L. Kaper

A very energetic supernova associated with the |[gamma]|-ray burst of 29 March 2003

Over the past five years evidence has mounted that long-duration (>2 s) γ-ray bursts (GRBs)—the most luminous of all astronomical explosions—signal the collapse of massive stars in our Universe. This evidence was originally based on the probable association of one unusual GRB with a supernova, but now includes the association of GRBs with regions of massive star formation in distant galaxies, the appearance of supernova-like ‘bumps’ in the optical afterglow light curves of several bursts and lines of freshly synthesized elements in the spectra of a few X-ray afterglows. These observations support, but do not yet conclusively demonstrate, the idea that long-duration GRBs are associated with the deaths of massive stars, presumably arising from core collapse. Here we report evidence that a very energetic supernova (a hypernova) was temporally and spatially coincident with a GRB at redshift z = 0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs, thereby favouring the ‘collapsar’ model.

Discovery of the nearby long, soft GRB 100316D with an associated supernova

We report the Swift discovery of the nearby long, soft gamma-ray burst GRB 100316D, and the subsequent unveiling of its low-redshift host galaxy and associated supernova. We derive the redshift of the event to be z = 0.0591 +/- 0.0001 and provide accurate astrometry for the gamma-ray burst (GRB) supernova (SN). We study the extremely unusual prompt emission with time-resolved gamma-ray to X-ray spectroscopy and find that the spectrum is best modelled with a thermal component in addition to a synchrotron emission component with a low peak energy. The X-ray light curve has a remarkably shallow decay out to at least 800 s. The host is a bright, blue galaxy with a highly disturbed morphology and we use Gemini-South, Very Large Telescope and Hubble Space Telescope observations to measure some of the basic host galaxy properties. We compare and contrast the X-ray emission and host galaxy of GRB 100316D to a subsample of GRB-SNe. GRB 100316D is unlike the majority of GRB-SNe in its X-ray evolution, but resembles rather GRB 060218, and we find that these two events have remarkably similar high energy prompt emission properties. Comparison of the host galaxies of GRB-SNe demonstrates, however, that there is a great diversity in the environments in which GRB-SNe can be found. GRB 100316D is an important addition to the currently sparse sample of spectroscopically confirmed GRB-SNe, from which a better understanding of long GRB progenitors and the GRB-SN connection can be gleaned.

Physical parameters of the high-mass X-ray binary 4U1700-37

We present the results of a detailed non-LTE analysis of the ultraviolet and optical spectrum of the O6.5 Iaf + star HD 153919 - the mass donor in the high-mass X-ray binary 4U1700-37. We find that the star has a luminosity log(L=L)= 5:82 0:07, Te = 35 000 1000 K, radius R = 21:9 +1:3 0:5 R, mass-loss rate ˙ M = 9:5 10 6 M yr 1 , and a significant overabundance of nitrogen (and possibly carbon) relative to solar values. Given the eclipsing nature of the system these results allow us to determine the most likely masses of both components of the binary via Monte Carlo simulations. These suggest a mass for HD 153919 of M= 58 11 M - implying the initial mass of the companion was rather high (>60 M). The most likely mass for the compact companion is found to be Mx = 2:44 0:27 M, with only 3.5 per cent of the trials resulting in a mass less than 2.0 M and none less than 1.65 M. Such a value is significantly in excess of the upper observational limit to the masses of neutron stars of 1.45 M found by Thorsett & Chakrabarthy (1999), although a mass of 1.86 M has recently been reported for the Vela X-1 pulsar (Barziv et al. 2001). Our observational data is inconsistent with the canonical neutron star mass and the lowest black hole mass observed (>4.4 M; Nova Vel). Significantly changing observational parameters can force the compact object mass into either of these regimes but, given the strong proportionality between M and Mx, the O-star mass changes by factors of greater than 2, well beyond the limits determined from its evolutionary state and surface gravity. The low mass of the compact object implies that it is dicult to form high mass black holes through both the Case A & B mass transfer channels and, if the compact object is a neutron star, would significantly constrain the high density nuclear equation of state.

THE STELLAR VELOCITY DISPERSION OF A COMPACT MASSIVE GALAXY AT z = 1.80 USING X-SHOOTER: CONFIRMATION OF THE EVOLUTION IN THE MASS-SIZE AND MASS-DISPERSION RELATIONS* , **

Recent photometric studies have shown that early-type galaxies at fixed stellar mass were smaller and denser at earlier times. In this Letter, we assess that finding by deriving the dynamical mass of such a compact quiescent galaxy at z = 1.8. We have obtained a high-quality spectrum with full UV-NIR wavelength coverage of galaxy NMBS-C7447 using X-Shooter on the Very Large Telescope. We determined a velocity dispersion of 294 ± 51 km s-1. Given this velocity dispersion and the effective radius of 1.64 ± 0.15 kpc (as determined from Hubble Space Telescope Wide Field Camera 3 F160W observations) we derive a dynamical mass of (1.7 ± 0.5) × 1011 M ☉. Comparison of the full spectrum with stellar population synthesis models indicates that NMBS-C774 has a relatively young stellar population (0.40 Gyr) with little or no star formation and a stellar mass of M ~ 1.5 × 1011 M ☉. The dynamical and photometric stellar masses are in good agreement. Thus, our study supports the conclusion that the mass densities of quiescent galaxies were indeed higher at earlier times, and this earlier result is not caused by systematic measurement errors. By combining available spectroscopic measurements at different redshifts, we find that the velocity dispersion at fixed dynamical mass was a factor of ~1.8 higher at z = 1.8 compared with z = 0. Finally, we show that the apparent discrepancies between the few available velocity dispersion measurements at z > 1.5 are consistent with the intrinsic scatter of the mass-size relation. Footnote* Based on X-Shooter-VLT observations collected at the European Southern Observatory, Paranal, Chile. Footnote** Based on observations with the NASA/ESA Hubble Space Telescope (HST), obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

Galaxy counterparts of metal-rich damped Lyα absorbers – I. The case of the z= 2.35 DLA towards Q 2222−0946

We have initiated a survey using the newly commissioned X-shooter spectrograph to target candidate relatively metal-rich damped Lyα absorbers (DLAs). Our rationale is that highmetallicity DLAs due to the luminosity–metallicity relation likely will have the most luminous galaxy counterparts. In addition, the spectral coverage of X-shooter allows us to search for not only Lyα emission, but also rest-frame optical emission lines. We have chosen DLAs where the strongest rest-frame optical lines ([O II], [O III], Hβ and Hα) fall in the nearinfrared atmospheric transmission bands. In this first paper resulting from the survey, we report on the discovery of the galaxy counterpart of the zabs = 2.354 DLA towards the z = 2.926 quasar Q 2222−0946. This DLA is amongst the most metal-rich z > 2 DLAs studied so far at comparable redshifts and there is evidence for substantial depletion of refractory elements on to dust grains. We measure metallicities from Zn II ,S iII ,N iII ,M nII and Fe II of −0.46 ± 0.07, −0.51 ± 0.06, −0.85 ± 0.06, −1.23 ± 0.06 and −0.99 ± 0.06, respectively. The galaxy is detected in the Lyα ,[ OIII] λλ4959, 5007 and Hα emission lines at an impact parameter of about 0.8 arcsec (6 kpc at zabs = 2.354). Based on the Hα line, we infer a

GRB hosts through cosmic time. VLT/X-Shooter emission-line spectroscopy of 96 γ-ray-burst-selected galaxies at 0.1 <z < 3.6

We present data and initial results from VLT/X-Shooter emission-line spectroscopy of 96 galaxies selected by long γ-ray bursts (GRBs) at 0.1 2 by ~0.4 dex. These properties of GRB hosts and their evolution with redshift can be understood in a cosmological context of star-forming galaxies and a picture in which the hosts’ properties at low redshift are influenced by the tendency of GRBs to avoid the most metal-rich environments.

Diffuse interstellar bands in NGC 1448

We present spectroscopic VLT/UVES observations of two emerging supernovae, the Type Ia SN 2001el and the Type II SN 2003hn, in the spiral galaxy NGC 1448. Our high resolution and high signal-to-noise spectra display atomic lines of Ca  ,N a ,T i and K  in the host galaxy. In the line of sight towards SN 2001el, we also detect over a dozen diffuse interstel- lar bands (DIBs) within NGC 1448. These DIBs have strengths comparable to low reddening galactic lines of sight, albeit with some variations. In particular, a good match is found with the line of sight towards the σ type diffuse cloud (HD 144217). The DIBs towards SN 2003hn are significantly weaker, and this line of sight has also lower sodium column density. The DIB central velocities show that the DIBs towards SN 2001el are closely related to the strongest interstellar Ca  and Na  components, indicating that the DIBs are preferentially produced in the same cloud. The ratio of the λ 5797 and λ 5780 DIB strengths (r ∼ 0.14) suggests a rather strong UV field in the DIB environment towards SN 2001el. We also note that the extinction estimates obtained from the sodium lines using multiple line fitting agree with reddening estimates based on the colors of the Type Ia SN 2001el.

The MiMeS survey of magnetism in massive stars: introduction and overview

The Magnetism in Massive Stars (MiMeS) survey represents a highprecision systematic search for magnetic fields in hot, massive OB stars. To date, MiMeS Large Programs (ESPaDOnS@CFHT, Narval@TBL, HARPSpol@ESO3.6) and associated PI programs (FORS@VLT) have yielded nearly 1200 circular spectropolarimetric observations of over 350 OB stars. Within this sample, 20 stars are detected as magnetic. Follow-up observations of new detections reveals (i) a large diversity of magnetic properties, (ii) ubiquitous evidence for magnetic wind confinement in optical spectra of all magnetic O stars, and (iii) the presence of strong, organized magnetic fields in all known Galactic Of?p stars, and iv) a complete absence of magnetic fields in classical Be stars.

The Highly Energetic Expansion of SN 2010bh Associated with GRB 100316D

Wepresentthespectroscopicandphotometricevolutionofthenearby(z = 0.059)spectroscopicallyconfirmedType Ic supernova, SN 2010bh, associated with the soft, long-duration gamma-ray burst (X-ray flash) GRB 100316D. Intensive follow-up observations of SN 2010bh were performed at the ESO Very Large Telescope (VLT) using the X-shooter and FORS2 instruments. Thanks to the detailed temporal coverage and the extended wavelength range (3000‐24800 A), we obtained an unprecedentedly rich spectral sequence among the hypernovae, making SN 2010bh one of the best studied representatives of this SN class. We find that SN 2010bh has a more rapid rise to maximum brightness (8.0 ± 1.0 rest-frame days) and a fainter absolute peak luminosity (Lbol ≈ 3 × 10 42 ergs −1 ) than previously observed SN events associated with GRBs. Our estimate of the ejected 56 Ni mass is 0.12±0.02 M� . From the broad spectral features, we measure expansion velocities up to 47,000 km s −1 , higher than those of SNe 1998bw (GRB 980425) and 2006aj (GRB 060218). Helium absorption lines Hei λ5876 and Hei 1.083 μm, blueshifted by ∼20,000‐30,000 km s −1 and ∼28,000‐38,000 km s −1 , respectively, may be present in the optical spectra. However, the lack of coverage of the Hei 2.058 μm line prevents us from confirming such identifications. The nebular spectrum, taken at ∼186 days after the explosion, shows a broad but faint [Oi] emission at 6340 A. The light curve shape and photospheric expansion velocities of SN 2010bh suggest that we witnessed a highly energetic

HOW SPECIAL ARE DARK GAMMA-RAY BURSTS: A DIAGNOSTIC TOOL

We present here a comprehensive study of the optical/near-infrared (IR) upper limits for gamma-ray bursts that have an X-ray afterglow. We have extrapolated the X-ray afterglows to optical wavelengths based on the physics of the fireball blast wave model and compared these results with optical upper limits for a large sample of bursts. We find a small set of only three bursts out of a sample of 20 for which the upper limits are not compatible with their X-ray afterglow properties within the context of any blast wave model. This sparse sample does not allow us to conclusively determine the cause of this optical/near-IR deficit. Extinction in the host galaxy is a likely cause, but high redshifts and different afterglow mechanisms might also explain the deficit in some cases. We note that the three bursts appear to have higher than average gamma-ray peak fluxes. In a magnitude versus time diagram the bursts are separated from the majority of bursts with a detected optical/near-IR afterglow. However, two gamma-ray bursts with an optical afterglow (one of which is highly reddened) also fall in this region with dark bursts, making it likely that dark bursts are at the faint end of the set of optically detected bursts, and therefore the dark bursts likely form a continuum with the bursts with a detected optical afterglow. Our work provides a useful diagnostic tool for follow-up observations for potentially dark bursts; applied to the events detected with the Swift satellite, it will significantly increase our sample of truly dark bursts and shed light upon their nature.