| No. 12 - February 12, 2003 | Edited by Thierry Montmerle & Marc Türler |
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This is the first issue of this Newsletter following the start of INTEGRAL's routine
operations.
After the excitement of the
first images and
ESA's press release
on December 18, as well as some worries concerning JEM-X (see below),
the effort now focuses on the optimization of the software to get rapidly
meaningful scientific results.
The ISDC is becoming more operational every day, as detailed in several articles in the ISDC News section. The expected rate of one gamma-ray burst per month in the IBIS field-of-view is confirmed, since three have already been caught by the IBAS system, although a lot of work is still required to optimize their location (see below). Last Friday, the first beautiful light curve of the Crab pulsar, the main calibration source, has been obtained by IBIS and JEM-X (see the INTEGRAL News section), validating the excellent performance of the spacecraft and its instruments.
No doubt the two other instruments are frantically gathering results as well. We certainly hope to hear from them in our next issue. In the mean time, off-stage rumors tell us that a special issue of the Astronomy & Astrophysics journal is in preparation to be issued before the end of the year.
We'll keep you informed, as before: the launch issue of the Newletter received over 1000 hits !
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| Overview of INTEGRAL and ISDC Operations since Launch | ||
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Roland Walter (ISDC Geneva) |
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The INTEGRAL operations during the early mission phases took place as planned.
The spacecraft and the instruments have first been commissioned and their performance verified. During that period INTEGRAL observed empty fields and the Cygnus region.
Since revolution 11 the mission planning has been driven by the observation database of the INTEGRAL Science Operation Centre (ISOC).
Nominal operations started on revolution 26 (december 30, 2002) with the first accepted observations of the AO-1 program. Since then 7 targets from the open program have been observed for 12 different guest observers (several observations were amalgamated). One of those observation was a target of opportunity. In addition 3 Galactic Plane Scans have been performed as part of the INTEGRAL Core Program.
The operations have been essentially flawless with 80% of the available time spent observing science targets (15% of the time is spent below the radiation belts).
Over that time 3 gamma-ray bursts have been detected in the instrument field of view (see below) and some new sources have been detected. Now and since revolution 39, INTEGRAL is observing the Crab for calibration purposes.
The telemetry has been received and processed at the ISDC continuously since the launch. Since revolution 20 a scientific analysis of the data is running routinely on all data from the ISGRI and JEM-X instruments with the main purpose to detect bright (100 mCrab) transients. The results of that analysis (sky images) are screened by scientists. Automatic alerts for the detection of new sources or strong variations are being tuned.
As the real-time telemetry (TM) contains gaps a consolidated TM archive is built at the Mission Operation Center (in ESOC) and sent off-line to ISDC. The consolidated telemetry and all the necessary auxiliary files are now processed almost routinely at the ISDC since two weeks. The result of that processing (about 6.5 GB worth of data per revolution) is used to populate the INTEGRAL archive. It is expected that the current processing backlog will be resolved by the end of March.
About 10 days of data, taken between the official end of the PV phase (december 17, 2002) and the start of the AO-1 program will become public immediately. The first public event lists will be made available in the archive on March 3.
Scientific analysis software is used on real data almost since launch. The first priority has been to improve the imaging software both in terms of performance and stability. The sensitivity achieved by the current software still needs to be improved to match the instrument capabilities.
The performance of the software will be checked quantitatively using the Crab observation that is going on now. Depending on those results the standard analysis of the first observations should start at the end of March and the first AO-1 observers should receive their data in April.
| First Gamma-Ray Bursts detected by IBAS | ||
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S. Mereghetti, D. Götz (IASF Milano) & J. Borkowski (ISDC Geneva) |
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Since the beginning of the INTEGRAL observations three GRBs have been detected within the IBIS field of view. After the ones of November 25 and December 19, we were waiting for the January burst, which arrived just in time on the last day of the month: GRB030131 !
During the Performance and Verification phase, the IBAS software devoted to the automatic localization of GRBs, has been running with the delivery of Alert Packets to external users disabled. This allowed us to further test the system and to perform minor changes to the software in order to better adapt it to the in-flight performances of the instruments.
The first GRB in the IBIS field of view (GRB021125,
GCN
1706) occurred during an observation in which most of the telemetry
was allocated to PICsIT for calibration purposes. Thus only a limited fraction
of the ISGRI counts could be transmitted to the ground and, due to the
resulting gaps in the ISGRI data, IBAS was in ``idle mode''.
The image on the right is also available as an animation showing the evolution of the ISGRI image and light curve of GRB021125, the first gamma-ray burst imaged by INTEGRAL.
The burst was discovered by IBIS scientists at MOC and analyzed at the ISDC and at
the Instrument Teams Institutes (Figure 1). After this event, we introduced
some changes in the IBAS software in order to be able to detect GRBs also
during observations with limited ISGRI telemetry allocation, although such
an instrument configuration is not supposed to occur often during
routine operations.
Figure 1 Localization of GRB021125. The large circle (20' radius) is the first error region obtained with the IBAS programs, while the small one is the refined position (2' radius) obtained after a preliminary boresight correction (GCN 1714). The parallelogram is the IPN error box (GCN 1709).
The second GRB in the IBIS field of view (GRB021219,
GCN1766)
was found and correctly localized by IBAS in real time. The IBAS position,
obtained 10 seconds after the start of the burst, was distributed
as an internal Alert Packet. This triggered an interactive analysis to verify
the event and to derive a more accurate position. The final 4' radius error
box was subsequently confirmed by the Inter-Planetary Network (IPN) triangulation
(Figure 2).
Based on the good performances of IBAS on GRB021219, it was decided to start
the external distribution of Alert Packets on January 17.
Figure 2 Localization of GRB021219. The first IBAS error circle has a radius of 20' ( GCN 1766), The final localization obtained with an off-line analysis, shown by the small circle (4' radius, GCN 1768) is consistent with the IPN annulus (GCN 1772).
Unfortunately the coordinates of the next burst (GRB030131, GCN 1836) could not be distributed in real time, since the GRB was detected during a satellite slew. This resulted in a smaller signal to noise and a larger uncertainty on its position. An Offline Alert Packet with the preliminary position was delivered manually after two hours. Subsequent analysis reduced the positional uncertainty to a 5' radius (GCN 1847).
The time delays with which the positions of these GRBs were made public
are shown by the three lines in the right part of
Figure 3. INTEGRAL
is the first mission for which such short delays have been achieved so
early after the launch. The improvement in performance for these three
GRBs is also visible from the figure. We are confident that IBAS
will soon reach its goal of delivering GRB positions at the arcmin level
in near real time.
Figure 3 Time delays in the localization of the first three GRBs detected in the IBIS field of view. The three lines refer to public delivery of the GRB positions. The two points to the left indicate the delays of internal alerts for GRB021219 (blue asterisk) and GRB030131 (red square).
We remind to all the interested users that the most efficient way to receive the coordinates of INTEGRAL GRBs with the shortest time delay is to directly receive the IBAS Alert Packets. The required procedure is explained on the IBAS software page.
| Observing with INTEGRAL at the ISDC | ||
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Thierry J.-L. Courvoisier (ISDC Geneva) |
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The performance verification phase of INTEGRAL was finished at the end of December. Since then the observation programme is made of open time observations and garanteed time observations (mainly regular scans of the galactic plane) with some time reserved for calibration purpose, like in February when INTEGRAL is observing at the Crab in order to obtain the best possible set of data to characterise the response of the instruments.
INTEGRAL is in continous contact with the ground stations when observations are performed, the telemetry is routed in real time (within few seconds) to the ISDC. At ISDC the telemetry is scanned for the presence of gamma ray bursts which are then announced to the interested communities (see the article on the burst alert system). The telemetry is also organised in science windows, corresponding in essence to one pointing or one slew in a dithering pattern. The data are decoded and the pointing data are analysed within about two hours of reception in a quick look analysis. This allows scientists at ISDC to spot new bright transient sources and to announce them to the astronomical community through IAU circulars in a short time to allow for observations in other wavebands. This already occured once (IAU circular 8063).
More detailed analysis of the data using the Offline Scientific Analysis (OSA) tools is possible from then onward outside the operational network.
As a result of this organisation it is possible for observers at the ISDC to have a first view of the data from their observations within few hours. The ISDC can indeed (with the permission of ESA, note that in the case of amalgameted observations ESA will request the approval of all PIs) provide access to the observers to the data of a given observation. This possibility can be used by any observer wishing to have a first view of the data content before the distribution of the data. This distribution occurs after ISDC has received the consolidated data from ESA, processed and archived these data offline. The whole process is expected to take approximately one month.
The fast variations of many high energy sources can make a first analysis of the data in a short time very valuable. The ISDC is therefore making efforts to allow observers to visit ISDC, access their data and perform a first analysis there. These visits have the additional advantage of familiarising the observers with the INTEGRAL data and data analysis tools prior to installing the software at their institutes.
In order to make use of this possibility, observers should visit the ISDC and have an account there. The account and the data will in general only be available during the physical presence of the observer at ISDC, no systematic remote access will be possible. Masha Chernyakowa is responsible for the organisation of such visits. We expect to be able to host one or possibly two observers at any one time. We will arrange for an ISDC scientist to serve as a host and guide through the early steps in the data analysis.
| First Release of Offline Scientific Analysis Software | ||
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Isabelle Lecoeur-Taïbi & Peter Kretschmar (ISDC Geneva) |
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ISDC plans to make the first public release of its Offline Scientific Analysis (OSA) software suite at the end of March. This is a major improvement over the OSA pre-release published in September before the INTEGRAL launch. It is based on the experiences gained during the early mission, mainly the PV phase, and the corresponding improvements to the analysis software and instrument calibration. Since all these activities are still ongoing, possibilities to get quantitative results will be rather limited, but the release will allow observers to familarize themselves with the installation and use of the analysis software and get a first look at their data. The main focus will be on the imaging software.
The release will contain instrument specific analysis software for the four INTEGRAL instruments, generic tools, installation scripts, test data and documentation. The documentation includes, e.g., installation guide, instrument specific analysis user manuals and information about how to download calibration data and catalogs. The software will be available as downloadable tar files from the ISDC software page. Most of the software will be distributed as source code, some parts may be distributed in binary form.
While Solaris is the reference operating system, the software is being tested under both Solaris and Linux with the aim of providing fully functional versions on both platforms.
A second OSA public release is planned for autumn of this year. In the meantime so-called production releases will be available at ISDC which will integrate the continuous improvements of the analysis software. These production releases are intended for internal ISDC and instrument team usage. They will be less well tested and documented compared to public releases and only very limited support will be possible for these.
| Start of Operations in the ``Barn'' | ||
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Simon Shaw (ISDC Geneva) |
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Previously a toolshed with a stamped earth floor, low wooden ceiling and no windows, the Barn at the ISDC now has a quite different use. The building was renovated and converted in 1999 to provide a hardware room and office space as part of the infrastructure improvements at Ecogia for the INTEGRAL mission. The Barn is now the Operations Room at the ISDC, where the INTEGRAL telemetry is received via the frame relay link with the Mission Operation Centre (MOC).
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Within a few seconds of the telemetry being sent to Earth by INTEGRAL, it starts to be processed by the Near Real Time (NRT) data pipeline. The INTEGRAL Burst Alert System (IBAS) also checks the telemetry for any possible gamma ray bursts. Already the IBAS system has triggered on many bursts, mainly seen in the SPI-ACS, but there have also been three so far seen in the ISGRI field of view. The second of these, on December 19th, occurred at the same time as a visit to the Barn of a large contingent of students. Hopefully they were impressed by us organising a gamma ray burst especially for them !
Four Operators are responsible for ensuring that the telemetry from INTEGRAL is received and processed correctly. The Operators work in pairs on a shift basis of three days, which is synchronised with the INTEGRAL orbital period. During the shift the Operators monitor the progress of the NRT pipelines and the behaviour of the instruments aboard INTEGRAL. The Operators are also responsible for processing the Consolidated (CONS) data, which arrives a few weeks after each observation on CDs from MOC. The NRT data is subject to occassional gaps in the telemetry, which can be retrieved later by MOC and written to the CONS CDs. This data is processed in the same way as the NRT data and provides a complete data set for each observation that will ultimately be sent to the appropriate PIs.
Picture 1:
Members of the Operations Team pose for the camera in the
Barn as the very first telemetry packets arrive from INTEGRAL just after
launch on October 17, 2002. Anti-clockwise from bottom right: Simon Shaw, Linda
Martins, Philippe Meynis, Patrick Haymoz and Nami Mowlavi.
In addition to the Operators the shift team also contains a `Scody' (short for Scientist on Duty - the initial anacronym was rejected after its English translation was revealed !). Within a couple of hours of the telemetry being received in the Barn the Scody is able to see images from the INTEGRAL instruments via the Quick Look Analysis (QLA). The Scody's job is to monitor these images to look for new sources or for strange behaviour from known sources that may trigger a Target of Opportunity observation. The Scody's are drawn from a pool of 16 scientists at the ISDC and are responsible for following one revolution's data every 6 weeks or so.
The shift team is supervised by one of two Operations Coordinators who individually oversee between two and five shifts before handing over to each other. This is to ensure the continuity of information from one shift to the next when the operators change. The Operations Coordinators are on call, via a mobile phone, for 24 hours a day during the shift. SMS messages are automatically distributed by the ISDC system in the event of serious alerts, ranging from a break in the telemetry receipt from MOC to an alert generated by IBAS for a gamma ray burst in the field of view of ISGRI. The number of alerts sent to the mobile phones has been small, although not small enough that the choice of a particularly loud ring tone has not been questioned occassionally by the Coordinators at 3am !
Picture 2:
The day of the launch and the operations room becomes an
exciting tourist attraction in the hours following the upper stage
separation. Fortunately it is somewhat less crowded now !
Due to being at the front end of ISDC operations, the Barn can be an exciting place to work. This was especially true on the day of the launch when it was possible for us to monitor the spacecraft telemetry directly and know when important events were happening, such as the upper stage separation, solar array deployment etc. It was a truly impressive experience for all of the team to be able to view the spectacle of the Proton launch as our work started in earnest. Since then things seem to have proceeded very smoothly. Over the last few months our experience with the operations system and the spacecraft have improved and we have moved from technical monitoring of the spacecraft condition towards assessing the quality of the science data produced by INTEGRAL.
If there is a bad aspect to working in the Barn it would be that we seemed to miss out on the quantity of champagne afforded to some members of the ISDC as we started to work on the day of the launch. Hopefully there will be many more opportunities to raise a toast in the future, as we wish INTEGRAL a long and successful mission !
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| IBIS Observation of the Crab Pulsar | ||
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Pietro Ubertini (IAS Roma) on behalf of the IBIS Team |
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One hour after INTEGRAL was pointed towards the Crab Pulsar, on Friday the 7th of February starting at 06.00 UT, the IBIS Team at MOC (A.Bazzano, E.M. Quadrini, G. La Rosa and A. Segreto) was able to produce in quasi real time a beautiful Crab pulse time profile at different energies shown in the figure on the right (produced with dedicated software by A. Segreto).
This has allowed to verify in almost real time the correct behaviour of
the instrument and the expected position of the Crab in the centre of the
field of view of the IBIS telescope.
At the same time was also tested that the counting rate from the Crab was
the expected ones and the correctness of a software ``patch'' previously
implemented via telecommand on the Instrument Application Software.
This patch was installed in order to discard on-board ``bad events''
triggered by high energy particles inpinging on the ISGRI detector modules
ensuring a reduction of the transmitted background event rate.
The INTEGRAL calibration activity, mainly dedicated to IBIS for the initial 10 days, is continuing very succesfully. The initial timing, spectral and imaging Crab calibration result already confirmed the great scientific performance and capability of the IBIS telescope for which the IBIS and other INTEGRAL Teams should be thanked.
| JEM-X Anode Losses and Operational Changes | ||
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Peter Kretschmar (ISDC Geneva) & Niels Lund (DSRI Copenhagen) on behalf of the JEM-X Team |
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The activation of the two JEM-X detectors after the launch went smoothly and first results looked promising. But at the beginning of November it was noted that a gradual loss of active anodes was taking place in both JEM-X detectors with several anodes already being severely affected.
A clear cause for this problem has not yet been established although the most probable reason are occasional discharges caused by heavy nuclei cosmic rays. While erosion of microstrips by charged particles had been a concern during the development, measures had been taken and special accelerator test had been done concluding that the flight configuration should be safe.
After some analysis of the problem, the decision was taken to operate the detectors with reduced high voltage, lowering the gas gain by a factor of about 2.6. With the reduced high voltage no further anode losses have been observed.
The current state can be seen in the
image on the right
showing detector maps of the two JEM-X units from an empty field observation
of December 25. Vertical dark stripes indicate lost anodes.
The expected sharp increase of instrumental background at the rim of the
detectors is also clearly visible. The small rectangular sections at
the top are the locations of the calibration sources, whose events
are extracted from the science data. With the changed high voltage
and anode losses the spill over around some of these sources has
increased.
The main impact of the reduced high voltage on the scientific performance is a raised threshold at the lower end of the energy range, now at about 4.5 keV, affecting measurements of spectral continua below the iron line. The effects on other properties like, e.g., on-board background reduction, position or energy resolution are being studied, leading where necessary to changes in the configuration and in calibration files.
At the last meeting of the INTEGRAL Science Working Team it was decided that as a baseline for routine operations only one JEM-X detector, JEM-X 2, shall be operated. In this way one detector is kept in reserve should further anode degradation be observed. This decision may be rediscussed after the current calibration observations of the Crab where both units are used and fully analyzed.
While the high voltage and subsequent configuration changes clearly influence the properties of the instrument and have had repercussions for the scientific analysis, interesting results are still being obtained. Three examples are shown below:
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We therefore suggest you to use the Physics archive search page to find astro-ph for a given author, object name or keyword. Otherwise, you can directly subscribe to the e-mail distribution of astro-ph from here.
| XMM-Newton study of hard X-ray sources in IC 443 | |
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F. Bocchino1, A.M. Bykov2 1. INAF, Osservatorio Astronomico di Palermo, Italy 2. A.F. Ioffe Institute for Physics and Technology, St. Petersburg, Russia | |
| Accepted for publication in A&A on December 16th, 2002 | |
| Abstract. We present XMM-Newton observations of hard X-ray emission from the field of IC 443, a supernova remnant interacting with a molecular cloud. The hard emission from the field is dominated by 12 isolated sources having 2-10 keV flux greater than 10-14 erg cm-2 s-1. Only a fraction of the sources are expected to be extragalactic or stars on statistical grounds, while the others may be associated with the remnant. We have analyzed near-infrared K band and also DSS optical data for all of the detected sources, finding that six X-ray sources are located in a relatively small 15x15 arcmin region where there is strong 2.2 micron infrared emission, indicating interaction with a molecular cloud. The source 1SAX J0618.0+2227, the brightest in this region (excluding the plerion), is resolved with XMM into two sources, one of which is extended and has a hard power law spectrum photon index about 1.5) and shows some indications of spectral line signatures (e.g. Si), while the other is point-like and has a featureless spectrum of steeper photon index about 2.2. Possible interpretations of some of the discrete sources in terms of interaction between the SNR and the molecular cloud are discussed. | |
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E-mail contact | Preprint access |
| Radio / X-ray correlation in the low/hard state of GX 339-4 | |
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S. Corbel (Univ. Paris 7 and CEA Saclay), M.A. Nowak (MIT), R.P. Fender (U.
Amsterdam), A.K. Tzioumis (ATNF), S. Markoff (MIT) | |
| Accepted for publication in A&A on January 6 2003 | |
| Abstract. We present the results of a long-term study of the black hole candidate GX 339-4 using simultaneous radio (from the Australia Telescope Compact Array) and X-ray (from the Rossi X-ray Timing Explorer and BeppoSAX) observations performed between 1997 and 2000. We find strong evidence for a correlation between these two emission regimes that extends over more than three decades in X-ray flux, down to the quiescence level of GX 339-4. This is the strongest evidence to date for such strong coupling between radio and X-ray emission. We discuss these results in light of a jet model that can explain the radio/X-ray correlation. This could indicate that a significant fraction of the X-ray flux that is observed in the low-hard state of black hole candidates may be due to optically thin synchrotron emission from the compact jet. | |
| Preprint access | |
| Models for the positive latitude e+e- annihilation feature | |
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P. von Ballmoos1, N. Guessoum2, P. Jean1,
J. Knoedlseder1 1. Centre d'Etude Spatiale des Rayonnements, 9, Av. du Colonel Roche, 31028 Toulouse, France 2. American University of Sharjah, College of Arts & Sciences, Physics Unit, Sharjah, UAE | |
| Accepted for publication in A&A on August 2, 2002 | |
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Abstract. Galactic maps of e+e- annihilation
radiation based on CGRO-OSSE, SMM and TGRS data have indicated the existence of
an extended component at positive Galactic latitudes (l = -2 deg,
b = 7 deg), in addition to the emission from the galactic bulge and disk
(Purcell et al. 1997, Cheng et al. 1997, Milne et al. 2000, Milne et al. 2001).
This Positive Latitude Enhancement (PLE) was first attributed to an
``annihilation fountain'' in the Galactic center (Dermer and Skibo 1997) but has
since been the object of several models.
After discussing the observational evidence for the PLE, we investigate various models for the PLE : besides the scenarios proposed in the literature, we have introduced a number of models requiring relatively modest positron rates due to a local origin of the e+e- emission (local galactic-, solar system-, earth- and spacecraft-environment origins). The various scenarios for the PLE are constrained in the light of the latest OSSE-SMM-TGRS data analysis results : we have looked at the possible positron production mechanisms as well as the annihilation conditions in the different physical environments (temperature and dust grain content) proposed for the positive-latitude region. By constraining those parameters, based on the recent limits for the line width and the Positronium fraction, we found that some of the models can essentially be discarded. A number of other scenarios will have to await further measurements and maps, such as will be possible with INTEGRAL's SPI and IBIS instruments. We present a table/checklist of model-falsification criteria. | |
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| A Mass Model for Estimating the Gamma Ray Background of the Burst and Transient Source Experiment | |
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S.E. Shaw1, 2, M.J. Westmore1, A.J. Bird1,
A.J. Dean1, C. Ferguson1, et al. 1. Department of Physics and Astronomy, University of Southampton, SO17 1BJ, UK 2. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland | |
| Accepted for publication in A&A 398, 391-402 on 7 November 2002 | |
| Abstract. Orbiting x-ray and gamma ray instruments are subject to large background count rates due to local particle fluxes in the space environment. The ability of an instrument to make calibrated measurements of the flux from a source of interest is highly dependent on accurately determining the background level. We present here a method of calculating the energy dependent background flux for any point in the complete data set recorded by the Burst and Transient Source Experiment (BATSE) in its nine year mission. The BATSE Mass Model (BAMM) uses a Monte Carlo mass modelling approach to produce a data base of the gamma ray background which is then filtered to simulate the background count rate with a 2.048 second time resolution. This method is able to reduce the variations in the background flux by a factor of 8 - 10, effectively `flat-fielding' the detector response. With flat-fielded BATSE data it should be possible to use the Earth occultation technique to produce a hard x-ray all sky survey to the 1-2 mCrab sensitivity limit. BAMM is also capable of estimating the contribution to the spectra measured from gamma ray sources due to the reprocessing of source photons in inactive material surrounding a gamma ray detector. Possible applications of this aspect of the model in the area of Gamma Ray Burst spectral analysis are discussed. | |
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E-mail contact | Preprint access |
| Gamma-Ray Burst Detection with INTEGRAL/SPI | |
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A. von Kienlin1, Nikolas Arend1, G.
Lichti1, Andrew Strong1 & Paul Connell2
1. Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse, Garching, Germany 2. The University of Birmingham, Edgbaston, Birmingham, United Kingdom | |
| Accepted for publication in SPIE Conf. Proc., 4851, X-ray and Gamma-ray Telescopes and Instruments for Astronomy, Feb. 2003 | |
| Abstract. The spectrometer SPI, one of the two main instruments of the INTEGRAL spacecraft, has strong capabilities in the Field of Gamma-Ray Burst (GRB) detections. In its 16 degree Field of View (FoV) SPI is able to trigger and to localize GRBs. With its large anticoincidence shield (ACS) of 512 kg of BGO crystals SPI is able to detect GRBs quasi omnidirectionally with a very high sensitivity. The ACS GRB alerts will provide GRB arrival times with high accuracy but with no or very rough positional information. The expected GRB detection rate in SPI's FoV will be one per month and for the ACS around 300 per year. At MPE two SPI software contributions to the real-time INTEGRAL burst-alert system (IBAS) at the INTEGRAL science data centre ISDC have been developed. The SPI-ACS branch of IBAS will produce burst alerts and light-curves with 50 ms resolution. It is planned to use ACS burst alerts in the 3rd interplanetary network. The SPI-FoV branch of IBAS is currently under development at MPE. The system is using the energy and timing information of single and multiple events detected by the Germanium-camera of SPI. Using the imaging algorithm developed at the University of Birmingham the system is expected to locate strong bursts with an accuracy of better than 1 degree. | |
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E-mail contact | Preprint access |
| The intrinsic emission of Seyfert galaxies observed with BeppoSAX/PDS | |
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S. Deluit and T. Courvoisier 1. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland 2. Geneva Observatory, 51 Chemin des Maillettes, CH-1290 Sauverny, Switzerland | |
| Accepted for publication in A&A 399 on November, 27 | |
| Abstract. We present a study of the hard X-ray spectrum (>15 keV) of different classes of Seyfert galaxies observed with BeppoSAX/PDS. Using hard X-ray data, we avoid absorption effects modifying the Seyfert emission and have direct access to the central engine of these sources. The aim of this study is first to characterize the general properties of the hard X-ray spectrum of Seyfert 1, 1.5 and 2 galaxies and secondly to compare their intrinsic emission to test unified models according to which all the classes have the same nucleus. We compute the average spectrum of 14 Sy 1, 9 Sy 1.5 and 22 Sy 2 galaxies observed by the PDS (15-136 keV). The average spectrum of Sy 1 differs from that of Sy 2, the first requiring the presence of a high energy cutoff which is absent in the second. We also show that the reflection component is possibly more important in the Sy 2 emission. The nature of Sy 1.5 galaxies is ambiguous as they have a negligible reflection component (like Sy 1) and do not require a cutoff (like Sy 2). | |
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E-mail contact | Preprint access |
| The HRX-BL Lac sample - evolution of BL Lac objects | |
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V. Beckmann1,2,3, D. Engels2, N. Bade2 & O. Wucknitz2 1. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland 2. Hamburger Sternwarte, Gojenbergsweg 112, D-21029 Hamburg, Germany 3. Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, D-72076 Tübingen, Germany | |
| Accepted for publication in A&A on February 12, 2003 | |
| Abstract. The unification of X-ray and radio selected BL Lacs has been an outstanding problem in the blazar research in the past years. Recent investigations have shown that the gap between the two classes can be filled with intermediate objects and that apparently all differences can be explained by mutual shifts of the peak frequencies of the synchrotron and inverse Compton component of the emission. We study the consequences of this scheme using a new sample of X-ray selected BL Lac objects comprising 104 objects with z<0.9 and a mean redshift z = 0.34. 77 BL Lacs, of which the redshift could be determined for 64 (83%) objects, form a complete sample. The new data could not confirm our earlier result, drawn from a subsample, that the negative evolution vanishes below a synchrotron peak frequency log νpeak = 16.5. The complete sample shows negative evolution at the 2σ level (< Ve/Va> = 0.42 +- 0.04). We conclude that the observed properties of the HRX BL Lac sample show typical behaviour for X-ray selected BL Lacs. They support an evolutionary model, in which flat-spectrum radio quasars (FSRQ) with high energetic jets evolve towards low frequency peaked (mostly radio-selected) BL Lac objects and later on to high frequency peaked (mostly X-ray selected) BL Lacs. | |
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E-mail contact | Preprint access |
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