INTEGRAL and Swift follow-up observations of XMMSL1 J171900.4- 353217

Following the detection of hard X-ray emission from XMMSL1 J171900.4-353217 (Atel #2607) with INTEGRAL (Atel #2803), a Swift/XRT follow-up observation (2 ks) was performed on 2010 August 20 from 13:03 to 14:53, simultaneously with the newly INTEGRAL observation of the same FOV (2010 August 19 at 17:13 to 2010 August 20 at 15:08, PI R.

Terrier). In the Swift/XRT FOV only one X-ray source is detected at a position consistent with that of XMMSL1 J171900.4-353217. The source spectrum was best fit (chi^2_red/dof=0.97/27) by using an absorbed power-law model with N_h=(5.1-1.2+1.4)E22 cm^(-2) and Gamma=2.1+/-0.5. The estimated 2-10 keV flux is 2.6E-11 erg/cm^2/s (2-10 keV).

XMMSL1 J171900.4-353217 was not detected in the simultaneous INTEGRAL observations. We estimated a 3 sigma upper limit on its X-ray flux of 11 mCrab (~2.6E-10 erg/cm^2/s) in the 3-20 keV energy band (Jem-X, exposure time 5.5 ks), 3.5 mCrab (~2.7E-11 erg/cm^2/s) in the 20-40 keV energy band, and 5.5 mCrab (~3.9E-11 erg/cm^2/s) in the 40-80 keV energy band (ISGRI, exposure time 75 ks).

These results suggest that XMMSL1 J171900.4-353217 might have undergone a re-brightening after its previous return to quiescence (Atel #2738) and is now fading again (the highest flux measured by Swift/XRT from this source was of ~5E-11 erg/cm^2/s, i.e. a factor of ~2 larger than the current value).

We performed a fit of the combined Swift/XRT and ISGRI spectrum (we used the spectrum discussed in Atel #2803) with an absorbed power-law model and included a constant to account for variability and inter-calibration between the two instruments. We obtained spectral parameter completely compatible with those reported above and a value of the inter-calibration constant of 2.2-1.3+3.3.

This suggests that the variation of the source X-ray flux between the two observations was not dramatic. We thanks the Swift team for their support and rapid scheduling of the observation of XMMSL1 J171900.4-353217.