Link between magnetars and Fast radio bursts

An international campaign including ground-based and space telescopes, including the INTEGRAL satellite, discovered end of April 2020 very short pulses in both X-rays and radio waves coming from a compact object in the Galaxy, the magnetar SGR 1935+2154. The simultaneous observation of these signals is seen for the first time in this type of source and attests a connection between magnetars and Fast radio bursts, a class of radio sources whose origin is today poorly known. This work, that includes researchers from the Astrophysics Department/ AIM Laboratory of CEA-Irfu of Paris-Saclay, is published in The Astrophysical Journal Letters and subject press release of a European Space Agency (ESA).

The hot heart of the SN 1987A supernova

An international team, led by astronomers from Cardiff University, with the contribution of the Astrophysics Department of CEA-Irfu, may have spotted for the first time the compact remains of the last star explosion visible by eye that occurred on February 23, 1987 in a nearby galaxy, the Large Magellanic Cloud, only 160 000 light-years away.
Using the high-resolution images of the ALMA radio telescope in the Atacama Desert in northern Chile, the team discovered a small area of dust, warmer than its environment, which may correspond to the supposed location of the compact neutron star that should have formed during the explosion according to theoretical models. This compact object had been searched without success for more than 30 years. This indirect discovery nevertheless requires to be confirmed by additional data. These results are published in The Astrophysical Journal.

After a decade-long search, scientists have for the first time detected a gamma-ray burst in very-high-energy gamma light. This discovery was made in July 2018 by the H.E.S.S. collaboration using the  huge 28-m telescope of the H.E.S.S. array in Namibia. Surprisingly, this Gamma-ray burst, an extremely energetic flash following a cosmological cataclysm, was found to emit very-high-energy gamma-rays long after the initial explosion. This discovery was published in Nature.

 

 

Optical follow-up of gravitionnal waves

The first results of the space mission SVOM (for Space-based multi-band astronomical Variable Objects Monitor) have just fallen before the launch scheduled for the end of 2021. How is this possible? Quite simply because this ambitious Franco-Chinese mission, which aims at studying gamma-ray bursts of the Universe, is also developing a network of ground-based cameras able to detect the emission of visible light that follows the outbreak of these bursts, the most violent known explosions. This network, dubbed Ground-based Wide Angle Camera (GWAC), is already in operation at the Xinglong Observatory in Northeast Beijing (China). Its test version, dubbed Mini-GWAC, successfully concluded a first campaign of monitoring and real-time follow-up of gravitational wave sources discovered by the LIGO (USA) and Virgo (Italy) facilities. These results are being published in the journal Research in Astronomy and Astrophysics.

Two chimneys of hot gas found around the central back hole

Thanks to the X-ray satellites Chandra and XMM-Newton, an international team including the Department of Astrophysics of CEA-Irfu has just discovered the existence of two bubbles of hot gas escaping to distances of about 500 light-years, on both sides of the massive black hole environment, in the center of our galaxy. Like the messages of Native Americans transmitted by smoke bubbles visible from afar, these "hot gas chimneys" tell us today about the intense past activity of the black hole and the central regions of our Galaxy. These results are published in the journal Nature of March 21, 2019.

Outstanding results from this Japanese X-rays observatory

Despite a short period of activity, the japanese space agency (Jaxa) Hitomi satellite has shown its full potential by delivering relevant information’s on several celestial objects. In a series of works based on these observations and gathered in an issue of the review Publications of the Astronomical Society of Japan (PASJ), the Hitomi collaboration (among it researchers from the Astrophysical Department of CEA-Irfu Saclay) presents results that take advantage of the exceptional spectral resolution of the SXS spectrometer, one of the payload instrument. At the heart of this work is a detailed study of the dynamics of plasma in the center of an active galactic nucleus, of the ejecta of several supernova remnants, of the composition of matter in a binary system or the search for X and radio correlations in the Crab pulsar thanks to the high temporal resolution. Performed during the verification and calibration phase of the instruments before the satellite failed, these observations and the quality of the results confirm the community's choice on the instruments and the high potential of the high resolution X-rays spectroscopy. The Hitomi team is currently preparing its successor, Xrism (X-Ray Imaging and Spectroscopy Mission) and ESA is on its side working on the Athena project, a major X-rays observatory in which CEA is deeply involved

 

Read more in : Haute résolution pour le satellite Hitomi (in French)

A prototype of the MXT camera arrived at the CNES in Toulouse on 25 October 2018. This is the Structural and Thermal Model (STM), which will be integrated into the telescope that will be sent to China to be mounted on the SVOM satellite Qualification Model.


The objective of this model is to validate the thermo-mechanical design of the camera. It also makes it possible to check the manufacturing and assembly capacity of the various components, which represent more than 1,000 elements. The model realized includes all the camera subassemblies with a good level of representativeness of the flight model, both on its external design (interfaces with the telescope) and on its internal design (harnesses, connectors...). The electrical parts (detector, electronic boards, motor) are replaced by weights and heaters to simulate their mechanical and thermal behaviour. 

X-ray photons were detected for the first time in late August 2018 with an engineering model of the SVOM MXT focal plane. This is an important step towards the validation of the design of the detection chain.
The MXT telescope, for Microchannel X-ray Telescope, will be flown on board the SVOM satellite, a collaborative project between France (CNES) and China (CAS, CNSA) to study gamma-ray bursts. It aims at detecting soft X-rays (0.2 to 10 keV) at during the early phases of the afterglow emission, and at providing an accurate (smaller than 1 arc minute) position of the burst. Irfu is in charge of the design and realization of the telescope camera, integrating a pnCCD (provided by MPE) X-ray imaging spectrometer assembled on a dedicated ceramic board. The flight model of the detector must be integrated into the camera in one year from now.



 

A hundred years old mystery might get resolved with the detection of neutrinos by the IceCube collaboration coming from a known active black hole. Irfu, which coordinate those observations with the H.E.S.S. telescope, did not detect anything for now but the multi-messenger astronomy has just begun…

An instability to trigger the initial rotation of a neutron star.

The birth spin of a neutron star is a key parameter to better understand the nature of its progenitor as well as the dynamical processes at play during the collapse of a massive star. However, the distribution of initial pulsar spins is poorly known. A study led by R. Kazeroni from SAP/CEA and his collaborators, using numerical simulations, emphasized the efficiency of a hydrodynamic instability named “SASI” to impart a rotational velocity to the neutron star. Surprisingly, the simulations show that, in some cases, the direction of rotation of the compact object is opposite to the perturbation which triggers the rotation. These results are published in the journal Monthly Notices of the Royal Astronomical Society.

The enigma of the quasi-periodic oscillations

A team of researchers from CEA (Astrophysical Department and CEA-DAM) and the LUTH Laboratory (Paris Observatory) has just published a comprehensive study of an enigmatic phenomenon of quasi-periodic oscillations at the surface of strongly magnetic white dwarfs also called "Polars ". These dense stars are orbiting a companion and capture its material that falls freely toward the white dwarf poles. Strongly heated to millions of degrees, the hot gas or plasma then emits mainly in X-rays. Thanks to detailed numerical simulations of the plasma behavior, the researchers were able to reconstruct the existence of strong instabilities leading to rapid oscillations in the luminosity with timescales of only a few seconds. However, using the database of the XMM-Newton satellite, these oscillations were sought unsuccessfully by the team, in the X-ray emission of over 20 Polars. This contradiction leads today researchers to propose to study the phenomenon in the laboratory. Indeed, similar physical conditions can currently be replicated by large power lasers like the LMJ [1]. The control of plasma instabilities is a key element for nuclear fusion by magnetic (ITER experience) ou inertiel confinement (laser Mégajoule) and instabilities of white dwarfs could contribute to a better understanding of this general phenomenon. These results are the subject of two articles published in the journal Astronomy & Astrophysics, July 2015.

 

see the movie of the numerical simulation (short version)
Progress and involvement of the CEA into this chinese and french space mission

2014 has been a fruitful year for SVOM (Space-based multiband astronomical Variable Objects Monitor), a chinese and french space mission dedicated to the study of gamma-ray bursts. The decisions taken at the highest level, the governments in March and the respective space agencies in August, restart the project after a frozen period. As a direct result, two important meetings of the consortium (kick-off meeting) took place in September, one at CNES in Toulouse and the other at Shanghai. These meetings mainly based on technical aspects of the project are an important step towards the realization of the satellite payload of the mission which is scheduled to be launched in 2021. CEA-IRFU and its Astrophysics Department play a major role in this project in partnership with CNRS and under the overall responsibility of CNES.

For a more detailed account, see the French version.

Molecular clouds reveal a giant outburst of the supermassive black hole at the centre of the Galaxy

The central black hole of the Galaxy, today surprisingly quiet, has undergone, several hundred years ago, a violent phase of activity. This is the conclusion reached by an international team led by astrophysicists of the APC laboratory and including scientists of the Service d'Astrophysique of CEA-Irfu, by studying the high energy emission of molecular clouds located in the central regions of the Galaxy. The scientists have indeed discovered complex variations of this emission, with some of them showing propagation velocity greater than the speed of light. They reveal that a giant outburst, most probably generated by the black hole, took place about 400 years ago. The powerful flare is visible today after reflection by the molecular clouds that play the role of celestial mirrors. The recent history of the region retraced in this way shows that the black hole of the galactic centre is not so different from the supermassive black holes of the active galactic nuclei. This work, based on two long term observing programs of the XMM-Newton and Integral satellites, is the object of two complementary publications in  The Astrophysical Journal.

INTEGRAL discovers a factory of positrons in the Milky Way (10 January 2008)

Surprisingly, an asymmetry in the distribution of antimatter in the central regions of our Galaxy has just been discovered. By adding all scientific data acquired since five years by the spectrometer SPI aboard the INTEGRAL satellite, a European research group, including scientists from the Service d'Astrophysique at CEA-IRFU , has observed a gamma-ray photon emission of an energy of 511 keV, which is characteristic for the annihilation of electrons and their antimatter particles, the positrons. The researchers could determine the morphology of the 511 keV emission in the central regions of our Galactic disk, which reveals to be asymmetric and very similar to the distribution of a certain type of X-ray binary sources. For some time already these objects are thought to be efficient factories for positron production, and could explain the origin of these antimatter particles in the central regions of our Galactic disk. This work has been published in the scientific journal Nature on January 10th, 2008.

 

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