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HESS J1614-518: detection of X-ray emitting stars by Swift/XRT possibly associated with an open cluster

ATEL # 1047; R. Landi, N. Masetti, L. Bassani (INAF/IASF, Bologna), S.A. Cellone (UNLP, La Plata), G.E. Romero (IAR/UNLP, La Plata), P. Ubertini (INAF/IASF, Rome) and A.J. Dean (Univ. Southampton)
on 5 Apr 2007; 15:48 UT
Password Certification: Raffaella Landi (

Subjects: Optical, X-ray, >GeV, Stars

A recent 5 ks exposure of HESS J1614-518 with Swift/XRT reveals 4 new X-ray sources inside the TeV error box in addition to the two objects (#1 and #2 in the image available at the link reported at the bottom of this ATel) first reported by Landi et al. (ApJ 651, 190, 2006). These new sources are located at:

#3: RA(J2000)=16h 14m 01.5s, Dec(J2000)=-51d 54m 25.9s (4.9 sigma)

#4: RA(J2000)=16h 14m 08.8s, Dec(J2000)=-51d 53m 57.9s (3.1 sigma)

#5: RA(J2000)=16h 14m 48.0s, Dec(J2000)=-51d 48m 30.7s (4.2 sigma)

#6: RA(J2000)=16h 14m 59.6s, Dec(J2000)=-51h 39m 02.8s (2.9 sigma)

and have a typical positional uncertainty of 6 arcsec.

Sources #3 and #5 are probably stars (HD145542 and HD140753) of K3III and B9V spectral type respectively. Recent optical follow-up observations with the REOSC spectrograph of the 2.15m 'Jorge Sahade' telescope at CASLEO (Argentina) of the counterparts of the two brightest sources (#1 and #2) indicate that also these are both stars, one (#2) of intermediate spectral type and the other (#1) of unclear spectral classification but with a very reddened continuum.

It is interesting to note that close to source #1 (42 arcsec away) there is a young open cluster, C 1609-517, characterized by the following parameters: E(B-V)=2, 1 kpc distance and age 40 Myr (Piatti, Claria & Bica, A&A 360, 529, 2000). It is quite possible that the stars detected in X-rays are part of this cluster. The recent discovery of the unidentified gamma-ray source TeV J2032+4130 in the vicinity of Cyg OB2 by HEGRA (Aharonian et al., A&A, 393, L37, 2002), and HESS J1303-631 in the vicinity of Cen OB1 by HESS (Aharonian et al., A&A, 439, 1013, 2005) have renewed interest in young open clusters as possible sites for the acceleration of cosmic rays and for the emission of TeV gamma-rays; we thus suggest further multiwavebands studies of C 1609-517 which is so far the only potential counterpart of HESS J1614-518.

Swift/XRT image of the HESS J1614-518 field

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R. E. Rutledge , Editor
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