SLSN 2017egm in a solar-metallicity host but in a young, metal poor population (Izzo et al. 2018)
Our main interest is the study of (massive) stellar explosions, their environments and hosts.
Gamma-ray bursts are some of the most luminous explosions in the Universe. They are divided in long and short GRBs possibly reflecting two different progenitor types (death of a massive star vs. coalescence of two compact objects). Despite two decades of afterglow observations many mysteries still remain. HETH has designated ToO programs at different telescopes to follow GRB afterglows (e.g. GTC, OSN, ALMA and PdB). HETH people are also member of the European X-shooter collaboration on GRBs.
At HETH we study GRBs across all wavelengths from X-ray to radio. We focus on peculiar events such as the famous "Christmas Burst", GRB 101225A. The afterglow of this peculiar GRB showed mostly thermal emission in contrast to the usual power-law behaviour and we interpreted it as a merger system where, in the final GRB, the jet interacted with a thick shell ejected some years before the GRB.
Along with their prompt emission powered by jets, GRBs also produce a special kind of supernova explosions, called "broad-lined type Ic". These stellar explosions contain neither hydrogen nor helium, and the ejecta expands at very high speeds, typically 10% of light speed. Recently, a link has also been established between GRBs and superluminous SNe for GRB 111209A/SN 2011kl (see also Kann et al. 2016). At HETH we have a dedicated observing program to follow-up these SNe with the GTC.
In August 2017, much earlier than ever expected, the first simultaneous detection of a gravitational wave source coming from a binary neutron star merger and a short GRB had been possible. This confirmed many models both on NS-NS mergers and of the progenitors of short GRBs. At HETH we were and are part of several large collaborations to study these events at all wavelengths. For the next LIGO run we are part of the ENGRAVE consortium at ESO and several other large efforts.
Supernovae come in many different flavours and most (except SNe Ia) are related to the death of a more or less massive star. At HETH we are predominantly interested in SNe IIn (narrow lines from interaction with circumstellar material), superluminous supernovae and broad-line SNe Ic. HETH has several ongoing observing programs at GTC, OSN and CAHA.
Once again, we like the odd and exceptional events such as the impostor/SN IIn SN 2015bh, a possible analogue of SN 2009ip. This possible SN showed a series of outbursts varying by about 2 mag over at least 21 years and at a position in the HR diagram similar to the events of Eta Carina, albeit at lower luminosities. In 2015 it experienced first a larger "precursor" and then the more luminous "main event" whose lightcurve resembled a normal SN IIn but with a total luminosity on the edge of a real core-collapse event. The spectra clearly showed the traces of previous larger ejections of material. The late time behaviour of this event and SN 2009ip let us speculate that the star might not have exploded but is on the way to become a Wolf-Rayet star after shedding its outer envelope.
Thanks to their high luminosity, GRBs can be used as lighthouses to study the ISM in their host galaxies up to very high redshifts. The ISM imprints absorption lines onto the smooth afterglow continuum. Medium to high resolution spectra are especially suited for this purpose: Study the kinematics of the ISM by identifying several components, observe line variability to infer distances (usually fine-structure lines, but also varying HI asbsorpion has been observed in Thöne et al. 2011), study the chemical abundances and trace the metallicity evolution and infer extinction properties in the line-of-sight. Within the European X-shooter collaboration, HETH members are working on various sample papers using more than 70 spectra collected by X-shooter since 2009.
Furthermore, at HETH we study host properties by observing them directly in emission. GRB hosts are thought to be a population of young, blue and star-forming galaxies, often subluminous, in particular at low redshift while SLSN hosts are probably even more extreme galaxies (see e.g. Thöne et al. 2015). HETH people are members of the SHOALS and SUSHIES (SLSN host galaxies) collaborations to study GRB and SLSN hosts.
Another main interest of HETH is the detailed study of nearby GRB and SN environment using IFU spectroscopy and other resolved techniques such as narrow-band tuneable filters (at OSIRIS/GTC). The hosts of GRB 060505 (Thöne et al. 2015) and GRB 100316D (Izzo et al. 2017) are two out of only three GRB hosts so far studied with 3D spectra and we are part of several collaborations to study a larger sample of hosts with resolved techniques. Izzo et al. 2018 recently published a resolved study on the SLSN Type I SN 2017egmin a seemingly solar metallicity host, where the SLSN originated in an underlying, metal-poor and young stellar population.
The progenitors of classical novae are white dwarfs in tight binary systems which accrete matter from a companion star and gas piles up on its surface. Once the pressure and temperature at the base of the layer reaches a critical value, thermonuclear reactions ignite the gas. Novae have been observed for over 100 years, but new instruments are revealing important details behind the emisson mechanisms as well as the geometry of the ejecta.
High-resolution spectrograph lead to the discovery of lithium during the early nova phase (Izzo et al. 2015) This has important consequences for the chemical enrichment of Li in the Galaxy: observations of young stellar populations show an over-abundance of Li in their spectra, whose origin is still unclear. The detection of Li and Be in V5668 Sgr (Molaro et al. 2016) which decays into lithium after 56 days, suggests that classical novae represent the main farms of lithium in the Galaxy. Izzo et al. 2018 have now also detected Be in a fast nova, adding this class to the sources of Li in the Galaxy. We furthermore use IFU data to study the asphericity and kinematics in nova shells, i.e. at very late phases. The match with archival data from ESO-VLT and the Hubble Space Telescope, as well as the use of incoming GAIA data, is funamental to study a reliable use of novae as local distance indicators and as possible progenitors of Supernovae Ia.
GRB-SNe have a luminosity-stretch relationship (Cano et al. 2014) that is analogous to the luminosity-decline relationship measured for SNe Ia. The latter has been succesfully used to demonstrate the existance of Dark Energy, which culminated in being awarded the Nobel Prize in Physics in 2011. While the field of GRB-SN-cosmology is still in its infancy, it has already been demonstrated that GRB-SN can also be used to constrain the Hubble constant (Cano, Jakobsson & Geirsson 2014) and the mass and energy density of the cosmos (Li, Hjorth & Wojtak 2014) . Additional studies are ongoing to reduce the amount of scatter in Hubble diagrams of GRB-SN and enhance their role as cosmological probes.
Using SNe Ia for cosmology is currently limited to redshifts around z~1.5-2, hence we have little information about the era when the first starts and galaxies formed and the initial large-scale structures begun to cluster. GRBs are a unique probe for this "dark" era since they have been observed out to redshifts of nearly 10 (the current record is GRB 090429B at z = 9.4). At HETH we study how to use GRBs as distance indicators up to these high redshifts. Recently a correlation has been proposed (Izzo et al. 2015), that has a tight data scatter and intrinsically links prompt and afterglow quantities. The study of large datasets of GRB, coupled with advanced analysis techniques, will allow us to measure accurately the evolution history at very large redshifts and obtain information about the nature of the Dark Energy.
GRBspec is a database that collects spectroscopy of gamma-ray burst, afterglows, their associated supernovae and their host galaxies. It includes GRB information (duration, energetics, redshifts, etc.), the spectroscopic data, such as 1D and 2D data with their associated error frames, and the associated measurements to the spectra (equivalent widths, column densities, or line fluxes). GRBspec is currently the largest database of its kind in the world and it keeps growing through the work of HETH and the contribution of other scientists from around the world.
The project is supported by a 2016 BBVA Foundation Grant for Researchers and Cultural Creators.
Many of the advances in research come hand in hand with technological developments. HETH has been leading a feasibility study and the conceptual design phase of OCTOCAM, an instrument concept developed at IAA since 2009, and participates in the science teams of HiPERCAM at the 10.4m GTC (La Palma, Spain), and SOXS at the 3.6m NTT (La Silla, Chile).
OCTOCAM will be the next facility instrument of the 8.1m Gemini South telescope, in Chile. It is an 8-channel imager and spectrograph, simultaneously imaging a field of view of 3’x3’ in g'r'i'z'YJH and K bands, or obtaining long slit spectroscopy with R=4000 between 3700 and 23500 Å. State-of-the-art detectors allow observations with high time resolution, opening a window in the wavelength range - spectral resolution - temporal resolution diagram not covered by any other instrument until now. Its main science goal is the study of transients and is specifically thought as LSST follow-up instrument. Until Dec. 2017, OCTOCAM was lead by the HETH group with Antonio de Ugarte Postigo as PI and Christina Thöne as PM Spain in collaboration with Southwest Research Institute, George Washington University and FRACTAL S.L.N.E. On Dec. 5, 2017, SwRI decided to terminate the subcontract with IAA "for convenience" to take full control of the development of the instrument after tedious discussions and psychological warfare. OCTOCAM at Gemini webpage IAA press release
HETH is currently proposing a new workhorse instrument for GTC, which has recently issued a call for a second generation instrument (link to the call) . The first concept will be presented at the "VI Science with the GTC" meeting in Valencia in Dec. 2018. Stay tuned!
HETH was founded in 2012 and is not only a young group but is also composed of young researchers. And we are probably the most international group at IAA.
HETH in September 2018 (with visitors O. Nentvich and R. Martone)
Recent publications and highlights. A full publication list can be found in this ADS repository