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Correlating The WFC and the
IBIS hard X-ray survey
F. Capitanio1, A. J. Bird2, A. Bazzano1 and P. Ubertini1
1) IASF-Roma INAF, Rome, Italy
2) School of Physics and Astronomy, University of Southampton, Southampton, UK
Beppo SAX
BeppoSAX was an Italian-Dutch X-ray satellite.
It was launched in 1996 and it observed the X-ray sky for 6 years.
The payload was characterised by a wide energy range (0.1-300 keV)
NFI instruments coaligned to the Z axis
of the satellite:
LECS (0.1-10 keV)
MECS (1.3-10 keV)
HPGSPC (4-120 keV)
PDS (15-300 keV)
Two Wide Field
Cameras aligned
with the Y axis of
the satellite.
WFCs Observations and characteristics
The two WFCs on board BeppoSAX satellite, were mounted 180 degrees away from
each other and perpendicular to the pointing direction of the Narrow Field
Instruments (NFI), looking at two different sky zones during any NFI pointing.
In this way, during the 6 years of BeppoSAX operational life, the WFCs secondary
mode observations covered all the sky, with at least one pointing (typically 100 ksec).
Moreover, two times a year the WFCs observed, as the primary instrument, the
galactic bulge region. The time devoted to this program corresponds to 8% of the total
observing time. Twelve such campaigns were carried out amounting to a total net
exposure up to 6 Msec.
Aim of the work:
We analysed all the BeppoSAX Wide Field
Camera pointings available providing a mosaic of
the images of all the single pointing observations
and search the map for sources as has been made
for the IBIS survey.
This work is optimised for faint persistent
sources searching.
Each excess found in the WFCs maps was
searched also in the IBIS maps in order to better
distinguish between structures of the IBIS survey
mosaics and sources.
IBIS and WFC Common characteristics:
-Coded mask
-Large FOV
-pointings covering most of the sky
IDEA….
Do the same work made
for IBIS also with the
WFC data, using the same
tools and techniques
developed for the IBIS
survey
Beppo-SAX WFC survey
The WFC exposure map
1.5x107 s
5x105 s
6x106 s
The IBIS exposure map
6x105 s
4x104 s
8x106 s
3x106 s
The maps:
The method:
We analysed all the available OPs with the WFCs
Data Analysis System, extracting the images for two
energy ranges: 3-17 keV and 17-28 keV. The latter
band was selected to allow a direct comparison
between WFCs and IBIS.
The WFC standard software uses the IROS method to
extract sources from the shadowgrams of the WFC
coded masks.
Following the IROS procedures, we forced the
software to extract a big number of sources for each
OP images, effectively cleaning down into the noise.
A mosaic of images, for both energy ranges, produced
by IROS software, has been generated using the same
software used for the IBIS survey.
In this way the eventually false detections extracted by
``stressing'' the WFC software have been eliminated.
Source list generation
The sources position and flux were identified using a barycentering method to determine the
centroid of the source profile. The mean flux of the sources was derived from the count rate at the
position of the source maximum significance, using the same software developed for the IBIS
survey. A second method based on SExtractor 2.4.4 software has been used to cross check the
results.
17-28 keV
3-17 keV
Peakfind
SExtractor
Source list 1
Source list 2
The list of excesses was then checked manually to
eventually remove ghosts and structures
ISGRI/WFC sources correlation
All the WFCs excesses were compared with the INTEGRAL
lowest energy range maps, 17-30 keV and with the total lists of
excesses produced for the IBIS survey.
7 possible new
sources ?
336 excesses
167 detected
also by IBIS
306 sources
139 detected only by
WFCs
30 not firm
identification
WFC catalogue: different source types
Comparison with IBIS survey
Great WFC
exposure of
the GC region
WFCs: softer energy
coverage
•Different class of sources
•IBIS: less explored energy
range
•IBIS greater sensitivity
•Hard sources
•Transient sources
•The two satellites
operated in a different
time period
Different class of
sources
Soft sources
Percentage of different source types detected only by WFCs and by both WFCs
and IBIS.
1ES1210-646
IBIS
18-60 keV and 20-200 keV
survey 3 mosaic
A paper on the INTEGRAL and WFC data
has been just submitted by Masetti et al.
WFC
3-17 keV and 17-28 keV
Differences and similarities between our
WFC catalogue and the official one.
(Verrecchia et al. 2007)
•The official WFC catalogue published in July 2007 by Verrecchia et
al. is based on analysis of each single pointing observations.
•Our work is instead based on mosaic maps searching.
Official catalogue: 253
46 only reported in the
official catalogue
Our catalogue: 306
207
coincident
sources
99 only reported in
our catalogue
15 IGR sources and 10 SWIFT sources
7 new source candidates
Some example of detections
The case of
IGR J17091-3624
In’t Zand e al. 2003
The sources reported only by our catalogue are mostly
concentrated in the two sky zone at higher exposure
Work in progress: light curves production
We are producing now the light curves of all the WFC catalogue
sources extracting the counts from each single WFC pointing
observations.
4U1630-47
ASM: 1.5-10 keV
WFC: 3-17 keV
IGR J17091-3624
In’t Zand e al. 2003
1996
2001
Future applications:
•Construct a combined catalogue of transient
and persistent sources
•study of the sources population characteristics
•Long term variability studies (using combined
light curves)
•to use the same method with other coded mask
instruments like INTEGRAL/JEM-X or
SWIFT/BAT
Thank you