| No. 13 - June 16, 2003 | Edited by Thierry Montmerle & Marc Türler |
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Image:
INTEGRAL exposure map (IBIS field-of-view) of the whole sky in galactic
coordinates from Launch (October 17, 2002) up to May 20, 2003. The
integration time is color coded according to the scale at the bottom.
K. Ebisawa (ISDC/GSFC)
The INTEGRAL operations are going on very smoothly. The instruments are performing well and many new sources have already been discovered near the galactic centre as reported in several IAU Circulars and Astronomical Telegrams.
The ISDC released already twice the INTEGRAL Off-line Scientific Analysis (OSA) software and the data distribution to guest observers is now rapidly catching up with a natural early mission delay.
Of course there is still a lot to be done to improve the software and to better characterize the behaviour of the instruments. Nevertheless, INTEGRAL is well on track and all conditions seem to be met for ensuring a long and fruitful mission!
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| INTEGRAL Operations are Nominal | ||
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Roland Walter (ISDC Geneva) |
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The AO-1 observing programme started on December 30, 2002 after 2 months of performance verification. It was interrupted by a calibration campaign performed on the Crab nebula from February 7 to 27. During that period the instruments were further tuned in particular to optimize their telemetry usage. To save telemetry bandwidth the spectrometer was then operated in spectral mode, loosing timing information for the single events.
Figure 1:
Map of the sky (in galactic coordinates) showing all accepted AO-1 open time targets (TOO's and GRB's
excluded) and pointed Core Programme observations (TOO's excluded). C. Winkler (ISOC/ESTEC)
After some further instrument tuning and update of on-board software it was decided beginning of April to switch the spectrometer back to normal mode. However 20 to 30% of the data were still lost because of the limited telemetry bandwidth available. This problem was solved on May 21, when the INTEGRAL telemetry rate could be increased from 90 to 113 kbit/sec thus allowing all scientifically valuable data to be sent to ground.
Since the beginning of the AO-1 programme about 82% of the time is devoted to science exposures, 12% is spent within the radiation belts, about 3% is spent for the slews between science exposures and 3% of the time is spent for various operational overheads (reaction wheel bias, ground station handovers, and beginning/end of revolution activities).
The first Galactic Center Deep Exposure (GCDE), a major part of the INTEGRAL Core Programme was performed between February 28 and May 1st which led to the issue of numerous IAU circulars and Astronomical Telegrams from the ISDC. The Galactic Plan Scans (GPS) are performed regularly as well.
Figure 2:
IBIS/ISGRI mosaic image of the Galaxy in the 15-40 keV energy band. The image
includes all Galactic Plane Scans (GPS) and all Galactic Center Deep Exposures
(GCDE) from launch up to revolution 67 (May 4, 2003).
42 open time observations have been completely or partially observed. 6 of them are amalgamated, i.e. will be distributed to several observers. 23 observations have already been distributed to guest observers.
The processing backlog since launch has been catched up. Currently there is a 6-8 weeks delay between the end of the observation and the data distribution by the ISDC. About 3 weeks are necessary for the ISDC to receive consolidated telemetry from the Mission Operation Center (MOC), 2 weeks are necessary to get the final schedulling information indicating that an observation is complete and about 2 to 3 weeks are needed for data processing and distribution.
INTEGRAL operations are now nominal and very successful. The emphasis is now on improving the scientific analysis and publishing the first INTEGRAL scientific results. This will be done before the end of the year in a special issue of Astronomy & Astrophysics.
| Off-line Scientific Analysis Software Releases and Status | ||
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Isabelle Lecoeur-Taïbi & Peter Kretschmar (ISDC Geneva) |
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The INTEGRAL Off-line Scientific Analysis was publicly released on April 2, 2003. With its 4 analysis scripts (one per instrument - the IBIS imager, the SPI spectrometer, the JEM-X monitor and the OMC camera) and some generic tools this release was an important milestone for the ISDC. Some test data of the Crab were provided as a first installation check and used for an analysis example in the User Manuals. The main aim of this release was to allow the observers to get familiar with the use of the software and to perform a first analysis of their own data.
While limited in functionality beyond the imaging step, considerable effort was spent to ensure that analyzing large and varied datasets was possible for users. As we could judge from the Helpdesk requests, the installation process on SUN/Solaris and Linux machines ran quite smoothly and there were no major execution problems.
An intermediate update of the OSA suite (OSA 1.1), mainly including various bug fixes, has been made available in late May on the ISDC software page. This new release remains focused on imaging capabilities, but some algorithms were improved and the Instrument Characteric files (background models, response matrices...) were also updated (OSA_IC 1.1), as well as the five User Manuals.
Image:
SPI image in the 20-200 keV energy band showing both the Crab nebula and
the 4th Gamma-Ray Burst (GRB) seen in the INTEGRAL field-of-view on
February 27, 2003 at 08:42 UT. It was obtained with the SPIROS software for a
time interval of 18 sec (including the burst), using detectors 0-18 (single +
PSD events) and with an empty field observation as a background model.
V. Beckmann (ISDC)
Critical appraisal of the results obtained with this software, as part of the overall scientific validation, has turned up a long list of issues and shortcomings. As an example, derived source fluxes have been shown to depend non-trivially on the position in the field of view or on deadtime effects. The causes of these problems lie partially with the analysis software, partially with the calibration data in use. Work is underway to resolve the known issues but this is often a difficult and lengthy process.
ISDC will issue updates of OSA at regular intervals thus making available the latest improvements to the software. A new release, which will extend the functionalities to spectral analysis, is planned in July 2003. Another one is foreseen for October 2003. Intense work is ongoing to improve the software and calibration data and to test the software and results before these releases.
| Auxiliary Data Status | ||
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Roland Walter (ISDC Geneva) |
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The auxiliary data distributed to the observers, and freely available in the archive, are good in general. One exception is the time correlation that is affected by a number of small problems affecting timing at the level of the millisecond. Some new corrections will be implemented in the software but this will not happen before later this year. The main problems are:
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| IBAS breaks a record in GRB localization | ||
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S. Mereghetti, D. Götz (IASF Milano) & J. Borkowski (ISDC Geneva) |
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Three more gamma-ray bursts have been localized by IBAS since our last report in the ISDC Newsletter: GRB 030227, GRB 030320 and GRB 030501.
Very interesting results have been obtained for GRB 030227. This is the first GRB for which the rapid localization provided by IBAS led to the identification of an optical transient and an X-ray afterglow. The other major ESA astrophysical satellite, XMM-Newton, was pointed at the location of GRB 030227 after only eight hours and could detect the X-ray afterglow while its emission was still relatively bright. In fact a variable source was detected well within the IBAS error circle with an X-ray flux decay well described by a power law function with index [delta] ~ 1 (see figure 1). The brightness of the source and the short delay between the localization and the afterglow observation allowed us to study the properties of the X-ray emission in detail. The spectrum of the afterglow is a power law, but, in addition to the absorption caused by the interstellar gas of our Galaxy, it requires a second absorption component at a redshift greater than 1. These results led to the first paper reporting INTEGRAL data published in a scientific journal (Mereghetti et al., 2003, ApJ 590, L73)
Figure 1:
Light curve of the GRB 030227 afterglow measured with the EPIC camera on board
XMM-Newton.
On Labour day we were woken up at 5:10 a.m. (CET) by GRB 030501. The automatic detection and localization of this GRB was very successful: after only 30 seconds after the beginning of the burst, its position with an accuracy of 4.5 arcmin was distributed on Internet.
Figure 2:
Lightcurve of GRB 030501 measured with IBIS/ISGRI. The arrival time of the
IBAS alert packet to the clients is marked by the blue line. Half of the delay
is due to the buffering of the data on board and to the transmission of the
data from the satellite to ISDC. The delay induced by IBAS itself is 12
seconds.
Such a good combination of short delay and small error box had never been achieved before for a GRB ! The burst was 40 seconds long and the first optical observations were made by robotic telescopes starting less than 20 seconds after the IBAS trigger. Unfortunately, this burst was at very low Galactic latitude (b=-0.25 degrees) and deep optical searches could not be performed due to the very high absorption.
If the next GRB is located in a more favorable position and a similarly good localization achieved by IBAS we can surely expect exciting results.
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| INTEGRAL and XMM-Newton observations of the weak GRB 030227 | |
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S. Mereghetti1, D. Götz1, A. Tiengo 1, V. Beckmann 2,3, et
al. 1. Istituto di Astrofisica Spaziale e Fisica Cosmica, Sezione di Milano "G. Occhialini" - CNR v.Bassini 15, I-20133 Milano, Italy 2. IAAT, Universität Tübingen, Sand1, D-72076 Tübingen, Germany 3. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland | |
| Accepted for publication in ApJL on April 26, 2003 | |
| Abstract. We present INTEGRAL and XMM-Newton observations of the prompt gamma-ray emission and the X-ray afterglow of GRB030227, the first GRB for which the quick localization obtained with the INTEGRAL Burst Alert System (IBAS) has led to the discovery of X-ray and optical afterglows. GRB030227 had a duration of about 20 s and a peak flux of 1.1 photons cm-2 s-1 in the 20-200 keV energy range. The time averaged spectrum can be fit by a single power law with photon index about 2 and we find some evidence for a hard to soft spectral evolution. The X-ray afterglow has been detected starting only 8 hours after the prompt emission, with a 0.2-10 keV flux decreasing as t-1 from 1.3x10-12 to 5x10-13 erg cm-2 s-1. The afterglow spectrum is well described by a power law with photon index 1.94±0.05 modified by a redshifted neutral absorber with column density of several 1022 cm-2. A possible emission line at 1.67 keV could be due to Fe for a redshift z=3, consistent with the value inferred from the absorption. | |
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E-mail contact | Preprint access |
| XMM-Newton study of the persistent X-ray source 1E 1743.1-2843 located in the Galactic Center direction | |
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D. Porquet1, J. Rodriguez1,2, S.Corbel1,3, P. Goldoni1, et
al. 1. Service d'Astrophysique, CNRS URA 2052, CEA Saclay, F-91191 Gif Sur Yvette, FRANCE 2. INTEGRAL Science Data Centre, ch. d' Ecogia 16, CH-1290 Versoix, Switzerland 3. Universite Paris VII, federation APC, 2, place Jussieu F-75005 Paris Cedex, FRANCE | |
| Accepted for publication in A&A on May 26, 2003 | |
| Abstract. We report the results of an XMM-Newton observation of the persistent X-ray source 1E1743.1-2843, located in the Galactic Center (GC) direction. We determine the position of the source at αJ2000=17h46m21.0s, δJ2000=-28deg43'44" (with an uncertainty of 1.5"), which is the most accurate to date, and will enable cross-identifications at other wavelengths. The source was bright during this observation (L2-10keV ~ 2.7 x 1036 d210kpc erg/s for a power-law continuum), with no significant variability. We propose that 1E1743.1-2843 may be explained in terms of a black hole candidate in a low/hard state. There is an indication that the source exhibits different states from a comparison of our results with previous observations (e.g., ART-P, BeppoSAX). However, the present spectral analysis does not rule out the hypothesis of a neutron star low-mass X-ray binary as suggested previously. If ! 1E1743.1-2843 is actually located in the GC region, we might expect to observe significant 6.4keV fluorescent iron line emission from nearby molecular clouds (e.g., GCM+0.25+0.01). | |
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E-mail contact | Preprint access |
| Chandra X-Ray Observatory observations of the globular cluster M28 and its millisecond pulsar B1821-24 | |
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W. Becker, D.A. Swartz, G.G. Pavlov, R.F. Elsner, J. Grindlay, et al. 1. MPE Garching 2. MSFC & USRA 3. Pennstate University | |
| Accepted for publication in ApJ in May 2003 | |
| Abstract. We report here the results of the first Chandra X-Ray Observatory observations of the globular cluster M28 (NGC 6626). 46 X-ray sources are detected, of which 12 lie within one core radius of the center. We show that the apparently extended X-ray core emission seen with the ROSAT HRI is due to the superposition of multiple discrete sources for which we determine the X-ray luminosity function down to a limit of about 6 1030 erg/s. For the first time the unconfused phase-averaged X-ray spectrum of the 3.05-ms pulsar B1821-24 is measured and found to be best described by a power law with photon index ~ 1.2. Marginal evidence of an emission line centered at 3.3 keV in the pulsar spectrum is found, which could be interpreted as cyclotron emission from a corona above the pulsar's polar cap if the the magnetic field is strongly different from a centered dipole. The unabsorbed pulsar flux in the 0.5-8.0 keV band is ~3.5 10-13 ergs/s/cm2. Spectral analysis of the 5 ! brightest unidentified sources is presented. Based on the spectral parameters of the brightest of these sources, we suggest that it is a transiently accreting neutron star in a low-mass X-ray binary, in quiescence. Fitting its spectrum with a hydrogen neutron star atmosphere model yields the effective temperature Teff∞ = 90+30-10 eV and the radius RNS∞ = 14.5+6.9-3.8 km. In addition to the resolved sources, we detect fainter, unresolved X-ray emission from the central core of M28. Using the Chandra-derived positions, we also report on the result of searching archival Hubble Space Telescope data for possible optical counterparts. | |
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E-mail contact | |
| Spectral evolution of the microquasar XTE J1550-564 over its entire 2000 outburst | |
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J. Rodriguez1, S. Corbel2, J. Tomsick3 1. CEA Saclay, DSM/DAPNIA/Service d'astrophysique, Bat. 709 Orme des Merisiers, F-91191 Gif Sur Yvette Cedex, FRANCE, and ISDC ch. d' Ecogia 16, CH-1290 Versoix, Switzerland 2. CEA Saclay/ Universite Paris 7, Federation APC, 2 place Jussieu, 75005 Paris, France. 3. Center for Astrophysics and Space Sciences, Code 0424, Universi ty of California at San Diego, La Jolla, CA 92093, USA | |
| Accepted for publication in ApJ on June 11, 2002 | |
| Abstract. We report on RXTE observations of the microquasar XTE J1550-564 during a ~70 day outburst in April-June 2000. We present the PCA+HEXTE 3-200 keV energy spectra of the source, and study their evolution over the outburst. The spectra indicate that the source transited from an initial Low Hard State (LS), to an Intermediate State (IS) characterized by a ~1 Crab maximum in the 1.5-12 keV band, and then back to the LS. The source shows an hysteresis effect such that the second transition occurs at a 2-200 keV flux that is half of the flux at the first transition. This behavior is similar to what observed in other sources and favors a common origin for the state transitions in soft X-ray transients. In addition, the first transition occurs at a ~constant 2-200 keV flux, which probably indicates a change in the relative importance of the emitting media, whereas the second transition occurs during a time when the flux gradually decreases, which probably indicates that it is driven by a drop in the mass accretion rate. In both LS, the spectra are characterized by the presence of a strong power-law tail (Compton corona) with a variable high energy cut-off. During the IS, the spectra show the presence of a ~0.8 keV thermal component which we attribute to an optically thick accretion disk. The inner disk radius as infered from disk-blackbody fits to the energy spectrum remains relatively constant throughout the IS. This suggests that the disk may be close to its last stable orbit during this period. We discuss the apparently independent evolution of the two media, and show that right after the X-ray maximum on MJD 51662, the decrease of the source luminosity is due to a decrease of the power-law luminosity, at a constant disk luminosity. The detection of radio emission, with a spectrum typical of optically thin synchrotron emission, soon after the X-ray peak, and the sudden decrease of the power law luminosity at the same time may suggest that the corona is ejected and further detected as a discrete radio ejection. | |
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| Chandra Detection of the X-ray counterpart of the High-magnetic field Radio Pulsar J1119-6127 in the Supernova Remnant G292.2-0.5 | |
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M. Gonzalez and S. Safi-Harb University of Manitoba, Canada | |
| Accepted for publication in ApJ Letters on May 22, 2003 | |
| Abstract. We report the Chandra Advanced CCD Imaging Spectrometer detection of the X-ray counterpart of the high magnetic field, ~1600 year-old, 407 ms radio pulsar J1119-6127 associated with the supernova remnant G292.2-0.5. The powerful imaging capability of Chandra also unveiled, for the first time, a faint 3"x6" pulsar wind nebula (PWN) at energies above ~1.2 keV. The X-ray emission from the pulsar and its associated nebula is well described by an absorbed power law model with a photon index of 2.2 (1.9-2.8). The corresponding 0.5-10 keV unabsorbed X-ray luminosity is 5.5(2.2-15.5)x1032 ergs/s (at 6 kpc). When compared to two other pulsars with similar spin and magnetic properties, J1119-6127 stands out as being the least efficient at turning rotational kinetic energy into X-ray emission. This study shows that high magnetic field radio pulsars can be significant X-ray emitters and Chandra is needed to study the emission properties of the pulsars and associated faint PWNe. | |
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E-mail contact | Preprint access |
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