SIMBAD references

Following a significant detection of the neutron star transient Aql X-1 during the RXTE/PCA Galactic bulge scan observations on October 13, 2011 ( http://lheawww.gsfc.nasa.gov/users/craigm/galscan/html/Aql_X-1.html we carried out a Swift/XRT ToO observation with the windowed timing mode at 23:23 (UT) on October 14, 2011 with a net exposure of 975

seconds. The Swift/XRT confirmed a bright X-ray source at a position consistent with Aql X-1. The XRT spectrum in the 0.5-8 keV range is well-described by an absorbed blackbody plus power-law with a temperature of 0.84 ± 0.14 keV, a photon index of 1.93 ± 0.22, and a hydrogen column density NH of (0.44 ± 0.06) x 10^22 cm^-2 (chi^2/dof = 277/272). The absorbed flux was 3.8 x 10^-10 erg cm^-2 s^-1

in the 0.5-10 keV range. This bright level of X-ray emission therefore indicates that Aql X-1 has now started a new outburst. The previous

one was in July-October 2010 (ATels #2742, #2850, #2911).

The Swift/BAT hard X-ray transient monitor also reports a flux increase from Aql X-1 in the 15-50 keV band. Starting on 2011 October

11, the flux rose to 0.0023 ± 0.0011 ct/s (∼10 mCrab) and has risen slowly since then to 0.0034 ± 0.0014 (∼15 mCrab) on October 14. Note that this is still well below the peak reached in the 2010 outburst of > 100 mCrab.

Further monitoring with Swift will be planned every two days. Observations at other wavelengths are strongly encouraged. We thank the Swift team for a prompt scheduling of our observation.