Outburst of the X-ray transient in NGC 6440 and identification of the optical and quiescent X-ray counterparts
ATel #74; Jean in 't Zand (SRON, Utrecht), Dave Pooley and Walter Lewin (MIT), Marten van Kerkwijk and Frank Verbunt (University Utrecht)
on 31 Aug 2001; 12:24 UT
Credential Certification: Erik Kuulkers (E.KUulkers@sron.nl)
Subjects: Optical, X-ray, Binary, Globular Cluster, Neutron Star, Transient
We have obtained observations with ESO NTT SUSI2 in B and R and with
Chandra ACIS-S of the transient in NGC6440, which is in outburst again
since before 2001 Aug 14, as discovered with RXTE ASM
(http://xte.mit.edu/asmlc/ASM.html). The Chandra position of the
transient coincides with the brightest source (of some 20 detected
sources) in our 2000 July 4 Chandra observation, obtained when the
transient was not active, and with the optical variable V2 which was
active during 1998 August outburst of the transient (In 't Zand et
al. 1999, A&A 345, 100; Verbunt et al. 2000, A&A 359, 960). Our
optical observations in B show that V2 is bright again, and thus
confirm that this variable is the optical counterpart of the
transient. We encourage further optical observations.
A first analysis of the quiescent Chandra source confirms that its
spectrum can be described with that of a neutron star atmosphere
(Zavlin et al. 1996 A&A 315, 141), as expected for a soft X-ray
transient in quiescence, with the distance and interstellar absorption
of NGC6440. A paper describing these results in more detail is in
preparation.
