NICER / ISS Science Nugget
for September 10, 2020
A NICER View of the 2020 outburst of PSR J1846-0258
PSR J1846-0258 is a young neutron star in the supernova remnant Kes 75; its spin period is about 0.32 seconds. In early August 2020, NASA's Swift observatory and the JAXA MAXI payload on ISS detected a powerful X-ray flare from this young pulsar. Target of Opportunity (TOO) observations by NICER were requested by multiple groups, complementing an ongoing Guest Observer (GO) study of this pulsar.
Analysis of GO data acquired by NICER before and after the reported flare showed interesting evolution in the spectral and timing properties of this pulsar. Early-summer 2020 observations showed an increase in X-ray flux compared to normal levels, even before the detected X-ray flare in August (see Figure). As reported in Astronomer's Telegram #13985, Kuiper et al. showed, among other findings, that the pulsed fraction of PSR J1846 substantially increased while its spin period changed by one part in a million during a prolonged outburst after the flare.
One of the TOO requests came from radio astronomers who wanted contemporaneous and simultaneous radio and X-ray coverage of PSR J1846 during this outburst. Several NICER observations were scheduled to coincide with NASA's Deep Space Network (DSN) radio observations in order to find correlations that have been seen in outbursts ofsimilar systems with extremely high magnetic fields. In addition to providing critical communication infrastructure for NASA missions, DSN is also an extremely valuable resource for astrophysics since its global coverage enables excellent visibility for much of the sky. As reported in Astronomers Telegram #13988 by Majid et al., DSN was able to place a 7-sigma upper limit on radio pulsations corresponding to NICER's detected x-ray pulsations. PSR J1846-0258 has no known radio counterpart and this stringent upper limit on radio emission during an x-ray outburst further constrains models of this fascinating source.
Figure: NICER measured pulsed X-ray flux from PSR J1846-0258 in the 2.5-10 keV energy band, including GO observations beginning in March 2020 as well as densely sampled TOO observations after the Swift flare detection on August 1st (dotted line) through to August 24th (Modified Julian Date or MJD 59085).