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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 (jmmiller@cfa.harvard.edu)

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 comparison.

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