INTEGRAL detection of two Seyfert 1 galaxies: ESO 140-43 and ESO 141-55

ATel #1264; V. Beckmann (ISDC), D. Petry (MPE), G. Weidenspointner (MPE & MPI HLL)
on 8 Nov 2007; 15:05 UT
Credential Certification: Volker Beckmann (Volker.Beckmann@obs.unige.ch)

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A region centered roughly on RA 18:30 h, DEC -60 deg (constellation Pavo) was observed by INTEGRAL from 2007 Oct 29 to Nov 4 for about 378 ks. In this observation, proposed to observe extended Galactic diffuse emission, we discovered in IBIS/ISGRI sky maps two new INTEGRAL hard X-ray (20-100 keV) sources:
1) A source with 14 sigma significance at position RA = 18 45 10, DEC = -62 21 21 (J2000.0; estimated uncertainty 2 arcmin), consistent with ESO 140-43, a Seyfert-1 galaxy at z=0.0141. A power-law fit resulted in a spectral index of Γ = 1.8 ± 0.3 and a flux of 1.7e-11 erg/cm**2/sec (20-40 keV) and 2.6e-11 erg/cm**2/sec (40-100 keV), respectively. The combined JEM-X and ISGRI data show an overall luminosity of L=3e43 erg/sec in the 5-100 keV energy band. INTEGRAL's optical monitor OMC gives a V-band magnitude of 13.4 mag.
2) Another source with 19 sigma at position RA = 19 21 19, DEC = -58 39 49 (J2000.0; estimated uncertainty 2 arcmin), consistent with ESO 141-55, a Seyfert-1 galaxy at z=0.0366. Here, a power-law spectral fit resulted in a photon index of Γ = 1.9 ± -0.4 and a flux of 1.9e-11 erg/cm**2/sec (20-40 keV) and 1.2e-11 erg/cm**2/sec (40-60 keV), respectively. The combined spectrum gives a luminosity of 2e44 erg/sec in the 5-60 keV band, and also this source has V=13.4 mag according to the OMC.

Both objects have not previously been detected above 20 keV. They were detected in soft X-rays by ROSAT (0.1-2.4 keV, Voges et al., 1999, A&A, 349, 389) and RXTE (3-20 keV, Revnivtsev et al., 2004, A&A, 418, 927). ESO 141-55 was also detected by ASCA (0.7-2 keV, Ueda et al., 2005, ApJS, 161, 185).

Results based on spectral modelling (fluxes in erg cm^-2 s^-1):

  
                 ESO 140-43       ESO 141-55
  
-------------------------------------------------------------
  
 Γ               1.7 ± 0.2         1.9 ± 0.4
  
 fX(5-20 keV)    0.9·10-11         3.4·10-11
  
 fX(20-40 keV)   1.7·10-11         1.9·10-11
  
 fX(40-100 keV)  2.6·10-11         2.8·10-11 (*)
  
 LX(5-100 keV)   3·1043 erg s-1    2.5·1044 erg s-1 (*)
  
 V               13.4 mag         13.4 mag
  
  
(*): extrapolated value

Images and spectra