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INTEGRAL observations of U Sco

ATEL # 2412; A. Manousakis (ISDC/Unige), M. Revnivtsev (IKI, Excellence Cluster Universe), R. Krivonos (MPA, IKI), E. Bozzo (ISDC/Unige)
on 2 Feb 2010; 13:20 UT
Distributed as an Instant Email Notice (Nova)
Password Certification: Nami Mowlavi (Nami.Mowlavi@obs.unige.ch)

Subjects: Optical, X-ray, Gamma Ray, Nova

The recurrent Nova U Sco was discovered in outburst on 28 January 2010 (http://www.aavso.org/publications/alerts/alert415.shtml).
From 2010-01-28 17:01:43 to 2010-01-29 05:10:01 (exposure time ~45 ks), INTEGRAL was observing the field
around Sco X-1 (PI M. Revnivtsev), and U Sco was inside the IBIS/ISGRI and JEMX-2 fields of view.

The source was not detected by INTEGRAL X and gamma-ray instruments. We derived an 2 sigma upper limits on the source X-ray flux:
4 mCrab in the 20-40 keV energy band, 5 mCrab in the 40-80 keV energy band, 10 mCrab in 3-10 keV energy band.

Faintness of the source in X-ray energy band broadly resembles its behavior during outburst in 1999, and it likely caused by absence of enough amount of
interstellar material, which can be shocked by outflowing shell to produce hot X-ray emitting plasma. Supersoft X-ray emission at energies lower
than ~0.5-0.7 keV, which might be expected from this source at later stages of the outburst can not be detected by INTEGRAL.

U Sco was instead detected by the Optical Monitor on-board INTEGRAL. The visual (V- band) magnitude of the source was V=8.76+-0.01 on
2010-01-28 23:31 UTC. This result is in a good agreement with AAVSO announcement (see link above).


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R. E. Rutledge , Editor
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