arXiv subjects

M. Servillat

Publications and source records attributed to M. Servillat.

At least 19 recordsLinked to original sources

arXiv2022

CompOSE Reference Manual

CompOSE (CompStar Online Supernovae Equations of State) is an online repository of equations of state (EoS) for use in nuclear physics and astrophysics, e.g., in the description of compact stars or the simulation of core-collapse supernovae and neutron-star mergers, see http://compose.obspm.fr. The main services, offered via the website, are: a collection of data tables in a flexible and easily extendable data format for different EoS types and related physical quantities with extensive documentation and referencing; software for download to extract and to interpolate these data and to calculate additional quantities; webtools to generate EoS tables that are customized to the needs of the users and to illustrate dependencies of various EoS quantities in graphical form. This manual is an update of previous versions that are available on the CompOSE website, at arXiv:1307.5715 [astro-ph.SR], and that was originally published in the journal "Physics of Particles and Nuclei" with doi:10.1134/S1063779615040061. It contains a detailed description of the service, containing a general introduction as well as instructions for potential contributors and for users. Short versions of the manual for EoS users and providers will also be available as separate publications.

astro-ph.HE↗

arXiv2018

The radius of the quiescent neutron star in the globular cluster M13

X-ray spectra of quiescent low-mass X-ray binaries containing neutron stars can be fit with atmosphere models to constrain the mass and the radius. Mass-radius constraints can be used to place limits on the equation of state of dense matter. We perform fits to the X-ray spectrum of a quiescent neutron star in the globular cluster M13, utilizing data from ROSAT, Chandra and XMM-Newton, and constrain the mass-radius relation. Assuming an atmosphere composed of hydrogen and a 1.4${\rm M}_{\odot}$ neutron star, we find the radius to be $R_{\rm NS}=12.2^{+1.5}_{-1.1}$ km, a significant improvement in precision over previous measurements. Incorporating an uncertainty on the distance to M13 relaxes the radius constraints slightly and we find $R_{\rm NS}=12.3^{+1.9}_{-1.7}$ km (for a 1.4${\rm M}_{\odot}$ neutron star with a hydrogen atmosphere), which is still an improvement in precision over previous measurements, some of which do not consider distance uncertainty. We also discuss how the composition of the atmosphere affects the derived radius, finding that a helium atmosphere implies a significantly larger radius.

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arXiv2017

Understanding the environment around the intermediate mass black hole candidate ESO 243-49 HLX-1

Aims. ESO 243-49 HLX-1, otherwise known as HLX-1, is an intermediate mass black hole (IMBH) candidate located 8" (3.7 Kpc) from the centre of the edge-on S0 galaxy ESO 243-49. How the black hole came to be associated with this galaxy, and the nature of the environment in which it resides, are still unclear. Using multi-wavelength observations we investigate the nature of the medium surrounding HLX-1, search for evidence of past mergers with ESO 243-49 and constrain parameters of the galaxy. Methods. We reduce and analyse integral field unit observations of ESO 243-49 that were taken with the MUSE instrument on the VLT. Using complementary multi-wavelength data, including X-Shooter, HST, Swift, Chandra and ATCA data, we further examine the vicinity of HLX-1. We additionally examine the nature of the host galaxy and estimate the mass of the central supermassive black hole (SMBH) in ESO 243-49. Results. No evidence for a recent minor-merger that could result in the presence of the IMBH is discerned, but the data are compatible with a scenario in which minor mergers may have occurred in the history of ESO 243-49. The MUSE data reveal a rapidly rotating disc in the centre of the galaxy, around the SMBH. The mass of the SMBH at the centre of ESO 243-49 is estimated to be 0.5-23 $\times$ 10$^7$ M$_\odot$. Studying the spectra of HLX-1, that were taken in the low/hard state, we determine H$_α$ flux variability to be at least a factor 6, compared to observations taken during the high/soft state. This H$_α$ flux variability over one year indicates that the line originates close to the IMBH, excluding the possibility that the line emanates from a surrounding nebula or a star cluster. The large variability associated with the X-ray states of HLX-1 confirms that the H$_α$ line is associated with the object and therefore validates the distance to HLX-1.

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arXiv2016

The Gamma-ray Cherenkov Telescope for the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) is a forthcoming ground-based observatory for very-high-energy gamma rays. CTA will consist of two arrays of imaging atmospheric Cherenkov telescopes in the Northern and Southern hemispheres, and will combine telescopes of different types to achieve unprecedented performance and energy coverage. The Gamma-ray Cherenkov Telescope (GCT) is one of the small-sized telescopes proposed for CTA to explore the energy range from a few TeV to hundreds of TeV with a field of view $\gtrsim 8^\circ$ and angular resolution of a few arcminutes. The GCT design features dual-mirror Schwarzschild-Couder optics and a compact camera based on densely-pixelated photodetectors as well as custom electronics. In this contribution we provide an overview of the GCT project with focus on prototype development and testing that is currently ongoing. We present results obtained during the first on-telescope campaign in late 2015 at the Observatoire de Paris-Meudon, during which we recorded the first Cherenkov images from atmospheric showers with the GCT multi-anode photomultiplier camera prototype. We also discuss the development of a second GCT camera prototype with silicon photomultipliers as photosensors, and plans toward a contribution to the realisation of CTA.

astro-ph.IM↗

arXiv2016

Inauguration and First Light of the GCT-M Prototype for the Cherenkov Telescope Array

The Gamma-ray Cherenkov Telescope (GCT) is a candidate for the Small Size Telescopes (SSTs) of the Cherenkov Telescope Array (CTA). Its purpose is to extend the sensitivity of CTA to gamma-ray energies reaching 300 TeV. Its dual-mirror optical design and curved focal plane enables the use of a compact camera of 0.4 m diameter, while achieving a field of view of above 8 degrees. Through the use of the digitising TARGET ASICs, the Cherenkov flash is sampled once per nanosecond continuously and then digitised when triggering conditions are met within the analogue outputs of the photosensors. Entire waveforms (typically covering 96 ns) for all 2048 pixels are then stored for analysis, allowing for a broad spectrum of investigations to be performed on the data. Two prototypes of the GCT camera are under development, with differing photosensors: Multi-Anode Photomultipliers (MAPMs) and Silicon Photomultipliers (SiPMs). During November 2015, the GCT MAPM (GCT-M) prototype camera was integrated onto the GCT structure at the Observatoire de Paris-Meudon, where it observed the first Cherenkov light detected by a prototype instrument for CTA.

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arXiv2016

The GCT camera for the Cherenkov Telescope Array

The Gamma-ray Cherenkov Telescope (GCT) is proposed for the Small-Sized Telescope component of the Cherenkov Telescope Array (CTA). GCT's dual-mirror Schwarzschild-Couder (SC) optical system allows the use of a compact camera with small form-factor photosensors. The GCT camera is ~0.4 m in diameter and has 2048 pixels; each pixel has a ~0.2 degree angular size, resulting in a wide field-of-view. The design of the GCT camera is high performance at low cost, with the camera housing 32 front-end electronics modules providing full waveform information for all of the camera's 2048 pixels. The first GCT camera prototype, CHEC-M, was commissioned during 2015, culminating in the first Cherenkov images recorded by a SC telescope and the first light of a CTA prototype. In this contribution we give a detailed description of the GCT camera and present preliminary results from CHEC-M's commissioning.

astro-ph.IM↗

arXiv2015

Discovery of a red supergiant counterpart to RX~J004722.4-252051, a ULX in NGC 253

We present two epochs of near-infrared spectroscopy of the candidate red supergiant counterpart to RX~J004722.4-252051, a ULX in NGC 253. We measure radial velocities of the object and its approximate spectral type by cross-correlating our spectra with those of known red supergiants. Our VLT/X-shooter spectrum is best matched by that of early M-type supergiants, confirming the red supergiant nature of the candidate counterpart. The radial velocity of the spectrum, taken on 2014, August 23, is $417 \pm 4$ km/s. This is consistent with the radial velocity measured in our spectrum taken with Magellan/MMIRS on 2013, June 28, of $410 \pm 70$ km/s, although the large error on the latter implies that a radial velocity shift expected for a black hole of tens of $M_\odot$ can easily be hidden. Using nebular emission lines we find that the radial velocity due to the rotation of NGC 253 is 351 $\pm$ 4 km/s at the position of the ULX. Thus the radial velocity of the counterpart confirms that the source is located in NGC 253, but also shows an offset with respect to the local bulk motion of the galaxy of 66 $\pm$ 6 km/s. We argue that the most likely origin for this displacement lies either in a SN kick, requiring a system containing a $\gtrsim 50$ $M_\odot$ black hole, and/or in orbital radial velocity variations in the ULX binary system, requiring a $\gtrsim 100$ $M_\odot$ black hole. We therefore conclude that RX~J004722.4-252051 is a strong candidate for a ULX containing a massive stellar black hole.

astro-ph.HE↗

arXiv2015

Data model issues in the Cherenkov Telescope Array project

The planned Cherenkov Telescope Array (CTA), a future ground-based Very-High-Energy (VHE) gamma-ray observatory, will be the largest project of its kind. It aims to provide an order of magnitude increase in sensitivity compared to currently operating VHE experiments and open access to guest observers. These features, together with the thirty years lifetime planned for the installation, impose severe constraints on the data model currently being developed for the project. In this contribution we analyze the challenges faced by the CTA data model development and present the requirements imposed to face them. While the full data model is still not completed we show the organization of the work, status of the design, and an overview of the prototyping efforts carried out so far. We also show examples of specific aspects of the data model currently under development.

astro-ph.IM↗

arXiv2014

HI study of the environment around ESO 243-49, the host galaxy of an intermediate mass black hole

The lenticular galaxy ESO 243-49 hosts the ultraluminous X-ray source HLX-1, the best candidate intermediate mass black hole (IMBH) currently known. The environments of IMBHs remain unknown, however the proposed candidates include the nuclei of dwarf galaxies or globular clusters. Evidence at optical wavelengths points at HLX-1 being the remnant of an accreted dwarf galaxy. Here we report the Australia Telescope Compact Array radio observations of HI emission in and around ESO 243-49 searching for signatures of a recent merger event. No HI line emission is detected in ESO 243-49 with a 5$σ$ upper limit on the HI gas mass of a few $10^8 M_{\odot}$. A likely reason for this non-detection is the cluster environment depleting ESO 243-49's HI gas reservoir. The upper limit is consistent with an interpretation of HLX-1 as a dwarf satellite of ESO 243-49, however more sensitive observations are required for a detection. We detect ~$5 \times 10^8 M_{\odot}$ of HI gas in the peculiar spiral galaxy AM 0108-462, located at a projected distance of ~170 kpc from ESO 243-49. This amount of HI gas is ~10 times less than in spiral galaxies with similar optical and near-infrared properties in the field, strengthening the conclusion that the cluster environment indeed depletes the HI gas reservoir of these two galaxies. Here we also report observations of AM 0108-462 in several optical and near-infrared bands using the Magellan 6.5 m telescopes, and archival X-ray and ultraviolet observations with XMM-Newton and Swift. These data combined with the HI line data suggest it is likely that AM 0108-462 is experiencing a merger event.

astro-ph.HE↗

arXiv2014

Near-infrared counterparts of ultraluminous X-ray sources

In this paper we present the results of the first systematic search for counterparts to nearby ultraluminous X-ray sources (ULXs) in the near-infrared (NIR). We observed 62 ULXs in 37 galaxies within 10 Mpc and discovered 17 candidate NIR counterparts. The detection of 17 out of 62 ULX candidates points to intrinsic differences between systems that show and those that do not show infrared emission. For six counterparts we conclude from the absolute magnitudes and - - in some cases - additional information such as morphology and previously reported photometric or spectroscopic observations, that they are likely background active galactic nuclei or ULXs residing in star clusters. Eleven counterparts have absolute magnitudes consistent with them being single red supergiant stars. Alternatively, these systems may have larger accretion discs that emit more NIR light than the systems that we do not detect. Other scenarios such as emission from a surrounding nebula or from a compact radio jet are also possible, although for Holmberg II X-1 the NIR luminosity far exceeds the expected jet contribution. The eleven possible red supergiant counterparts are excellent candidates for spectroscopic follow-up observations. This may enable us to measure the mass function in these systems if they are indeed red supergiant donor stars where we can observe absorption lines.

astro-ph.HE↗

arXiv2013

Optical variability of the accretion disk around the intermediate mass black hole ESO 243-49 HLX-1 during the 2012 outburst

We present dedicated quasi-simultaneous X-ray (Swift) and optical (Very Large Telescope (VLT), V- and R-band) observations of the intermediate mass black hole candidate ESO 243-49 HLX-1 before and during the 2012 outburst. We show that the V-band magnitudes vary with time, thus proving that a portion of the observed emission originates in the accretion disk. Using the first quiescent optical observations of HLX-1, we show that the stellar population surrounding HLX-1 is fainter than V~25.1 and R~24.2. We show that the optical emission may increase before the X-ray emission consistent with the scenario proposed by Lasota et al. (2011) in which the regular outbursts could be related to the passage at periastron of a star circling the intermediate mass black hole in an eccentric orbit, which triggers mass transfer into a quasi-permanent accretion disk around the black hole. Further, if there is indeed a delay in the X-ray emission we estimate the mass-transfer delivery radius to be ~1e11 cm.

astro-ph.HE↗

arXiv2012

The accretion disc, jets and environment of the intermediate mass black hole candidate ESO 243-49 HLX-1

The Ultra Luminous X-ray (ULX) source HLX-1 in the galaxy ESO 243-49 has an observed maximum unabsorbed X-ray luminosity of 1.3e42 erg/s (0.2-10.0 keV). From the conservative assumption that this value exceeds the Eddington limit by at most a factor of 10, the minimum mass is then 500 solar masses. The X-ray luminosity varies by a factor of 40 with an apparent recurrence timescale of approximately one year. This X-ray variability is associated with spectral state transitions similar to those seen in black hole X-ray binaries. Here we discuss our recent modelling of all the X-ray data for HLX-1 and show that it supports the idea that this ULX is powered by sub- and near Eddington accretion onto an intermediate mass black hole. We also present evidence for transient radio emission which is consistent with a discrete jet ejection event as well as comment on the nature of the environment around HLX-1 in light of recent Hubble Space Telescope photometry.

astro-ph.HE↗

arXiv2012

Investigating slim disk solutions for HLX-1 in ESO 243-49

The hyper luminous X-ray source HLX-1 in the galaxy ESO 243-49, currently the best intermediate mass black hole candidate, displays spectral transitions similar to those observed in Galactic black hole binaries, but with a luminosity 100-1000 times higher. We investigated the X-ray properties of this unique source fitting multi-epoch data collected by Swift, XMM-Newton & Chandra with a disk model computing spectra for a wide range of sub- and super-Eddington accretion rates assuming a non-spinning black hole and a face-on disk (i = 0 deg). Under these assumptions we find that the black hole in HLX-1 is in the intermediate mass range (~2 x 10^4 M_odot) and the accretion flow is in the sub-Eddington regime. The disk radiation efficiency is eta = 0.11 +/-0.03. We also show that the source does follow the L_X ~ T^4 relation for our mass estimate. At the outburst peaks, the source radiates near the Eddington limit. The accretion rate then stays constant around 4 x 10^(-4) M_odot yr^(-1) for several days and then decreases exponentially. Such "plateaus" in the accretion rate could be evidence that enhanced mass transfer rate is the driving outburst mechanism in HLX-1. We also report on the new outburst observed in August 2011 by the Swift-X-ray Telescope. The time of this new outburst further strengthens the ~1 year recurrence timescale.

astro-ph.HE↗

arXiv2012

A Young Massive Stellar Population Around the Intermediate Mass Black Hole ESO 243-49 HLX-1

We present Hubble Space Telescope and simultaneous Swift X-ray telescope observations of the strongest candidate intermediate mass black hole ESO 243-49 HLX-1. Fitting the spectral energy distribution from X-ray to near-infrared wavelengths showed that the broadband spectrum is not consistent with simple and irradiated disc models, but is well described by a model comprised of an irradiated accretion disc plus a stellar population with a mass ~1E6 Msun. The age of the population cannot be uniquely constrained, with both very young and very old stellar populations allowed. However, the very old solution requires excessively high levels of disc reprocessing and an extremely small disc, leading us to favour the young solution with an age of ~13 Myr. In addition, the presence of dust lanes and the lack of any nuclear activity from X-ray observations of the host galaxy lead us to propose that a gas-rich minor merger may have taken place less than ~200 Myr ago. Such a merger event would explain the presence of the intermediate mass black hole and support a young stellar population.

astro-ph.CO↗

arXiv2011

Correcting the Astrometry of DASCH scanned plates

We describe the process implemented in the DASCH pipeline which applies a reliable astrometric correction to each scanned plate. Our first blind astrometric fit resolves the pointing, scale and orientation of the plate in the sky using astrometry. net code. Then we iteratively improve this solution with WCSTools imwcs. Finally, we apply a 6th order polynomial fit with SCAMP to correct the image for distortions. During a test on 140 plates, this process has allowed us to successfully correct 79% of the plates. With further refinements of the process we now reach a 95% success rate after reprocessing all our scanned plates (~11 000 in Nov. 2010). We could extract a lightcurve for 2.85 times more objects than with the previous Pipeline, down to magnitude 17. The resulting median RMS error is 0.13" for objects with mag. 8 to 17.

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arXiv2010

Discovery of a Second Transient Low-Mass X-ray Binary in the Globular Cluster NGC 6440

We have identified a new transient luminous low-mass X-ray binary, NGC 6440 X-2, with Chandra/ACIS, RXTE/PCA, and Swift/XRT observations of the globular cluster NGC 6440. The discovery outburst (July 28-31, 2009) peaked at L_X~1.5*10^36 ergs/s, and lasted for <4 days above L_X=10^35 ergs/s. Four other outbursts (May 29-June 4, Aug. 29-Sept. 1, Oct. 1-3, and Oct. 28-31 2009) have been observed with RXTE/PCA (identifying millisecond pulsations, Altamirano et al. 2009a) and Swift/XRT (confirming a positional association with NGC 6440 X-2), with similar peak luminosities and decay times. Optical and infrared imaging did not detect a clear counterpart, with best limits of V>21, B>22 in quiescence from archival HST imaging, g'>22 during the August outburst from Gemini-South GMOS imaging, and J>~18.5$ and K>~17 during the July outburst from CTIO 4-m ISPI imaging. Archival Chandra X-ray images of the core do not detect the quiescent counterpart, and place a bolometric luminosity limit of L_{NS}< 6*10^31 ergs/s (one of the lowest measured) for a hydrogen atmosphere neutron star. A short Chandra observation 10 days into quiescence found two photons at NGC 6440 X-2's position, suggesting enhanced quiescent emission at L_X~6*10^31 ergs/s . NGC 6440 X-2 currently shows the shortest recurrence time (~31 days) of any known X-ray transient, although regular outbursts were not visible in the bulge scans before early 2009. Fast, low-luminosity transients like NGC 6440 X-2 may be easily missed by current X-ray monitoring.

astro-ph.HE↗

arXiv2010

Chandra and Swift Follow-up Observations of the Intermediate Mass Black Hole in ESO243-49

The brightest Ultra-Luminous X-ray source HLX-1 in the galaxy ESO 243-49 provides strong evidence for the existence of intermediate mass black holes. As the luminosity and thus the mass estimate depend on the association of HLX-1 with ESO 243-49, it is essential to confirm its affiliation. This requires follow-up investigations at wavelengths other than X-rays, which in-turn needs an improved source position. To further reinforce the intermediate mass black hole identification, it is necessary to determine HLX-1's environment to establish whether it could potentially form and nourish a black hole at the luminosities observed. Using the High Resolution Camera onboard Chandra, we determine a source position of RA=01h10m28.3s and Dec=-46d04'22.3". A conservative 95% error of 0.3" was found following a boresight correction by cross-matching the positions of 3 X-ray sources in the field with the 2MASS catalog. Combining all Swift UV/Optical Telescope uvw2 images, we failed to detect a UV source at the Chandra position down to a 3sigma limiting magnitude of 20.25 mag. However, there is evidence that the UV emission is elongated in the direction of HLX-1. This is supported by archival data from GALEX and suggests that the far-UV emission is stronger than the near-UV. This could imply that HLX-1 may be situated near the edge of a star forming region. Using the latest X-ray observations we deduce the mass accretion rate of a 500 Msun black hole with the observed luminosity and show that this is compatible with such an environment.

astro-ph.HE↗

arXiv2010

Further Observations of the Intermediate Mass Black Hole Candidate ESO 243-49 HLX-1

The brightest Ultra-Luminous X-ray source HLX-1 in the galaxy ESO 243-49 currently provides strong evidence for the existence of intermediate mass black holes. Here we present the latest multi-wavelength results on this intriguing source in X-ray, UV and radio bands. We have refined the X-ray position to sub-arcsecond accuracy. We also report the detection of UV emission that could indicate ongoing star formation in the region around HLX-1. The lack of detectable radio emission at the X-ray position strengthens the argument against a background AGN.

astro-ph.HE↗