Eta Carinae's Recovery from the 2020 X-ray Minimum as Seen by NICER\
ATel #13636; David A. Espinoza-Galeas (CUA/GSFC), Michael Francis Corcoran (CUA/GSFC), Kenji Hamaguchi (UMBC/GSFC), Theodore Gull (NASA/GSFC \& STScI), Noel Richardson (ERAU), Christopher Russell (CUA/GSFC), Augusto Damineli (IAG/USP), Felipe Navarete (IAG/USP), Desmond Hillier (U. Pittsburgh), Anthony Moffat (U. Montreal), Gerd Weigelt (MPIfR), Andy Pollock (U. Sheffield), Zaven Arzoumanian (NASA/GSFC), Keith C. Gendreau (NASA/GSFC)
on 15 Apr 2020; 19:03 UT
Credential Certification: Michael Corcoran (michael.f.corcoran@nasa.gov)
Subjects: X-ray, Binary, Star, Variables
Referred to by ATel #: 13738
Eta Carinae (Eta Car) is a super-massive, long-period, eccentric, unstable Colliding Wind Binary (CWB) system which experiences periodic X-ray minima near periastron passage. Eta Car has been observed by The Neutron Star Interior Composition Explorer (NICER) payload on-board the International Space Station (ISS) since 2017. NICER provides frequent monitoring of the X-ray spectrum of Eta Car, especially during the most recent X-ray minimum which began on 13 February 2020 (ATEL #13516). Eta Car reached its maximum X-ray flux on 7 January 2020 (3.30 x 10^{-10} ergs/cm2/s) followed by a rapid plunge to its minimum (0.03 x 10^{-10} ergs/cm2/s) before the last periastron, which occurred near 17 February 2020. Here we report that NICER's recent Eta Car observations show a clear increase in flux between 0.5 - 9.0 keV starting approximately on 15 March 2020. This is only 30 days since the start of the X-ray minimum. NICER observations over the last week show that the X-ray flux is nearly constant, indicating the colliding wind X-ray emission has fully recovered from the X-ray minimum to a level consistent with that seen in previous cycles. This is the shortest recovery from the X-ray minimum yet observed in Eta Car. The figure in the link below shows the X-ray flux measured with NICER compared to previous X-ray observations.
Comparison of the X-ray minima of Eta Car over 5 Orbital Cycles