NICER / ISS Science Nugget for April 18, 2019

NICER Observations of a Possible SN 1a: AT2019daj

Over the past week, NICER chased down an optical transient found within the positional error-box of a LIGO gravitational-wave event. After the initial NICER observations were made, follow-up optical investigations determined that the transient source was unrelated to LIGO, but instead a likely supernova (SN) detected on March 27, 2019, by a robotic ground-based telescope.

NICER detected X-rays in excess of background models, and additional observations were executed, yielding a spectrum that revealed line emission characteristic of carbon, oxygen, and other low-atomic-number elements (see figure). A follow-up optical spectrum was obtained that indicated this target is a Type 1a supernova: one that occurs when a white dwarf star reignites due to mass accumulation from a binary companion.

Prior to this observation, early X-rays had only been seen in one other Type 1a SN. NICER's observation may be a much more significant detection of early X-rays, and a spectrum measurement, from such a SN. The team is working to make sure that the NICER results are not dominated by a foreground "interloper" object.