X-ray counterparts to unidentified INTEGRAL sources
The recent 1000-orbit INTEGRAL all-sky survey catalog
(
Bird et al. 2016, ApJS 223, 15)
lists 219 hard X-ray sources whose nature is
still unknown. To optically identify and classify these objects, an
enhancement of the source localization to arcsec level is necessary.
This is routinely done by means of X-ray follow-up observations of the
sky regions surrounding the high-energy emitters, as recently reported
by Landi et al.
(
2017, MNRAS 470, 1107),
where a single counterpart was pinpointed for each of
the 13 unidentified INTEGRAL sources. In a few cases the sources were
found to be associated with either AGN or cataclysmic variable binary
systems, while in other cases the X-ray counterpart is still optically
unclassified. A campaign of optical/IR observations of these X-ray
counterparts is now underway to classify these newly detected
high-energy emitters and assess their ultimate nature.
A collection of X-ray graphs presented in the work by Landi et al.
(2017) is shown in the image to highlight the diversity and sometimes
the complexity of the sky region observed:
Fig. 1a,b (top) are NuSTAR images of the SWIFT J0924.2−3141 field: over
the entire waveband (3-79 keV) two sources are clearly visible (Fig.
1a), but at high energies (15-79 keV) only one source (#1) is still
detected (Fig. 1b); this source is a Sey1.8 galaxy at z=0.042 (error
circles from the inside out are: 90% confidence for Swift/BAT, 90% and
99% confidence for INTEGRAL/IBIS/ISGRI).
Fig. 2 is the Swift/XRT 0.3–10 keV image of the IGR J14059−6116 field.
The only source detected within the 99% confidence INTEGRAL/IBIS/ISGRI
error circle (black-dotted) also lies within the positional uncertainty
of the Fermi source 3FGL J1405.4−6119 (black-dash–dotted ellipse). WISE
colours indicate a non-blazar nature.
Fig. 3 is the Swift/XRT 0.3-10 keV image of the IGR J17508−3219 field.
Two sources are detected within the 90% (#1) and 99% (#2) confidence
INTEGRAL/IBIS/ISGRI error circles (black and black-dotted,
respectively). Object #2 is the star HIP 87368 (HD 162186) of spectral
type G3IV(e), unlikely to emit at high energies. Therefore, source #1 is
the most likely counterpart.
Reference:
"Investigating the X-ray counterparts to unidentified sources in
the 1000-orbit INTEGRAL/IBIS catalogue",
R. Landi, L. Bassani, A. Bazzano, A.J. Bird, M. Fiocchi, A. Malizia,
F. Panessa, V. Sguera, P. Ubertini,
http://adsabs.harvard.edu/abs/2017MNRAS.470.1107L
2017, MNRAS 470, 1107
