Joint European X-ray Monitor: JEM-X

 

Principal Investigator:

Jérôme Chenevez, DTU SPACE, Copenhagen, Denmark

with collaborating scientific institutes in Denmark (DTU Lyngby), Finland (Metorex Espoo, U Helsinki), Spain (U Valencia, INTA Madrid), Italy (INAF/IASF-Frascati, U Ferrara, INAF/IASF-Palermo, INAF/IASF-Bologna), USA (NASA/GSFC Greenbelt), Sweden (Observatory Stockholm), United Kingdom (U Cambridge), Poland (Copernicus Center Warsaw, Space Research Center Warsaw), Russia (IKI Moscow).

 

The Joint European X-Ray Monitor (JEM-X) supplements the main INTEGRAL instruments (Spectrometer and Imager) and plays a crucial role in the detection and identification of the gamma-ray sources, as well as in the analysis and scientific interpretation of INTEGRAL gamma-ray data. JEM-X makes observations simultaneously with the main gamma-ray instruments and provides images with arcminute angular resolution in the 3 - 35 keV prime energy band. The baseline photon detection system consists of two identical high pressure imaging microstrip gas chambers (1.5 bar, 90% Xenon + 10% Methane), at nominal gas gain of 1500. Each detector unit views the sky through its coded aperture mask located at a distance of approximately 3.2 m above the detection plane.

For more details we refer the interested reader to ISOC's Announcement of Opportunity documentation of the JEM-X Observer's Manual and to a sequence of papers on the JEM-X payload in the A&A Special Letters issue on: First science with INTEGRAL. This issue also contains various other papers on the first results from in-flight observations. For a description of the JEM-X data analysis we refer to, e.g., Westergaard et al. (2003, A&A 411, L257). The validation reports of the ISDC Off-line Scientific Analysis (OSA) software package released by the ISDC for JEM-X, as well as descriptions of the data analysis pipelines and modules and the use of the OSA software can be found at the ISDC website (https://www.astro.unige.ch/integral/analysis#Documentation).

JEM-X page at DTU Space, Copenhagen, Denmark

 

Overview of scientific capabilities of JEM-X

 

Energy range 3 - 35 keV
Detector area 500 cm2 (single unit)
Energy resolution 1.3 keV @ 10 keV
Field of view (diameter) 4.8° (fully illuminated)
7.5° (half response)*
13.2° (zero response)
Angular resolution 3' (FWHM)
Point source location accuracy 1' (90% confidence, 15σ isolated source)
Continuum sensitivity for a single JEM-X unit
(isolated source on-axis)		 1.2e-4 ph/(cm2 s keV) [3σ in 10e5 s, @ 6 keV, ΔE=E/2]
1.0e-4 ph/(cm2 s keV) [3σ in 10e5 s, @ 30 keV, ΔE=E/2]
Line sensitivity for a single JEM-X unit
(isolated source on-axis)		 1.6e-4 ph/(cm2 s) [3σ in 10e5 s, @ 6 keV]
1.3e-4 ph/(cm2 s) [3σ in 10e5 s, @ 20 keV]
Timing accuracy (3σ)

122 μs (relative timing)
≈1 ms (absolute timing)

* At this angle the sensitivity is reduced by a factor 2 relative to the on-axis sensitivity. In practice, the transmission of the collimator beyond an off-axis angle of 5° is so low that only the very brightest sources can be observed at larger angles.

 

 

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