Date UT Instrument 6 Jan. 1981 Einstein HRI 13-15 July 1994 ROSAT HRI (cannot find exact times in the literature) 18 Dec. 2000 ~10:00-20:00 Chandra HRC (only occasion when 45 min X-ray pulsations were seen) 24-25 Feb. 2003 15:59-00:19 Chandra ACIS 25 Feb. 2003 00:30-20:14 Chandra HRC 25-26 Feb. 2003 23:26-08:08 Chandra ACIS 28-29 Apr. 2003 17:01-21:46 XMM-Newton EPIC & RGS Fred Jansen 25-27 Nov. 2003 23:34-09:28 XMM-Newton EPIC & RGS GBR 27-29 Nov. 2003 23:27-12:16 XMM-Newton EPIC & RGS GBR 24-25 Feb. 2007 20:37-03:01 XMM-Newton EPIC & RGS Randy Gladstone NH 3 Mar. 2007 07:39-14:41 XMM-Newton EPIC & RGS Randy Gladstone NH 7 Mar. 2007 13:15-20:20 XMM-Newton EPIC & RGS Randy Gladstone NH 8-9 Mar. 2007 20:12-02:19 XMM-Newton EPIC & RGS Randy Gladstone NH 2011 TOO GBR Will's JGR paper 15-16 Apr. 2014 21:35-09:10 XMM-Newton EPIC & RGS Ralph Kraft 20 Apr. 2014 02:51-14:56 XMM-Newton EPIC & RGS Ralph Kraft 18-19 May 2016 13:25-03:28 XMM-Newton EPIC & RGS Will Dunn Nature paper 24 May 2016 10:04-22:31 XMM-Newton EPIC & RGS Will Dunn Nature paper 19 June 2017 00:20-23:47 XMM-Newton EPIC & RGS Will Dunn