arXiv subjects

J. -F. Olive

Publications and source records attributed to J. -F. Olive.

18 recordsLinked to original sources

arXiv2022

Discovery of a recurrent spectral evolutionary cycle in the ultra-luminous X-ray sources Holmberg II X-1 and NGC 5204 X-1

Most ultra-luminous X-ray sources (ULXs) are now thought to be powered by stellar-mass compact objects accreting at super-Eddington rates. While the discovery of evolutionary cycles have marked a breakthrough in our understanding of the accretion flow changes in the sub-Eddington regime in Galactic Black Hole Binaries, their evidence in the super-Eddington regime remained elusive. However, recent circumstantial evidence had hinted the presence of a recurrent evolutionary cycle in two archetypal ULXs: Holmberg II X-1 and NGC 5204 X-1. Here we build on our previous work and exploit the long-term high-cadence monitoring of Swift-XRT in order to provide evidence of the evolutionary cycle in these two sources and investigate the main physical parameters inducing their spectral transitions. We study the long-term evolution of both sources using hardness-intensity diagrams (HID) and by means of Lomb-Scargle periodograms and Gaussian processes modelling to look for periodic variability. We show that both sources follow a recurrent evolutionary pattern in the HID that can be characterized by the hard ultraluminous (HUL) and soft ultraluminous (SUL) spectral regimes, and a third state with characteristics similar to the supersoft ultraluminous (SSUL) state. The transitions between the soft states seem aperiodic, as revealed by timing analysis of the light curve of Holmberg II X-1, albeit further investigation is warranted. The light curve of NGC 5204 X-1 shows a periodicity of $\sim$ 200 days, possibly associated with the duration of the evolutionary cycle. We support a scenario in which the spectral changes from HUL to SUL are due to a periodic increase of the mass-transfer rate and subsequent narrowing of the opening angle of the supercritical funnel. The narrower funnel, combined with stochastic variability imprinted by the wind, might explain the SUL--SSUL spectral changes.

astro-ph.HE↗

arXiv2021

Measurement of performance of the NectarCAM photodetectors

NectarCAM is a camera for the medium-sized telescopes of the Cherenkov Telescope Array (CTA), which covers the energy range of 100 GeV to 30 TeV. The camera is equipped with 265 focal plane modules (FPMs). Each FPM comprises 7 pixels, each consisting of a photo-multiplier tube, a preamplifier, an independently controlled power supply, and a common control system. We developed a dedicated test bench to validate and qualify the industrial FPM production and to measure the performance of each FPM in a dark room before its integration in the camera. We report the measured performance of 61 FPM prototypes obtained with our experimental setup. We demonstrate that the gains of the photo multiplier tubes are stable and that pulse widths, transit time spreads, afterpulse rates and charge resolutions are within the specifications for NectarCAM.

astro-ph.IM↗

arXiv2010

Spectral Lag Relations in GRB Pulses Detected with HETE-2

Using a pulse-fit method, we investigate the spectral lags between the traditional gamma-ray band (50-400 keV) and the X-ray band (6-25 keV) for 8 GRBs with known redshifts (GRB 010921, GRB 020124, GRB 020127, GRB 021211, GRB 030528, GRB 040924, GRB 041006, GRB 050408) detected with the WXM and FREGATE instruments aboard the HETE-2 satellite. We find several relations for the individual GRB pulses between the spectral lag and other observables, such as the luminosity, pulse duration, and peak energy (Epeak). The obtained results are consistent with those for BATSE, indicating that the BATSE correlations are still valid at lower energies (6-25 keV). Furthermore, we find that the photon energy dependence for the spectral lags can reconcile the simple curvature effect model. We discuss the implication of these results from various points of view.

astro-ph.HE↗

arXiv2008

Intrinsic properties of a complete sample of HETE-2 gamma-ray bursts. A measure of the GRB rate in the Local Universe

Aims: Taking advantage of the forthcoming Catalog of the HETE-2 mission, the aim of this paper is to evaluate the main properties of HETE-2 GRBs - the E_peak, the T_90 and the E_iso - in their source frames and to derive their unbiased distribution. Methods: We first construct a complete sample containing all the bursts localized by the WXM on-board HETE-2, which are selected with a uniform criterion and whose observed parameters can be constrained. We then derive the intrinsic E_peak, T_90 and E_iso distributions using their redshift when it is available, or their pseudo-redshift otherwise. We finally compute the number of GRB (N_Vmax) within the visibility volume (V_max) of each GRB, in order to derive a weight for each detected burst accounting both for the detection significance and the star formation history of the universe. Results: The unbiased distributions obtained clearly show the predominence of X-ray flashes (XRFs) in the global GRB population. We also derive the rate of local GRBs: R0^H2 > 11 Gpc-3 yr-1, which is intermediate between the local rate obtained by considering only the high-luminosity bursts (~1 Gpc-3 yr-1) and that obtained by including the low-luminosity bursts (>200 Gpc-3 yr-1).

astro-ph↗

arXiv2006

X-ray Flashes or soft Gamma-ray Bursts? The case of the likely distant XRF 040912

In this work, we present a multi-wavelength study of XRF 040912, aimed at measuring its distance scale and the intrinsic burst properties. We performed a detailed spectral and temporal analysis of both the prompt and the afterglow emission and we estimated the distance scale of the likely host galaxy. We then used the currently available sample of XRFs with known distance to discuss the connection between XRFs and classical Gamma-ray Bursts (GRBs). We found that the prompt emission properties unambiguously identify this burst as an XRF, with an observed peak energy of E_p=17+/-13 keV and a burst fluence ratio S(2-30keV)/S(30-400keV)>1. A non-fading optical source with R~24 mag and with an apparently extended morphology is spatially consistent with the X-ray afterglow, likely the host galaxy. XRF 040912 is a very dark burst since no afterglow optical counterpart is detected down to R>25 mag (3 sigma limiting magnitude) at 13.6 hours after the burst. The host galaxy spectrum detected from 3800A to 10000A, shows a single emission line at 9552A. The lack of any other strong emission lines blue-ward of the detected one and the absence of the Ly alpha cut-off down to 3800A are consistent with the hypothesis of the [OII] line at redshift z=1.563+/-0.001. The intrinsic spectral properties rank this XRF among the soft GRBs in the E_peak-E_iso diagram. Similar results were obtained for most XRFs at known redshift. Only XRF 060218 and XRF 020903 represent a good example of instrinsic XRF(i-XRF) and are possibly associated with a different progenitor population. This scenario may calls for a new definition of XRFs.

astro-ph↗

arXiv2006

HETE-2 Localizations and Observations of Four Short Gamma-Ray Bursts: GRBs 010326B, 040802, 051211 and 060121

Here we report the localizations and properties of four short-duration GRBs localized by the High Energy Transient Explorer 2 satellite (HETE-2): GRBs 010326B, 040802, 051211 and 060121, all of which were detected by the French Gamma Telescope (Fregate) and localized with the Wide-field X-ray Monitor (WXM) and/or Soft X-ray Camera (SXC) instruments. We discuss eight possible criteria for determining whether these GRBs are "short population bursts" (SPBs) or "long population bursts" (LPBs). These criteria are (1) duration, (2) pulse widths, (3) spectral hardness, (4) spectral lag, (5) energy Egamma radiated in gamma rays (or equivalently, the kinetic energy E_KE of the GRB jet), (6) existence of a long, soft bump following the burst, (7) location of the burst in the host galaxy, and (8) type of host galaxy. In particular, we have developed a likelihood method for determining the probability that a burst is an SPB or a LPB on the basis of its T90 duration alone. A striking feature of the resulting probability distribution is that the T90 duration at which a burst has an equal probability of being a SPB or a LPB is T90 = 5 s, not T90 = 2 s, as is often used. All four short-duration bursts discussed in detail in this paper have T90 durations in the Fregate 30-400 keV energy band of 1.90, 2.31, 4.25, and 1.97 sec, respectively, yielding probabilities P(S|T90) = 0.97, 0.91, 0.60, and 0.95 that these bursts are SPBs on the basis of their T90 durations alone. All four bursts also have spectral lags consistent with zero. These results provide strong evidence that all four GRBs are SPBs (abstract continues).

astro-ph↗

arXiv2005

Discovery of the short gamma-ray burst GRB 050709

Gamma-Ray Bursts (GRBs) fall into two classes: short-hard and long-soft bursts. The latter are now known to have X-ray and optical afterglows, to occur at cosmological distances in star-forming galaxies, and to be associated with the explosion of massive stars. In contrast, the distance scale, the energy scale, and the progenitors of short bursts have remained a mystery. Here we report the discovery of a short-hard burst whose accurate localization has led to follow-up observations that have identified the X-ray afterglow and (for the first time) the optical afterglow of a short-hard burst. These, in turn, have led to identification of the host galaxy of the burst as a late-type galaxy at z=0.16 showing that at least some short-hard bursts occur at cosmological distances in the outskirts of galaxies, and are likely to be due to the merging of compact binaries.

astro-ph↗

arXiv2005

HETE-2 Observation of two gamma-ray bursts at z > 3

GRB 020124 and GRB 030323 constitute half the sample of gamma-ray bursts with a measured redshift greater than 3. This paper presents the temporal and spectral properties of these two gamma-ray bursts detected and localized with HETE-2. While they have nearly identical redshifts (z=3.20 for GRB 020124, and z=3.37 for GRB 030323), these two GRBs span about an order of magnitude in fluence, thus sampling distinct regions of the GRB luminosity function. The properties of these two bursts are compared with those of the bulk of the GRB population detected by HETE-2. We also discuss the energetics of GRB 020124 and GRB 030323 and show that they are compatible with the Epeak - Eiso relation discovered by Amati et al. (2002). Finally, we compute the maximum redshifts at which these bursts could have been detected by HETE-2 and we address various issues connected with the detection and localization of high-z GRBs.

astro-ph↗

arXiv2004

HETE Observations of the Gamma-Ray Burst GRB030329: Evidence for an Underlying Soft X-ray Component

An exceptionally intense gamma-ray burst, GRB030329, was detected and localized by the instruments on board the High Energy Transient Explorer satellite (HETE) at 11:37:14 UT on 29 March 2003. The burst consisted of two \~10s pulses of roughly equal brightness and an X-ray tail lasting >100s. The energy fluence in the 30-400 keV energy band was 1.08e-4 erg/cm2, making GRB030329 one of the brightest GRBs ever detected. Communication of a 2 arcmin error box 73 minutes after the burst allowed the rapid detection of a counterpart in the optical, X-ray, radio and the ensuing discovery of a supernova with most unusual characteristics. Analyses of the burst lightcurves reveal the presence of a distinct, bright, soft X-ray component underlying the main GRB: the 2-10 keV fluence of this component is ~7e-6 erg/cm2. The main pulses of GRB030329 were preceded by two soft, faint, non-thermal bumps. We present details of the HETE observations of GRB030329.

astro-ph↗

arXiv2004

Time-resolved X-ray spectral modeling of an intermediate burst from SGR1900+14 observed by HETE-2/FREGATE and WXM

We present a detailed analysis of a 3.5 s long burst from SGR1900+14 which occurred on 2001 July 2. The 2-150 keV time-integrated energy spectrum is well described by the sum of two blackbodies whose temperatures are approximately 4.3 and 9.8 keV. The time-resolved energy spectra are similarly well fit by the sum of two blackbodies. The higher temperature blackbody evolves with time in a manner consistent with a shrinking emitting surface. The interpretation of these results in the context of the magnetar model suggests that the two blackbody fit is an approximation of an absorbed, multi-temperature spectrum expected on theoretical grounds rather than a physical description of the emission. If this is indeed the case, our data provide further evidence for a strong magnetic field, and indicate that the entire neutron was radiating during most of the burst duration.

astro-ph↗

arXiv2004

XMM-Newton spectral and timing analysis of the faint millisecond pulsars PSR J0751+1807 and PSR J1012+5307

We present XMM-Newton MOS imaging and PN timing data of the faint millisecond pulsars PSR J0751+1807 and PSR J1012+5307. We find 46 sources in the MOS field of view of PSR J0751+1807 searching down to an unabsorbed flux limit of 3 x 10^-15 ergs cm^-2 s^-1 (0.2-10.0 keV). We present, for the first time, the X-ray spectra of these two faint millisecond pulsars. We find that a power law model best fits the spectrum of PSR J0751+1807, Gamma=1.59+/-0.20, with an unabsorbed flux of 4.4 x 10^-14 ergs cm^-2 s^-1 (0.2-10.0 keV). A power law is also a good description of the spectrum of PSR J1012+5307, Gamma=1.78+/-0.36, with an unabsorbed flux of 1.2 x 10^-13 ergs cm^-2 s^-1 (0.2-10.0 keV). However, a blackbody model can not be excluded as the best fit to this data. We present some evidence to suggest that both of these millisecond pulsars show pulsations in this X-ray band. We find some evidence for a single broad X-ray pulse for PSR J0751+1807 and we discuss the possibility that there are two pulses per spin period for PSR J1012+5307.

astro-ph↗

arXiv2003

XMM-Newton spectral and timing observations of the millisecond pulsar PSR J0218+4232

We present XMM-Newton MOS imaging and PN timing data of the millisecond pulsar PSR J0218+4232. We confirm the previously detected pulsations of PSR J0218+4232 and we show that the folded lightcurve is dependent on energy. We present the broad band (0.2-10.0 keV) spectrum of this millisecond pulsar, as well as the spectra of: the pulsed emission, the individual pulses, the interpulse and the non-pulsed region and we compare our results with previous data from Rosat, BeppoSAX and Chandra. We discuss the results of the spectral fitting in the context of recent pulsar models.

astro-ph↗

arXiv2003

GRB 020531: A Short, Hard Gamma-Ray Burst Localized and Observed by HETE-2

The HETE-2 FREGATE and WXM instruments detected a short, hard GRB at 00:26:18.72 UT on 31 May 2002. A preliminary localization was reported as a GCN Position Notice 88 min after the burst, and a refined localization was disseminated 123 minutes later. An IPN localization of the burst was reported 18 hours after the GRB, and a refined IPN localization was disseminated ~5 days after the burst. The final IPN localization, disseminated on 25 July 2002, is a diamond-shaped region centered on RA=15h 15m 11.18s, Dec=-19o 24' 27.08" (J2000), and has an area of ~9 square arcminutes (99.7% confidence region). The prompt localization of the burst by HETE-2, coupled with the refinement of the localization by the IPN, made possible the most sensitive follow-up observations to date of a short, hard GRB at radio, optical, and X-ray wavelengths. The time history of GRB020531 at high (>30 keV) energies consists of a short, intense spike followed by a much less intense secondary peak, which is characteristic of many short, hard bursts. The duration of the burst increases with decreasing energy and the spectrum of the burst evolves from hard to soft, behaviors which are similar to those of long GRBs. This suggests that short, hard GRBs are closely related to long GRBs.

astro-ph↗

arXiv2003

Scientific Highlights of the HETE-2 Mission

The HETE-2 mission has been highly productive. It has observed more than 250 GRBs so far. It is currently localizing 25 - 30 GRBs per year, and has localized 43 GRBs to date. Twenty-one of these localizations have led to the detection of X-ray, optical, or radio afterglows, and as of now, 11 of the bursts with afterglows have known redshifts. HETE-2 has confirmed the connection between GRBs and Type Ic supernovae, a singular achievement and certainly one of the scientific highlights of the mission so far. It has provided evidence that the isotropic-equivalent energies and luminosities of GRBs are correlated with redshift, implying that GRBs and their progenitors evolve strongly with redshift. Both of these results have profound implications for the nature of GRB progenitors and for the use of GRBs as a probe of cosmology and the early universe. HETE-2 has placed severe constraints on any X-ray or optical afterglow of a short GRB. It is also solving the mystery of "optically dark' GRBs, and revealing the nature of X-ray flashes.

astro-ph↗

arXiv2003

HETE-2 Localization and Observation of the Bright, X-Ray-Rich Gamma-Ray Burst GRB021211

A bright, x-ray-rich GRB was detected by HETE-2 at 11:18:34.03 UT on 11 Dec 2002. The WXM localization was to 14' and relayed to the GCN 22 s after the start of the burst. The ground SXC localization was within 2' of R.A. 08h 09m 00s, Dec 06d 44' 20" (J2000). GRB021211 consists of a single, FRED-like pulse with t90s of 2.3 s (85-400 keV) and 8.5 s (2-10 keV). The peak photon number and photon energy fluxes in the 2-400 keV band, are 34.0 +/- 1.8 ph cm^-2 s^-1 and 1.68 +/- 0.11 x 10^-6 erg cm^-2 s^-1, respectively. The energy fluences in the 2-30 keV and 30-400 kev energy bands are S_X = 1.36 +/- 0.05 x 10^-6 erg cm^-2 and S_gamma 2.17 +/- 0.15 x 10^-6 erg cm^-2, respectively. Thus GRB021211 is an X-ray-rich GRB (S_X/S_gamma = 0.63 > 0.32). The spectrum is well-fit by a Band function (alpha = -0.805, beta = -2.37, E_peak = 46.8 keV). The prompt localization allowed the detection of an optical afterglow for what would otherwise have been an ``optically dark'' GRB. GRB 021211 demonstrates that some fraction of burst afterglows are ``optically dark'' because their optical afterglows at times > 1 hr after the burst are very faint, and thus have often escaped detection. GRB 021211 shows that such ``optically dim'' bursts can have very bright afterglows at times < 20 min after the burst.

astro-ph↗

arXiv2002

XMM-Newton observations of two black hole X-ray transients in quiescence

We report on XMM-Newton observations of GRO J1655-40 and GRS 1009-45, which are two black hole X-ray transients currently in their quiescent phase. GRO J1655-40 was detected with a 0.5 - 10 keV luminosity of 5.9 10^{31} erg/s. This luminosity is comparable to a previous Chandra measurement, but ten times lower than the 1996 ASCA value, most likely obtained when the source was not yet in a true quiescent state. Unfortunately, XMM-Newton failed to detect GRS 1009-45. A stringent upper limit of 8.9 10^{30} erg/s was derived by combining data from the EPIC-MOS and PN cameras. The X-ray spectrum of GRO J1655-40 is very hard as it can be fitted with a power law model of photon index ~ 1.3 +/- 0.4. Similarly hard spectra have been observed from other systems; these rule out coronal emission from the secondary or disk flares as the origin of the observed X-rays. On the other hand, our observations are consistent with the predictions of the disc instability model in the case that the accretion flow forms an advection dominated accretion flow (ADAF) at distances less than a fraction ~ 0.1 - 0.3) of the circularization radius. This distance corresponds to the greatest extent of the ADAF that is thought to be possible.

astro-ph↗

arXiv2002

Correlated timing and spectral behavior of 4U 1705-44

We follow the timing properties of the neutron star low-mass X-ray binary system 4U 1705-44 in different spectral states, as monitored by the Rossi X-ray Timing Explorer over about a month. We fit the power density spectra using multiple Lorentzians. We show that the characteristic frequencies of these Lorentzians, when properly identified, fit within the correlations previously reported. The time evolution of these frequencies and their relation with the parameters of the energy spectra reported in Barret & Olive (2002) are used to constrain the accretion geometry changes. The spectral data were fitted by the sum of a blackbody and a Comptonized component and were interpreted in the framework of a truncated accretion disk geometry, with a varying truncation radius. If one assumes that the characteristic frequencies of the Lorentzians are some measure of this truncation radius, as in most theoretical models, then the timing data presented here strengthen the above interpretation. The soft to hard and hard to soft transitions are clearly associated with the disk receding from and approaching the neutron star respectively. During the transitions, correlations are found between the Lorentzian frequencies and the flux and temperature of the blackbody, which is thus likely to be coming from the disk. On the other hand, in the hard state, the characteristic Lorentzians frequencies which are at the lowest, remained nearly constant despite significant evolution of the spectra parameters. The disk no longer contributes to the X-ray emission, and the blackbody is now likely to be emitted by the neutron star surface which is providing the seed photons for the Comptonization.

astro-ph↗

arXiv2002

HETE-2 Localization and Observations of the Short, Hard Gamma-Ray Burst GRB020531

The {\it HETE-2} (hereafter \HETE) French Gamma Telescope (FREGATE) and the Wide-field X-ray Monitor (WXM) instruments detected a short ($t_{50} = 360$ msec in the FREGATE 85-300 keV energy band), hard gamma-ray burst (GRB) that occurred at 1578.72 SOD (00:26:18.72 UT) on 31 May 2002. The WXM flight localization software produced a valid location in spacecraft (relative) coordinates. However, since no on-board real-time star camera aspect was available, an absolute localization could not be disseminated. A preliminary localization was reported as a GCN Position Notice at 01:54:22 UT, 88 min after the burst. Further ground analysis produced a refined localization, which can be expressed as a 90% confidence rectangle that is 67 arcminutes in RA and 43 arcminutes in Dec (90% confidence region), centered at RA = +15$^{\rm h}$ 14$^{\rm m}$ 45$^{\rm s}$, Dec = -19$^\circ$ 21\arcmin 35\arcsec (J2000). An IPN localization of the burst was disseminated 18 hours after the GRB (Hurley et al. 2002b). A refined IPN localization was disseminated $\approx$ 5 days after the burst. This hexagonal-shaped localization error region is centered on RA = 15$^{\rm h}$ 15$^{\rm m}$ 03.57$^{\rm s}$, -19$^\circ$ 24\arcmin 51.00\arcsec (J2000), and has an area of $\approx$ 22 square arcminutes (99.7% confidence region). The prompt localization of this short, hard GRB by \HETE and the anti-Sun pointing of the \HETE instruments, coupled with the refinement of the localization by the IPN, has made possible rapid follow-up observations of the burst at radio, optical, and X-ray wavelengths.

astro-ph↗