| No. 5 - March 27, 2001 | Edited by Thierry Montmerle & Marc Türler |
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The ISDC itself contributed to this high pressure, with its staff being involved in many proposals in all main fields of gamma-ray astronomy amounting to about 10% of the total requested time for AO-1. This means that the ISDC shares fully the scientific interests of the whole community, and is thus equally eager to be as efficient as possible and to obtain the best results.
It is no surprise, then, that ISDC scientists are heavily involved during the INTEGRAL operations, as described below by Nami Mowlavi. The necessity of responding to gamma-ray bursts or to transient sources translates into a sophisticated round-the-clock organization, in parallel with the more routine tasks of monitoring the continuous data processing and archiving.
On the other hand, time continues to fly, and while we're getting close to one year before launch, SPI is on its way to be calibrated as a whole. The ISDC will be part of the process, taking this opportunity to fully test its software on what can be considered as the first ``real-time'' data coming from INTEGRAL.
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| The ISDC during routine operations |
| Nami Mowlavi (ISDC Geneva) |
The ISDC has the role, within the INTEGRAL ground segment, to analyse, archive and distribute the data received from the satellite. The aim of this article is to give a basic overview of the organization of the ISDC during routine operations. I first present the different teams which will be working at the ISDC during operations, and then focus on the data processing performed at the ISDC as monitored by the so-called ``shift team''.
It must be noted that scientists at the ISDC are integrated in one or another of the teams mentioned above, most of them being in the team of instrument specialists. As a result, no science team is explicitely defined, though scientific research is actively conducted at the ISDC.
Near real time data from the INTEGRAL satellite are directly forwarded to the ISDC by the Mission Operations Center (MOC) in Darmstadt, Germany. These data are continuously received and monitored in the operations room by the pipeline operator, and automatically checked within a few seconds by the INTEGRAL Burst Alert System (IBAS) to search for gamma-ray bursts (GRBs).
In case of a GRB detection, an automatic alert is sent by the IBAS to a predefined list of people around the world in order to follow the event in other wavelengths as soon as possible. The scientist on duty would then analyse the data and confirm (or invalidate) the alert. Any interested person can register to the list (information will be provided in a coming issue of this Newsletter). It is expected that INTEGRAL should observe about one GRB per month. If its position is in the field of view of the Optical Monitoring Camera (OMC) on board INTEGRAL, an alert is sent to the MOC in order to command the satellite to track the GRB in the optical.
When a transient source is detected by the near real time data pipeline, the data are analysed by the scientist on duty. If the transient candidate is confirmed, a message is sent to the Project Scientist, who decides whether the transient object can be declared to be a target of opportunity (ToO). Further automatic and manual checks are performed on the near real time data in order to check the good performance of the instruments and analyse background data.
Consolidated data, on the other hand, are sent by the MOC to the ISDC on CD-roms about two weeks after reception of the near real time data. The consolidated data are also processed in the operations room at the ISDC. Standard data products are derived and archived. The quality of the standard data products is controlled by the scientist on duty. Sets of standard data products are declared ready for distribution after consultation with the INTEGRAL Science Operations Center (ISOC) in the Netherlands. They are then distributed to the observers on the requested medium.
The basic duration of a shift is of one revolution (i.e. 3 days). The shift team will be on duty from one perigee to the next. It is working at the ISDC eight hours a day from 9h00 to 18h00 from Monday to Sunday, and is on call for the rest of the time. The operations coordinator, on the other hand, stays on shift during two consecutive revolutions.
| Feedback about the Observation Simulator |
| Ada Paizis (ISDC Geneva) |
The INTEGRAL Observation Simulator (OSim) developed at the ISDC was made available in the last issue of this newsletter. If you tried to use it, we would be very interested in having your opinion about the OSim distribution. It will allow us to have an idea on how many of you tried to install and run the simulator. Your comments on the difficulties you encountered will be precious for us to improve future software deliveries.
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| The Status of the Spectrometer SPI |
| Gilbert Vedrenne (CESR Toulouse) and Volker Schönfelder (MPE Garching) |
The SPI instrument has been fully integrated with the SPICO cryocoolers from the
MMS Astrium company by the end of January. This was the last subsystem delivery.
In February, SPI was transported to INTESPACE in Toulouse where it
successfully withstood the tests of electro-magnetic compatibility (EMC).
The image on the right shows the SPI instrument
during these EMC tests (image courtesy J.-P. Roques).
Now, since the beginning of March, SPI goes through thermal vacuum tests,
still at INTESPACE.
This is the first time the instrument is complete, especially with the
Ge detector plane and the whole four-cryocooler system with its electronic
command.
The two stages of the preamplifiers are also at their nominal temperature.
Up to now the detector performances are nominal.
The tests will go on until end of March.
From April 10, SPI will be in Bruyères-le-Châtel (a nuclear research
facility near Paris, France) for a full month devoted to calibrations, using sources
and gamma-rays produced on proton accelerator targets.
Finally, at the beginning of May, the instrument will be delivered to Alenia for integration
on the satellite.
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| The X-ray view of the quasar MR2251-178 and its host cluster: variability, absorption, and intracluster gas emission | |
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Stefanie Komossa Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany | |
| Accepted for publication in A&A on December 13, 2000 | |
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Abstract. MR2251-178 was the first quasar initially discovered in X-rays, and the first one found to host a warm absorber.
The quasar turned out to be an outstanding object in many respects.
It has a high ratio of X-ray/optical luminosity, is surrounded by the largest quasar emission-line nebula known, and is located in the outskirts of a cluster of galaxies.
Here, we present results from an analysis of the X-ray spectral, temporal, and spatial properties of this source and its environment based on deep ROSAT observations.
Remarkably, we do not detect any excess X-ray cold absorption expected to originate from the giant gas nebula surrounding MR2251-178. This excludes the presence of a huge HI envelope around the quasar. The X-ray spectrum of MR2251-178 is best fit by a warm-absorbed powerlaw with an ionization parameter log U = 0.5 and a column density log Nw = 22.6 which, however, cannot be the same material as the giant optical emission line nebula. The mean (0.1-2.4)keV X-ray luminosity amounts to 1045 erg/s. A spatial analysis shows that the bulk of the X-ray emission from the quasar is consistent with a point source, as expected in view of the powerlaw-shaped X-ray spectrum and the rapid X-ray variability we detect. In addition, extended emission appears at weak emission levels, including a bridge between the quasar and the cD galaxy of the cluster. The X-ray emission from the intra-cluster medium is weak or absent. None of the other member galaxies of the cluster to which MR2251-178 belongs, are detected in X-rays. However, east of the quasar there is a significant excess of X-ray sources, several of them without optical counterparts on the UK Schmidt plates. | |
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E-mail contact | Preprint access |
| X-ray states and radio emission in the black hole candidate XTE J1550-564 | |
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S. Corbel et al. Univ. Paris VII & CEA Saclay & Harvard-CfA | |
| Accepted for publication in ApJ on February 2, 2001 | |
| Abstract. We report on radio and X-ray observations of the black hole candidate (BHC) XTE J1550-564 performed during its 2000 X-ray outburst. Observations have been conducted with the Australia Telescope Compact Array (ATCA) and have allowed us to sample the radio behavior of XTE J1550-564 in the X-ray Low Hard and Intermediate/Very High states. We observed optically thin radio emission from XTE J1550-564 five days after a transition to an Intermediate/Very High state, but we observed no radio emission six days later, while XTE J1550-564 was still in the Intermediate/Very High state. In the Low Hard state, XTE J1550-564 is detected with an inverted radio spectrum. The radio emission in the Low Hard state most likely originates from a compact jet; optical observations suggest that the synchrotron emission from this jet may extend up to the optical range. The total power of the compact jet might therefore be a significant fraction of the total luminosity of the system. We suggest that the optically thin synchrotron radio emission detected five days after the transition to the Intermediate/Very High state is due to a discrete ejection of relativistic plasma during the state transition. Subsequent to the decay of the optically thin radio emission associated with the state transition, it seems that in the Intermediate/Very High state the radio emission is quenched by a factor greater than 50, implying a suppression of the outflow. We discuss the properties of radio emission in the X-ray states of BHCs. | |
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E-mail contact | Preprint access |
| Observational evidence for mass ejection during soft X-ray dips in GRS 1915+105 | |
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S. V. Vadawale1, A. R. Rao1, A. Nandi2 and S. K.
Chakrabarti2 1. Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400 005, India. 2. S.N. Bose National Center for Basic Sciences, Salt Lake, Calcutta-700 091,India | |
| Accepted for publication in A&A Letters on March 1, 2001 | |
| Abstract. We investigate the connection between the X-ray and radio properties of the Galactic microquasar GRS 1915+105, by analyzing the X-ray data observed with RXTE, during the presence of a huge radio flare (~450 mJy). The X-ray lightcurve shows two dips of ~100 second duration. Detailed time resolved spectral analysis shows the existence of three spectral components: a multicolor disk-blackbody, a Comptonized component due to hot plasma and a power-law. We find that the Comptonized component is very weak during the dip. This is further confirmed by the PHA ratio of the raw data and ratio of the lightcurves in different energy bands. These results, combined with the fact that the 0.5-10 Hz QPO disappears during the dip and that the Comptonized component is responsible for the QPO lead to the conclusion that during the dips the matter emitting Comptonized spectrum is ejected away. This establishes a direct connection between the X-ray and radio properties of the source. | |
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E-mail contact | Preprint access |
| A Chandra Observation of M51: Active Nucleus and Nuclear Outflows | |
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Yuichi Terashima and Andrew S. Wilson 1. NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771 and Astronomy Department, University of Maryland, College Park, MD 20742 2. Astronomy Department, University of Maryland, College Park, MD 20742 | |
| Accepted for publication in ApJ on March 2 2001 | |
| Abstract. We present a Chandra ACIS-S observation of the nuclear region of the nearby spiral galaxy M51 (NGC 5194), which has a low-luminosity Seyfert 2 nucleus. The X-ray image shows the nucleus, southern extranuclear cloud, and northern loop, the morphology of the extended emission being very similar to those seen in radio continuum and optical emission line images. The X-ray spectrum of the nucleus is well represented by a model consisting of soft thermal plasma with kT ~ 0.5 keV, a very hard continuum, and an Fe Kα emission line at 6.45 keV with an equivalent width of > 2 keV. The very strong Fe line and the flat continuum indicate that the nucleus is obscured by a column density in excess of 1024 cm-2 and the spectrum is dominated by reflected emission from cold matter near the nucleus. The X-ray spectra of the extranuclear clouds are well fitted by a thermal plasma model with kT ~ 0.5 keV. This spectral shape and morphology strongly suggest that the clouds are shock heated by the bi-polar outflow from the nucleus. The shock velocities of the extranuclear cloud and northern loop inferred from the temperatures of the X-ray gas are 690 km/s and 660 km/s, respectively. By assuming a steady-state situation in which the emission of the extranuclear clouds is powered by the jets, the mechanical energy in the jets is found to be comparable to the bolometric luminosity of the nucleus. | |
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E-mail contact | Preprint access |
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