The New Magnetar SGR J1830−0645 in Outburst

• Published in: Astrophysical journal. Letters Vol. 907; no. 2; p. L34
• Main Authors: Zelati, F. Coti, Borghese, A., Israel, G. L., Rea, N., Esposito, P., Pilia, M., Burgay, M., Possenti, A., Corongiu, A., Ridolfi, A., Dehman, C., Viganò, D., Turolla, R., Zane, S., Tiengo, A., Keane, E. F.
• Format: Journal Article
• Language: English
• Published: Austin IOP Publishing 01.02.2021
• Subjects: Age; Blackbody; Fluence; Luminosity; Magnetars; Magnetic fields; Radio frequency; Radio telescopes; Soft x rays; Spectroscopic telescopes; Telescopes; X ray sources; X ray telescopes; X-ray bursts; X-ray fluxes; XMM (spacecraft)
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8213/abda52

Abstract The detection of a short hard X-ray burst and an associated bright soft X-ray source by the Swift satellite in 2020 October heralded a new magnetar in outburst, SGR J1830−0645. Pulsations at a period of ∼10.4 s were detected in prompt follow-up X-ray observations. We present here the analysis of the Swift/Burst Alert Telescope burst, of XMM-Newton and the Nuclear Spectroscopic Telescope Array observations performed at the outburst peak, and of a Swift/X-ray Telescope monitoring campaign over the subsequent month. The burst was single-peaked, lasted ∼6 ms, and released a fluence of ≈5 × 10 −9 erg cm −2 (15–50 keV). The spectrum of the X-ray source at the outburst peak was well described by an absorbed double-blackbody model plus a power-law component detectable up to ∼25 keV. The unabsorbed X-ray flux decreased from ∼5 × 10 −11 to ∼2.5 × 10 −11 erg cm −2 s −1 one month later (0.3–10 keV). Based on our timing analysis, we estimate a dipolar magnetic field ≈5.5 × 10 14 G at pole, a spin-down luminosity ≈2.4 × 10 32 erg s −1 , and a characteristic age ≈24 kyr. The spin modulation pattern appears highly pulsed in the soft X-ray band, and becomes smoother at higher energies. Several short X-ray bursts were detected during our campaign. No evidence for periodic or single-pulse emission was found at radio frequencies in observations performed with the Sardinia Radio Telescope and Parkes. According to magneto-thermal evolutionary models, the real age of SGR J1830−0645 is close to the characteristic age, and the dipolar magnetic field at birth was slightly larger, ∼10 15 G.