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INTEGRAL hard X-ray detection of HMXB GX 304-1 and H 1417-624

ATEL # 1613; A. Manousakis, V. Beckmann (ISDC, Switzerland), V. Bianchin (INAF/IASF-Bologna), S. Brandt, J. Chenevez (DTU/NSI, Denmark), W. Hermsen (SRON & UvA, The Netherlands), A. von Kienlin (MPE, Germany), R. Krivonos (IKI, Moscow & MPA, Garching), M. Mas-Hesse (LAEFF, Madrid), A. Parmar (ESA/ESTEC, The Netherlands), V. Reglero (GACE, Valencia)
on 10 Jul 2008; 18:19 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Volker Beckmann (Volker.Beckmann@obs.unige.ch)

Subjects: X-ray, Request for Observations, Binaries, Neutron Stars, Pulsars, Transients

We report on the first detection of the Be star HMXBs GX 304-1 and H 1417-624 above 20 keV with the IBIS/ISGRI X-ray imager on board INTEGRAL. From 2008-06-24 to 2008-07-09, INTEGRAL performed monitoring observations of the Galactic plane around l=305 degrees for a total exposure time of 352 ksec.

GX 304-1 was detected in all spacecraft revolutions, and shows brightening with time. H 1417-624 was detected only in revolution 699 and 700 (2008-07-04 to 2008-07-09). The spectrum of this HMXB can be fitted either by a black body or by a simple power law. We see indication for softening of the 18-60 keV spectrum as the source brightens, with a power law with photon index 2.3 +- 0.3 and 3.1 +- 0.5 for revolution 699 and 700, respectively. Both sources were also detected by JEM-X below 10 keV.

The evolution over the last revolutions is as follows (fluxes in mCrab in 20-40 keV, upper limits are 3 sigma values):

   revolution    exposure    GX 304-1     H 1417-624  
[ksec] flux flux
695 54.5 3.1+-0.6 < 2.3
696 66.5 5.0+-0.6 < 3.1
698 73.1 3.8+-0.7 < 3.8
699 78.7 5.0+-0.6 7.8+-0.7
700 79.2 6.9+-0.6 11.3+-1.3

INTEGRAL will continue to monitor these sources until 2008-07-23.


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