An artist impression of a neutron star system like IGR J17072-6143 that shows an accretion disc flowing matter from a companion star into the neutron star. It is likely that the inner portion of this accretion disk was obliterated by the massive burst which MAXI detected. Within a few days, the inner disc refilled with matter as the source returned to its quiescent state.

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