NICER / ISS Science Nugget
for January 12, 2023




A black-hole awakens after a nearly 25-year nap

On December 25, 2022, JAXA's MAXI payload detected brightening X-ray emission from the direction of a black-hole binary, XTE J2012+381, that was discovered and last seen in May 1998. With renewed mass transfer from a companion star, we witness again the formation of an accretion disk around a black hole, with gas heated to million-degree temperatures, and generating X-rays, by falling into the hole's gravitational well. Such outbursts are seen by Earth-bound telescopes from our Galaxy's population of black-hole binaries two or three times each year, and they last a few months.

MAXI's detection triggered NICER observations beginning on Dec. 26; preliminary results were reported in Astronomer's Telegram #15829 by W. Iwakiri (Chiba Univ., Japan) and collaborators. XTE J2012 continues to brighten (see Figure). Another recent Telegram (#15855) has reported that the system also brightened by a factor of 25 at radio wavelengths during a period of time when its X-ray spectrum as measured by NICER changed abruptly (at approximately 3.5x105 seconds in the figure). Radio emission is a hallmark of radiation from particles accelerated - by poorly understood processes - to relativistic speeds in a jet. Such multi-wavelength correlation studies probe the connection between accretion disks and the launching of jets, enabling us to better understand the mechanisms responsible for the copious and energetic emissions of black holes in binary systems.


NICER measurements of the X-ray emission from the black-hole binary XTE J2012+318 beginning on December 26, 2022. The top panel shows the rate of photon detections, including a slight jump at approximately 3.5x10^5 seconds. Points in the lower panel represent the ratio of photon counts in higher X-ray energies (2.5-12 keV;

Figure: NICER measurements of the X-ray emission from the black-hole binary XTE J2012+318 beginning on December 26, 2022. The top panel shows the rate of photon detections, including a slight jump at approximately 3.5x10^5 seconds. Points in the lower panel represent the ratio of photon counts in higher X-ray energies (2.5-12 keV; "hard") to those in a lower-energy band (0.5-2.5 keV; "soft"). Coincident with the uptick in total count rate, the source spectrum abruptly became softer. Radio observations find significant brightening at approximately the same time as this spectral change.



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