IGR/XTE J17464-3213: Magellan optical upper limits
ATel #141; D. Steeghs, J. M.Miller (CfA), D. Kaplan (Caltech), M. Rupen (NRAO)
on 7 Apr 2003; 22:10 UT
Credential Certification: Jon M. Miller (firstname.lastname@example.org)
Subjects: Radio, Infra-Red, Optical, X-ray, Gamma Ray, Binary, Black Hole, Transient
Referred to by ATel #: 146
We report optical observations of the field of the transient IGR/XTE
J17464-3213 using the Magic CCD camera on the Magellan-Clay telescope
at Las Campanas Observatory.
Johnson R and I-band images obtained on April 5 2003 with
an image seeing of 0.5" reveal no optical counterpart at the radio
position reported by Rupen et al. (ATEL #139) down to I~26 and R~26.5.
We spatially resolve the emission reported by Khamitov et al. (2003,
ATEL #140), and attribute their 'weak source' to a superposition of
several background sources. A close-up of the Magellan image
corresponding to roughly the HEAO error box width is linked below for
Using the Schlegel et al. (1998, ApJ 500, 525) extinction maps, the
extinction is estimated to amount to 6.7 mags in the I-band thus
setting a de-reddened upper limit of I>19 to any optical counterpart.
The RXTE-measured N_H (Markwardt & Swank 2003, ATEL #133) would give a
larger extinction (9.7 mags in I). However, this is not a parameter
which RXTE can measure well and we regard estimates from Schlegel
et al. (1998) to be more accurate.
The jet models proposed to describe the broad-band spectrum of, for
example, GX 339-4 (Markoff et al. 2003, A&A, 397, 645)
include many spectral components, such as pre-shock and post-shock
jet synchrotron emission. For most of the models considered,
predictions for either jet synchrotron components in I are within an
order of magnitude of the radio flux densities. Extrapolating the VLA
observations obtained the morning before our observations, and
assuming the same power-law index (Rupen, Miduszewski, and Dhawan
2003, ATEL #139), a de-reddened I magnitude of 11.3 would have been
expected. Our I-band limits are thus three orders of magnitude
fainter than this extrapolation and appear to rule out similar models
for IGR/XTE 17464-3213. In this particular case at least there is
no evidence for optically thick jet emission extending to the IR.
More recent VLA observations obtained on Sunday morning show a similar
flux density at 4.9 GHz compared to Friday morning (~20 mJy). However,
the spectrum from 4.9 to 8.5 to 43 GHz has changed slope to nu^=-0.05
as opposed to nu^+0.2 suggesting that the source is starting to
fade. These latest radio pointings would result in an extrapolated
I-band magnitude of I=12.9 as opposed to I=11.3 derived from the
Friday morning VLA data.
Magellan image: http://hea-www.harvard.edu/~dsteeghs/IGR1746_Magellan_I_zoom.gif
Link to Magellan I-band image