A large spin-up glitch revealed in energetic pulsar IGR J18490-0000 during NICER April-June 2024 monitoring observations

ATel #16691; L. Kuiper (SRON, The Netherlands), W. C.G. Ho (Haverford College, USA), C. M. Espinoza (USACH/CIRAS, Chile), Z. Arzoumanian (NASA GSFC, USA), K. Gendreau (NASA GSFC, USA), S. Bogdanov (Columbia University, USA), S. Guillot (IRAP/CNRS, France)
on 5 Jul 2024; 10:25 UT
Credential Certification: Lucien Kuiper (L.M.Kuiper@sron.nl)

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Continued NICER monitoring observations (PI, W. Ho) showed a large timing glitch in the energetic pulsar IGR J18490-0000 (pulse period 38.5 ms) occurring sometime between April 12, 2024, and May 12, 2024 (MJD 60412.6 - 60442.9). This triggered DDT/ToO observations that began on June 6, 2024.

Analyzing and combining the NICER data (cleaned; 2.2-8 keV; 21.8 ks exposure) from all post-glitch observations (MJD 60442.9 - 60486.5) yielded a frequency jump size of +4.52E-5 Hz and a frequency derivative step size of -7.8E-13 Hz/s, evaluated at an assumed glitch epoch of MJD 60428 (midpoint of MJD 60412.6 and 60442.9; uncertainty +/- 15 days) comparing the well-established pre-glitch and (yet) poorly defined post-glitch ephemerides. This frequency jump is the fourth largest among all known glitches.

Extrapolated across the time frame during which the glitch occurred, these measurements translate to fractional frequency and frequency derivative step sizes of Dnu/nu = +(1.74 +/- 0.04)E-6 and Dnudot/nudot = +0.082 +/- 0.025, respectively. From its discovery as a rotation-powered pulsar in Nov/Dec 2010 RXTE PCA data until May 2024 (about 13.4 years time lapse), IGR J18490-0000 had not experienced a notable timing glitch/anomaly. On the contrary, IGR J18490-0000 demonstrated extremely stable rotation behaviour using NICER data from (monthly) monitoring observations that commenced on Feb. 13, 2018. This made it even possible to obtain astrometry with sub-arcsec accuracy (Ho et al., in prep.). Further NICER post-glitch observations will enable us to better characterize the glitch properties by extending the post-glitch baseline.

NICER is a 0.2-12 keV X-ray telescope operating on the International Space Station. The NICER mission and portions of the NICER science team activities are funded by NASA.