Optical Observations of XTE J1810-197 and SGR 1806-20
ATel #195; Solen Balman (METU, Ankara), Samar Safi-Harb (U. of Manitoba, Canada), Alaa I. Ibrahim (NASA/GSFC & GWU), Jean H. Swank (NASA/GSFC), Craig Markwardt (NASA/GSFC & UMD)
on 26 Sep 2003; 21:19 UT
Credential Certification: Alaa I. Ibrahim (alaa@milkyway.gsfc.nasa.gov)
Subjects: Optical, X-ray, Neutron Star, Soft Gamma-ray Repeater, Pulsar
Referred to by ATel #: 203
We have observed the Chandra error boxes of the newly discovered Anomalous X-ray Pulsar candidate XTE J1810-197 (also known as CXOU J180951.1-194351; IAUC 8168 , IAUC 8190 ) and the Soft Gamma Repeater SGR 1806-20 (Kaplan et al. 2002) with the 1.5 m Russian-Turkish Telescope, RTT150 (Antalya, Turkey) on 2003 September 3 and 6. Optical Cousins R filter images of both fields were obtained using the ANDOR CCD (2048x2048 pixels, 0.24" pixel scale and 8'x8' Field of View) with 15 min exposure times for XTE J1810-197 (3 frames) and 3 min exposure times for SGR 1806-20 (9 Frames). Seeing was about 2". The data was reduced using ESO-MIDAS software with standard cleaning and calibration processes and photometry was performed on each and/or aligned and merged images to obtain stellar magnitudes.
We do not detect an optical counterpart for either of the sources. Our analysis shows that a limiting magnitude of 21.5 (2 sigma) in the Rc band is achieved for both of the X-ray sources. Since SGR 1806-20 was intermittently burst-active from July 14 to the time of the observation, this is a limit on the optical magnitude during a (mild) SGR active phase. The derived upper limit rules out any main sequence or giant star as a counterpart for the sources and would be consistent with a magnetospheric origin for the optical emission from AXPs and SGRs. It is compatible with the other non-detections/upper limits (>23.5 mag) placed on AXPs in the optical wavelengths (Israel et al. 2002; 2003; Hulleman et al. 2001) - except for 4U0142+61, for which an optical counterpart was identified (Hulleman et al. 2000). This supports the proposed AXP nature of XTE J1810-197 and the conjectured connection between AXPs and SGRs as magnetars.
This telegram is citable
