A magnetar outburst with atypical evolution: the case of Swift J1555.2-5402
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2025
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| author | Borghese, A. Zelati, F. Coti Imbrogno, M. Israel, G. L. De Grandis, D. Pacholski, D. P. Trudu, M. Burgay, M. Mereghetti, S. Rea, N. Esposito, P. Pilia, M. Possenti, A. Turolla, R. Ducci, L. |
| author_facet | Borghese, A. Zelati, F. Coti Imbrogno, M. Israel, G. L. De Grandis, D. Pacholski, D. P. Trudu, M. Burgay, M. Mereghetti, S. Rea, N. Esposito, P. Pilia, M. Possenti, A. Turolla, R. Ducci, L. |
| contents | The magnetar Swift J1555.2-5402 was discovered in outburst on 2021 June 3 by the Burst Alert Telescope on board the Swift satellite. Early X-ray follow-up revealed a spin period P~3.86 s, a period derivative Pdot~3e-11 s/s, dozens of short bursts, and an unusually flux decline. We report here on the X-ray monitoring of Swift J1555.2-5402 over the first ~29 months of its outburst with Swift, NICER, NuSTAR, INTEGRAL and Insight-HXMT, as well as radio observations with Parkes soon after the outburst onset. The observed 0.3-10 keV flux remained at levels >~1e-11 erg/cm^2/s for nearly 500 days before dropping by a factor of ~10 from its June 2021 peak towards the end of the monitoring campaign. During this time span, the spectrum was dominated by a single blackbody, with temperature attaining approximately a constant value (~1.2 keV) while the inferred radius shrank from ~1.7 km to ~0.3 km (assuming a source distance of 10 kpc). The long-term spin-down rate (Pdot~3.6e-11 s/s) is only ~15 % higher than that measured in the first 30 days. No periodic or burst-like radio emission was detected, in line with what has been previously reported using different radio facilities. The persistently high temperature, shrinking hotspot, and a prolonged bright flux plateau followed by a fast dimming observed during the outburst evolution pose a challenge for the outburst mechanisms proposed so far. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2512_08692 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | A magnetar outburst with atypical evolution: the case of Swift J1555.2-5402 Borghese, A. Zelati, F. Coti Imbrogno, M. Israel, G. L. De Grandis, D. Pacholski, D. P. Trudu, M. Burgay, M. Mereghetti, S. Rea, N. Esposito, P. Pilia, M. Possenti, A. Turolla, R. Ducci, L. High Energy Astrophysical Phenomena The magnetar Swift J1555.2-5402 was discovered in outburst on 2021 June 3 by the Burst Alert Telescope on board the Swift satellite. Early X-ray follow-up revealed a spin period P~3.86 s, a period derivative Pdot~3e-11 s/s, dozens of short bursts, and an unusually flux decline. We report here on the X-ray monitoring of Swift J1555.2-5402 over the first ~29 months of its outburst with Swift, NICER, NuSTAR, INTEGRAL and Insight-HXMT, as well as radio observations with Parkes soon after the outburst onset. The observed 0.3-10 keV flux remained at levels >~1e-11 erg/cm^2/s for nearly 500 days before dropping by a factor of ~10 from its June 2021 peak towards the end of the monitoring campaign. During this time span, the spectrum was dominated by a single blackbody, with temperature attaining approximately a constant value (~1.2 keV) while the inferred radius shrank from ~1.7 km to ~0.3 km (assuming a source distance of 10 kpc). The long-term spin-down rate (Pdot~3.6e-11 s/s) is only ~15 % higher than that measured in the first 30 days. No periodic or burst-like radio emission was detected, in line with what has been previously reported using different radio facilities. The persistently high temperature, shrinking hotspot, and a prolonged bright flux plateau followed by a fast dimming observed during the outburst evolution pose a challenge for the outburst mechanisms proposed so far. |
| title | A magnetar outburst with atypical evolution: the case of Swift J1555.2-5402 |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2512.08692 |