INTEGRAL observations of the Galactic Center region: Sgr A* and SAX J1808.4-3658

Following the recent report of enhanced activity from Sgr A* (ATeLs #12768, #13007, #13023), we report measurements derived from INTEGRAL observations. Sgr A* is not detected by the imaging pipeline in the combined images covering the Galactic Center region performed from 2019-08-15 15:10:48 to 2019-08-16 08:20:18.

We derive a flux upper limit by forcing the IBIS/ISGRI spectral extraction at the source location. Assuming a power-law spectrum with index -2 (ATeL #13023) and exploiting an exposure of 36 ks, the 3 sigma upper limit is 4e-11 erg/s/cm^2 in the 30-50 keV energy band, which corresponds to 1e-10 erg/s/cm^2 in the 5-16 keV band.

The JEM-X 3 sigma upper limit is 1e-10 erg/cm2/s (6.5 mCrab) in the 3-10 keV band and 1.5e-10 erg/cm2/s (13.5 mCrab) in the 10-25 keV for 10 ks on-source time. In the same observation, we could detect with IBIS/ISGRI at a significance of about 7 sigma, the accreting millisecond pulsar SAX J1808.4-3658, recently reported to be in outburst (ATeL #12964,, #13001, #13022).

We performed spectral extraction of IBIS/ISGRI data only, as the source is outside the JEM-X field of view. The power-law index is 2.6-0.8+1.2, while the 30-50 keV flux of SAX J1808.4-3658 is 9.3±2.4 × 1e-11 erg/s/cm^2, which corresponds to about 18±5 mCrab (uncertainties at 90% c.l.).