The Galactic Center magnetar SGR J1745-2900 is in X-ray quiescence
ATel #14661; N. Rea (ICE-CSIC), G. Ponti (INAF, MPE), F. Coti Zelati (ICE-CSIC), A. Borghese (ICE-CSIC), P. Esposito (IUSS, INAF), G. L. Israel (INAF), and the GRAVITY GC team
on 26 May 2021; 09:33 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Nanda Rea (rea@ice.csic.es)
Subjects: X-ray, Neutron Star, Soft Gamma-ray Repeater, Transient, Pulsar, Magnetar
The Galactic Center magnetar (SGR J1725-2900) was discovered on 2013 April 25, when it emitted a short X-ray burst (Kennea et al. 2013) coupled with a powerful long-term X-ray outburst (Rea et al. 2013; Mori et al. 2013). In the past years it has been slowly decaying toward quiescence (Coti Zelati et al. 2017; Rea et al. 2020). This intriguing source is unique among magnetars for its position at less than 2.5" from our massive black hole, SgrA*, and its bright and variable radio pulsed emission. The magnetar did not show further short X-ray bursts during its long-term outburst decay.
On 2021 May 19 (19:22:03.94 UT) the Fermi-GBM team reported on a magnetar-like X-ray burst from the direction of SGR J1725-2900, with a duration of about 0.3s, and with an average photon flux in the 10-300 keV band of 9.5(7) ph/s/cm^2 (Lesage et al. 2021, GCN 30058).
The Chandra X-ray Observatory observed the Galactic Center on 2021 May 23, for about 20ks in TE-mode with the aim point on the ACIS-S3 CCD (OBSID: 22592; PI: Ponti). The magnetar was found at a count rate of 2.4(3)x10^-3 count/s, consistent with recent observations performed in August 2019 (Rea et al. 2020). We conclude that SGR J1725-2900 is not undergoing a second outburst, while it is still at its X-ray quiescent flux.
The emission of short X-ray bursts in magnetars with such low X-ray quiescent level (Lqui~5x10^33 erg/s; Rea et al. 2020) are usually followed by a bright X-ray outburst, although we cannot exclude this being an exception. Given the very large error box of the Fermi-GBM detection (3.97 degrees; Lesage private communication), it is possible that the short X-ray burst detected by Fermi-GBM was not emitted by SGR J1725-2900, but it was due to another magnetar in that direction.
