2,475 research outputs found
In-flight calibration of the INTEGRAL/IBIS mask
Since the release of the INTEGRAL Offline Scientific Analysis (OSA) software
version 9.0, the ghost busters module has been introduced in the INTEGRAL/IBIS
imaging procedure, leading to an improvement of the sensitivity around bright
sources up to a factor of 7. This module excludes in the deconvolution process
the IBIS/ISGRI detector pixels corresponding to the projection of a bright
source through mask elements affected by some defects. These defects are most
likely associated with screws and glue fixing the IBIS mask to its support.
Following these major improvements introduced in OSA 9, a second order
correction is still required to further remove the residual noise, now at a
level of 0.2-1% of the brightest source in the field of view. In order to
improve our knowledge of the IBIS mask transparency, a calibration campaign has
been carried out during 2010-2012. We present here the analysis of these data,
together with archival observations of the Crab and Cyg X-1, that allowed us to
build a composite image of the mask defects and to investigate the origin of
the residual noise in the IBIS/ISGRI images. Thanks to this study, we were able
to point out a simple modification of the ISGRI analysis software that allows
to significantly improve the quality of the images in which bright sources are
detected at the edge of the field of view. Moreover, a refinement of the area
excluded by the ghost busters module is considered, and preliminary results
show improvements to be further tested. Finally, this study indicates further
directions to be investigated for improving the ISGRI sensitivity, such as
taking into account the thickness of the screws in the mask model or studying
the possible discrepancy between the modeled and actual mask element bridges.Comment: accepted for publication in the proceedings of "An INTEGRAL view of
the high-energy sky (the first 10 years)" 9th INTEGRAL Workshop, October
15-19, 2012, Paris, France, in Proceedings of Science (INTEGRAL 2012), Eds.
A. Goldwurm, F. Lebrun and C. Winkler,
(http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=176), id 154; 6 pages, 4
figures, see the PoS website for the full resolution versio
The First INTEGRAL AGN Catalog
We present the first INTEGRAL AGN catalog, based on observations performed
from launch of the mission in October 2002 until January 2004. The catalog
includes 42 AGN, of which 10 are Seyfert 1, 17 are Seyfert 2, and 9 are
intermediate Seyfert 1.5. The fraction of blazars is rather small with 5
detected objects, and only one galaxy cluster and no star-burst galaxies have
been detected so far. A complete subset consists of 32 AGN with a significance
limit of 7 sigma in the INTEGRAL/ISGRI 20-40 keV data. Although the sample is
not flux limited, the distribution of sources shows a ratio of obscured to
unobscured AGN of 1.5 - 2.0, consistent with luminosity dependent unified
models for AGN. Only four Compton-thick AGN are found in the sample. Based on
the INTEGRAL data presented here, the Seyfert 2 spectra are slightly harder
(Gamma = 1.95 +- 0.01) than Seyfert 1.5 (Gamma = 2.10 +- 0.02) and Seyfert 1
(Gamma = 2.11 +- 0.05).Comment: 17 pages, 12 figures, accepted for publication in Ap
- …