A month of monitoring the new magnetar Swift J1555.2-5402 during an X-ray outburst

Abstract

The soft gamma-ray repeater Swift J1555.2-5402 was discovered by means of a 12-ms duration short burst detected with Swift BAT on 2021 June 3. Then 1.6 hours after the first burst detection, NICER started daily monitoring of this X-ray source for a month. The absorbed 2-10 keV flux stays nearly constant at around 4e-11 erg/s/cm2 during the monitoring timespan, showing only a slight gradual decline. A 3.86-s periodicity is detected, and the time derivative of this period is measured to be 3.05(7)e-11 s/s. The soft X-ray pulse shows a single sinusoidal shape with a root-mean-square pulsed fraction that increases as a function of energy from 15% at 1.5 keV to 39% at 7 keV. The equatorial surface magnetic field, characteristic age, and spin-down luminosity are derived under the dipole field approximation to be 3.5e+14 G, 2.0 kyr, and 2.1e+34 erg/s, respectively. An absorbed blackbody with a temperature of 1.1 keV approximates the soft X-ray spectrum. Assuming a source distance of 10 kpc, the peak X-ray luminosity is ~8.5e+35 erg/s in the 2--10 keV band. During the period of observations, we detect 5 and 37 short bursts with Swift/BAT and NICER, respectively. Based on these observational properties, especially the inferred strong magnetic field, this new source is classified as a magnetar. We also coordinated hard X-ray and radio observations with NuSTAR, DSN, and VERA. A hard X-ray power-law component that extends up to at least 40 keV is detected at 3-sigma significance. The 10-60 keV flux, which is dominated by the power-law component, is ~9e-12 erg/s/cm2 with a photon index of ~1.2. The pulsed fraction has a sharp cutoff above 10 keV, down to ~10% in the hard-tail component band. No radio pulsations are detected during the DSN nor VERA observations. We place 7σ upper limits of 0.043mJy and 0.026 mJy on the flux density at S-band and X-band, respectively.

26 pages, 7 figures (3 figures in the appendix), 10 tables (9 tables in the appendix). Submitted to ApJL

References in corpus (37)

• A fast radio burst associated with a Galactic magnetar
• A bright millisecond-duration radio burst from a Galactic magnetar
• The strongest cosmic magnets: Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars
• INTEGRAL discovery of a burst with associated radio emission from the magnetar SGR 1935+2154
• 1E 1547.0-5408: a radio-emitting magnetar with a rotation period of 2 seconds
• HXMT Identification of a non-thermal X-ray burst from SGR J1935+2154 and with FRB 200428
• Discovery of luminous pulsed hard X-ray emission from anomalous X-ray pulsars 1RXS J1708-4009, 4U 0142+61 and 1E 2259+586 by INTEGRAL and RXTE
• A peculiar hard X-ray counterpart of a Galactic fast radio burst
• PINT: A Modern Software Package for Pulsar Timing
• Repeating Fast Radio Bursts from Magnetars with Low Magnetospheric Twist
• The Prelude to and Aftermath of the Giant Flare of 2004 December 27: Persistent and Pulsed X-ray Properties of SGR 1806-20 from 1993 to 2005
• The magnetar 1E 1547.0-5408: radio spectrum, polarimetry, and timing
• The Compact X-ray Source 1E 1547.0-5408 and the Radio Shell G327.24-0.13: A New Proposed Association between a Candidate Magnetar and a Candidate Supernova Remnant
• Radio emission evolution, polarimetry and multifrequency single pulse analysis of the radio magnetar PSR J1622-4950
• The variable radio-to-X-ray spectrum of the magnetar XTE J1810-197
• The first XMM-Newton observations of the Soft Gamma-ray Repeater SGR 1900+14
• A very young radio-loud magnetar
• Repeated, Delayed Torque Variations Following X-ray Flux Enhancements in the Magnetar 1E1048.1$-$5937
• Spectropolarimetric properties of Swift J1818.0$-$1607: a 1.4 s radio magnetar
• The X-ray reactivation of the radio bursting magnetar SGR 1935+2154
• The Sleeping Monster: NuSTAR observations of SGR 1806-20, 11 years after the Giant Flare
• The dynamic magnetosphere of Swift J1818.0$-$1607
• Post-Outburst Radio Observations of the High Magnetic Field Pulsar PSR J1119-6127
• NICER Observation of the Temporal and Spectral Evolution of Swift J1818.0-1607: a Missing Link between Magnetars and Rotation Powered Pulsars
• Spin-down rate and inferred dipole magnetic field of the soft gamma-ray repeater SGR 1627-41
• The X-ray evolution and geometry of the 2018 outburst of XTE J1810-197
• Two new outbursts and transient hard X-rays from 1E 1048.1$-$5937
• Pulse Phase-coherent Timing and Spectroscopy of CXOU J164710.2-45521 Outbursts
• The new magnetar SGR J1830-0645 in outburst
• Swift observations of two outbursts from the magnetar 4U 0142+61
• Simultaneous 2.25/8.60 GHz observations of the newly discovered magnetar -- Swift J1818.0-1607
• A systematic study of soft X-ray pulse profiles of magnetars in quiescence
• Observations of Radio Magnetars with the Deep Space Network
• The multi-outburst activity of the magnetar in Westerlund I
• The X-ray outburst of the Galactic Center magnetar over six years of Chandra observations
• Persistent Emission Properties of SGR J1935+2154 During Its 2020 Active Episode
• More than meets the eye: magnetars in disguise