Possible SGR-like bursts and X-ray brightening from the magnetar 1RXS J170849.0-400910
ATel #11871; George Younes (The George Washington University)
on 19 Jul 2018; 14:58 UT
Credential Certification: George Younes (gyounes@email.gwu.edu)
Subjects: X-ray, Gamma Ray, Neutron Star, Magnetar
Referred to by ATel #: 11873
Fermi GBM triggered on 2 bright SGR-like bursts on 2018 July 5th (GCN #22905). The two bursts were separated by 19 minutes, and locate to the same area in the sky, indicating a common origin. The 3 sigma contour of the first and brightest burst location encompass 2 known magnetars, CXOU J171405.7-381031 (Takuro et al. 2010) and 1RXS J170849.0-400910 (Israel et al. 1999). The latter is monitored by XRT with 1 observation every 20 days on average. We analyzed the first (and currently only) XRT observation of 1RXS J170849.0-400910 that is taken after the GBM triggers (obsID 00035318161, observation date 2018 July 17). We find an absorption corrected 0.5-10 keV flux of about (3.6\pm0.4)e-10 erg/s/cm2. This flux level is a factor 2 to 3 brighter than its historic flux (Campana et al. 2007, Scholz et al. 2014). We also analyzed three Swift XRT observations from the source taken prior to the 2 GBM bursts (obs IDs 00035318157, 00035318159, 00035318160), the last of which was taken on 2018 June 27. We fit all spectra simultaneously and find that the 3 observations prior to the GBM triggers are consistent with the same flux level of about (2.0\pm0.2)e-10 erg/s/cm2, 80% dimmer than the current value from the source. We conclude that the brightening in the magnetar 1RXS J170849.0-400910 is likely real and took place subsequent to June 27. Further, the brightening is accompanied by a marginal hardening of the spectrum.
Given the location of the 2 bursts in the sky and the contemporaneous detection of X-ray brightening from 1RXS J170849.0-400910, we conclude that these 2 events are likely associated. We note that such bright bursts, if indeed related to 1RXS J170849.0-400910, are detected from this magnetar for the first time (see also ATEL#10107).
We strongly encourage X-ray and multi-wavelength follow-up observations of the source to cover its first reported outburst.
