Detection of hard X-ray pulsations in non-ULX X-ray pulsar 3X J0042 in M31
Abstract
We report the detection of hard X-ray pulsations from the M31 accreting non-ULX X-ray pulsar 3X J0042 (3XMM J004232.1+411314) using archival NuSTAR observations. The source has a spin period of ~3 s and an orbital period of ~4.15 hr, with coherent pulsations previously detected only in XMM-Newton observations. We reanalyse all five publicly available NuSTAR observations by correcting the photon arrival times for binary motion and optimizing the orbital epoch and projected semi-major axis. Coherent pulsations are detected in all five observations. The broad-band pulse profiles show similar morphology across the five observations spanning ~2.3 yr, with no significant long-term evolution. The pulse profile also shows energy dependence, with structured, non-sinusoidal profiles below ~20 keV and a less structured profile at higher energies. The pulse periods show an overall decrease over the ~2.3 yr NuSTAR baseline, continuing the long-term spin-up trend observed in the ~16 yr of XMM-Newton observations, but with a faster average spin-up rate of ~-1.1e-10 s/s compared to the earlier reported ~-6e-11 s/s. The short orbital period and inferred low-mass companion star shows it to be a low-mass X-ray binary containing a magnetized neutron star, with systems such as Her X-1, 3A 1822-371, and XMM J174457-2850.3 providing closer Galactic comparisons. This work represents the first detection of hard X-ray pulsations from a non-ULX extragalactic accreting pulsar.
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BibTeX
@misc{rikame2026detection,
title = {{Detection of hard X-ray pulsations in non-ULX X-ray pulsar 3X J0042 in M31}},
author = {Ketan Rikame and Biswajit Paul},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.10699},
eprint = {2609.10699},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.10699},
}
RIS
TY - UNPB
TI - Detection of hard X-ray pulsations in non-ULX X-ray pulsar 3X J0042 in M31
AU - Ketan Rikame
AU - Biswajit Paul
PY - 2026
DA - 2026/09/09
PB - arXiv
DO - 10.48550/arxiv.2609.10699
UR - https://arxiv.org/abs/2609.10699
AB - We report the detection of hard X-ray pulsations from the M31 accreting non-ULX X-ray pulsar 3X J0042 (3XMM J004232.1+411314) using archival NuSTAR observations. The source has a spin period of ~3 s and an orbital period of ~4.15 hr, with coherent pulsations previously detected only in XMM-Newton observations. We reanalyse all five publicly available NuSTAR observations by correcting the photon arrival times for binary motion and optimizing the orbital epoch and projected semi-major axis. Coherent pulsations are detected in all five observations. The broad-band pulse profiles show similar morphology across the five observations spanning ~2.3 yr, with no significant long-term evolution. The pulse profile also shows energy dependence, with structured, non-sinusoidal profiles below ~20 keV and a less structured profile at higher energies. The pulse periods show an overall decrease over the ~2.3 yr NuSTAR baseline, continuing the long-term spin-up trend observed in the ~16 yr of XMM-Newton observations, but with a faster average spin-up rate of ~-1.1e-10 s/s compared to the earlier reported ~-6e-11 s/s. The short orbital period and inferred low-mass companion star shows it to be a low-mass X-ray binary containing a magnetized neutron star, with systems such as Her X-1, 3A 1822-371, and XMM J174457-2850.3 providing closer Galactic comparisons. This work represents the first detection of hard X-ray pulsations from a non-ULX extragalactic accreting pulsar.
ER -