arXiv subjects

A. von Kienlin

Publications and source records attributed to A. von Kienlin.

At least 73 records · Page 4Linked to original sources

arXiv2007

INTEGRAL and Multiwavelength Observations of the Blazar Mrk 421 during an Active Phase

A ToO observation of the TeV-emitting blazar Mrk 421 with INTEGRAL was triggered in June 2006 by an increase of the RXTE count rate to more than 30 mCrab. The source was then observed with all INTEGRAL instruments with the exception of the spectrometer SPI for a total exposure of 829 ks. During this time several outbursts were observed by IBIS and JEM-X. Multiwavelength observations were immediately triggered and the source was observed at radio, optical and X-ray wavelengths up to TeV energies. The data obtained during these observations are analysed with respect to spectral evolution and correlated variability. Preliminary results of the analysis are presented in this poster.

astro-ph↗

arXiv2007

INTEGRAL and Magnetars

Thanks to INTEGRAL's long exposures of the Galactic Plane, the two brightest Soft Gamma-Ray Repeaters, SGR 1806-20 and SGR 1900+14, have been monitored and studied in detail for the first time at hard-X/soft-gamma rays. SGR 1806-20, lying close to the Galactic Centre, and being very active in the past two years, has provided a wealth of new INTEGRAL results, which we will summarise here: more than 300 short bursts have been observed from this source and their characteristics have been studied with unprecedented sensitivity in the 15-200 keV range. A hardness-intensity anticorrelation within the bursts has been discovered and the overall Number-Intensity distribution of the bursts has been determined. The increase of its bursting activity eventually led to the December 2004 Giant Flare for which a possible soft gamma-ray (>80 keV) early afterglow has been detected with INTEGRAL. The deep observations allowed us to discover the persistent emission in hard X-rays (20-150 keV) from 1806-20 and 1900+14, the latter being in quiescent state, and to directly compare the spectral characteristics of all Magnetars (two SGRs and three Anomalous X-ray Pulsars) detected with INTEGRAL.

astro-ph↗

arXiv2006

IGR J08408--4503: a new recurrent Supergiant Fast X-ray Transient

The supergiant fast X-ray transient IGR J08408-4503 was discovered by INTEGRAL on May 15, 2006, during a bright flare. The source shows sporadic recurrent short bright flares, reaching a peak luminosity of 10^36 erg s^-1 within less than one hour. The companion star is HD 74194, an Ob5Ib(f) supergiant star located at 3 kpc in the Vela region. We report the light curves and broad-band spectra (0.1-200 keV) of all the three flares of IGR J08408-4503 detected up to now based on INTEGRAL and Swift data. The flare spectra are well described by a power-law model with a high energy cut-off at ~15 keV. The absorption column density during the flares was found to be ~10^21 cm^-2, indicating a very low matter density around the compact object. Using the supergiant donor star parameters, the wind accretion conditions imply an orbital period of the order of one year, a spin period of the order of hours and a magnetic field of the order of 10^13 G.

astro-ph↗

arXiv2006

Observations of the intense and ultra-long burst GRB041219a with the Germanium Spectrometer on INTEGRAL

GRB041219a is the brightest burst localised by INTEGRAL. The intense burst occurred about ~250s after the precursor and the long delay enabled optical and near infrared telescopes to observe the prompt emission. We present comprehensive results of the temporal and spectral analyses, including line and afterglow searches using the spectrometer, SPI, aboard INTEGRAL, BAT on Swift and ASM on RXTE. We avail of multi-wavelength data to generate broadband spectra of GRB041219a and afterglow. Spectra for the burst and sub-intervals were fit by the Band model and also by the quasithermal model. The high resolution Germanium spectrometer data were searched for emission and absorption features and for gamma-ray afterglow. The overall burst and sub-intervals are well fit by the Band model. The photon index below the break energy shows a marked change after the quiescent time interval. In addition the spectra are well described by a black body component with a power law. The burst was detected by BAT and ASM during the long quiescent interval in SPI indicating the central engine might not be dormant but that the emission occurs in different bands. No significant emission or absorption features were found and limits of 900 eV and 120 eV are set on the most significant features. No gamma-ray afterglow was detected from the end of the prompt phase to ~12 hours post-burst. Broadband spectra of the prompt emission were generated in 7 time intervals using gamma-ray, x-ray, optical and near-infrared data and these were compared to the high-redshift burst GRB050904. The optical and gamma-ray emission are correlated in GRB041219a. The spectral lag was determined using data from the BAT and it changes throughout the burst. A number of pseudo-redshifts were evaluated and large dispersion in values was found.

astro-ph↗

arXiv2005

26Al in the inner Galaxy

We performed a spectroscopic study of the 1809 keV gamma-ray line from 26Al decay in the Galaxy using the SPI imaging spectrometer with its high-resolution Ge detector camera on the INTEGRAL observatory. We analyzed observations of the first two mission years, fitting spectra from all 7130 telescope pointings in narrow energy bins to models of instrumental background and the 26Al sky. Instrumental background is estimated from independent tracers of cosmic-ray activation. The shape of the 26Al signal is compared to the instrumental response to extract the width of the celestial line. We detect the 26Al line at \~16sigma significance. The line is broadened only slightly, if at all; we constrain the width to be below 2.8 keV (FWHM, 2 sigma). The average Doppler velocities of 26Al at the time of its decay in the interstellar medium (decay time~1.04 My) therefore are probably around 100 km/s, in agreement with expectations from Galactic rotation and interstellar turbulence. The flux and spatial distribution of the emission are found consistent with previous observations. The derived amount of 26Al in the Galaxy is 2.8 (+/-0.8) M_solar.

astro-ph↗

arXiv2005

Two years of INTEGRAL monitoring of the Soft Gamma-Ray Repeater SGR 1806-20: from quiescence to frenzy

SGR 1806-20 has been observed for more than 2 years with the INTEGRAL satellite. In this period the source went from a quiescent state into a very active one culminating in a giant flare on December 27 2004. Here we report on the properties of all the short bursts detected with INTEGRAL before the giant flare. We derive their number-intensity distribution and confirm the hardness-intensity correlation for the bursts found by Gotz et al. (2004a). Our sample includes a very bright outburst that occurred on October 5 2004, during which over one hundred bursts were emitted in 10 minutes, involving an energy release of 3 x 1E42 erg. We present a detailed analysis of it and discuss our results in the framework of the magnetar model.

astro-ph↗

arXiv2005

INTEGRAL and XMM-Newton observations of the low-luminosity and X-ray rich burst GRB 040223

GRB 040223 was observed by INTEGRAL and XMM-Newton. GRB 040223 has a peak flux of (1.6+/-0.13) x10^-8 ergs cm^-2 s^-1, a fluence of (4.4+/-0.4)x10^-7 ergs cm^-2 and a steep photon power law index of -2.3+/-0.2, in the energy range 20-200 keV. The steep spectrum implies it is an x- ray rich GRB with emission up to 200 keV and E_peak < 20 keV. If E_peak is < 10 keV, it would qualify as an x-ray flash with high energy emission. The x-ray data has a spectral index beta_x = -1.7+/-0.2, a temporal decay of t^(-0.75+/-0.25) and a large column density of (1.8 x 10^22) cm^-2. The luminosity-lag relationship was used to obtain a redshift (z = 0.1+0.04-0.02). The isotropic energy radiated in gamma-rays and x-ray luminosity after 10 hours are factors of 1000 and 100 less than classical GRBs. GRB 040223 is consistent with the extrapolation of the Amati relation into the region that includes XRF 030723 and XRF 020903.

astro-ph↗

arXiv2005

An exceptionally bright flare from SGR1806-20 and the origins of short-duration gamma-ray bursts

Soft-gamma-ray repeaters (SGRs) are galactic X-ray stars that emit numerous short-duration (about 0.1 s) bursts of hard X-rays during sporadic active periods. They are thought to be magnetars: strongly magnetized neutron stars with emissions powered by the dissipation of magnetic energy. Here we report the detection of a long (380 s) giant flare from SGR 1806-20, which was much more luminous than any previous transient event observed in our Galaxy. (In the first 0.2 s, the flare released as much energy as the Sun radiates in a quarter of a million years.) Its power can be explained by a catastrophic instability involving global crust failure and magnetic reconnection on a magnetar, with possible large-scale untwisting of magnetic field lines outside the star. From a great distance this event would appear to be a short-duration, hard-spectrum cosmic gamma-ray burst. At least a significant fraction of the mysterious short-duration gamma-ray bursts therefore may come from extragalactic magnetars.

astro-ph↗

arXiv2005

The first giant flare from SGR 1806-20: observations with the INTEGRAL SPI Anti-Coincidence Shield

A giant flare from the Soft Gamma-ray Repeater SGR 1806-20 has been detected by several satellites on 2004 December 27. This tremendous outburst, the first one observed from this source, was a hundred times more powerful than the two previous giant flares from SGR 0525-66 and SGR 1900+14. We report the results obtained for this event with the Anticoincidence Shield of the SPI spectrometer on board the INTEGRAL satellite, which provides a high-statistics light curve at E>~80 keV. The flare started with a very strong pulse, which saturated the detector for ~0.7 s, and whose backscattered radiation from the Moon was detected 2.8 s later. This was followed by a ~400 s long tail modulated at the neutron star rotation period of 7.56 s. The tail fluence corresponds to an energy in photons above 3 keV of 1.6x10^44 (d/15 kpc)^2 erg. This is of the same order of the energy emitted in the pulsating tails of the two giant flares seen from other soft repeaters, despite the hundredfold larger overall emitted energy of the SGR 1806-20 giant flare. Long lasting (~1 hour) hard X-ray emission, decaying in time as t^-0.85, and likely associated to the SGR 1806-20 giant flare afterglow has also been detected.

astro-ph↗

arXiv2004

INTEGRAL and XMM-Newton Observations of GRB040106

On January 6th 2004, the IBAS burst alert system triggered the 8th gamma-ray burst (GRB) to be located by the INTEGRAL satellite. The position was determined and publicly distributed within 12s, prompting ESA's XMM-Newton to execute a ToO observation just 5 hours later, during which an X-ray afterglow was detected. The GRB had a duration ~52s with two distinct pulses separated by \~42s. Here we present the results of imaging and spectral analyses of the prompt emission from INTEGRAL data and the X-ray afterglow from XMM-Newton data. The gamma-ray spectrum is consistent with a single power-law of photon index -1.72 +/- 0.15. The fluence (20-200 keV) was 8.2 x 10^-7 erg cm^-2. The X-ray afterglow (F_nu (t) propto nu^-beta_X t^-delta) was extremely hard with beta_X = 0.47 +/- 0.01 and delta = 1.46 +/- 0.04. The 2-10 keV flux 11 hours after the burst was 1.1 x 10^-12 erg cm^-2 s^-1. The time profile of the GRB is consistent with the observed trends from previous analysis of BATSE GRBs. We find that the X-ray data are not well-fit by either a simple spherical fireball or by a speading jet, expanding into a homogeneous medium or a wind environment. Based on previously determined correlations between GRB spectra and redshift, we estimate a redshift of ~0.9^+0.5_-0.4 (1 sigma) and a lower limit on the isotropic radiated energy of ~5 x 10^51 erg in this burst.

astro-ph↗

arXiv2004

Search for 44Ti gamma-ray line emission from GRO J0852-4642 with INTEGRAL/SPI

The gamma-ray source GRO J0852-4642, discovered by COMPTEL, is a possible counterpart of the supernova remnant RX J0852-4622. Detection of radioactive decay from 44Ti nuclei would proof it to be the youngest and nearest supernova remnant known so far. During the first year of INTEGRAL core program, the Vela region was observed twice in all for more than 2000 ks. Among other nucleosynthesis studies, one of the most important scientific goals of this observation is the detection of 44Ti gamma-ray lines expected at 68 keV, 78 keV and 1157 keV. For this purpose the INTEGRAL Spectrometer (SPI), with its very high energy resolution thanks to its germanium detector camera is the key instrument, permitting a precise determination of gamma-ray line intensities and profiles. The upper limit for the 78.4 keV 44Ti gamma-ray line emission derived from the first analysis is 1.1 x 10^{-4} gamma/cm2s. This value is mainly dominated by systematic uncertainties in the treatment of the instrumental background. By accumulating more observation time in the next years of the mission and by improving the background understanding, a reliable 44Ti flux for GRO J0852-4642 or an upper limit which constrains the COMPTEL flux can be expected.

astro-ph↗

arXiv2004

Measurements of Gamma-Ray Bursts (GRBs) with Glast

One of the scientific goals of the main instrument of GLAST is the study of Gamma-Ray Bursts (GRBs) in the energy range from ~20 MeV to ~300 GeV. In order to extend the energy measurement towards lower energies a secondary instrument, the GLAST Burst Monitor (GBM), will measure GRBs from ~10 keV to ~25 MeV and will therefore allow the investigation of the relation between the keV and the MeV-GeV emission from GRBs over six energy decades. These unprecedented measurements will permit the exploration of the unknown aspects of the high-energy burst emission and the investigation of their connection with the well-studied low-energy emission. They will also provide ne insights into the physics of GRBs in general. In addition the excellent localization of GRBs by the LAT will stimulate follow-up observations at other wavelengths which may yield clues about the nature of the burst sources.

astro-ph↗

arXiv2004

Gamma-Ray Bursts Observed with the Spectrometer SPI Onboard INTEGRAL

The spectrometer SPI is one of the main detectors of ESA's INTEGRAL mission. The instrument offers two interesting and valuable capabilities for the detection of the prompt emission of Gamma-ray bursts. Within a field of view of 16 degrees, SPI is able to localize Gamma-ray bursts with an accuracy of 10 arcmin. The large anticoincidence shield, ACS, consisting of 512 kg of BGO crystals, detects Gamma-ray bursts quasi omnidirectionally above ~70 keV. Burst alerts from SPI/ACS are distributed to the interested community via the INTEGRAL Burst Alert System. The ACS data have been implemented into the 3rd Interplanetary Network and have proven valuable for the localization of bursts using the triangulation method. During the first 8 months of the mission approximately one Gamma-ray burst per month was localized within the field of fiew of SPI and 145 Gamma-ray burst candidates were detected by the ACS from which 40 % have been confirmed by other instruments.

astro-ph↗

arXiv2004

The INTEGRAL Burst Alert System: Results and Future Perspectives

The INTEGRAL Burst Alert System (IBAS) is the software for real time detection of Gamma Ray Bursts (GRBs) and the rapid distribution of their coordinates. IBAS has been running almost continuously at the INTEGRAL Science Data Center since the beginning of the INTEGRAL mission, yielding up to now accurate localizations for 12 GRBs detected in the IBIS field of view. IBAS is able to provide error regions with radius as small as 3 arcminutes (90% c.l.) within a few tens of seconds of the GRB start. We present the current status of IBAS, review the results obtained for the GRBs localized so far, and briefly discuss future prospects for using the IBAS real time information on other classes of variable sources.

astro-ph↗

arXiv2004

Al(26) Studies with INTEGRAL's Spectrometer SPI

Al(26) radioactivity traces recent nucleosynthesis throughout the Galaxy, and is known to be produced in massive stars and novae. The map from its decay gamma-ray line suggests massive stars to dominate, but high-resolution line spectroscopy is expected to supplement imaging of Al(26) source regions and thus to help decide about the Al(26) injection process and interstellar environment, hence about the specific massive-star subgroup and phase which produces interstellar Al(26). The INTEGRAL Spectrometer SPI has observed Galactic Al(26) radioactivity in its 1809 keV gamma-ray line during its first inner-Galaxy survey. Instrumental background lines make analysis difficult; yet, a clear signal from the inner Galaxy agrees with expectations. In particular, SPI has constrained the line width to exclude previously-reported line broadenings corresponding to velocities >500 km/s. The signal-to-background ratio of percent implies that detector response and background modeling need to be fine-tuned to eventually enable line shape deconvolution in order to extract source location information along the line of sight.

astro-ph↗

arXiv2004

The INTEGRAL view of the Soft Gamma-ray Repeater SGR 1806-20

We present the results obtained by INTEGRAL on the Soft-Gamma Ray Repeater SGR 1806-20. In particular we report on the temporal and spectral properties of the bursts detected during a moderately active period of the source in September and October 2003 and on the search for quiescent emission.

astro-ph↗

arXiv2004

The Sample of Gamma-ray Bursts Observed With SPI-ACS

The SPI anticoincidence shield consists of 91 BGO crystals and is operated as a nearly omnidirectional gamma-ray burst detector above ~75 keV. Since the start of the mission 269 gamma-ray burst candidates have been detected. 110 bursts have been confirmed with the instruments included in the 3rd Interplanetary Network. Here we present a preliminary statistical analysis of the SPI-ACS sample of gamma-ray bursts and gamma-ray burst candidates; in particular we discuss the duration distribution of the bursts. A prominent population of short burst candidates (duration <200ms) is found which is discovered to be strongly contaminated by cosmic-ray nuclei interacting in the detectors.

astro-ph↗

arXiv2004

Preliminary INTEGRAL Analysis of GRB040106

On January 6th 2004, the IBAS burst alert system triggered the 8th gamma-ray burst (GRB) to be detected by the INTEGRAL satellite. The position was determined and publicly distributed within 12s, enabling ESA's XMM-Newton to take advantage of a ToO observation just 5 hours later during which the x-ray afterglow was detected. Observations at optical wavelengths also revealed the existence of a fading optical source. The GRB is ~52s long with 2 distinct peaks separated by ~24s. At gamma-ray energies the burst was the weakest detected by INTEGRAL up to that time with a flux in the 20-200 keV band of 0.57 photons/cm^2/s. Nevertheless, it was possible to determine its position and extract spectra and fluxes. Here we present light curves and the results of imaging, spectral and temporal analyses of the prompt emission and the onset of the afterglow from INTEGRAL data.

astro-ph↗