We report on the discovery of a new transient source, IGR J17177-3656, detected during the INTEGRAL observation performed from 2011-03-15 09:23 to 2011-03-15 22:42 UT.
The source was detected by IBIS/ISGRI at a significance level of 13 and 9 standard deviations, in the 20-40 keV and 40-80 keV energy bands, respectively. The corresponding fluxes were 20+/-1 and 22+/-2 mCrab (exposure time is 24 ks).
The source is also marginally detected by combining the two JEM-X units in the 10-20 keV band with a flux of 8+/-3 mCrab (total exposure 12.5 ks). It is not detected in the 3-10 keV band with a 3 sigma upper limit of 5 mCrab.
The best determined source position from the IBIS/ISGRI data is at: RA = 259.414 (17:17:39) Dec = -36.938 (-36:56:17) (J2000) with a 90% confinement radius of 2.2 arcmin.
The best position determined from the JEM-X monitor is RA=259.443 (17:17:46), Dec=-36.945 (-36:56:42) (J2000) with a 90% confinement radius of 1.5 arcmin, fully consistent with the ISGRI position.
The IBIS/ISGRI spectrum (20-150 keV) can be well described by a power-law with photon index 1.8+/-0.3 (chi2/dof=0.5 for 8 dof). The estimated 20-100 keV flux is 3.7e-10 erg/s/cm2. We could not detect any significant variability during the observation.
A subsequent INTEGRAL observation from the Galactic bulge monitoring program was performed on 2011-03-16 from 12:33 to 14:51 UT (exposure of 5.4 ks): the source flux in the 20-40 keV (40-80 keV) band was 23+/-4 mCrab (30+/-6 mCrab), suggesting an increasing luminosity trend.
Previous INTEGRAL observations of the region were performed between 2011-03-13 03:21 and 2011-03-13 16:39. We derived a 5 sigma upper limit on the source flux in the 20-40 keV band of 7 mCrab, exploiting an IBIS/ISGRI effective exposure time of 8 ks.
A Swift/XRT pointed observation in the region of the source was performed between 2011-01-27 08:21 and 2011-01-27 08:30 (exposure time is 548 s), no source was detected in the FOV with a 3 sigma upper limit of 1.5e-12 erg/s/cm2 in the 1-10 keV band (0.05 mCrab), assuming a power-law spectrum with photon index 1.8 and Galactic absorption (NH = 1.2e22 cm-2).
We encourage multiwavelength observations to investigate the nature of the system, which has the typical characteristics of either an X-ray transient in an initial hard state or a transient highly absorbed source.
|Publication date||16 Mar 2011|
|Publication status||Published - 16 Mar 2011|
|Series||The Astronomer's telegram|