The optical counterpart to the transient X-ray pulsar SAX J2103.5+4545
ATel #173; Pablo Reig (University of Valencia) and Fotis Mavromatakis (University of Crete)
on 7 Aug 2003; 17:00 UT
Credential Certification: Pablo Reig (pablo.reig@uv.es)
Subjects: Optical, Binary, Transient, Pulsar
Referred to by ATel #: 175
We report observations of the likely optical counterpart to the 358.61-s X-ray
pulsar SAX J2103.5+4545 (Hulleman et al. 1998, A&A, 337,L25).
Optical photometric observations of the field around the best-fit BeppoSAX
position (R.A:=21:03:33, DEC = +45:45.0) carried out on 2003 June 8.96
with the 1.3-m telescope of the Skinakas Observatory (Crete, Greece)
revealed several Halpha emitters but only one inside the ~2arc-min
BeppoSAX radius error circle. The coordinates of the proposed optical
counterpart are RA=21:03:35.7 DEC=+45:45:04 (Eq. 2000), that is, ~30
arc-sec Eastward of the X-ray position. Measured photometric magnitudes
are B=15.3, V=14.2, R=13.7.
An intermediate resolution spectrum of this star taken on 2003 August 1.92
with the 1.3-m telescope of the Skinakas Observatory shows a red-dominated
double-peaked H-alpha emission line with an equivalent width of EW=-2.5A
and the presence of Helium. These spectral characteristics together with
the modulation of the X-ray flux with the orbital period of 12.68 days
(Baykal et al. 2000, ApJ, 544, L129) suggest that the system is a Be/X-ray
binary.
Further optical observations are underway to determine the spectral type and
confirm if the object is a Be star.
