Gamma-ray burstsStrange GRBs and GRB-supernovae
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 2017 we discovered an additional component in the earliest ever obtained GRB-SN spectra only two days after explosion. We detected very fast (1/3 of the speed of light), Fe-rich material that we associated with a cocoon around the actual GRB jet transporting material from the very inside of the star. The fact that the GRB was at rather short distance (160 Mpc) and that the GRB-SN was one of the faintest observed possibly helped with the detection of these features. The findings were published in Nature (Izzo et al. 2019)
Press release on jet-cocoon signatures in a GRB-SN
Gravitational wavesElectromagnetic counterparts across the spectrum
The discovery of an electromagnetic counterpart and a short GRB to the gravitational wave signal of a binary neutron star merger (GW 170817) was THE discovery of 2017 and possibly the decade. It not only confirmed many theories about gravitational wave signals, it also confirmed the long-suggested connection between the merger of two compact objects and short GRBs. It also allowed us to get the first spectra of a kilonova, the explosion produced by the debris left over after the merger, and to study its early type host galaxy in unprecendeted detail. More than 100 papers have since been published on only this event.
With the LIGO O3 run, joined by Virgo, started in April 2019 to last about a year, we expect more of these events, albeit possibly at larger distance. The first months have shown that GW 170817 indeed has been a very lucky coincidence rather than the norm. HETH people are active members of the ENGRAVE and GRANDMA collaborations to discover and follow-up the counterparts of GWs using different techniques.
Press release on GW/GRB 170817A.
SupernovaeExtreme events and outliers
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.
Press release on SN 2015bh
Hosts GRBs hosts near and far, SN hosts and explosion sites
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.
We also use data in CO and HI to study the hosts of stellar explosions. These allow us to determine the gas available for star-formation, especially for massive stars. Many galaxies with no apparently peculiarities in ionized gas traced e.g. by Halpha, show complicated kinematics and enhanced neutral/molecular gas fractions. de Ugarte Postigo et al. studied the host of GRB 190114C, the first GRB with confirmed emission at very high energies with the MAGIC telescope with HST and ALMA and found the GRB to be at a peculiar site at the center of its host and a gas rich interacting companion.
Press release on GRB 190114C
GRBspec and GRBphot A public database for GRB afterglow spectra and broad-band photometry
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.
Link to GRBspec
An additional database called ''GRBphot'' will soon be available as well, the largest collection of photometric data of GRB afterglows worldwide. It will include any afterglow and selected host photometry data from X-ray to radio as well as plotting and analysis tools.
The project is supported by a 2016 BBVA Foundation Grant for Researchers and Cultural Creators (GRBspec, PI A. de Ugarte Postigo) and an AYA-JIN fellowship (GRBphot, PI D. A. Kann)
Instrumentation
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 has been presented at the "VI Science with the GTC" meeting in Valencia in Dec. 2018. Stay tuned!