NICER Science Results

NICER Publications and Other Notable Items

• NICER Astronomer's Telegrams
Automated ADS query for Astronomer's Telegrams related to NICER
• NICER Refereed Papers
  
• Present NICER Science
• Use or Predict NICER Results


• Automated ADS Query
  A list of NICER publications including refereed and unrefereed articles (ATels, etc.) from July 2012 to present.
  
  
• NICER Selected Popular Publications
  
  
• NICER in the News
  
  
• NICER Science Nuggets
  High-level NICER science results, with a new science item posted every week. Listing also available by science topic.

Recent Science from NICER on the ISS

Telegrams from black holes

In the last week, a pair of rapid-communication online Astronomer's Telegrams (ATels) - based on prompt analysis of NICER observations - have captured some of the ways in which black holes in our Galaxy reveal themselves.

A previously unknown source of X-rays, now catalogued as MAXI J1744-294, was discovered in outburst by JAXA's MAXI ISS payload in January. G. Jaisawal (Technical Univ, of Denmark) and collaborators reported in ATel #17040 that NICER data yield an energy spectrum consistent with a black hole in a binary system, with mass transfer from the companion star forming a hot (6 million degree) accretion disk. Superposed on this broadband emission are characteristic spectral lines, predominantly of iron atoms in the disk - both neutral and ionized - that are fluorescing in X-rays. Such features are commonly seen from black-hole binaries; details of the line shapes provide insights into the mass and spin of the black hole, and how close to the event horizon the inner edge of the disk extends. An absence of brightness fluctuations suggests that the MAXI J1744 has already evolved into the "bright-soft" part of its outburst and will soon fade into quiescence.

By contrast, the black-hole binary IGR J17091-3624 is known principally for unusual variability in its brightness: on timescales of tens of seconds, IGR J17091 shows systematic, repeating fluctuations that sometimes resemble the patterns in electrocardiograms, and thus are called "heartbeat" cycles. F. Vincentelli (Southampton Univ., UK) and collaborators report in ATel #17038 on NICER observations following the announcement of a new outburst detected by the European INTEGRAL gamma-ray telescope. The team reports evidence of less-organized variability, so-called quasi-periodic oscillations (Figure 2), repeating roughly every 5 seconds. Expectations are that the IGR J17091 outburst is in its early stages, and that heartbeat modes - which likely signal stable pressure waves traveling through the accretion disk - will emerge as the accretion process becomes better established. Additional NICER observations are planned.