I. Felix Mirabel

Formation of a Black Hole in the Dark

We show that the black hole in the x-ray binary Cygnus X-1 was formed in situ and did not receive an energetic trigger from a nearby supernova. The progenitor of the black hole had an initial mass greater than 40solar masses, and during the collapse to form the ∼10–solar mass black hole of Cygnus X-1, the upper limit for the mass that could have been suddenly ejected is ∼1 solar mass, much less than the mass ejected in a supernova. The observations suggest that high-mass stellar black holes may form promptly, when massive stars disappear silently.

Fast Sinusoidal Oscillations in the Radio Flux of GRS 1915+105

We report the observation of events with fast (≤1 hr) time variability in Very Large Array observations of the Galactic superluminal source GRS 1915+105. The database consists of observations made at 67 epochs over 3 yr. We have detected fast variations on three occasions. Here we report the most remarkable of the events, observed in 1995 September 6. Over a period of approximately 2 hr, the 3.6 cm flux density of GRS 1915+105 showed several clear sinusoidal oscillations with period of 30.2 ± 0.4 minutes, going from ~40 to ~65 mJy. We discuss possible scenarios for the production of this fast sinusoidal variation in the radio flux density and propose that the variability could be the result of a hot spot orbiting the collapsed companion of the binary system.

The galaxy density environment of gamma-ray burst host galaxies

We analyze cross-correlation functions between Gamma-Ray Burst (GRB) hosts and surrounding galaxies. We have used data obtained with the Very Large Telescope at Cerro Paranal (Chile), as well as public Hubble Space Telescope data. Our results indicate that Gamma-Ray Burst host galaxies do not reside in high galaxy density environments. Moreover, the host-galaxy cross-correlations show a relatively low amplitude. Our results are in agreement with the cross-correlation function between star-forming galaxies and surrounding objects in the HDF-N.

Large scale studies of the surroundings of GRS 1915+105

Abstract We have carried out radio studies of the surroundings of the superluminal microquasar GRS 1915+105. Our main goal was to understand the possible relation of GRS 1915+105 with two infrared/radio sources that appear symmetrically located with respect to GRS 1915+105 and aligned with the position angle of the relativistic ejecta. We have also studied a nearby supernova remnant to test if the event that created the remnant could have been the progenitor of this hard X-ray binary.

Soft Gamma-ray Repeaters in clusters of massive stars

Infrared observations of the environment of the two Soft Gamma-ray Repeaters (SGRs) with the best known locations on the sky show that they are associated with clusters of massive stars. Observations with ISO revealed that SGR 1806−20 is in a cluster of giant massive stars, still enshrouded in a dense cloud of gas and dust [1]. SGR 1900+14 is at the edge of a similar cluster that was recently found hidden in the glare of a pair of M5 supergiant stars [2]. Since none of the stars of these clusters has shown in the last years significant flux variations in the infrared, these two SGRs do not form bound binary systems with massive stars. SGR 1806−20 is at only ∼0.4 pc, and SGR 1900+14 at ∼0.8 pc from the centers of their parental star clusters. If these SGRs were born with typical neutron star runaway velocities of ∼300 km s−1, they are not older than a few 103 years. We propose that SGR 1806−20 and SGR 1900+14 are ideal laboratories to study the evolution of supernovae explosions inside interstellar bubbles...

Microquasars as heating sources of the intergalactic medium during reionization of the Universe

The effect of the primeval sources of radiation and particles on the thermodynamical state of the intergalactic medium during the epoch of reionization is still unclear. In this work, we explore the contribution of electrons accelerated in the jets of high-redshift microquasars to heating and ionizing the intergalactic medium. We develop Monte Carlo simulations of the propagation and energy deposition of these electrons as they travel away from their sources. We find that microquasars contribute significantly to heating the intergalactic medium and are effective ionizers only near the galaxies. Their effect on heating is of the same order of magnitude as that of cosmic rays from supernovae.

Stellar black holes: Cosmic history and feedback at the dawn of the universe

Significant historic cosmic evolution for the formation rate of stellar black holes is inferred from current theoretical models of the evolution of massive stars, the multiple observations of compact stellar remnants in the near and distant universe, and the cosmic chemical evolution. The mean mass of stellar black holes, the fraction of black holes/neutron stars, and the fraction of black hole high mass X-ray binaries (BH-HMXBs)/solitary black holes increase with redshift. The energetic feedback from large populations of BH-HMXBs form in the first generations of star burst galaxies has been overlooked in most cosmological models of the reionization epoch of the universe. The powerful radiation, jets, and winds from BH-HMXBs heat the intergalactic medium over large volumes of space and keep it ionized until AGN take over. It is concluded that stellar black holes constrained the properties of the faintest galaxies at high redshifts. I present here the theoretical and observational grounds for the historic cosmic evolution of stellar black holes. Detailed calculations on their cosmic impact are presented elsewhere (Mirabel, Dijkstra, Laurent, Loeb, & Pritchard 2011).

Microquasars in the Galaxy

Microquasars are black-hole X-ray binaries with relativistic jets that mimic phenomena seen in quasars. We will present recent results on GRS 1915+105 as well as on other microquasars that show the close connection between instabilities in the accretion disk (seen in X-rays) and the ejection of relativistic plasma clouds (seen in radio). The possibility of a connection between these objects and gamma-ray sources is suggested by the possible association of a microquasar with an EGRET source.

VLA observations of the high-velocity bipolar OH absorption in L1551

The VLA was used to map the high-velocity 1667 MHz OH absorption in L1551. The OH shows the same bipolar geometry seen in CO. The OH absorption is detected along the NW edge of the SW lobe and along the SE edge of the NE lobe, indicating that the high-velocity OH is located in the walls of the bipolar cavities created by the wind of L1551 IRS 5. The OH is detected only at the end of the bipolar lobes. It is suggested that this peculiar spatial distribution is due to an OH enhancement in the outer parts of the outflow as shock-produced H2O is photodissociated by the interstellar UV radiation field. 28 references.

Infrared observations and energetic outburst of GRS 1915+105

Many near-infrared wavelengths observations, carried out since 1993 on the galactic superluminal source of relativistic ejections GRS 1915+105, have yielded the following important results: 1) The infrared counterpart of the microquasar GRS 1915+105 exhibits various variations in the 1.2–2.2 μm band: the strongest are of ∼1 magnitude in a few hours and of ∼2 magnitudes over longer intervals of time [2]. 2) The strikingly similar infrared properties of GRS 1915+105 and of SS 433 suggest that GRS 1915+105 consists of a collapsed object (neutron star or black hole) with a thick accretion disk in a high mass and luminous binary system [2]. 3) During an intense and long-term X-ray outburst of GRS 1915+105 in 1995 August, we observed the time-delayed reverberation of the radio flare and ejection event in the infrared wavelengths, the observed spectrum of the enhanced infrared emission suggesting the appearance of a warm dust component [6]. 4) A near-infrared jet, ejected by GRS 1915+105, discovered by Sams et a...