Pulsars are well studied all over the electromagnetic spectrum, and the Crab pulsar may be the most studied object in the sky. Nevertheless, a high-quality optical to near-infrared spectrum of the ...Crab or any other pulsar has not been published to date. Obtaining a properly flux-calibrated spectrum enables us to measure the spectral index of the pulsar emission, without many of the caveats from previous studies. This was the main aim of this project, but we could also detect absorption and emission features from the pulsar and nebula over an unprecedentedly wide wavelength range. A spectrum was obtained with the X-shooter spectrograph on the Very Large Telescope. Particular care was given to the flux-calibration of these data. A high signal-to-noise spectrum of the Crab pulsar was obtained from 300 to 2400nm. The spectral index fitted to this spectrum is flat with alpha_nu=0.16 +- 0.07. For the emission lines we measure a maximum velocity of 1600 km/s, whereas the absorption lines from the material between us and the pulsar is unresolved at the 50 km/s resolution. A number of Diffuse Interstellar Bands and a few near-IR emission lines that have previously not been reported from the Crab are highlighted.
Short Gamma-Ray Bursts (SGRBs) are produced by the coalescence of compact binary systems which are remnants of massive stars. GRB 160410A is classified as a short-duration GRB with extended emission ...and is currently the farthest SGRB with a redshift determined from an afterglow spectrum and also one of the brightest SGRBs to date. The fast reaction to the Neil Gehrels Swift Observatory alert allowed us to obtain a spectrum of the afterglow using the X-shooter spectrograph at the Very Large Telescope (VLT). The spectrum shows several absorption features at a redshift of z=1.7177, in addition, we detect two intervening systems at z=1.581 and z=1.444. The spectrum shows ly-alpha in absorption with a column density of log N(HI)=21.2+/-0.2 cm\(^{-2}\) which, together with FeII, CII, SiII, AlII and OI, allow us to perform the first study of chemical abundances in a SGRB host galaxy. We determine a metallicity of X/H=-2.3+/-0.2 for FeII and -2.5+/-0.2 for SiII and no dust depletion. We also find no evidence for extinction in the afterglow spectral energy distribution (SED) modeling. The environment has a low degree of ionisation and the CIV and SiIV lines are completely absent. We do not detect an underlying host galaxy down to deep limits. Additionally, we compare GRB 160410A to GRB 201221D, another high-z short GRB that shows absorption lines at z=1.045 and an underlying massive host galaxy.
We have acquired Hubble Space Telescope (HST) and Very Large Telescope near-infrared spectra and images of supernova (SN) Refsdal after its discovery as an Einstein cross in fall 2014. The HST light ...curve of SN Refsdal has a shape consistent with the distinctive, slowly rising light curves of SN. 1987A-like SNe, and we find strong evidence for a broad H alpha P-Cygni profile and Na I D absorption in the HST grism spectrum at the redshift (z = 1.49) of the spiral host galaxy. SNe. IIn, largely powered by circumstellar interaction, could provide a good match to the light curve of SN Refsdal, but the spectrum of a SN IIn would not show broad and strong H alpha and Na I D absorption. From the grism spectrum, we measure an H alpha expansion velocity consistent with those of SN. 1987A-like SNe at a similar phase. The luminosity, evolution, and Gaussian profile of the H alpha emission of the WFC3 and X-shooter spectra, separated by similar to 2.5 months in the rest frame, provide additional evidence that supports the SN. 1987A-like classification. In comparison with other examples of SN. 1987A-like SNe, photometry of SN Refsdal favors bluer B - V and V - R colors and one of the largest luminosities for the assumed range of potential magnifications. The evolution of the light curve at late times will provide additional evidence about the potential existence of any substantial circumstellar material. Using MOSFIRE and X-shooter spectra, we estimate a subsolar host-galaxy metallicity (8.3 +/- 0.1 dex and <8.4 dex, respectively) near the explosion site.
Previous studies have shown that the incidence rate of intervening strong Mg II absorbers towards gamma-ray bursts (GRBs) were a factor of 2-4 higher than towards quasars. Exploring the similar sized ...and uniformly selected legacy data sets XQ-100 and XSGRB, each consisting of 100 quasar and 81 GRB afterglow spectra obtained with a single instrument (VLT/X-shooter), we demonstrate that there is no disagreement in the number density of strong Mg II absorbers with rest-frame equivalent widths W-r(lambda 2796) > 1 angstrom towards GRBs and quasars in the redshift range 0.1 less than or similar to z less than or similar to 5. With large and similar sample sizes, and path length coverages of Delta z = 57.8 and 254 : 4 for GRBs and quasars, respectively, the incidences of intervening absorbers are consistent within 1 sigma uncertainty levels at all redshifts. For absorbers at z < 2.3, the incidence towards GRBs is a factor of 1.5 +/- 0.4 higher than the expected number of strong Mg II absorbers in Sloan Digital Sky Survey (SDSS) quasar spectra, while for quasar absorbers observed with X-shooter we find an excess factor of 1.4 +/- 0.2 relative to SDSS quasars. Conversely, the incidence rates agree at all redshifts with reported high-spectral-resolution quasar data, and no excess is found. The only remaining discrepancy in incidences is between SDSS Mg II catalogues and high-spectral-resolution studies. The rest-frame equivalent-width distribution also agrees to within 1 sigma uncertainty levels between the GRB and quasar samples. Intervening strong Mg II absorbers towards GRBs are therefore neither unusually frequent, nor unusually strong.
Multi-messenger astronomy received a great boost following the discovery of kilonova AT2017gfo, the optical counterpart of the gravitational wave source GW170817 associated with the short gamma-ray ...burst GRB 170817A. AT2017gfo was the first kilonova that could be extensively monitored in time both photometrically and spectroscopically. Previously, only few candidates have been observed against the glare of short GRB afterglows. In this work, we aim to search the fingerprints of AT2017gfo-like kilonova emissions in the optical/NIR light curves of 39 short GRBs with known redshift. For the first time, our results allow us to study separately the range of luminosity of the blue and red components of AT2017gfo-like kilonovae in short GRBs. In particular, the red component is similar in luminosity to AT2017gfo, while the blue kilonova can be more than 10 times brighter. Finally, we find further evidence to support all the claimed kilonova detections and we exclude an AT2017gfo-like kilonova in GRBs 050509B and 061201.
A&A 629, A131 (2019) We report the detections of molecular hydrogen (H$_2$), vibrationally-excited
H$_2$ (H$^*_2$), and neutral atomic carbon (CI), in two new afterglow spectra
of GRBs\,181020A ...($z=2.938$) and 190114A ($z=3.376$), observed with X-shooter
at the Very Large Telescope (VLT). Both host-galaxy absorption systems are
characterized by strong damped Lyman-$\alpha$ absorbers (DLAs) and substantial
amounts of molecular hydrogen with $\log N$(HI, H$_2$) = $22.20\pm
0.05,~20.40\pm 0.04$ (GRB\,181020A) and $\log N$(HI, H$_2$) = $22.15\pm
0.05,~19.44\pm 0.04$ (GRB\,190114A). The DLA metallicites, depletion levels and
dust extinctions are Zn/H = $-1.57\pm 0.06$, Zn/Fe = $0.67\pm 0.03$, and
$A_V = 0.27\pm 0.02$\,mag (GRB\,181020A) and Zn/H = $-1.23\pm 0.07$, Zn/Fe
= $1.06\pm 0.08$, and $A_V = 0.36\pm 0.02$\,mag (GRB\,190114A). We then examine
the molecular gas content of all known H$_2$-bearing GRB-DLAs and explore the
physical conditions and characteristics of these systems. We confirm that H$_2$
is detected in all CI- and H$^*_2$-bearing GRB absorption systems, but that
these rarer features are not necessarily detected in all GRB H$_2$ absorbers.
We find that a large molecular fraction of $f_{\rm H_2} \gtrsim 10^{-3}$ is
required for CI to be detected. The defining characteristic for H$^*_2$ to be
present is less clear, though a large H$_2$ column density is an essential
factor. We then derive the H$_2$ excitation temperatures of the molecular gas
and find that they are relatively low with $T_{\rm ex} \approx 100 - 300$\,K,
however, there could be evidence of warmer components populating the high-$J$
H$_2$ levels in GRBs\,181020A and 190114A. Finally, we demonstrate that the
otherwise successful X-shooter GRB afterglow campaign is hampered by a
significant dust bias excluding the most dust-obscured H$_2$ absorbers from
identification Abridged.
Here we built up a sample of 22 GRBs at redshifts \(z > 2\) observed with X-shooter to determine the abundances of hydrogen, metals, dust, and molecular species. This allows us to study the ...metallicity and dust depletion effects in the neutral ISM at high redshift and to answer the question whether (and why) there might be a lack of H\(_2\) in GRB-DLAs. We fit absorption lines and measure the column densities of different metal species as well as atomic and molecular hydrogen. The derived relative abundances are used to fit dust depletion sequences and determine the dust-to-metals ratio and the host-galaxy intrinsic visual extinction. There is no lack of H\(_2\)-bearing GRB-DLAs. We detect absorption lines from H\(_2\) in 6 out of 22 GRB afterglow spectra, with molecular fractions ranging between \(f\simeq 5\cdot10^{-5}\) and \(f\simeq 0.04\), and claim tentative detections in three other cases. The GRB-DLAs in the present sample have on average low metallicities (\(\mathrm{X/H}\approx -1.3\)), comparable to the rare population of QSO-ESDLAs (log N(HI) \(> 21.5\)). H\(_2\)-bearing GRB-DLAs are found to be associated with significant dust extinction, \(A_V > 0.1\) mag, and have dust-to-metals ratios DTM\( > 0.4\). All of these systems exhibit column densities of log N(HI) \(> 21.7\). The overall fraction of H\(_2\) detections is \(\ge 27\)% (41% including tentative detections), which is three times larger than in the general population of QSO-DLAs. For \(2<z<4\), and for log N(HI) \(> 21.7\), the H\(_2\) detection fraction is 60-80% in GRB-DLAs as well as in extremely strong QSO-DLAs. This is likely a consequence of the fact that both GRB- and QSO-DLAs with high N(HI) probe sight-lines with small impact parameters that indicate that the absorbing gas is associated with the inner regions of the absorbing galaxy, where the gas pressure is higher and the conversion of HI to H\(_2\) takes place.
GRB 190114C is the first GRB for which the detection of very-high energy emission up to the TeV range has been reported. It is still unclear whether environmental properties might have contributed to ...the production of these very high-energy photons, or if it is solely related to the released GRB emission. The relatively low redshift of the GRB (z=0.425) allows us to study the host galaxy of this event in detail, and to potentially identify idiosyncrasies that could point to progenitor characteristics or environmental properties responsible for such a unique event. We use ultraviolet, optical, infrared and submillimetre imaging and spectroscopy obtained with HST, VLT and ALMA to obtain an extensive dataset on which the analysis of the host galaxy is based. The host system is composed of a close pair of interacting galaxies (Delta v = 50 km s^-1), both of which are well-detected by ALMA in CO(3-2). The GRB occurred within the nuclear region (~170 pc from the centre) of the less massive but more star-forming galaxy of the pair. The host is more massive (log(M/M_odot)=9.3) than average GRB hosts at that redshift and the location of the GRB is rather unique. The enhanced star-formation rate was probably triggered by tidal interactions between the two galaxies. Our ALMA observations indicate that both host galaxy and companion have a high molecular gas fraction, as has been observed before in interacting galaxy pairs. The location of the GRB within the core of an interacting galaxy with an extinguished line-of-sight is indicative of a denser environment than typically observed for GRBs and could have been crucial for the generation of the very-high-energy photons that were observed.
Nature 575 (2019) 459-463 Long-duration gamma-ray bursts (GRBs) originate from ultra-relativistic jets
launched from the collapsing cores of dying massive stars. They are
characterised by an initial ...phase of bright and highly variable radiation in
the keV-MeV band that is likely produced within the jet and lasts from
milliseconds to minutes, known as the prompt emission. Subsequently, the
interaction of the jet with the external medium generates external shock waves,
responsible for the afterglow emission, which lasts from days to months, and
occurs over a broad energy range, from the radio to the GeV bands. The
afterglow emission is generally well explained as synchrotron radiation by
electrons accelerated at the external shock. Recently, an intense, long-lasting
emission between 0.2 and 1 TeV was observed from the GRB 190114C. Here we
present the results of our multi-frequency observational campaign of
GRB~190114C, and study the evolution in time of the GRB emission across 17
orders of magnitude in energy, from $5\times10^{-6}$ up to $10^{12}$\,eV. We
find that the broadband spectral energy distribution is double-peaked, with the
TeV emission constituting a distinct spectral component that has power
comparable to the synchrotron component. This component is associated with the
afterglow, and is satisfactorily explained by inverse Compton upscattering of
synchrotron photons by high-energy electrons. We find that the conditions
required to account for the observed TeV component are not atypical, supporting
the possibility that inverse Compton emission is commonly produced in GRBs.
With actual test data collected from the 230kV pipe-type cable described in reference (1), computer models were developed which allow the determination of the thermal characteristics and the ampacity ...of direct buried pipe-type cable splices. Computer techniques developed in (1), the accuracy of which were verified by field data collected from operating pipe cables, were again used in developing the computer models for this project.
