Swift/XRT follow-up observation of IGR J18179-1621

J. Li*, S. Zhang, Y. P. Chen, M. Tuerler, J. Chenevez, E. Bozzo, C. Ferrigno, A. Tramacere, I. Caballero, J. Rodriguez, M. Cadolle-Bel, C. Sanchez-Fernandez, M. Del Santo, A. Tarana, M. Fiocchi, P. R. den Hartog, I. Kreykenbohm, M. Kuehnel, A. Paizis, G. PuehlhoferK. Watanabe, G. Weidenspointner

*Corresponding author for this work

Research output: Other contributionNet publication - Internet publicationResearch


Following the discovery of IGR J18179-1621 (Tuerler et al. ATel #3947) on 2012-02-29, we requested two Swift ToO, which were executed on 2012-02-29 from 20:10:02 to 22:00:01 UT and on 2012-03-01 15:25:55 from to 2012-03-01 15:59:48 UT for a total exposure of ~3.9 ks. These two observations were carried out in Photon Counting mode and the sky image is piled up. We have corrected the pile up effect in our analysis. Using the online Swift tool we find an enhanced position of

RA = 274.4675 (18h 17m 52.20s),
Dec = -16.3589 (-16d 21' 31.9'') (J2000),

with a 90% confidence level error of 2.2 arcsec, consistent with the position measured by INTEGRAL/JEM-X (ATel #3947)(We have used the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue, see http://www.swift.ac.uk/user_objects and Evans et al. 2009, MNRAS, 397, 1177).

The two XRT spectra can be well fitted (reduced chi^2=0.72 for 47 dof and reduced chi^2=0.98 for 49 dof ) with an absorbed power-law model. The spectral parameters we derived in the 1-10 keV energy band are (model and flux uncertainties are 90% c. l.): In 2012-02-29, N_H = 11.0+/-2.7 e22 atoms/cm2 and photon index = 0.4+/-0.4. The 1-10 keV unabsorbed flux is 4.5+/-0.5 e-10 erg/cm2/s. In 2012-03-01, N_H = 15.1+/-3.6 e22 atoms/cm2 and photon index = 0.7+/-0.4. The 1-10 keV unabsorbed flux is 4.2+/-0.8 e-10 erg/cm2/s.

We derive from Swift/XRT a flux, between 3-10 keV, of 21.5+/-1.8 mCrab on 2012-02-29 and 22.0+/-2.2 mCrab on 2012-03-01, consistent with what was derived from JEM-X observation (ATel #3947).This may mean that IGR J18179-1621 now is still in a relatively bright phase.

No significant variation of the source spectral parameters are revealed in the XRT data.

Original languageEnglish
Publication date2 Mar 2012
Publication statusPublished - 2 Mar 2012
SeriesThe Astronomer's telegram
NumberATel #3950


  • X-ray
  • Black hole
  • Neutron star
  • Transient
  • Gamma ray
  • Binary
  • Pulsar


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