CaltechAUTHORS
Published October 10, 2021 | Version Published + Submitted
Journal Article Open

A Month of Monitoring the New Magnetar Swift J1555.2−5402 during an X-Ray Outburst

Creators

  • 1. ROR icon RIKEN
  • 2. ROR icon Massachusetts Institute of Technology
  • 3. ROR icon National Changhua University of Education
  • 4. ROR icon Istanbul University
  • 5. ROR icon Technical University of Denmark
  • 6. ROR icon George Washington University
  • 7. ROR icon University of Maryland, College Park
  • 8. ROR icon Sabancı University
  • 9. ROR icon Goddard Space Flight Center
  • 10. ROR icon University of Maryland, Baltimore County
  • 11. ROR icon University of Tampa
  • 12. ROR icon Hiroshima University
  • 13. ROR icon Universities Space Research Association
  • 14. ROR icon Jet Propulsion Lab
  • 15. ROR icon California Institute of Technology
  • 16. ROR icon McGill University
  • 17. ROR icon West Virginia University
  • 18. ROR icon Haverford College
  • 19. ROR icon United States Naval Research Laboratory
  • 20. ROR icon Los Alamos National Laboratory
  • 21. ROR icon Aoyama Gakuin University
  • 22. ROR icon National Astronomical Observatory of Japan
  • 23. ROR icon University of Tokyo

Abstract

The soft gamma-ray repeater Swift J1555.2−5402 was discovered by means of a short burst detected with Swift BAT on 2021 June 3. Then, 1.6 hr after the burst, the Neutron star Interior Composition Explorer (NICER) started daily monitoring of this target for a month. The absorbed 2–10 keV flux stayed nearly constant at around 4 × 10⁻¹¹ erg s⁻¹ cm⁻² during the monitoring, showing only a slight gradual decline. An absorbed blackbody with a temperature of 1.1 keV approximates the soft X-ray spectrum. A 3.86 s periodicity is detected, and the period derivative is measured to be 3.05(7) × 10⁻¹¹ s s⁻¹. The soft X-ray pulse shows a single sinusoidal shape with an rms 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 3.5 × 10¹⁴ G, 2.0 kyr, and 2.1 × 10³⁴ erg s⁻¹, respectively. We detect 5 and 45 bursts with Swift/BAT and NICER, respectively. Based on these properties, this new source is classified as a magnetar. A hard X-ray power-law component that extends up to at least 40 keV is detected with the Nuclear Spectroscopic Telescope Array (NuSTAR). The 10–60 keV flux is ∼9 × 10⁻¹² erg s⁻¹ cm⁻² with a photon index of ∼1.2. The pulsed fraction has a sharp cutoff at around 10 keV with an upper limit (≲10%) in the hard-tail band. No radio pulsations are detected during the DSN or VERA observations. The 7σ upper limits of the flux density are 0.043 and 0.026 mJy at the S and X bands, respectively.

Additional Information

© 2021. The American Astronomical Society. Received 2021 August 5; revised 2021 September 8; accepted 2021 September 10; published 2021 October 5. The authors are grateful to the NICER, NuSTAR, Swift, and DSN scheduling and operation teams. We thank Francesco Coti Zelati, Alice Borghese, Nanda Rea, Gian Luca Israel, and Paolo Esposito for helpful discussion about the initial observation and for preparing the GCN reports. We also acknowledge Alice Borghese for her request of the Swift observation at the earliest phase of the outburst. We thank Mareki Honma, Takaaki Jike, Aya Yamauchi, Toshio Terasawa, and Tomoya Hirota for useful comments on the VERA observation and all the staff of Mizusawa VLBI Observatory of NAOJ for operating the VERA array. T.E. and S.K. are supported by JSPS/MEXT KAKENHI grant Nos. 17K18776, 18H04584, 18H01246, 19K14712, and 21H01078. A.B.P. is a McGill Space Institute (MSI) Fellow and a Fonds de Recherche du Quebec—Nature et Technologies (FRQNT) postdoctoral fellow. W.C.G.H. acknowledges support through grant 80NSSC20K0278 from NASA. NICER research at NRL is supported by NASA. W.A.M. is grateful to the DSN scheduling team and the Canberra Deep Space Communication Complex (CDSCC) staff for scheduling and carrying out the radio observations with the DSN. A portion of this research was performed at the Jet Propulsion Laboratory, California Institute of Technology, under a Research and Technology Development Grant through a contract with the National Aeronautics and Space Administration. U.S. government sponsorship is acknowledged. Facilities: NICER - , NuSTAR - , Swift - , DSN - , VERA. - Software: HEAsoft (v6.27.2; NASA High Energy Astrophysics Science Archive Research Center (HEASARC), 2014), astropy (Astropy Collaboration et al. 2013; Price-Whelan et al. 2018), PRESTO (Ransom et al. 2002), FETCH (Agarwal et al. 2020), PINT (v0.8.2; Luo et al. 2021), XSPEC (Arnaud 1996), NICERDAS (v2020-04-23_V007a).

Attached Files

Published - Enoto_2021_ApJL_920_L4.pdf

Submitted - 2108.02939.pdf

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2108.02939.pdf

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Additional details

Identifiers

Eprint ID
111379
Resolver ID
CaltechAUTHORS:20211012-211827984

Related works

Describes
https://arxiv.org/abs/2108.02939 (URL)

Funding

Japan Society for the Promotion of Science (JSPS)
17K18776
Japan Society for the Promotion of Science (JSPS)
18H04584
Japan Society for the Promotion of Science (JSPS)
18H01246
Japan Society for the Promotion of Science (JSPS)
19K14712
Japan Society for the Promotion of Science (JSPS)
21H01078
McGill Space Institute
Fonds de recherche du Québec - Nature et technologies (FRQNT)
NASA
80NSSC20K0278
NASA/JPL/Caltech

Dates

Created
2021-10-13
Created from EPrint's datestamp field
Updated
2023-03-16
Created from EPrint's last_modified field

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NuSTAR