| No. 17 - 21 April 2005 | Edited by Marc Türler & Pierre-Olivier Petrucci |
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This time, the Newsletter is more focussed on science news than software
issues. This does not mean that software development stopped at the ISDC and in
the Instrument Teams. Actually there was a lot of effort invested in the development of OSA 5, which is now being tested and evaluated. A
special issue of the Newsletter will be released together with OSA 5 in one or
two months.
As more and more INTEGRAL data become public (see the
image), the ISDC is now providing a new
interactive WWW tool to access INTEGRAL source results.
The policy for gamma-ray bursts was also relaxed to make
lightcurves and other results rapidly available for the community.
The Science News section includes articles on very interesting INTEGRAL scientific results. You will find there amazing images from the INTEGRAL Galactic Bulge Monitoring showing the ever-changing gamma-ray sky; impressive cyclotron lines observed in V 0332+53 during it's recent outburst; the SPI/ACS lightcurve of the dramatic giant gamma-ray flare of December 27, 2004 from the soft-gamma repeater SGR 1806-20; the 2003 outburst of the microquasar XTE J1550-564, which was detected by PICsIT; and finally the surprising sounds corresponding to the pulse frequency of the six accreting X-ray millisecond pulsars and in particular of the fastest of all the recently discovered IGR J00291+5934.
We encourage INTEGRAL observers to be present at the ISDC during their observation. This will allow them to access the real time data and to react in case of interesting events.
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| Public Access to INTEGRAL Source Results | ||
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P. Kubanek (ISDC & Astron. Inst. Czech Republic), M. Beck, M. Meharga & R. Walter (ISDC) |
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The INTEGRAL Source Results WWW
page is now providing an interactive access to scientific results for a
selection of sources. Those results are generated from public data, which are
available in the INTEGRAL Archive. These results currently generated with the
OSA 4.2 software are also accessible through W3 Browse or ftp.
The new interface provides access to:
The image shows the top of the INTEGRAL Source Results main page. The plot below is an example lightcurve for the source GX 354-0, with ISGRI fluxes in red and JEM-X fluxes in green.
OMC lightcurves for the selected high energy sources will soon be made available through the same interface. ISGRI and JEM-X products will be regenerated with OSA 5 over the summer of 2005.
An on-line User Guide for this tool is now available.
| Scientific Analysis Developments for OSA 5 | ||
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Roland Walter (ISDC) |
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The next release of the Off-line Scientific Analysis (OSA 5) software package is foreseen for the beginning of June. The new software is currently being integrated and tested. Once all technical problems are solved, the last step before release is the scientific evaluation of the results and the update of the documentation.
It is too early to give a detailed description of the improvements in OSA 5 for all instruments, this will be included in a special issue of the Newsletter to be release together with OSA 5. However as ISGRI and JEM-X are the most sensitive instruments for most point sources and are therefore used by the largest user community, a particular effort has been done during the last months to improve the analysis software and calibration for those instruments.
The ISGRI analysis is very significantly improved in areas including noisy pixel flagging, off axis correction, energy calibration, background maps and extraction software. Those improvements reduce the systematic errors in all areas.
OSA 5 will also provide a much better modeling of the JEM-X collimator and new imaging spectral and light curve extraction software. The image quality has improved very much and the results obtained by the various extraction methods are more consistent.
The usability (manuals, GUI) and portability (Mac OSX, larger variety of Linux systems, simplified binary installation) of the software has also been improved.
With the release of OSA5 and of the "INTEGRAL Source Results" interface, the tools are
available to quickly look at the available public data and to perform deeper analysis.
| IBAS News and Change in Policy on GRB Results | ||
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Sandro Mereghetti (IASF/CNR, Milano, Italy) |
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In the last months IBAS has continued to provide quick and accurate GRB error boxes at the rate expected for the dimensions of the IBIS field of view. Up to now 23 bursts have been localized. The case of GRB 041219 demonstrates once more that INTEGRAL GRBs can be very interesting: thanks to the rapid IBAS localization of this long lasting burst, the RAPTOR automatic telescope could observe it in the optical simultaneously with the gamma-ray emission. This is only the second burst for which the prompt optical emission has been observed. Surprisingly the properties in the optical of these two bursts are very different (see the paper by Vestrand et al. 2005 to appear in Nature [astro-ph/0503521]). GRB 041219 was also seen by Swift, which had been launched just one month earlier, but was not yet distributing localizations in real time.
Swift is now working very successfully and according to our best expectations. In these 5 months it has located more than 30 gamma-ray bursts. Moreover it has opened a new era in data right policies: all the Swift GRB data are public and the information derived by the teams of the Swift instruments is immediately disseminated through GCN circulars.
The IBAS Team, supported by several scientists of the GRB community, proposed that a similar policy be applied to all the INTEGRAL GRB data. This issue was discussed by the members of the INTEGRAL Science Working Team (ISWT) who could not approve it since that would violate the rights of accepted guest observers proposals.
However, the ISWT allowed to quickly release more information resulting
from the IBAS off-line analysis. The PI's with accepted AO-3 proposals on
GRBs agreed with this new policy. Following this decision, in addition to
the results distributed for INTEGRAL GRBs up to now (position, duration
and peak flux), also the total fluence, peak energy (if it can be
determined) and light curve (in the 20-200 keV, plot available on the
IBAS page) will be communicated by the IBAS Team as soon as they can be derived.
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| INTEGRAL Galactic Bulge Monitoring Program | ||
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E. Kuulkers (ESA/ESAC, Spain), S. Shaw (ISDC, Geneva), A. Paizis (ISDC Geneva/IASF Milano), N. Mowlavi, T. Courvoisier (ISDC, Geneva), K. Ebisawa (NASA/GSFC, USA), P. Kretschmar (ESA/ESAC, Spain), C. Markwardt (NASA/GSFC, USA), T. Oosterbroek, A. Orr (ESA/ESTEC, Netherlands), R. Wijnands (UvA, Netherlands) |
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Since 2005, February
17, i.e., from the start of AO-3, INTEGRAL is performing frequent monitoring of
the Galactic Bulge region, whenever it is visible (see also the announcement in
ATel #438). This is
done under an approved AO-3 proposal (PI: Kuulkers); one complete hexagonal
dither pattern (7 pointings of 1800 seconds each) is performed during each
INTEGRAL revolution (i.e., roughly every 3 days). As a service to the
scientific community, the IBIS/ISGRI and JEM-X light curves are made publicly
available as soon as possible after the observations are performed. The
information is given in two energy bands, 3-10 keV and 10-25 keV for JEM-X,
20-60 keV and 60-150 keV for IBIS/ISGRI. In addition, IBIS/ISGRI mosaic images
of each hexagonal observation are given, with information on the detected
sources. The results, as well as more information about the program, can be
retrieved from the Bulge Monitoring WWW page.
Figure 1: April's INTEGRAL Picture of the Month, updated up to revolution 304. Shown is the hard X-ray outburst of GRO J1655-40 as monitored by the Galactic Bulge Monitoring program, as well as the IBIS/ISGRI 20-60 keV mosaic images per revolution. Credits: M. Homminga (ESA/ESAC)
Precisely at the start of this program the black-hole X-ray transient GRO
J1655-40 was reported to become active (ATel #414; see also ATel
#422 and ATel #432). The light
curve shown in Figure 1 is derived from the IBIS/ISGRI 20-60 keV band
individual pointings obtained up to now (about 150 counts/s corresponds to 1
Crab on-axis); earlier results were reported in ATel #438 and ATel
#442. The figure shows the evolution over the last couple of months and
demonstrates the wealth of the monitoring program. Note that GRO J1655-40 was
observed at a large off-axis angle (~15 degrees from the center of the field of
view; so is in the partially coded field of view of IBIS/ISGRI and not visible
with X-ray monitor JEM-X). The INTEGRAL GRO J1655-40 light curves nicely
complements observations at soft X-ray (RXTE) and radio
(VLA) wavelengths.
Figure 2: All IBIS/ISGRI 20-60 keV mosaic images per revolution from the Galactic Bulge Monitoring program stacked into a movie.
A new INTEGRAL source, named IGR J17098-3628, was announced by Grebenev et al. in ATel #444 (see also ATel #447). It nicely appeared as a new bright source in our program in revolution 299 (on 2005, March 25/26), up to 150 keV. It subsequently faded in the next revolutions (see also ATel #453).
When pointing with the mouse over each time span of observations in Figure 1,
the mean 20-60 keV mosaiced image appears corresponding to each complete
dither observation, which shows the detection significances on a square root
colour scale. The brightest sources are annotated. To emphasize variability, in
Figure 2 the mosaiced images are combined into a `movie'. Most of the sources
vary on timescales of a few days; clearly, the Galactic Bulge region is a
region rich in bright and variable high-energy X-ray and gamma-ray sources,
and a place to stay tuned on.
| INTEGRAL Observation of V 0332+53 in Outburst | ||
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I. Kreykenbohm (IAA Tübingen & ISDC), N. Mowlavi, N. Produit, S. Soldi, R. Walter, P. Dubath (ISDC), P. Lubinski (Copernicus Ast. Center/ISDC), M. Türler (ISDC), W. Coburn (SSL/UC Berkeley), A. Santangelo (IAA Tübingen), R. E. Rothschild (CASS/UC San Diego), R. Staubert (IAA Tübingen) |
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V 0332+53 is a recurrent transient high mass X-ray pulsar. Since the first recorded outburst (1.4 Crab in the maximum) in 1973 (Terrell et al. 1984) the system has so far exhibited three more outbursts: 1983, 1989, and 2004/2005. Based on a distance of 7 kpc (Negueruela et al. 1999), the maximum X-ray luminosity reached during the 1973 outburst was > 1038 erg sec-1 - close to the Eddington luminosity.
After 15 years of quiescence, the source entered an outburst in November 2004
as observed by the ASM onboard RXTE (Swank et al. 2004 ATel #349). The X-ray
flux increased continously and reached 1 Crab in the 2-12 keV band in December
2004 (Remillard et al. 2004 ATel #371). Subsequent
pointed observations with RXTE revealed the presence of three cyclotron lines
at 26 keV, 49 keV, and 74 keV (Coburn et al. 2005 ATel #381).
Integral performed a TOO observation of the source on 2005 January 6-10 as soon as pointing constraints allowed resulting in 100 ksec of data. This first observation was followed by more TOO observations to monitor the decline of the outburst (see ISDC-News 16-FEB-2005).
The analysis of the first TOO observation showed that the source is pulsating strongly with a period of P = 4.3751 sec and exhibiting a clear double pulse at higher energies.
To fit the joint JEM-X and ISGRI spectrum we used the cutoffpl model which describes the overall shape of the continuum reasonably well. Above 20 keV, however, large absorption line like structures due to the cyclotron lines are present. The fundamental line at 25 keV was found to have a non-Gaussian shape and we used two Gaussians to fit the line. After fitting also the beautiful first harmonic at 50 keV, significant line like residuals still remain at 72 keV which are due to the second harmonic cyclotron line. We thus confirm that V0332+53 exhibits three cyclotron lines.
The figure shows the analysis of the combined JEM-X (red) and IBIS/ISGRI (blue) spectrum of V 0332+53 in outburst. a) data + folded cutoffpl model b) residuals for model without any CRSFs c) after fitting the fundamental 25 keV line d) the fundamental line and the first harmonic at 50 keV have been fitted e) all three lines have been fitted
The analysis has been published recently in an A&A letter (Kreykenbohm et al. 2005). For more information, please contact Ingo Kreykenbohm.
References
Negueruela et al., 1999, MNRAS 307, 695
Terrell J., Priedhorsky W.C., 1984, ApJ 285, L15
| Long lasting emission after the SGR 1806-20 Giant Flare: a gamma-ray afterglow ? | ||
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D. Götz, S. Mereghetti (IASF-Milano), A. von Kienlin, A. Rau, G. Lichti (MPE, Garching), G. Weidenspointner, P. Jean (CESR, Toulouse) |
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An extremely strong burst was discovered in the data of the Anti-Coincidence Shield (ACS) of SPI on December 27 2004. The peculiarity of this burst was that it had a pulsating tail extending for hundreds of seconds. Even if no positional information can be derived with the ACS, IBAS scientists immediately realized that they were dealing with a giant flare from the Soft Gamma-Ray Repeater SGR 1806-20 and announced it to the scientific community (Borkowski et al. 2004). In fact the periodicity of 7.56 s seen in the ACS data is the unequivocal signature of SGR 1806-20, which is normally observed at lower energy due to the neutron star rotation. The initial spike of the flare was so bright that also its reflection from the Moon was seen in the ACS data after a delay of 2.8 s due to the light travel time!
Many other satellites observed this event and provided a wealth of new
results, such as the burst spectrum, the determination of the total emitted
energy (SPI-ACS could provide only a lower limit due to the saturation of the
instrument) and the pulse shape of the tail (e.g. Hurley et al. 2005 (RHESSI);
Palmer et al. 2005 (Swift)). The SPI-ACS, however, has two advantages compared
to the other satellites: its large effective area above 80 keV and the
INTEGRAL orbit which allows for long uninterrupted observations. Thanks to
these unique properties, the ACS was able to measure a second component after
the pulsating tail (t > 400 s). As visible in the figure, the count rate
increased again, forming a long bump which peaked around t ~ 700 s and returned
to the pre-flare background level at t ~ 3000-4000 s. The most likely
association of this long lasting component to SGR 1806-20 is discussed in a Letter recently accepted for publication in The Astrophysical
Journal.
The figure shows the SPI-ACS light curve of the Giant Flare from SGR 1806-20 (binsize 50 s). The yellow part represents the instrumental background, the red part the flare and its pulsating tail and the blue part the high-energy afterglow. The inset shows the first part of the pulsating tail binned at 7.56 s.
The Giant Flare from SGR 1806-20, behaves in many respect as a scaled down version of a GRB. An afterglow, due to interaction of the relativistically ejected material with the surrounding medium, is expected, and it has indeed been observed in the radio band (Cameron et al. 2005, Gaensler et al. 2005). It is likely that the long lasting emission detected with the ACS is the early part of this afterglow, seen here for the first time in the hard X-ray / soft gamma-ray band (E>80 keV).
After accounting for the background, estimated from a linear fit to the ACS count rate for t<0 s and t>4000 s, the time profile decay in the interval t=500-4000 s can be reasonably well described by a power law F ~ t-0.85. The fluence in the 400-4000 s time interval is 1.6 1044 erg for E > 3 keV, approximately equal to that contained in the pulsating tail (assuming a distance of 15 kpc).
Applying the formalism derived for GRB afterglows to these data, one can infer some physical properties. For example, the early time of the gamma-ray afterglow onset implies a relatively small bulk Lorentz factor Gamma ~15. This is smaller than the typical values for gamma-ray bursts, but consistent, considering the large involved uncertainties, with the mildly relativistic outflow inferred from the modeling of the radio data (Granot et al. 2005).
References
Brokowski J. et al. 2004, GCN 2920
Cameron P.B. et al., 2005, Nature, in press, astro-ph/0502428
Gaensler B.M. et al. 2005, Nature, in press, astro-ph/0502393
Granot J. et al. 2005, ApJ submitted, astro-ph/0503251
Hurley K. et al. 2005, Nature, in press, astro-ph/0502329
Palmer D.M. et al. 2005, Nature, in press, astro-ph/0503030
| The outburst of XTE J1550-564 in 2003 as seen by IBIS | ||
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Luigi Foschini (IASF/CNR, Bologna, Italy) |
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XTE J1550-564 is a low-mass X-ray binary system composed of a late type
subgiant (G8 IV to K4 III) coupled with a black hole with dynamical mass
in the range 8.4-11.2 solar masses. The source was known to display
outbursts, like in 1998-1999 (Kubota and Makishima, 2004), in 2000
(Tomsick et al. 2001a, Rodriguez et al. 2003), in 2001 (Tomsick et al.
2001b), 2002 (Belloni et al. 2002), and 2003 (Dubath et al., 2003). The
spectrum can show some anomalies, specifically in the high state, with
strong Comptonization (Kubota and Makishima 2004).
The figure shows the IBIS (ISGRI+PICsIT) unfolded spectrum of XTE J1550-564.
On 2003, March 24.2, XTE J1550-564 went in outburst and was detected by INTEGRAL when performing the Core Programme observations (Dubath et al. 2003). Soon after the discovery, a ToO was activated and INTEGRAL observed the microquasar three times: during the revolution 55 (27-28 March, 100 ks), revolutions 57-58 (3-5 April, 100 ks), and revolution 60 (11-12 April, 100 ks). A report of the analysis of IBIS/ISGRI Core Programme data was published by Arefiev et al. (2004), while Sturner & Shrader (2005) reported on the outburst with ISGRI, SPI, and JEM-X data. Here we shortly report about the IBIS (ISGRI+PICsIT) ToO observation, in order to show the capabilities of PICsIT in improving the spectral analysis. We report only about the overall spectrum, integrated over the whole ToO observation.
The addition of the PICsIT data allows to constrain the high energy part of the spectrum as shown in the figure. The IBIS (ISGRI+PICsIT) spectrum is well fit with the Comptonization model by Titarchuk (1994) with these parameters: seed photons temperature T0 < 6.4 keV, electron temperature Te = 51 ± 2 keV, optical depth τ=1.42 ± 0.06, and the normalization of (3.2 ± 0.1 10-3 ph cm-2 s-1 keV-1 at 1 keV (χ2=21.7, dof=25, reduced χ2=0.87, Prob.=0.653, 5% systematics). This result is consistent with the results obtained by Sturner & Shrader (2005).
References
Arefiev V.A., 2004, Astronomy Letters, accepted for publication (astro-ph/0404460)
Belloni T. et al., 2002, A&A 390, 199
Dubath P., et al., 2003, IAUC 8100
Kubota A., Makishima K., 2004, ApJ 601, 428
Rodriguez J., et al, 2003, ApJ 595, 1032
Sturner S.J. & Shrader C.R., 2005, ApJ, in press (astro-ph/0502498)
Tomsick J.A., et al., 2001a, ApJ 569, 223
Tomsick J.A., et al., 2001b, IAUC 7575
Titarchuk L., ApJ 434, 570
| Sounds of Accreting Millisecond Pulsars | ||
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Simon Shaw (Southampton Univ. & ISDC) |
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The discovery of IGR J00291+5934 (see the article in Newsletter #16), the fastest accreting milli-second X-ray pulsars, was an opportunity to compare its pulse frequency to that of the five other objects of its class. As the frequencies of the pulsars are similar to the frequencies of sound waves that can be heard by the human ear, a way to compare them is to generate the sounds corresponding to their frequency.
The audio wave (.wav) files below represent what these objects would sound like if their pulsation frequencies are played as sound waves. The files are 18 seconds long, representing the pulsars' behaviour since Jan 2000 to the present day. The 6 pulsars are observed during brief events where they brighten (called a "flare") - this is represented by an increase in volume in the following sound files. Some of these objects also seem to flare repeatedly, every 2-3 years or so.
IGR J00291+5934
All pulsars, steady chord
All pulsars, steady chord + flares
All pulsars, flares only
The sound for each pulsar was made with the following parameters. A simple sine wave of the appropriate frequency was used and, for the flares, the volume was modulated by the lightcurves presented in the recent review by R. Wijnands (astro-ph/0501264):
Pulsar Name Pulse Frequency Nearest Musical Flare length
(Hz) Note (days)
=============== =============== =============== ============
IGR J00291+5934 599 D5 (= 587 Hz) 40 - repeat ~3 yrs
SAX J1808.4-3658 401 G4 (= 392 Hz) 40 - repeat ~2 yrs
XTE J1751-305 435 A4 (= 440 Hz) 20
XTE J0929-314 185 = F#3 40
XTE J1807-294 191 G3 (= 196 Hz) 120
XTE J1814-338 314 D#4 (= 311 Hz) 40
| Unveiling the nature of the high energy source IGR J19140+0951 | |
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J. Rodriguez1, C. Cabanac2, D.C.
Hannikainen3, et al. 1. CEA Saclay, DSM/DAPNIA/SAp, Orme des Merisiers, Bat 709 F-91191 Gif sur Yvette, France & ISDC, Versoix Switzerland 2. Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53X, 38041 Grenoble, France 3. Observatory, PO Box 14, 00014 University of Helsinki, Finland | |
| Accepted for publication in A&A (2005, vol. 432, p.235) on December, 21, 2004 | |
| Abstract. We report on high energy observations of IGR J19140+0951 performed with RXTE on three occasions in 2002, 2003 and 2004, and INTEGRAL during a very well sampled and unprecedented high energy coverage of this source from early-March to mid-May 2003. Our analysis shows that IGR J19140+0951 spends most of its time in a very low luminosity state, probably corresponding to the state observed with RXTE, and characterised by thermal Comptonisation. In some occasions we observe variations of the luminosity by a factor of about 10 during which the spectrum can show evidence for a thermal component, besides thermal Comptonisation by a hotter plasma than during the low luminosity state. The spectral parameters obtained from the spectral fits to the INTEGRAL and RXTE data strongly suggest that IGR J19140+0951 hosts a neutron star rather than a black hole. Very importantly, we observe variations of the absorption column density (with a value as high as 1023 cm-2 ). Our spectral analysis also reveals a bright iron line detected with both RXTE/PCA and INTEGRAL/JEM-X, at different levels of luminosity. We discuss these results and the behaviour of IGR J19140+0951, and show, by comparison with other well known systems (Vela X-1, GX 301-2, 4U 2206+54), that IGR J19140+0951 is most probably a High Mass X-ray Binary. | |
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E-mail contact | Preprint access |
| Characterizing a new class of variability in GRS 1915+105 with simultaneous INTEGRAL/RXTE observations | |
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D.C. Hannikainen1, J. Rodriguez2, O Vilhu1 et al. 1. Observatory, PO Box 14, FIN-00014 University of Helsinki, Finland 2. CEA Saclay, DSM/DAPNIA/Service d'Astrophysique, Bat. 709, Orme des Merisiers, Gif-sur-Yvette Cedex 91191, France & ISDC Switzerland | |
| Accepted for publication in A&A on February 2005 | |
| Abstract. We report on the analysis of 100 ks INTEGRAL observations of the Galactic microquasar GRS 1915+105. We focus on INTEGRAL Revolution number 48 when the source was found to exhibit a new type of variability as preliminarily reported in Hannikainen et al. (2003). The variability pattern, which we name xi, is characterized by a pulsing behaviour, consisting of a main pulse and a shorter, softer, and smaller amplitude precursor pulse, on a timescale of 5 minutes in the JEM-X 3-35 keV lightcurve. We also present simultaneous RXTE data. From a study of the individual RXTE/PCA pulse profiles we find that the rising phase is shorter and harder than the declining phase, which is opposite to what has been observed in other otherwise similar variability classes in this source. The position in the colour-colour diagram throughout the revolution corresponds to State A (Belloni et al. 2000) but not to any previously known variability class. We separated the INTEGRAL data into two subsets covering the maxima and minima of the pulses and fitted the resulting two broadband spectra with a hybrid thermal non-thermal Comptonization model. The fits show the source to be in a soft state characterized by a strong disc component below 6 keV and Comptonization by both thermal and non-thermal electrons at higher energies. | |
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E-mail contact | Preprint access |
| A XMM-Newton View of the Soft Gamma-Ray Repeater SGR 1806-20: Long Term Variability in the Pre-Giant Flare Epoch | |
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S. Mereghetti1, A. Tiengo1, P. Esposito1, D. Gotz1, L. Stella2, G. L.
Israel2, N. Rea2 , M. Feroci, R. Turolla3, and S. Zane 1. INAF - IASF Milano 2. INAF - Oss. Astron. di Roma 3. Universita' di Padova | |
| Accepted for publication in ApJ on April 12, 2005 | |
| Abstract. The low energy (<10 keV) X-ray emission of the Soft Gamma-ray Repeater SGR 1806-20 has been studied by means of four XMM-Newton observations carried out in the last two years, the latest performed in response to a strong sequence of hard X-ray bursts observed on 2004 October 5. The source was caught in different states of activity: over the 2003-2004 period the 2-10 keV flux doubled with respect to the historical level observed previously. The long term raise in luminosity was accompanied by a gradual hardening of the spectrum, with the power law photon index decreasing from 2.2 to 1.5, and by a growth of the bursting activity. The pulse period measurements obtained in the four observations are consistent with an average spin-down rate of 5.5 10-10 s/s, higher than the values observed in the previous years. The long-term behavior of SGR 1806-20 exhibits the correlation between spectral hardness and spin-down rate previously found only by comparing the properties of different sources (both SGRs and Anomalous X-ray Pulsars). The best quality spectrum (obtained on 6 September 2004) cannot be fitted by a single power law, but it requires an additional blackbody component (kT = 0.79 keV, R = 1.9 (d/15 kpc)2 km), similar to the spectra observed in other SGRs and in Anomalous X-ray Pulsars. No spectral lines were found in the persistent emission, with equivalent width upper limits in the range 30-110 eV. Marginal evidence for an absorption feature at 4.2 keV is present in the cumulative spectrum of 69 bursts detected in September-October 2004. | |
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E-mail contact | Preprint access |
| The First Giant Flare from SGR 1806-20: Observations using the anticoincidence shield of the spectrometer on INTEGRAL | |
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S. Mereghetti1, D. Gotz1, A. von Kienlin2, A. Rau2, G. Lichti2, G.
Weidenspointner3, and P. Jean
3 1. INAF - IASF Milano 2. MPE - Garching 3. CESR - Toulousee | |
| Accepted for publication in ApJ Letters on April 1, 2005 | |
| Abstract. A giant flare from the Soft Gamma-ray Repeater SGR 1806-20 has been discovered with the INTEGRAL gamma-ray observatory on 2004 December 27 and detected by many other satellites. This tremendous outburst, the first one observed from this source, was a hundred times more powerful than the two giant flares previously observed from other Soft Gamma-ray Repeaters (SGR). The 50 ms resolution light curve obtained with the Anticoincidence Shield of the INTEGRAL spectrometer SPI, which provides a high effective area above ~80 keV, shows evidence for emission lasting about one hour after the start of the outburst. This component, which decays in time as ~t-0.85, could be the first detection of a hard X-ray afterglow associated to an SGR giant flare. The short (0.2 s) initial pulse was so strong to saturate the detector for ~0.7 s, and its backscattered radiation from the Moon was detected 2.8 s later. The following ~400 s long tail, modulated at the neutron star rotation period of 7.56 s, had a fluence of 2.6x10-4 erg cm-2 above 80 keV, which extrapolating to lower energies corresponds to an emitted energy of 1.6 1044 d215 kpc erg at E > 3 keV. This is of the same order of that in the pulsating tails of the two giant flares seen from other SGRs, despite the hundredfold larger overall emitted energy of the 2004 December 27 event. | |
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E-mail contact | Preprint access |
| Three XMM-Newton observations of the Anomalous X--ray Pulsar 1E 1048.1-5937: long term variations in spectrum and pulsed fraction | |
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A. Tiengo1, S. Mereghetti1, R. Turolla2, S. Zane3, N. Rea, L. Stella, G. L. Israel 1. INAF - IASF Milano 2. Universita' di Padova 3. MSSL - UCL - London | |
| Accepted for publication in A&A on March 17, 2005 | |
| Abstract. We report the results of a recent (July 2004) XMM-Newton Target of Opportunity observation of the Anomalous X-ray pulsar 1E 1048.1-5937, together with a detailed re-analysis of previous observations carried out in 2000 and 2003. In July 2004 the source had a 2-10 keV flux of 6.2x10-12 erg cm-2 s-1 and a pulsed fraction PF=0.68. The comparison of the three data sets shows the presence of an anti-correlation between flux and pulsed fraction, implying that previous estimates of the source energetics based on the assumption of a large and constant pulsed fraction might be significantly underestimated. The source spectrum is well described by a power law plus blackbody model (kT ~ 0.63 keV, photon index Gamma ~ 2.7-3.5) or, alternatively, by the sum of two blackbodies of which the hotter is Comptonized by relativistic electrons. In this case the temperatures are kT_1 ~ 0.2-0.3 keV and kT_2 ~ 0.4-0.5 keV and the emitting area of the cooler component is consist! ent with the whole neutron star surface. The long term luminosity variation of a factor >~2 is accompanied by relatively small variations in the spectral shape. Phase resolved spectroscopy indicates a harder spectrum in correspondence of the pulse maximum. No spectral features have been detected with 4 sigma limits on the equivalent width in the range ~10-220 eV, depending on line energy and width. | |
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| Discovery of the INTEGRAL X/γ-ray transient IGR J00291+5934: A Comptonised accreting ms pulsar? | |
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S. E. Shaw1,2, N. Mowlavi2, J. Rodriguez3, P. Ubertini4, F. Capitanio4, et al. 1. School of Physics and Astronomy, University of Southampton, SO17 1BJ, UK 2. INTEGRAL Science Data Centre, CH-1290 Versoix, Switzerland 3. CEA Saclay, DSM/DAPNIA/SAp (CNRS FRE 2591), F-91191 Gif Sur Yvette Cedex, France | |
| Accepted for publication in A&A on January 23, 2005 | |
| Abstract. We report the discovery of a high-energy transient with the IBIS/ISGRI detector on board the INTEGRAL observatory. The source, namely IGR J00291+5934, was first detected on 2nd December 2004 in the routine monitoring of the IBIS/ISGRI 20-60 keV images. The observations were conducted during Galactic Plane Scans, which are a key part of the INTEGRAL Core Programme observations. After verifying the basic source behaviour, the discovery was announced on 3rd December. The transient shows a hard Comptonised spectrum, with peak energy release at about 20 keV and a total luminosity of ~0.9 * 1036erg/s in the 5-100 keV range, assuming a distance of 3 kpc. Following the INTEGRAL announcement of the discovery of IGR J00291+5934, a number of observations were made by other instruments. We summarise the results of those observations and, together with the INTEGRAL data, identify IGR J00291+5934 as the 6th member of a class of accreting X-ray millisecond pulsars. | |
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