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

Enoto, Teruaki and Ng, Mason and Hu, Chin-Ping and Güver, Tolga and Jaisawal, Gaurava K. and O’Connor, Brendan and Göğüş, Ersin and Lien, Amy and Kisaka, Shota and Wadiasingh, Zorawar and Majid, Walid A. and Pearlman, Aaron B. and Arzoumanian, Zaven and Bansal, Karishma and Blumer, Harsha and Chakrabarty, Deepto and Gendreau, Keith and Ho, Wynn C. G. and Kouveliotou, Chryssa and Ray, Paul S. and Strohmayer, Tod E. and Younes, George and Palmer, David M. and Sakamoto, Takanori and Akahori, Takuya and Eie, Sujin (2021) A Month of Monitoring the New Magnetar Swift J1555.2−5402 during an X-Ray Outburst. Astrophysical Journal Letters, 920 (1). Art. No. L4. ISSN 2041-8205. doi:10.3847/2041-8213/ac2665.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Enoto, Teruaki0000-0003-1244-3100
Ng, Mason0000-0002-0940-6563
Hu, Chin-Ping0000-0001-8551-2002
Güver, Tolga0000-0002-3531-9842
Jaisawal, Gaurava K.0000-0002-6789-2723
O’Connor, Brendan0000-0002-9700-0036
Göğüş, Ersin0000-0002-5274-6790
Lien, Amy0000-0002-7851-9756
Kisaka, Shota0000-0002-2498-1937
Wadiasingh, Zorawar0000-0002-9249-0515
Majid, Walid A.0000-0002-4694-4221
Pearlman, Aaron B.0000-0002-8912-0732
Bansal, Karishma0000-0002-7418-7862
Blumer, Harsha0000-0003-4046-884X
Chakrabarty, Deepto0000-0001-8804-8946
Gendreau, Keith0000-0001-7115-2819
Ho, Wynn C. G.0000-0002-6089-6836
Kouveliotou, Chryssa0000-0003-1443-593X
Ray, Paul S.0000-0002-5297-5278
Strohmayer, Tod E.0000-0001-7681-5845
Younes, George0000-0002-7991-028X
Palmer, David M.0000-0001-7128-0802
Sakamoto, Takanori0000-0001-6276-6616
Akahori, Takuya0000-0001-9399-5331
Eie, Sujin0000-0003-0340-0651
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).
Funding AgencyGrant Number
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 InstituteUNSPECIFIED
Fonds de recherche du Québec - Nature et technologies (FRQNT)UNSPECIFIED
Subject Keywords:Magnetars; Magnetic fields; Neutron stars; Pulsars; Soft gamma-ray repeaters; X-ray transient sources
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Magnetars (992); Magnetic fields (994); Neutron stars (1108); Pulsars (1306); Soft gamma-ray repeaters (1471); X-ray transient sources (1852)
Record Number:CaltechAUTHORS:20211012-211827984
Persistent URL:
Official Citation:Teruaki Enoto et al 2021 ApJL 920 L4
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111379
Deposited By: George Porter
Deposited On:13 Oct 2021 16:28
Last Modified:13 Oct 2021 16:28

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