Einstein Probe discovery of the magnetar EP J223759.5+531421
Abstract
We report the discovery and early outburst evolution of the new Galactic magnetar EP J223759.5+531421, detected by the Einstein Probe Wide-field X-ray Telescope on 2026 June 28. Follow-up observations with Einstein Probe, XMM--Newton, NuSTAR, SVOM, and IXPE revealed coherent X-ray pulsations at P ~ 6s and an average period derivative of Pdot ~ 2.8x10^{-12} s/s. These values imply a nominal polar dipolar magnetic field of B_dip ~ 2.6x10^{14} Gauss and a characteristic age of tau_c ~ 34 kyr, although the structured timing residuals suggest possible torque variability. The rms pulsed fraction is approximately 20-25% below ~7 keV and decreases at higher energies. The broadband spectra require multiple thermal components and a hard power-law tail. Adopting a distance of 3.3 kpc, the 0.5-30 keV luminosity declined from 1.2x10^{35} to 5.7x10^{34} erg/s during the first month, accompanied by a decrease in the inferred thermal-emitting areas. At this distance, the Galactic latitude b=-4.56 deg corresponds to a height of approximately 0.26 kpc below the Galactic plane, which is difficult to reconcile with the nominal characteristic age under a simple midplane-birth scenario even for an extreme proper motion velocity. Short X-ray bursts independently confirm the magnetar nature of the source. No near-infrared or radio counterpart were detected by GTC, Medicina or FAST, respectively, down to K_s>21 mag and S_{1.25 GHz} <2.3 microJy. These observations demonstrate the potential of the Einstein Probe WXT monitoring to uncover previously quiescent Galactic magnetars and follow their outbursts from their earliest observed stages.
Related
- IXPE Observation of the New Magnetar Source EP J223759.5+531421
- IXPE observation of the new magnetar source EP J223759.5+531421
- The (missing) gamma-ray counterparts to Einstein Probe events. I: Search for keV-GeV counterparts of Einstein Probe fast X-ray transients
- Search for high-energy neutrinos from Einstein Probe detected Fast X-ray Transients using 14 years of IceCube muon track data
- Candidate X-ray Counterparts of Ultra-High-Energy Emission of the Galactic Microquasar V4641 Sgr Revealed by Einstein Probe
BibTeX
@misc{rea2026einstein,
title = {{Einstein Probe discovery of the magnetar EP J223759.5+531421}},
author = {N Rea and F Coti Zelati and A Borghese and Y.L Wang and H Yang and X Mao and C.-Y Dai and E Arrigoni and J Bai and G Bernardi and M Burgay and S Cao and A Coleiro and D de Grandis and P Esposito and H Feng and Y.-C Fu and A Geminardi and D Götz and S Guillot and Y Huang and M Imbrogno and G.L Israel and C Jin and A Kong and Y Li and L Lin and C.-S Liu and C Maitra and A Marino and S Mereghetti and J.-U Ness and S Ng and M Pilia and A Possenti and H Sun and L Tao and R Taverna and A Tiengo and R Turolla and W Yuan and S Zane and B Zhang and L.-X Zhang and Z Zhang and W.-W Zhu and Y.-C Zou},
howpublished = {HAL},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.25990},
eprint = {2609.25990},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05785797v1},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Einstein Probe discovery of the magnetar EP J223759.5+531421
AU - N Rea
AU - F Coti Zelati
AU - A Borghese
AU - Y.L Wang
AU - H Yang
AU - X Mao
AU - C.-Y Dai
AU - E Arrigoni
AU - J Bai
AU - G Bernardi
AU - M Burgay
AU - S Cao
AU - A Coleiro
AU - D de Grandis
AU - P Esposito
AU - H Feng
AU - Y.-C Fu
AU - A Geminardi
AU - D Götz
AU - S Guillot
AU - Y Huang
AU - M Imbrogno
AU - G.L Israel
AU - C Jin
AU - A Kong
AU - Y Li
AU - L Lin
AU - C.-S Liu
AU - C Maitra
AU - A Marino
AU - S Mereghetti
AU - J.-U Ness
AU - S Ng
AU - M Pilia
AU - A Possenti
AU - H Sun
AU - L Tao
AU - R Taverna
AU - A Tiengo
AU - R Turolla
AU - W Yuan
AU - S Zane
AU - B Zhang
AU - L.-X Zhang
AU - Z Zhang
AU - W.-W Zhu
AU - Y.-C Zou
PY - 2026
DA - 2026/09/22
PB - HAL
DO - 10.48550/arxiv.2609.25990
UR - https://hal.science/hal-05785797v1
AB - We report the discovery and early outburst evolution of the new Galactic magnetar EP J223759.5+531421, detected by the Einstein Probe Wide-field X-ray Telescope on 2026 June 28. Follow-up observations with Einstein Probe, XMM--Newton, NuSTAR, SVOM, and IXPE revealed coherent X-ray pulsations at P ~ 6s and an average period derivative of Pdot ~ 2.8x10^{-12} s/s. These values imply a nominal polar dipolar magnetic field of B_dip ~ 2.6x10^{14} Gauss and a characteristic age of tau_c ~ 34 kyr, although the structured timing residuals suggest possible torque variability. The rms pulsed fraction is approximately 20-25% below ~7 keV and decreases at higher energies. The broadband spectra require multiple thermal components and a hard power-law tail. Adopting a distance of 3.3 kpc, the 0.5-30 keV luminosity declined from 1.2x10^{35} to 5.7x10^{34} erg/s during the first month, accompanied by a decrease in the inferred thermal-emitting areas. At this distance, the Galactic latitude b=-4.56 deg corresponds to a height of approximately 0.26 kpc below the Galactic plane, which is difficult to reconcile with the nominal characteristic age under a simple midplane-birth scenario even for an extreme proper motion velocity. Short X-ray bursts independently confirm the magnetar nature of the source. No near-infrared or radio counterpart were detected by GTC, Medicina or FAST, respectively, down to K_s>21 mag and S_{1.25 GHz} <2.3 microJy. These observations demonstrate the potential of the Einstein Probe WXT monitoring to uncover previously quiescent Galactic magnetars and follow their outbursts from their earliest observed stages.
ER -