IGR J17464-3213 = XTE J17464-3213: Request for IR Observations
ATel #139; M. P. Rupen, A. J. Mioduszewski, and V. Dhawan (NRAO)
on 4 Apr 2003; 21:08 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Michael P. Rupen (mrupen@nrao.edu)
Subjects: Radio, Infra-Red, X-ray, Gamma Ray, Request for Observations, Binary, Black Hole, Transient
Referred to by ATel #: 141
We report further radio observations of the X-ray transient and black
hole candidate IGR J17464-3213 = XTE J17464-3213 (ATEL #132; ATEL #133;
IAUC 8105 ) from the Very Large Array (VLA). The source continues to
brighten, and appears now to be doubling in flux density every two days.
Observations on 4 April 2003 UT give flux densities of 20.0+/-0.2 mJy
at 4.9 GHz, and 22.1+/-0.2 mJy at 8.5 GHz. The radio spectrum has remained
remarkably constant at nu^+0.2, characteristic of optically-thick synchrotron
emission.
If this spectrum continues into the near infrared, as expected in some jet
models (e.g. Markoff et al. 2003 A&A 397, 645), the K band magnitude would
be between 9th and 11th. Even with 2-3 magnitudes of K band extinction (based
on the X-ray absorption column density, ATEL #133), this should be easily
detectable. Even upper limits would be very useful indeed, in constraining
these models, and in showing whether there is a chance that some of the
X-ray emission is synchrotron.
Such associated infrared emission has already been observed in some
sources (e.g., GRS 1915+105, Fender & Pooley 1998, MNRAS 300, 573; GX 339-4,
Corbel & Fender 2002, ApJL 573, L35), but never before in combination with
such a stable and slow flux increase. One expects rapid variations, simply
because the size of the emitting region is so small, if the flat spectrum is
due to synchrotron self-absorption. Simple calculations give sizes of order
or less than a few tenths of a milliarcsecond; this corresponds to a few 10s of
light-minutes at the distance of the Galactic center, so one might hope to
see significant variations in some 10s of minutes in the near IR.
We therefore urgently request infrared observations of this source, as
soon as possible. The radio spectrum has held steady for about a week, and
the flux density seems only to increase, but this is unlikely to continue
for long.
The best position so far (from the VLA, IAUC 8105 ) is
17 46 15.61 +/- 0.01s -32 13 59.9 +/- 1" (J2000)
(we have a heavily elongated NS beam). This will improve when we have a
chance to look more carefully at the data.
