Optical counterpart to IGR J11435-6109
ATel #370; José Miguel Torrejón, Ignacio Negueruela (Universidad de Alicante)
on 20 Dec 2004; 12:36 UT
Credential Certification: Ignacio Negueruela (ignacio@dfists.ua.es)
Subjects: Optical, X-ray, Binary, Star, Transient, Pulsar
Optical observations of the field of the 162-s pulsar IGR J11435-6109 (ATel #350, #359, #362) were conducted during the nights of December 14th and 15th with the 3.5-m NTT (La Silla) as backup for another programme.
As a likely identification of the INTEGRAL source with 1RXS J114358.1-610736 had been proposed (ATel #350), we first took a spectrum of the only star within the error circle of the ROSAT source (about 1" from the nominal position of the ROSAT source), USNO-B1.0 0288-0337417 (RA: 11h43m58.5s, Dec: -61d07'37"). The spectrum corresponds to an M star, with pronounced molecular bands. 1RXS J114358.1-610736 is hence associated with an active corona and is not the same source as IGR J11435-6109.
Moreover, slitless spectroscopy of the field reveals a moderately bright nearby object with H-alpha in emission. This is USNO-B1.0 0288-0337948 (RA: 11h44m10.7s, Dec: -61d07'02"), with magnitudes
listed as b2=13.17, r2=12.95, i=11.61. The object lies within the BeppoSAX WFC error circle for IGR J11435-6109 (about 1.2' away from its nominal position) and also about 1.2' away from the Einstein
position for 2E 1141.6-6050. It is 3' away from the centre of the INTEGRAL/IBIS error circle.
Long-slit spectroscopy of USNO-B1.0 0288-0337948 shows it to be a Be star of approximate spectral type B3. This is hence very likely the counterpart to IGR J11435-6109. The source would be a Be/X-ray transient, as suggested by the X-ray properties (ATel #362). Further analysis is in progress.
