This is brief summary of the joint discussion about GRB afterglows held in Marbelladuring the Gamma-Ray Burst Symposium 2012. It is based on hints proposed by many authorsin their talks and offers a (personally biased) view of some of the open issues in thefield. No attempts have actually been applied to really cover all the discussed subjects,and consequently only a few topics are chosen as representatives of the activities goingon in the field, admittedly with some emphasis for observational results.

Due to their extreme luminosities, gamma-ray bursts (GRBs) can be detected in hostileregions of galaxies, nearby and at very high redshift, making them important cosmologicalprobes. The investigation of galaxies hosting long-duration GRBs (whose progenitor is amassive star) demonstrated their connection to star formation. Still, the link to thetotal galaxy population is controversial, mainly because of the small-number statistics:~1, 100 are the GRBs detected so far, ~280 those with measured redshift, and~70 the hosts studied in detail. These are typically low-redshift(z < 1.5), low luminosity, metal poor, and star-forming galaxies. Onthe other hand, at 1.5 < z < 4, massive, metal rich and dusty,interacting galaxies are not uncommon. The most distant population(z > 4) is poorly explored, but the deep limits reached point towardsvery small and star-forming objects, similar to the low-z population.This “back to the future” behavior is a natural consequence of the connection of long GRBsto star formation in young regions of the universe.

We present a preliminary data release from our multi-year campaign at Keck Observatory tostudy the host galaxies of a large sample of Swift-era gamma-ray bursts via multi-colorground-based optical imaging and spectroscopy. With over 160 targets observed to date (andalmost 100 host detections, most of which have not previously been reported in theliterature) our effort represents the broadest GRB host survey to date. While targetingwas heterogeneous, our observations span the known diversity of GRBs including shortbursts, long bursts, spectrally soft GRBs (XRFs), ultra-energetic GRBs, X-ray faint GRBs,dark GRBs, SN-GRBs, and other sub-classes. We also present a preview of our database(currently available online via a convenient web interface) including a catalog ofmulti-color photometry, redshifts and line ID’s. Final photometry and reduced imaging andspectra will be available in the near future.

We present the redshift results from a Very Large Telescope (VLT) program aimed atoptimizing the legacy value of the Swift mission: to characterize ahomogeneous, X-ray selected, sample of 69 GRB host galaxies. Fifteen new redshifts havebeen secured, resulting in a 77% (53/69) redshift completion, making the survey the mostcomprehensive in terms of redshift completeness of any sample to the full Swiftdepth, available to date. We present the cumulative redshift distribution andderive a conservative, yet small, associated uncertainty. We constrain the fraction ofSwift GRBs at high redshift to a maximum of 14% (5%) forz > 6 (z > 7). The mean redshift of the hostsample is assessed to be . Using this more complete sample, we confirm previous findingsthat the GRB rate at high redshift () appears to be in excess of predictions based onassumptions that it should follow conventional determinations of the star formationhistory of the universe, combined with an estimate of its likely metallicity dependence.This suggests that either star formation at high redshifts has been significantlyunderestimated, for example due to a dominant contribution from faint, undetectedgalaxies, or that GRB production is enhanced in the conditions of early star formation,beyond those usually ascribed to lower metallicity.

We present the results of SAO RAS 6-m BTA spectral observations of GRBs and XRFs with thesigns of SNe: GRB/XRF 060218 (SN 2006aj) and XRF 080109 (SN 2008D). The properties ofthese events are similar to those of usual core-collapse SNe without GRBs. Some spectralfeatures in the cases of SN 2006aj and SN 2008D may be interpreted as hydrogen and heliumtraces. This supports an idea of presence of a relic envelope around the progenitor starand the shock break-out effects observed in X-rays, UV and optics.

The Italian-French X-shooter GRB host program started at the end of 2009 and allowed usto collect the spectra of about 30 host galaxies in the 300–2400 nm range from a redshiftof about z = 0.1 to z = 2.7. We are using these spectra to retrieve information on thehost metallicities, star formation rates and extinctions. An accurate slit positioningallowed us to discover in some cases close-by galaxies at the same redshift than the GRBhost. Thanks to the comparison of the afterglow and host spectra, it is possible to assessfor possible interactions of these systems. We also looked for the counterparts of theforeground absorbers present in the afterglow spectra, but we obtained very fewidentifications.

Recently, it has been suggested that the metallicity aversion of long-duration gamma-raybursts (LGRBs) is not intrinsic to their formation, but rather a consequence of theanti-correlation between star-formation and metallicity seen in the general galaxypopulation. To investigate this proposal, we compare the metallicity of the hosts ofLGRBs, broad-lined Type Ic (Ic-bl) supernovae (SNe), and Type II SNe to each other and tothe metallicity distribution of star-forming galaxies using the SDSS to represent galaxiesin the local universe and the TKRS for galaxies at intermediate redshifts. The differingmetallicity distributions of the LGRB hosts and the star-formation in local galaxiesforces us to conclude that the low-metallicity preference of LGRBs is not primarily drivenby the anti-correlation between star-formation and metallicity, but rather must beoverwhelmingly due to the astrophysics of the LGRBs themselves. Three quarters of our LGRBsample are found at metallicities below 12+log(O/H) < 8.6, whileless than a tenth of local star-formation is at similarly low metallicities. However, ourSN samples are statistically consistent with the metallicity distribution of the generalgalaxy population. Using the TKRS population of galaxies, we are able to exclude thepossibility that the LGRB host metallicity aversion is caused by the decrease in galaxymetallicity with redshift. The presence of the strong metallicity difference between LGRBsand Ic-bl SNe largely eliminates the possibility that the observed LGRB metallicity biasis a byproduct of a difference in the initial mass functions of the galaxy populations.Rather, metallicity below half-solar must be a fundamental component of the evolutionaryprocess that separates LGRBs from the vast majority of Ic-bl SNe and from the bulk oflocal star-formation.

The brightest gamma-ray bursts (GRBs) would be detectable at very high redshifts and sooffer a probe of star-formation and galaxy evolution into the reionization era and evenbeyond. Localisation of their bright afterglows pinpoints their host galaxies, howeverfaint, and can give not only redshifts but also metallicity estimates, information on thepresence of dust and molecules, and HI column densities. Statistical samples ofwell-observed GRBs at high redshift may therefore reveal the evolution of the global starformation rate, chemical enrichment, far-ultraviolet escape fraction and the faint-end ofthe galaxy luminosity function; all of which are very difficult to establish viaconventional galaxy searches. To date, only a handful ofz > 6 GRBs have been identified, but their presenceat z > 8 begins to realise their potential assearchlights to illuminate the early Universe.

Observed properties of gamma-ray burst (GRB) host galaxies are important clues tounderstand the nature of GRB progenitors. However, the properties of the host galaxiesdon’t directly tell us the nature of the GRB progenitors, and the decipherment of the cluerelies on our understanding of general galaxies. The relation between stellar mass, starformation rate (SFR), and metallicity of star forming galaxies (so called the fundamentalmetallicity relation) has recently attracted attention regarding its possible impact uponour understanding on the properties of the long GRB host galaxies. In this study, I showthe possibility of redshift evolution of the mass–SFR–metallicity relation which has beenclaimed to be independent of redshift, and discuss implications of the evolving relationfor the properties of GRB/SN host galaxies.

Long gamma-ray bursts (GRBs) pinpoint star-forming galaxies as they are linked to thedeaths of massive stars. In most cases, these galaxies have been found to be blue,sub-luminous and of low-metallicity. However, our recent survey have demonstrated that asizeable fraction of GRBs reside in massive, dusty and star-forming extremely red objects(EROs, (R − K)AB > 3.5).The most remarkable case is the host of GRB 080207, one of the reddest galaxies everassociated with a GRB. This discovery suggests that at least a fraction of GRB afterglowstrace a subpopulation of massive starburst galaxies, which are markedly different from themost studied blue, sub-luminous and compact GRB host galaxies.

The photometric redshifts were derived, based on photometry data in visual and infrared.Deep fields were observed during gamma-ray bursts investigation with the SAO RAS 6-metertelescope (BTA), Spitzer and Hubble Space Telescope. BTA BVRI images were used, as well asF475W, F606W, F814W of ACS at the Hubble Space Telescope and Spitzer IRAC ch1 3.6μm, ch3 5.7 μm. Each BTA BVRI exposure was aboutone-hour long, reaching objects up to the ~27th stellar magnitude. The GRB 021004 fieldwas investigated. A catalog of 874 discovered objects is being made as well as colordiagrams and Hubble diagram for these objects.

The radio galaxy RC J0311+0507 was investigated in the “Big Trio” project, which aims tosearch for distant radio galaxies. Optical spectroscopy performed at the 6-m telescopemeasured its redshift as 4.514. The source is one of the most luminous objects in the highredshift Universe having L  ≈  3 × 1029W Hz-1 at 500 MHz, thatsuggests the presence of a super massive black hole with a mass of about1010 M⊙ inside the parent galaxy. Mechanisms ofthe formation of galaxies with black holes of such masses in the early stage of theUniverse is not yet clear. Based on a collection of deep images taken in 10 optical andinfrared bands we started a photometric study of the environment of this radio galaxy todetect possible neighborhood.

Because of time constraints, there was no discussion on GRB host galaxies. Nevertheless,it is worth to extract the main points from the talks and posters presented during theconference.

We are in an exciting period of discovery for gamma-ray bursts (GRBs). The Swiftobservatory is detecting  ~90 GRBs yr-1, providing arcsecondlocalizations and sensitive observations of the prompt and afterglow emission. Inaddition, rapid-response telescopes on the ground are providing new capabilities to studyoptical and radio emissions. The combined data set is enabling great advances in ourunderstanding of GRBs including afterglow physics, short burst origin, and theGRB-supernova connection.

We describe the current, 9-spacecraft Interplanetary Network (IPN). The IPN detects about325 gamma-ray bursts per year, of which about 100 are not localized by any other missions.We give some examples of how the data, which are public, can be utilized.

Here we briefly summarize our long period experience of constructing and operatingwide-field monitoring cameras with sub-second temporal resolution to look for opticalcomponents of GRBs, fast-moving satellites and meteors. General requirements for hardwarefor such systems are discussed along with algorithms of real-time detection andclassification of various kinds of short optical transients. We also give a status reporton the next generation, multi-objective and transforming monitoring system, theMegaTORTORA, whose 6-channel (Mini-MegaTORTORA-Spain) and 9-channelprototypes (Mini-MegaTORTORA-Kazan) we are building now at SAO RAS. This system combines awide field of view with subsecond temporal resolution in monitoring regime, and is able toreconfigure itself, in a fractions of second, to follow-up mode which has bettersensitivity and provides us with multi-color and polarimetric information on detectedtransients simultaneously.

Bootes-IR (Castro-Tiradoet al.2005) is a robotic observatory based around a 60 cm alt-az telescope(dubbed T60) that can slew rapidly while carrying heavy instrumentation at the Nasmythfoci. Initially commissioned with an optical camera, with which the optical afterglow toGRB 060707 (http://gcn.gsfc.nasa.gov/gcn3/5290.gcn3) was discovered, we haveconcentrated our efforts on the near-IR (0.8–2.5 μm) camera (BIRCAM) forwhich the telescope was specifically designed. The telescope is installed at theObservatorio de Sierra Nevada near Granada in Spain, at an altitude of 3000 m and in anarea of very low humidity. The telescope, dome, camera and liquid nitrogen generation andrefilling systems have all been recently brought back into operation, and routineobservations are expected to begin within the next few months.

BOOTES-1B and BOOTES-2 were first to follow-up the Swift GRB 080605.Observations started 44 s after the GRB trigger, discovering the optical afterglow withthe brightness of R = 14.7. A power-law decay with anα = 1.27 ± 0.04 was observed during the first ~600 s after thetrigger.

Pi of the Sky is a system of wide field-of-view robotic telescopes which search for shorttimescale astrophysical phenomena, especially for prompt optical GRB emission. The systemis designed for autonomous operation, follows the predefined observing strategy and adoptsit to the actual conditions. We describe the current status of telescopes located in Chileand Spain and prospects for future development.

GLORIA stands for “GLObal Robotictelescopes Intelligent Array” GLORIA will be the firstfree and open-access network of robotic telescopes in the world It will be a Web 2.0environment where users can do research in astronomy by observing with robotic telescopesand/or analyzing data that other users have acquired with GLORIA, or from other freeaccess databases, like the European Virtual Observatory.