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We just submitted this as ATel 139. This source may currently be 11-13th
mag. in the near IR, although the probable extinction rules out optical
observations; it may also be highly variable, though that's far from clear
at the moment. Have a look if you can -- this is turning into a very
interesting source!
Clear skies,
Michael Rupen
NRAO/Socorro
mrupen@nrao.edu
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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)
Password Certification: Michael P. Rupen (mrupen@nrao.edu)
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.
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