NEOWISE Mid-Infrared Observations of the Outburst in the Nucleus of NGC 1566

ATel #11913; R. M. Cutri (Caltech/IPAC), A. K. Mainzer (JPL), S. D. Van Dyk (Caltech/IPAC), N. Jiang (USTC)
on 5 Aug 2018; 00:21 UT
Credential Certification: Roc Cutri (roc@ipac.caltech.edu)

Tweet

NEOWISE (Mainzer et al. 2014, ApJ, 792, 30) has observed the Seyfert 1.5 galaxy NGC 1566 every six months beginning in January 2014. During each measurement epoch, NEOWISE acquired 30 to 47 separate 7.7 sec exposures covering the object over the span of three to five days. The mid-infrared light curves (http://web.ipac.caltech.edu/staff/roc/ngc1566/ngc1566_lcurve.pdf) of the object show that the nucleus brightened by one magnitude at 3.4 microns and 1.4 magnitudes at 4.6 microns between January 2017 and July 2018.

Elevated levels of X-ray emission from the nucleus of NGC 1566 were reported in June 2018 (ATel #11754, #11783). An ASAS-SN V-band light curve (ATel #11893) shows the nuclear outburst began to be visible in September 2017. The rise in the mid-infrared flux between July 2017 and January 2018 is consistent with the better-sampled V-band light curve. The amplitude of the outburst in the mid-infrared is considerably larger than in the V-band, but that may be a result of less dilution by stellar emission at the longer wavelengths.

The mid-infrared light curves also show evidence for small amplitude variations prior to the start of the outburst, with maxima on or before January 2014 and between January and July 2016. The 8.25 arcsec radius aperture mid-infrared measurements do not appear to be influenced by supernova ASASSN-14ha (ATel #6460, #6461, #6480; Valenti et al. 2016, MNRAS, 459, 3939) in September 2014 that was just outside of the measurement aperture. However, the supernova is detected in a difference image formed by subtracting NEOWISE January 2014 data from January 2015 data.

The NEOWISE light curves of the nucleus are based on fluxes measured in an 8.25 arcsec radius aperture relative to a sky reference brightness measured in an annular region with inner and outer radii of 50 and 70 arcsec, respectively. Measurements from exposures that may be corrupted by image smearing caused by spacecraft jitter are excluded.

NEOWISE is a project of the Jet Propulsion Laboratory/California Institute of Technology, funded by the Planetary Science Division of the National Aeronautics and Space Administration. NEOWISE images and photometry for observations acquired through December 13, 2017 are available from the NASA/IPAC Infrared Science Archive (https://irsa.ipac.caltech.edu).

NEOWISE Light Curves of NGC1566