XMM-Newton and NuSTAR observations of SGR 1935+2154 during its latest activation in 2022 October

ATel #15745; A. Y. Ibrahim, E. Parent, R. Sathyaprakash, A. Marino, F. Coti Zelati, N. Rea (ICE, CSIC-IEEC), A. Borghese (IAC), G. L. Israel (INAF-OAR), P. Esposito (IUSS) on behalf of a larger collaboration
on 4 Nov 2022; 16:58 UT
Credential Certification: Alice Borghese (aborghese@iac.es)

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After the recent re-activation of the magnetar SGR 1935+2154 on 2022 October 12 (GCN#32675, Atel #13685, #15667), we activated our XMM-Newton+NuSTAR pre-approved ToO program.

Two XMM-Newton observations were acquired on 2022 October 15 (Start: 2022-10-15 19:39:46 UTC, End: 2022-10-16 12:10:02 UTC; exposure time: 42 ks) and 2022 October 22 (Start: 2022-10-22 03:13:53 UTC, End: 2022-10-22 22:18:05 UTC; exposure time: 48 ks). Two NuSTAR observations were also performed on 2020 May 20 (Start: 2022-10-18 21:51:09 UTC, End: 2022-10-20 00:56:09 UTC; exposure time: 50 ks) and on 2022 October 22 (Start: 2022-10-22 22:21:09 UTC, End: 2022-10-24 03:11:09 UTC; exposure time: 51 ks).

The source was detected up to 25 keV at both epochs and several short X-ray bursts were observed. We performed a joint fit for the quasi-simultaneous XMM-Newton and NuSTAR spectral data in the 0.3-25 keV energy range. The spectrum of the persistent emission was well modeled by an absorbed black-body model plus a power-law component. We fixed the hydrogen column density to N_H = 2.3e22 cm^-2 (Borghese et al. 2022). We derived a blackbody temperature kT = 0.46+/-0.01 keV and a power-law photon index Gamma = 1.45+/-0.02 for the first epoch, and kT = 0.45+/-0.01 keV, Gamma = 1.33+/-0.02 for the second epoch (1 sigma c.l.). We reported a 0.3-25 keV observed flux of (1.375+/-0.001)e-11 ergs/cm^2/s and (1.170+/-0.001)e-11 ergs/cm^2/s for the first and the second epoch, respectively.

We derived a phase coherent timing solution covering the 59868.006-59857.544 MJD period. Our timing analysis led us to estimate a spin frequency of F0 = 0.30752682(4) Hz (P = 3.2517489(4) s) and a spin frequency derivative of F1=-5.2(1)x10^-12 Hz/s (Pdot = 5.5(1)x10^-11 s/s) with a reference epoch 59868.16 MJD (2022-10-16 03:50:24 UTC).

We list below the times of the brightest bursts identified from our preliminary analysis. We encourage radio observers to contact us if they have acquired simultaneous data. The times are referred to the solar system barycenter (ephemeris DE 200):
XMM-Newton 2022 Oct 15 20:26:14
XMM-Newton 2022 Oct 16 03:53:09
XMM-Newton 2022 Oct 16 10:35:28
XMM-Newton 2022 Oct 16 10:45:14
XMM-Newton 2022 Oct 16 12:05:02
NuSTAR 2022 Oct 19 06:26:30
NuSTAR 2022 Oct 19 07:56:59
NuSTAR 2022 Oct 19 09:48:57
NuSTAR 2022 Oct 19 11:26:30
NuSTAR 2022 Oct 19 13:21:32
NuSTAR 2022 Oct 19 17:46:13
NuSTAR 2022 Oct 20 00:13:18
XMM-Newton 2022 Oct 22 04:46:14
XMM-Newton 2022 Oct 22 04:53:17
XMM-Newton 2022 Oct 22 05:26:30
XMM-Newton 2022 Oct 22 06:12:48
XMM-Newton 2022 Oct 22 06:18:35
XMM-Newton 2022 Oct 22 09:29:30
XMM-Newton 2022 Oct 22 10:01:26
XMM-Newton 2022 Oct 22 13:11:34
XMM-Newton 2022 Oct 22 14:18:58
XMM-Newton 2022 Oct 22 15:41:35
XMM-Newton 2022 Oct 22 16:25:02
XMM-Newton 2022 Oct 22 16:31:34
XMM-Newton 2022 Oct 22 16:40:48
XMM-Newton 2022 Oct 22 16:42:44
XMM-Newton 2022 Oct 22 17:37:27
NuSTAR 2022 Oct 22 22:57:24
NuSTAR 2022 Oct 23 21:58:06
NuSTAR 2022 Oct 23 22:50:23

We thank the XMM-Newton and NuSTAR teams for the prompt reaction after our trigger, and for the large effort in planning these observations.