Internal INTEGRAL Science Workshop: Summary

On the initiative of J.-P. Roques and C. Winkler, an Internal INTEGRAL Science Workshop was held at ESTEC from January 18 to 21. The purpose was not only to present the latest scientific results (after the INTEGRAL workshop #5 in Munich, 2004), but also to provide a forum for discussion on instrument (cross-)calibration, software performance and other issues. More than 100 participants from ISWT and collaborating teams attended a lively and productive workshop with many new exciting scientific results, demonstrating the power of INTEGRAL observations with improved calibration and software.

In the first session on payload and software performance, the good status of all instruments was demonstrated. Impressive progress has been achieved in the deconvolution of IBIS data and the suppression of systematics. Sub-mCrab sources are visible in deep mosaics reaching the predicted sensitivity. Hard work is also ongoing for JEM-X promising significant progress. All this is to become part of the next analysis software release from ISDC. SPI and OMC continue to perform well.

The following session presented results from the INTEGRAL surveys. These continue to find new sources, many of which are obscured at classical (soft) X-ray energies and to provide new and sometimes unexpected information about the high energy spectrum of known source classes. Follow-up observations at other wavelengths complement the INTEGRAL observations.

Updated results on the galactic diffuse emission, a topic for which INTEGRAL plays a very important role, were presented in the next session.

New key results from nucleosynthesis and gamma-ray line spectroscopy were presented, including the 511 keV all-sky map featuring dominant emission from the galactic bulge region and a 511 keV spectrum, with most stringent constraints on line energy and width, showing that annihilation takes place in a warm (8000 K), weakly ionized interstellar medium. The detection of gamma-ray line emission from interstellar Fe⁶⁰ at 1173 and 1333 keV and the detection of Ti⁴⁴ emission at 68 keV from the SNR Cas A were announced.

In the session on compact sources, several presentations, e.g. on H1744-322 or GX 339-4, demonstrated how the observations in the soft gamma energy range complement and extend the X-ray data for transient sources. Frequently, the outburst is first visible in the harder band, or, due to the spectral evolution, shows a very different evolution than in the soft X-ray range alone. For various sources (msec pulsars, AXPs, SGRs, bursters) hard emission is detected above 100 keV, for some, like the Anomalous X-ray Pulsars (AXP), this comes as a surprise, since they were known for their soft X-ray spectra. First results on the very recent INTEGRAL TOO observation of V0332+53 were presented from all 4 INTEGRAL instruments, only ~1 week after the data became publicly available, showing the impressive cyclotron line features visible in the spectra up to 70 keV.

In the AGN session results were presented for sources where INTEGRAL makes it possible to monitor Comptonization components. This area will benefit strongly from the improvements in the analysis demonstrated in the first session.

The impressive results obtained with the IBAS GRB alert system were summarized in the last session. INTEGRAL delivers good localization for faint bursts, with the underluminous GRB 031203 pointing at a possible faint - and largely unknown - GRB population. GRB 041219 was observed together with the Swift satellite (see below). While Swift has a much larger field of view, INTEGRAL remains more sensitive on axis by 20-40%.

Under certain circumstances INTEGRAL can even localize sources far outside its field of view! For strong bursts, the source position can eventually be reconstructed from Compton scattering information in the IBIS layers using a satellite and instrument mass model. Another example is the super giant flare from SGR 1806-20 (27 Dec) observed at 106° off-axis (see below).

Looking ahead, preparations for the 6th INTEGRAL workshop (June 2006, St. Petersburg/Russia) are commencing.

Peter Kretschmar - ISOC Operations Scientist, January 2005