Additional material for ATel 1981:
IGR J18284-0345: a new hard X-ray transient detected by INTEGRAL

by T. Blanchard (ISDC), V. Beckmann (APC), J. Chenevez (DTU/NSI), S. Corbel (CEA Saclay), M. Del Santo (INAF/IASF Roma), N. Gehrels (NASA/GSFC), D. Götz (CEA Saclay), C. Ferrigno (ISDC), J. A. Kennea (PSU), F. Mattana (APC), S. Mereghetti, A. Paizis, L. Sidoli (INAF/IASF Milano), K. Watanabe (FGCU), G. Weidenspointner (MPI HLL), J. A. Zurita Heras (CEA Saclay), on behalf of a larger collaboration

The IBIS/ISGRI and the JEM-X1 instrument aboard INTEGRAL discovered a new X-ray source during an observation of the inner Galactic disk conducted from 2009 March 18 at 18:37 UT to March 19, 6:22 UT. The new source, IGR J18284-0345 was detected at RA=277.114, DEC=-3.764 (J2000) in the 20-40 keV energy band by ISGRI with 6.3 sigma detection significance for 27 ksec on-source expsoure time and about 3 sigma in JEM-X1 (3-10 keV; 8 ksec). The flux of the source was about 10 mCrab at 3-10 keV and 6 mCrab in the 10-25 keV and in the 20-40 keV energy band, respectively. No source had been reported in the X-rays at this position previous to this finding within the error circle of 4 arcmin. Analysis of 4.8 Msec of IBIS/ISGRI data on the source position gives a marginal detection of 3.9 sigma, indicating strong source variability.

Swift has performed a follow-up observation of the source, starting at 2009 March 20 at 15:58 UT for an effective on source time of 1.9 ksec. Swift/XRT detected one source within the INTEGRAL error circle at RA=277.125, DEC=-3.762 with an uncertainty of 4 arcsec. The spectrum can be fit together with the INTEGRAL data by a black body model with kT = 4.0 ± 0.2 keV. The intrinsic absorption is not well constrained and has been fixed to the Galactic value of NH = 5.6e21 1/cm**2. The model flux of IGR J18284-0345 is 3.5e-11 erg/cm**2/sec and 1.4e-10 erg/cm**2/sec in the 2-10 keV and 2-30 keV band, respectively.
No source has been reported within the Swift/XRT error circle and no source is visible in the Swift U, V, and B filter image or on plates of the Second Palomar Observatory Sky Survey (POSS-II).

Figure 1: INTEGRAL JEM-X1 3-10 keV significance map. The large circle indicates the 4 arcmin error circle of IBIS/ISGRI, the white cross indicates the position of the source detected by Swift/XRT.

Figure 2: Swift/UVOT V filter image. The circle indicates the Swift/XRT error circle of 4 arcsec.

Figure 3: POSS-II Infrared image. The circle indicates the Swift/XRT error circle of 4 arcsec.

Figure 4: Combined spectral plot, using Swift/XRT and INTEGRAL IBIS/ISGRI data of IGR J18284-0345 in E F_E versus energy. The data can be fit by a black body with kT=4 keV (reduced chi squared = 1.0). Note that the XRT and ISGRI data are not simultaneous. Fitting the Swift/XRT data alone by a black body model gives a temperature of kT = 3 ± 1 keV.

Swift/XRT and IBIS/ISGRI spectrum in fits format (gzipped tar file, including also the ARFs)
You will need also the Swift/XRT RMF swxpc0to12s0_20010101v011.rmf and the
IBIS/ISGRI RMF isgr_rmf_grp_0027.fits

Last update: March 21, 2009

In case of questions and comments: contact me at the APC.