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Vela X-1 in highly active hard X-ray state

ATel #1782; P. Soffitta, E. Costa, E. Del Monte, I. Donnarumma, Y. Evangelista, M. Feroci, I. Lapshov, F. Lazzarotto, L. Pacciani, M. Rapisarda, A. Argan, A. Trois , M. Tavani, G. Piano, G. Pucella, F. D'Ammando, V. Vittorini (INAF/IASF Roma), A. Bulgarelli, F. Gianotti, M. Trifoglio, G. Di Cocco, C. Labanti, F. Fuschino, M. Marisaldi, M. Galli, (INAF/IASF Bologna), A. Chen, S. Vercellone, A. Giuliani, S. Mereghetti, F. Perotti, P. Caraveo (INAF/IASF Milano), A. Pellizzoni (OAC/INAF Cagliari), G. Barbiellini, F. Longo, E. Vallazza (INFN Trieste), P. Picozza, A. Morselli (INFN Roma-2), M. Prest (Universita` dell'Insubria), P. Lipari, D. Zanello (INFN Roma-1), A. Rappoldi (INFN Pavia) and C. Pittori, F. Verrecchia, P. Santolamazza, B. Preger, P. Giommi (ASDC) and L. Salotti (ASI)
on 15 Oct 2008; 14:54 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Marco Feroci (marco.feroci@iasf-roma.inaf.it)

Subjects: X-ray, Request for Observations, Binary, Neutron Star, Transient

The current pointing of the AGILE mission at (l,b)=(256,-20), started on 10th October 2008, includes the Vela region. In particular, Vela X-1 lies at approximately 25 degrees off-axis. Between MJD 54750 and 54752 (October 11-13) this source was detected by SuperAGILE with a flux varying in the range 250 mCrab - 1 Crab in 20-60 keV. Starting on MJD 54752.5 the flux showed a large and intense flare lasting approximately 12 hours and peaking at 2.3 Crab (AGILE orbit - 90 minutes - average), with a rise time of about 7 hours. After the flare, the source flux averaged again at about 500 mCrab for one day and at MJD 54753.8 (October 14) started a new flare that is currently ongoing. In its brightest periods, the 283.5-s spin pulsation of the source was directly visible on the raw light curve of the SuperAGILE experiment. During this period of large activity the source also exhibited intense activity on short time scale. A short flare occurred today, 15th October 2008, at 05:49 UT and lasted about 100 s, during which the source average flux was about 4 Crabs. The AGILE pointing to the Vela region is planned to end on 17th October 2008, 12 UT. The SuperAGILE orbital light curve of Vela X-1 may be found at the AGILE Science Data Center website: http://agile.asdc.asi.it/news.html.