| No. 11 - October 25, 2002 | Edited by Thierry Montmerle & Marc Türler |
 |
 |
 |
| << Previous issue | Next issue >> |
| |||
| |||
|
| INTEGRAL was successfully launched ! |
A week ago, numerous red eyes were watching the various episodes of the
launch of INTEGRAL with what they had at hand, from a small portable computer
screen to a giant movie-size screen, or even being on-site at Baikonur.
As described in two contributions below,
the launch was perfect, but relief
really came after the separation between the Proton's last stage and the
satellite.
We should not forget also our colleagues at work (and not only
watching) while the launch was unfolding, at the MOC and at the ISDC.
This is already history... now comes the new science brought by INTEGRAL. We're not quite there yet, but step by step INTEGRAL awakes to the violent universe. Instruments are being switched-on one by one, flawlessly so far. We already have data at ISDC, even if they are not yet science data. For this, we'll have to wait for the real ``first light'', the observation of Cygnus X-1 due to take place around mid-November.
The articles contained in this first issue following launch focus on the state of preparation at the ISDC and on the first data collected by INTEGRAL. Everything works fine so far and this is certainly good news for young students wishing to start their PhD at the ISDC (see the Offer below) or elsewhere around the world.
You will also find here how the launch event was followed at the ISDC, in Toulouse, and even in Baikonur as experienced by somebody not involved in the INTEGRAL project.
Good reading, stay tuned for more ISDC and INTEGRAL news in the future, and long life to INTEGRAL!
 |
 |
|
| The ISDC at the time of launch |
| Thierry Courvoisier (PI of the ISDC) |
The ISDC (INTEGRAL Science Data Centre), whose Newsletter you are now reading, is the centre in charge of receiving the INTEGRAL telemetry, of decoding it, of analysing it a first time, of archiving it and of distributing the data and the results of the first analysis to the community. The ISDC is thus the prime point of contact between the INTEGRAL data and the community of users. We thought it appropriate at the time of launch of introducing the team doing this work.
The ISDC was established in 1995, at the same time as the instruments were
selected and following the same procedure.
The ISDC is funded by a consortium
of a dozen institutes in Europe and the US (see the map on the right).
Most partners in the consortium
contribute by providing manpower to the ISDC.
These people work in Ecogia and
are supported financially by their home institute. They form a privileged
link between their communities and the ISDC.
The ISDC is attached to the Geneva Observatory, actually the department of astronomy of the Geneva University. It is located in 3 buildings in a place called Ecogia, in Versoix, few kilometers from the Observatory. These buildings are called ``The Castle'', ``The Barn'' and the Pavilion. The first 2 names reflect the previous usage of the respective buildings and the pavilion its architecture. The operations of the ISDC take place in the barn, the other two buildings offer office space.
The picture on the left shows the ISDC main building ``the castle''. The picture on the right shows part of the screen wall in the barn used for operation monitoring.
The ISDC started as a very small team (mostly Roland Walter and Thierry
Courvoisier at the time of proposing the centre) and grew steadily, at a rate
close to our expectations of the beginning. There are now some 37 people
working in Ecogia for the ISDC.
A small number not included in this figure work remotely from their institute.
The team is made of software engineers, scientists and a small number of
support staff. The organization is rather simple, structured around a number of
teams responsible for given aspects like system software development and
maintenance, operations, quality control and scientific software development,
and instrument follow up and monitoring.
The figure on the left describes the organization and gives the names of the people. The picture on the right shows all the ISDC staff (except 3 members away on that day).
A large fraction of the software deals with instrument specific issues. This software was written in very close collaboration between the ISDC and the teams that have developed and built the instruments of INTEGRAL. The close links thus established between the instrument teams and the ISDC during the development of the centre will remain now that we start operations. This is deemed most important to be able to provide the best possible service to the astronomical community using INTEGRAL data.
ESA has also been an important partner in our development. Th other centres of the ground segment of the mission are the Mission Operations Centre (MOC in the jargon) located in the European Space Operations Centre in Darmstadt from where we receive the data and the INTEGRAL Science Operations Centre (ISOC) located at ESTEC. At ISOC our colleagues prepare the AO for observations, manage the selection process and transform the results of this selection in the observation timeline for the mission.
The ISDC staff have now worked for many years to prepare for the satellite operations. It is not without a certain apprehension that we stand at the beginning of the activities we have imagined and for which we have developed software, tools and procedures. We hope to have taken decisions as sensible as possible along the way and spent our efforts as efficiently as possible to provide to the community the services it expects to receive and to contribute thus to the success of the mission. This Newsletter has informed you of some steps in our development over the last years, it will keep you informed on the progress of the analysis of data. Our web site will also provide you with information on the data analysis and the products of the mission. We are very much looking forward to be in touch with all those involved in the INTEGRAL science.
| ISDC status one week after launch |
| Thierry J.-L. Courvoisier & Roland Walter (ISDC Geneva) |
INTEGRAL was launched on October 17 at 4:41 UT, i.e. 6:41 central European summer time by a Proton rocket from the Baikonour cosmodrom. The launch and early operations were all flawless. The satellite is now in orbit and its instruments and subsystems are being verified. At the time of writing the programme is taking place as well as possible.
The data are routed from the satellite to the ground stations in Belgium and/or in California continously, from there they are brought to ESOC where the commands are sent and the safety of the instruments and satellite are checked. The data are then routed to the ISDC for scientific processing.
ISDC has been receiving the telemetry in real time since the first
aquisition of signal at 8:01 (local time) on Thursday. We started our
processing of the data (pre-processing and pipelines) from 10 am onward on
the same day. Our processing has been successfully running since then.
The available data are displayed with our interactive tools (IOSM) in
the operations room (in a renovated barn) for the operational network and in
the office network where the
data are copied to be further analysed by instrument team and ISDC scientists
as they are processed. The data are thus available to
the instrument teams at ISDC 2 hours after having been obtained. We are
following housekeeping data as well as science telemetry when the
instruments are activated. We have to date seen science data from IREM, OMC,
JEM-X, PICsIT and ISGRI.
The figure on the right shows a typical PICsIT display of the interactive operations system monitoring (IOSM) available in the barn or in the offices. At the top left is a lego plot of all events, on the right a detector spectrum and the shadowgram images at low, medium and high energy are shown below (from left to right, respectively). Similar displays are also available for ISGRI.
PICsIT was switched on already in a way that allowed us to receive (background) science data on all modules. It was thus possible to try the offline science analysis (OSA) on these data. Indeed few hours after shadowgrams from PICsIT were available, it was possible to deconvolve them. This allowed IBIS and ISDC scientists to test the programmes and to understand what features of the background will need to be corrected for in future installations of the analysis software.
Our software system has been upgraded at both perigees to date (we are in the third revolution at the time of writing) to take into account the anomalies we detected and to provide improvements that are deemed important. These upgrades took place without causing any interruptions in the data stream and/or operations. We are thus keeping our system as well tuned as possible.
The operations of the ISDC system have also been very smooth with the shift team composed of 2 operations' coordinators and four operators well in control. The system is running alone during the nights with no problem.
| Data and software releases in the early mission phases |
| Thierry J.-L. Courvoisier (ISDC Geneva) |
The ISDC started receiving and processing INTEGRAL data shortly after the launch of INTEGRAL on October 17 at 10:00 CEST. While the very first data dealt only with spacecraft related information, instrument related data are already flowing in and scientificly relevant data are expected in the next days already.
It was decided many years ago that the commissioning and performance verification phases would last two months i.e. until December 16. These data belong to the members of the INTEGRAL Science Working Team (ISWT) made of the instrument and ISDC PIs, the mission scientists, the project scientist and representatives of the Russian and US astronomical communities. The data are routinely made available to these people at the ISDC from the launch. The observations that are needed to complete the calibration of the instruments after December 16 are public. This will apply to a set of observations planned for the end of this year and to the observation of the Crab that will be performed in February 2003 (solar constraints make it impossible to observe the Crab earlier). It will also apply to the routine calibration observations scheduled in the following years.
The Crab observations are essential to complete the calibration of the instruments. It is therefore not possible to provide all flight tested calibration files prior to these observations. It is therefore also not possible to perform the standard analysis fulfilling the quality criteria of the products. The standard analysis extracts from the data a series of high level products including fluxes and spectra. It is nonetheless possible to provide the INTEGRAL data to the community before then. The ISWT decided on the following scheme to bring data as quickly as possible to the community. Public data obtained after December 16 will be made public through the standard INTEGRAL archive without the corresponding high level products generated at the ISDC. As these high level products become available, ISDC will provide them on a special page on the web. The data will be brought into the archive following the normal procedure foreseen for the routine operations which implies that the data are consolidated by ESA staff at the mission operation centre in ESOC prior to being shipped to the ISDC where they are processed and archived. The first data are therefore expected to be available on January 7. The high level products will appear on the web from then onward at a rate that will reflect the progress in the tuning of the analysis software in the early mission phase.
The standard processing of the data and therefore the routine release of data will start after the observation of the Crab when the calibration files are such that minimal quality criteria are met. These criteria include that the source positions are measured with an accuracy of 5 arcminutes for IBIS and 2 arcminutes for JEM-X, that the energy scale is known to better than 2 keV up to 200 keV, that the SPI spectral resolution is better than 5 keV (FWHM) and that the flux of the Crab is measured to better than 30%. These criteria were selected to ensure that the data are meaningful without being so tight that it would take a long time to meet them. We therefore expect that routine data and analysis results will be available from April onward.
The analysis software developed by ISDC and instrument team staff will also be released to the community. A proper balance between software evolution, robustness and availability has to be kept, particularly in the early mission phases during which we expect the software to evolve rapidly. In order to keep this balance as well as possible we decided to freeze one version of the software at the end of the nominal performance verification phase December 16 and to prepare a formal public release of this set of software including the tests, debugging and documentation that this requires. This will lead to a formal release in march 2003. In the following period we expect these formal releases to take place every 6 months. In order to allow observers to use software faster than the 6 months formal release, ISDC will have a so-called ``production version'' of the analysis software that will be used at ISDC without guarantee of being bug-free. This software will be available to observers who wish to use it, with the same (lack of) guarantee than if they were at ISDC.
We hope that the approach taken for making the data and the software available to the community will meet your expectations.
| The launch event at the ISDC |
| Marc Türler (ISDC Geneva) |
On Thursday, October 17th, about 200 people were waked up unusually early by
their alarm clock set before 5:30. None of them wanted to miss the long awaited
event of INTEGRAL's launch and drove to the ISDC in the dark and under pouring rain.
The event started at 6:15 with the welcoming words of Thierry Courvoisier
addressed to the families and friends of the ISDC staff,
colleagues from the Geneva Observatory, journalists, and representatives
of the funding authorities. Sitting in two different rooms, everybody
could then follow ESA's T.V. program projected on big screens. The attention and
the excitement was growing among the audience up to the final count down that
everybody spoke for himself or loudly keeping their fingers crossed.
Two long seconds followed the zero before the expected smoke and flames finally
appeared; Proton was lifting-off!
Only a few minutes passed (picture on the left)
and the heavy rocket was no more than a little white spot in the blue sky of Kazakhstan.
A cup of coffee in one hand and a croissant in the other, much more
relaxed and smiling faces were meeting outside in a tent (picture on the right). Everybody was
impressed by the perfect and seemingly so easy lift-off and was hoping that
Proton's fourth stage will work as well in a few minutes above Argentina.
This did indeed happen as expected, INTEGRAL's solar panels deployed as
planned and the first telemetry stream arrived at the ISDC. INTEGRAL's launch
was a total success! While applauding, the crowd leaved the T.V. screens to get
a glass of champagne. The warm and friendly atmosphere inside the tent
contrasted with the cold and rainy weather outside. It was a great moment of
emotion for everybody and probably no one regretted to have been waken up so
early because of a rocket somewhere in Kazakhstan...
The event was widely reported in the local media, on radio, T.V. and in the newspapers and we, in Switzerland, had the impression to be part of this great project, the result of so much work in various countries all around the world. It's incredible that everything works in the end and that's why this wonderful launch will remain in our memories as a great success.
|
|
 |
|
| First data from the IBIS imager |
| Pietro Ubertini (IAS Roma) on behalf of the IBIS Team |
Dear ISDC newsletter reader,
it is with emotion that the IBIS team is pleased to inform you that we have the first IBIS light! In fact, PICsIT was switched on the morning of the 20th of October at 6.00 and the image of the first module (PDM1) was positively collected in photon-by-photon mode. It was great to see the gamma ray image, as we expected, even if the background count/rate was quite high due to the deep belt passage (data were taken just exiting the belt at about 50,000 km), the non optimised tuning of the electronics and, even more important, the absence of the VETO system on, due to waiting time for Satellite degassing. The temperature of the PICsIT modules was of about -10 degree C, due to absence of power on ISGRI and VETO systems. The full unit was then switched on and we got beautiful pictures of single and multiple events. IBIS was maintained on in this configuration for about 40 hours.
Two days after the first IBIS/PICsIT light, on wednesday the 23rd, the low energy detector ISGRI has been enabled to record the first photons in flight. The aim of this short initial switch on was to verify the funcionality of ISGRI after injection in orbit and have a rough idea of the initial background counting rate just coming out of a large dose during the deep belt passage. For thermal uniformity reasons, all the 8 MCEs were powered but only MDU4 was biased powered with a bias of -120 V for about one hour. The module temperature was around -10oC.
The first MDU4 image (see picture on the
right) shows the outstanding functionality of the detectors
and the good uniformity of the active module.
The first spectrum shows
Tungsten and (possibly) fluorescence lines as well as a weak 511 keV line
due to the calibration source, so far off and not removing the 511 keV (to
be tagged) photons.
This initial switch on demonstrates the excellent performance of ISGRI.
We have now to wait for the end of the VETO outgasing and the orbit
evolution to estimate the background.
The first IBIS images and spectra can be seen on the IBIS Home Page. We are now looking forward to see the Veto System doing his job, substantially "killing" the background, the Calibration Unit on and then the first "real" sky gamma ray image to come!
| First data from the Optical Monitoring Camera (OMC) |
| J. Miguel Mas Hesse (CSIC-INTA, Madrid, Spain) |
On Oct. 21st, 2002, at around 21:00, we proceeded to open the cover
protecting the OMC optical system and CCD. The portakabin at ESOC was full
from people, and the expectation was very high. Less than 3 minutes after
powering the Starsys, the telemetry sent by the cover micro-switches
indicated that the opening had been successful! Everybody was happy and
pleased, and the cava bottles were started to be open. Only the OMC team
was still anxious, since we waited for reception of the first image to
confirm that everything was working properly.
Few minutes afterwards we got
our first-light image (picture on the right). In real-time we checked the good focusing,
uniformity, lack of straylight,... and became then really satisfied.
We got
soon confirmation that the data had been properly received and processed at
ISDC. Later on we continued getting images and testing all OMC modes.
Everything is working smoothly up to now.
| The INTEGRAL Radiation Environment Monitor (IREM) |
| Wojtek Hajdas, Christina Eggel, Aliko Mchedlishvili & Paul Buehler (PSI, Switzerland) |
The first instrument, switched on already 9 hours after the launch, was IREM
- the INTEGRAL's Radiation Environment Monitor. It measures
ionizing particles impinging on the spacecraft and provides prompt
information on actual radiation levels on board.
Since October 17th the IREM works very well mapping passages through
the hazardous radiation belts where other instruments must go into a
safe operation mode.
The figure on the right shows count rates of three different IREM channels during the second crossing of INTEGRAL through the inner and outer radiation belts.
| Baikonur, October 17, 2002 |
| Julio Rodriguez |
Editors' note: This live report of INTEGRAL's launch was written by a friend of Thierry Courvoisier's son. They went together to Baikonur as part of a group.
Concrete : That is one material that is present in Central Asia. A residue from the Soviet Era. Baikonur's heart and soul, and all its' 4 story high, constructivist, functional, regularly displayed buildings are made of it. Kyzyl'Orda's university, Samarcands' factory chimneys and Boukhara's cold and empty square are all offsprings of Mother-concrete.
Suddenly the engines slowed down and the bus turned right and continued slowly on a bumpy, dusty and seldom traveled beaten track. After it stopped, we were informed that it was better to continue on foot. The Kazak Steppe was stroked by a sharp, icy wind. We got our cameras ready, covered ourselves with more sweatshirts and started to walk towards the indicated place. Realizing that we were running out of time we started to run on this soft but firm brownish yellow soil with its dried up, small brownish green plants, spreading on lands that have no ends.
No ends : There were no ends to the lands that we crossed with the bus. Just a straight black road, that had no curves what so ever, and itself had no ends. There were no ends to the imagination of Khivas' architects and craftsmen in decorating the attractive colored and symmetrical patterns of the mosques and minaret facades.
We stopped on a small plateau and with the help of binoculars, we thought we
could distinguish the launching platform but we were not sure of the exact spot.
The precise time was also unknown.
However, only a few minutes passed and
suddenly at the ``end '' of the desert, two black tours of smoke started to
inflate. In-between them, a gray-white thin line with, at the end of it, a
petal of flame, rose : the Proton was taking-off. It was unbelievable.
Unbelievable : To imagine Genghis Khan and Alexander the Greats' armies traversing the region without any natural reference point. It is hard to think that this steppe was once in history a great center of trade, where camels and horses transported wealthy merchandises through cities of unbelievable beauty. Unbelievable is also the work of the famous astronomer Ouloug Beg and his precise calculations.
It flew faster and faster, with a curving trajectory. It turned white with
the sun light after passing through a thin layer of clouds. A few seconds
later, it disappeared in higher, denser Cumulus. However, just before
vanishing, it produced a white cotton flower cloud.
Cotton : The flower that is everywhere in Uzbekistan. So soft, so harmless and so useful, it was, during the Soviet regime, Uzbekistan's main economical activity. However, because of the extended irrigated fields for the cotton plant to grow, it caused one of the most tragic ecological disaster of the 20th century : Aral Sea dryness.
We were all shouting out : "Did you see it ?". But 40-45 seconds after we saw the first spheres of smoke, silence imposed its reign : nobody talked. We stopped looking... we were just seeing. We stopped hearing... and began to listen. All our concentration converged to our ears. The air perspired a deep trembling sweat. We all heard the regular powerful vibrating roars that crossed through the striking winds and continued diverging straight ahead. The sound was so clear that we felt it.
We felt it ! The sun's heavy heat was felt in front of the barbed wire fence along the Amou Darya River that is the natural border between Afghanistan and Uzbekistan. We experienced the recitation of French poetry by a custom woman in the train's restaurant car at the Uzbek-kazak frontier. We felt the strong bitter taste of Kazak vodka. We felt Baikonur's soviet experience.
Going towards the Proton rocket was the main aim of the trip, but by taking the path between light and sound, we discovered a whole variety of new experiences.
| The pale faces at Toulouse |
| Thierry Montmerle (CEA Saclay) |
6 am, Thursday Oct. 17. Under the pouring rain, cars are jammed at the
entrance of CNES (the French Space Agency) in southern Toulouse. After a
swift security check, guests find their way into the large complex to reach
the "Leonardo da Vinci" circular building. Hands shake, smiles appear, but
the tension is high. Eyes are red. To the question: "Did you sleep well ?",
the most frequent answer is "So, so", or even "Not at all". The large screen
overlooking the room is blank...
At last, guests -over 200 or them, it seems- take their seats. A science
journalist arrives on the stage, and opens the show... The program aims at
informing the audience about INTEGRAL, in between the various steps of the
launch and orbit insertion -obviously nothing new for us scientists, but many
outside guests are present: CNES, CEA, and CNRS officials, journalists, even
some students. But still nothing on the screen, only oral news taken from
Baikonur from time to time: everything is OK, the launch sequence proceeds
as planned. Finally, two minutes before the scheduled launch time, the Proton
rocket appears on the screen !
Figure 1. On stage: funding actors (center, Dominique Le Quéau, Director of CESR; middle right, François Gounand, head of Division des Sciences de la Matière, CEA)
Countdown... The numbers appear : 5, 4, 3, 2, 1, 0. A big flame, exclamations
in the room... Liftoff ! Very little smoke (compared with the powder boosters
of the Shuttle or of Ariane), and a remarkably agile split-second start -as
if the 3.5 tons of INTEGRAL were just a feather. The clean flame of the
Proton becomes the only feature visible, then after just a few minutes, the
image disappears, under disappointed murmurs in the audience. No applause.
Everybody knows that key phases are yet to come: stage separation, injection
into the transfer orbit, re-start to reach the final orbit. To keep the
audience busy, several (French) actors of INTEGRAL are successively called on
the stage, from CNES, ESA, CEA, CNRS, etc. ISDC activities are described by
Gilbert Vedrenne. But murmurs keep going: "What's happening ? Is everything
OK ? We know all this, why don't they inform us ?"
Figure 2. On the floor: anxious faces (left to right: Geneviève Debouzy, Gilbert Vedrenne, Marie-Anne Clair)
Sure enough, very little information is coming through. The screen does not
display, as is the rule for Kourou launches, the altitude-time curve of the
satellite, with the major phases highlighted. A look around the dimly lit
room shows many pale, anxious faces...
Figure 3. Other anxious faces: among others Philippe Lavocat (left) and Jacques Paul (right).
But after several minutes of confusing information about the final separation of the satellite, we learn that INTEGRAL is at last set free and on the nominal trajectory ! Then, and only then, years of effort get their reward; applause and embraces erupt, the relief is perceptible. We also learn soon thereafter that the first telemetry packets have reached ISDC.
Last but not least, we can now head towards the breakfast table. A new chapter in the history of astronomy opens. It is 8:30 am.
|
|
 |
|
| Confirmation of Two Cyclotron Lines in Vela X-1 | |
|
I. Kreykenbohm1, W. Coburn1, J. Wilms1, P.
Kretschmar3, R. Staubert1 1. IAA Tuebingen 2. SSL, UC Berkeley 3. MPE Garching, ISDC | |
| Accepted for publication in A&A on Aug 9, 2002 | |
| Abstract. We present pulse phase-resolved X-ray spectra of the high mass X-ray binary Vela X-1 using the Rossi X-ray Timing Explorer. We observed Vela X-1 in 1998 and 2000 with a total observation time of ~90 ksec. We find an absorption feature at 23.3 +1.3 -0.6 keV in the main pulse, that we interpret as the fundamental cyclotron resonant scattering feature (CRSF). The feature is deepest in the rise of the main pulse where it has a width of 7.6 +4.4 -2.2 keV and an optical depth of 0.33 +0.06 -0.13. This CRSF is also clearly detected in the secondary pulse, but it is far less significant or undetected during the pulse minima. We conclude that the well known CRSF at 50.9 +0.6 -0.7 keV, which is clearly visible even in phase-averaged spectra, is the first harmonic and not the fundamental. Thus we infer a magnetic field strength of B=2.6 x 1012 G. | |
|
E-mail contact | Preprint access |
| Magnetic Fields of Accreting X-Ray Pulsars with the Rossi X-Ray Timing Explorer | |
|
W. Coburn1, W. A. Heindl2, R.E.
Rothschild2, D.E. Gruber2, I. Kreykenbohm3, et
al. 1. SSL, UC Berkeley 2. CASS, UC San Diego 3. IAA, Tuebingen | |
| Accepted for publication in ApJ on July 19, 2002 | |
| Abstract. Using a consistent set of models, we parameterized the X-ray spectra of all accreting pulsars in the Rossi X-ray Timing Explorer database which exhibit Cyclotron Resonance Scattering Features (CRSFs, or cyclotron lines). These sources in our sample are Her X-1, 4U 0115+63, Cen X-3, 4U 1626-67, XTE J1946-274, Vela X-1, 4U 1907+09, 4U 1538-52, GX 301-2, and 4U 0352+309 (X Per). We searched for correlations among the spectral parameters, concentrating on how the cyclotron line energy relates to the continuum and therefore how the neutron star B-field influences the X-Ray emission. As expected, we found a correlation between the CRSF energy and the spectral cutoff energy. However, with our consistent set of fits we found that the relationship is more complex than what has been reported previously. Also, we found that not only does the width of the cyclotron line correlate with the energy (as suggested by theory), but that the width scaled by the energy correlates with the depth of the feature. We discuss the implications of these results, including the possibility that accretion directly affects the relative alignment of the neutron star spin and dipole axes. Lastly, we comment on the current state of fitting phenomenological models to spectra in the RXTE/BeppoSAX era and the need for better theoretical models of the X-Ray continua of accreting pulsars. | |
|
E-mail contact | Preprint access |
| BL Lac Identification for the Ultraluminous X-ray Source Observed in the Direction of NGC 4698 | |
|
L. Foschini1, L.C. Ho2, N. Masetti1, M.
Cappi1, M. Dadina1, et al. 1. IASF-CNR, Sezione di Bologna (ex TeSRE), Via Gobetti 101, 40129 Bologna, Italy 2. The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101, USA | |
| Accepted for publication in A&A on September 20, 2002 | |
| Abstract. We report the identification of the optical and radio counterparts of the ultraluminous X-ray (ULX) source XMMU J124825.9+083020 (NGC4698-ULX1). The optical spectrum taken with the VLT yields a redshift of z=0.43, which implies that the ULX is not associated with the nearby galaxy NGC4698. The spectral energy distribution calculated from the available data indicates that the source is likely to be a BL Lac object. The possible synchrotron peak at X-ray energies suggests that this source may be a γ-ray emitter. | |
|
E-mail contact | Preprint access |
| BeppoSAX observations of synchrotron X-ray emission from radio quasars | |
|
P. Padovani1, L. Costamante2, G.
Ghisellini3, P. Giommi4, E. Perlman5 1. Space Telescope Science Institute, Baltimore, MD, USA/ESA Space Telescope Division 2. MPIfK, Heidelberg, Germany 3. Osservatorio Astronomico di Brera, Merate, Italy | |
| Accepted for publication in ApJ on August 5, 2002 | |
| Abstract. We present new BeppoSAX LECS, MECS, and PDS observations of four flat-spectrum radio quasars (FSRQ) having effective spectral indices αro and αox typical of high-energy peaked BL Lacs. Our sources have X-ray-to-radio flux ratios on average ~ 70 times larger than ``classical'' FSRQ and lie at the extreme end of the FSRQ X-ray-to-radio flux ratio distribution. The collected data cover the energy range 0.1 - 10 keV (observer's frame), reaching ~ 100 keV for one object. The BeppoSAX band in one of our sources, RGB J1629+4008, is dominated by synchrotron emission peaking at ~ 2 x 1016 Hz, as also shown by its steep (energy index αX ~ 1.5) spectrum. This makes this object the FIRST known FSRQ whose X-ray emission is not due to inverse Compton radiation. Two other sources display a flat BeppoSAX spectrum (αX ~ 0.7), with weak indications of steepening at low X-ray energies. The combination of BeppoSAX and ROSAT observations, (non-simultaneous) multifrequency data, and a synchrotron inverse Compton model suggest synchrotron peak frequencies ~ 1015 Hz although a better coverage of their spectral energy distributions is needed to provide firmer values. If confirmed, these values would be typical of ``intermediate'' BL Lacs for which the synchrotron and inverse Compton components overlap in the BeppoSAX band. Our sources, although firmly in the radio-loud regime, have powers more typical of high-energy peaked BL Lacs than of FSRQ, and indeed their radio powers put them near the low-luminosity end of the FSRQ luminosity function. We discuss this in terms of an anti-correlation between synchrotron peak frequency and total power, based on physical arguments, and also as possibly due to a selection effect. | |
|
E-mail contact | Preprint access |
| Large-Scale, Decelerating, Relativistic X-ray Jets from the Microquasar XTE J1550-654 | |
|
S. Corbel et al. University Paris VII (APC) & CEA Saclay | |
| Accepted for publication in Science 2002, 298, 196 | |
| Abstract. We have discovered at x-ray and radio wavelengths large-scale moving jets from the microquasar XTE J1550-654. Plasma ejected from near the black hole traveled at relativistic velocities for at least four years. We present direct evidence for gradual deceleration in a relativistic jet. The broadband spectrum of the jets is consistent with synchrotron emission from high energy (up to 10 TeV) particles accelerated in shock waves formed within the relativistic ejecta or by the interaction of the jets with the interstellar medium. XTE J1550-654 offers a unique opportunity to study the dynamical evolution of relativistic jets on time scales inaccessible for active galactic nuclei jets, with implications for our understanding of relativistic jets from Galactic x-ray binaries and active galactic nuclei. | |
|
E-mail contact | Preprint access or Science magazine |
|
|
 |
|
|
|
 |
 |