NICER / ISS Science Nugget
for June 3, 2021
NICER Captures the Likely Launch of a Wind by a Supermassive Black Hole
It is now known that almost all massive galaxies contain a supermassive black hole (SMBH) at their centers. Even though these SMBHs are several orders of magnitude smaller in size and lower in mass than their host galaxies, they control the growth of their hosts. One of the proposed mechanisms for how SMBHs alter the large-scale properties of their host galaxies is via powerful ejections of mass and energy in the form of an outflow or "wind". The exact mechanism for launching such powerful outflows is still a mystery.
On 9 February 2019, ground based telescopes identified visible-light brightening of the nucleus of a galaxy at a distance of 130 Mpc (about 430 million light-years). Optical spectra obtained in the month following the discovery indicated that this event, dubbed AT2019avd, was the likely result of a sudden influx of matter onto a previously dormant/weakly accreting SMBH. On 19 September 2020, NASA's Neil Gehrels Swift space observatory detected X-ray emission from this outburst. Encouraged by this X-ray detection, NICER launched a major monitoring campaign. NICER has been observing the target with a cadence of at least once every few days for the past nine months.
NICER X-ray spectra during the first few months only showed a single thermal emission component and an occasional second thermal component. Over the last few weeks, a new feature has emerged in the spectrum in addition to the thermal components (see Figure). This feature is similar to those from known active galactic nucleus winds and thus may be interpreted as a newly launched wind from the SMBH accretion disk. This was reported in Astronomer's Telegram 14664 by Pasham et al. Such an abrupt change in accretion properties of SMBHs has rarely been observed. The next steps are to model the wind and infer its kinetic energy, launching radius, and ionization state, to determinie whether such transient winds can inject enough energy into their host galaxies to alter their large-scale properties.
Figure: The top panel shows the NICER spectrum, in the 0.3-1.5 keV energy band, of AT2019avd using the past few weeks of data. The histogram is the best-fit model consisting of a thermal component and the bottom panel shows the residuals ([data-model]/error). The feature between 0.6-1.4 keV can be interpreted as evidence for a newly launched wind from a black hole's accretion disk.