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Swift detection of an X-ray transient possibly associated with IGR J17354-3255

ATel #2019; S. Vercellone (INAF-IASF Palermo), F. D'Ammando, E. Striani, M. Tavani (INAF-IASF Roma), S. Sabatini (INFN Roma-2), A. Bulgarelli, F. Gianotti, M. Trifoglio (INAF-IASF Bologna), M. Feroci, F. Lazzarotto, E. Del Monte (INAF-IASF Roma), C. Pittori, F. Verrecchia (ASDC), A. Pellizzoni, M. Pilia (INAF-OACagliari), A. Chen, A. Giuliani (INAF-IASF Milano), G. Piano, G. Pucella, V. Vittorini, E. Costa, I. Donnarumma, L. Pacciani, P. Soffitta, Y. Evangelista, I. Lapshov, M. Rapisarda, A. Argan, A. Trois, G. De Paris (INAF-IASF Roma), M. Marisaldi, G. Di Cocco, C. Labanti, F. Fuschino, M. Galli (INAF-IASF Bologna), P. Caraveo, S. Mereghetti, F. Perotti, M. Fiorini, A. Zambra (INAF-IASF Milano), G. Barbiellini, F. Longo, E. Moretti, E. Vallazza (INFN Trieste), P. Picozza, A. Morselli (INFN Roma-2), M. Prest (Universita` dell'Insubria), P. Lipari, D. Zanello (INFN Roma-1), P. Cattaneo (INFN Pavia), Rappoldi (INFN Pavia), P. Santolamazza, S. Colafrancesco, P. Giommi (ASDC), L. Salotti (ASI), P. Romano (INAF-IASF Palermo), D. N. Burrows (PSU), N. Gehrels (GSFC)
on 17 Apr 2009; 21:11 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Stefano Vercellone (stefano@iasf-milano.inaf.it)

Subjects: X-ray, Request for Observations, Transient

Referred to by ATel #: 2022, 2596

Following the AGILE/GRID detection of the candidate gamma-ray transient AGL J1734-3310 (Bulgarelli et al., ATel #2017), whose position is consistent with the INTEGRAL unidentified source IGR J17354-3255 (Kuulkers et al., ATel #874), we performed a Swift target of opportunity observation on the INTEGRAL source.

The field was observed with Swift/XRT for 5.3 ks from 2009-04-17 01:08:59 to 2009-04-17 07:57:56 UT. Within the 4 arcmin INTEGRAL error circle we detected two sources.

Source #1 (RA, DEC) = (17 35 27.16, -32 55 48.9) with an estimated error radius of 3.7 arcsec (90% c.l.). The source was detected with a mean count rate of CR = (1.14 +/- 0.07)E-01 counts/s. Throughout the observation, the count rate shows an increasing trend from 0.016 to 0.15 counts/s, hence displaying a dynamic range of the order of ten in about seven hours. The spectrum can be fit (reduced chi^2/dof = 1.06/15) with an absorbed blackbody with a temperature kT = 1.4 (-0.1, +0.3) keV and a high absorption column of NH = (5+/-2)E22 cm^-2, in excess of the Galactic one (1.2E22 cm^-2). The observed (unabsorbed) 0.3-10 keV flux is 1.1E-11 (1.6E-11) erg/cm^2/s.

Source #2 (RA, DEC) = (17 35 18.32, -32 54 22.9) with an estimated error radius of 5.0 arcsec (90% c.l.). The source was detected with a mean count rate of CR=(4.6 +/- 1.3)E-03 counts/s.

Analysis of archival Swift/XRT data (4.4 ks, from 2008-03-11 01:05:20 to 2008-03-11 10:52:57 UT), only reveals source #2 at a count rate of CR = (4.5 +/- 1.3)E-3 count/s, consistent with the one obtained during the most recent observation. Thus, we suggest a persistent nature for source #2, and propose source #1 as a possible counterpart of IGR J17354-3255. Furthermore, we can place a 3 sigma upper limit on source #1 at 4.7E-3 counts/s on 2008-03-11.