A very young radio-loud magnetar

Abstract

The magnetar Swift ,J1818.0-1607 was discovered in March 2020 when Swift detected a 9 ms hard X-ray burst and a long-lived outburst. Prompt X-ray observations revealed a spin period of 1.36 s, soon confirmed by the discovery of radio pulsations. We report here on the analysis of the Swift burst and follow-up X-ray and radio observations. The burst average luminosity was $L_{\mathrm{burst}}\sim 2\times 10^{39}$ erg/s (at 4.8 kpc). Simultaneous observations with XMM-Newton and NuSTAR three days after the burst provided a source spectrum well fit by an absorbed blackbody ($N_{\mathrm{H}}=(1.13\pm 0.03)\times 10^{23}$ cm${}^{-2}$ and $kT=1.16\pm 0.03$ keV) plus a power-law ($\Gamma =0.0\pm 1.3$) in the 1-20 keV band, with a luminosity of $\sim$$8\times 10^{34}$ erg/s, dominated by the blackbody emission. From our timing analysis, we derive a dipolar magnetic field $B\sim 7\times 10^{14}$ G, spin-down luminosity ${\dot{E}}_{\mathrm{rot}}\sim 1.4\times 10^{36}$ erg/s and characteristic age of 240 yr, the shortest currently known. Archival observations led to an upper limit on the quiescent luminosity $<$$5.5\times 10^{33}$ erg/s, lower than the value expected from magnetar cooling models at the source characteristic age. A 1 hr radio observation with the Sardinia Radio Telescope taken about 1 week after the X-ray burst detected a number of strong and short radio pulses at 1.5 GHz, in addition to regular pulsed emission; they were emitted at an average rate 0.9 min${}^{-1}$ and accounted for $\sim$50% of the total pulsed radio fluence. We conclude that Swift ,J1818.0-1607 is a peculiar magnetar belonging to the small, diverse group of young neutron stars with properties straddling those of rotationally and magnetically powered pulsars. Future observations will make a better estimation of the age possible by measuring the spin-down rate in quiescence.

10 pages, 4 figures, 1 table; revised version accepted for publication in The Astrophysical Journal Letters

References in corpus (10)

• A New Electron Density Model for Estimation of Pulsar and FRB Distances
• Rapid Cooling of the Neutron Star in Cassiopeia A Triggered by Neutron Superfluidity in Dense Matter
• 1E 1547.0-5408: a radio-emitting magnetar with a rotation period of 2 seconds
• Magnetar-like Emission from the Young Pulsar in Kes 75
• A long-period, violently-variable X-ray source in a young SNR
• A Magnetar-like Outburst from a High-B Radio Pulsar
• Magnetar-like activity from the central compact object in the SNR RCW103
• The fundamental plane for radio magnetars
• The Sleeping Monster: NuSTAR observations of SGR 1806-20, 11 years after the Giant Flare
• X-ray and Rotational Luminosity Correlation and Magnetic Heating of the Radio Pulsars

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• Discovery of ASKAP J173608.2-321635 as a Highly-Polarized Transient Point Source with the Australian SKA Pathfinder
• Long term radio and X-ray evolution of the magnetar Swift J1818.0-1607
• A broadband radio study of PSR J0250+5854: the slowest-spinning radio pulsar known
• High Frequency Radio Observations of Two Magnetars, PSR J1622$-$4950 and 1E 1547.0$-$5408
• $4-8\mathrm{GHz}$ Spectro-temporal Emission from the Galactic Center Magnetar $\mathrm{PSR}J1745-2900$
• Testing afterglow models of FRB 200428 with early post-burst observations of SGR 1935+2154
• Chandra observations of the newly discovered magnetar Swift J1818.0-1607
• Magnetar outburst and spin-down glitch
• X-ray burst and persistent emission properties of the magnetar SGR 1830-0645 in outburst
• On the radiation-loud and radiation-quiet anti-glitches in magnetar 1E 2259+586
• A month of monitoring the new magnetar Swift J1555.2-5402 during an X-ray outburst
• INTEGRAL limits on past high-energy activity from FRB 20200120E in M81
• A search for the guest star associated with Swift J1818.0-1607
• X-ray and Radio Bursts from the Magnetar 1E1547.0-5408