NICER / ISS Science Nugget for September 20, 2018

Accreting MSP IGR J17591-2342 continues to brighten

Only a couple weeks ago, NICER observations revealed that the new transient source IGR J17591-2342 is a new member of the class of accreting millisecond pulsars (see ISS Science Nugget 08/30/18). At that time, the best guess was that the transient source would soon fade away into invisibility. Instead, NICER has observed two re-brightenings of the source, with the second one reaching the brightest flux observed from this source so far, and still heading up!

This prompted the NICER team to release Astronomer's Telegram #12050, announcing this to the community.

NICER is continuing to monitor the source to track its flux, spectrum, and the characteristics of the pulsations seen from the neutron star as the outburst evolves. We are learning about the process of mass transfer that spins up millisecond pulsars to their incredibly fast periods.