ALBERT

Description: GRB 130925A was an unusual gamma ray burst (GRB), consisting of three distinct episodes of high-energy emission spanning ~20 ks, making it a member of the proposed category of ‘ultralong’ bursts. It was also unusual in that its late-time X-ray emission observed by Swift was very soft, and showed a strong hard-to-soft spectral evolution with time. This evolution, rarely seen in GRB afterglows, can be well modelled as the dust-scattered echo of the prompt emission, with stringent limits on the contribution from the normal afterglow (i.e. external shock) emission. We consider and reject the possibility that GRB 130925A was some form of tidal disruption event, and instead show that if the circumburst density around GRB 130925A is low, the long duration of the burst and faint external shock emission are naturally explained. Indeed, we suggest that the ultralong GRBs as a class can be explained as those with low circumburst densities, such that the deceleration time (at which point the material ejected from the nascent black hole is decelerated by the circumburst medium) is ~20 ks, as opposed to a few hundred seconds for the normal long GRBs. The increased deceleration radius means that more of the ejected shells can interact before reaching the external shock, naturally explaining both the increased duration of GRB 130925A, the duration of its prompt pulses, and the fainter-than-normal afterglow.

Description: Variable x-ray and gamma-ray emission is characteristic of the most extreme physical processes in the universe. We present multiwavelength observations of a unique gamma-ray-selected transient detected by the Swift satellite, accompanied by bright emission across the electromagnetic spectrum, and whose properties are unlike any previously observed source. We pinpoint the event to the center of a small, star-forming galaxy at redshift z = 0.3534. Its high-energy emission has lasted much longer than any gamma-ray burst, whereas its peak luminosity was approximately 100 times higher than bright active galactic nuclei. The association of the outburst with the center of its host galaxy suggests that this phenomenon has its origin in a rare mechanism involving the massive black hole in the nucleus of that galaxy.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Levan, A J -- Tanvir, N R -- Cenko, S B -- Perley, D A -- Wiersema, K -- Bloom, J S -- Fruchter, A S -- Postigo, A de Ugarte -- O'Brien, P T -- Butler, N -- van der Horst, A J -- Leloudas, G -- Morgan, A N -- Misra, K -- Bower, G C -- Farihi, J -- Tunnicliffe, R L -- Modjaz, M -- Silverman, J M -- Hjorth, J -- Thone, C -- Cucchiara, A -- Ceron, J M Castro -- Castro-Tirado, A J -- Arnold, J A -- Bremer, M -- Brodie, J P -- Carroll, T -- Cooper, M C -- Curran, P A -- Cutri, R M -- Ehle, J -- Forbes, D -- Fynbo, J -- Gorosabel, J -- Graham, J -- Hoffman, D I -- Guziy, S -- Jakobsson, P -- Kamble, A -- Kerr, T -- Kasliwal, M M -- Kouveliotou, C -- Kocevski, D -- Law, N M -- Nugent, P E -- Ofek, E O -- Poznanski, D -- Quimby, R M -- Rol, E -- Romanowsky, A J -- Sanchez-Ramirez, R -- Schulze, S -- Singh, N -- van Spaandonk, L -- Starling, R L C -- Strom, R G -- Tello, J C -- Vaduvescu, O -- Wheatley, P J -- Wijers, R A M J -- Winters, J M -- Xu, D -- New York, N.Y. -- Science. 2011 Jul 8;333(6039):199-202. doi: 10.1126/science.1207143. Epub 2011 Jun 16.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, University of Warwick, Coventry, UK. a.j.levan@warwick.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21680811" target="_blank"〉PubMed〈/a〉

Description: Long gamma-ray bursts (GRBs) are the most dramatic examples of massive stellar deaths, often associated with supernovae. They release ultra-relativistic jets, which produce non-thermal emission through synchrotron radiation as they interact with the surrounding medium. Here we report observations of the unusual GRB 101225A. Its gamma-ray emission was exceptionally long-lived and was followed by a bright X-ray transient with a hot thermal component and an unusual optical counterpart. During the first 10 days, the optical emission evolved as an expanding, cooling black body, after which an additional component, consistent with a faint supernova, emerged. We estimate its redshift to be z = 0.33 by fitting the spectral-energy distribution and light curve of the optical emission with a GRB-supernova template. Deep optical observations may have revealed a faint, unresolved host galaxy. Our proposed progenitor is a merger of a helium star with a neutron star that underwent a common envelope phase, expelling its hydrogen envelope. The resulting explosion created a GRB-like jet which became thermalized by interacting with the dense, previously ejected material, thus creating the observed black body, until finally the emission from the supernova dominated. An alternative explanation is a minor body falling onto a neutron star in the Galaxy.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Thone, C C -- de Ugarte Postigo, A -- Fryer, C L -- Page, K L -- Gorosabel, J -- Aloy, M A -- Perley, D A -- Kouveliotou, C -- Janka, H T -- Mimica, P -- Racusin, J L -- Krimm, H -- Cummings, J -- Oates, S R -- Holland, S T -- Siegel, M H -- De Pasquale, M -- Sonbas, E -- Im, M -- Park, W-K -- Kann, D A -- Guziy, S -- Garcia, L Hernandez -- Llorente, A -- Bundy, K -- Choi, C -- Jeong, H -- Korhonen, H -- Kubanek, P -- Lim, J -- Moskvitin, A -- Munoz-Darias, T -- Pak, S -- Parrish, I -- England -- Nature. 2011 Nov 30;480(7375):72-4. doi: 10.1038/nature10611.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉IAA - CSIC, Glorieta de la Astronomia s/n, 18008 Granada, Spain. cthoene@iaa.es〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22129726" target="_blank"〉PubMed〈/a〉

Description: Gamma-ray bursts (GRBs) are most probably powered by collimated relativistic outflows (jets) from accreting black holes at cosmological distances. Bright afterglows are produced when the outflow collides with the ambient medium. Afterglow polarization directly probes the magnetic properties of the jet when measured minutes after the burst, and it probes the geometric properties of the jet and the ambient medium when measured hours to days after the burst. High values of optical polarization detected minutes after the burst of GRB 120308A indicate the presence of large-scale ordered magnetic fields originating from the central engine (the power source of the GRB). Theoretical models predict low degrees of linear polarization and no circular polarization at late times, when the energy in the original ejecta is quickly transferred to the ambient medium and propagates farther into the medium as a blast wave. Here we report the detection of circularly polarized light in the afterglow of GRB 121024A, measured 0.15 days after the burst. We show that the circular polarization is intrinsic to the afterglow and unlikely to be produced by dust scattering or plasma propagation effects. A possible explanation is to invoke anisotropic (rather than the commonly assumed isotropic) electron pitch-angle distributions, and we suggest that new models are required to produce the complex microphysics of realistic shocks in relativistic jets.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wiersema, K -- Covino, S -- Toma, K -- van der Horst, A J -- Varela, K -- Min, M -- Greiner, J -- Starling, R L C -- Tanvir, N R -- Wijers, R A M J -- Campana, S -- Curran, P A -- Fan, Y -- Fynbo, J P U -- Gorosabel, J -- Gomboc, A -- Gotz, D -- Hjorth, J -- Jin, Z P -- Kobayashi, S -- Kouveliotou, C -- Mundell, C -- O'Brien, P T -- Pian, E -- Rowlinson, A -- Russell, D M -- Salvaterra, R -- di Serego Alighieri, S -- Tagliaferri, G -- Vergani, S D -- Elliott, J -- Farina, C -- Hartoog, O E -- Karjalainen, R -- Klose, S -- Knust, F -- Levan, A J -- Schady, P -- Sudilovsky, V -- Willingale, R -- England -- Nature. 2014 May 8;509(7499):201-4. doi: 10.1038/nature13237. Epub 2014 Apr 30.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK. ; INAF/Brera Astronomical Observatory, via Bianchi 46, I-23807 Merate (LC), Italy. ; 1] Department of Earth and Space Science, Osaka University, Toyonaka 560-0043, Japan [2] Astronomical Institute, Tohoku University, Sendai 980-8578, Japan [3] Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980-8578, Japan. ; Astronomical Institute 'Anton Pannekoek', University of Amsterdam, PO Box 94248, 1090 SJ Amsterdam, The Netherlands. ; Max-Planck-Institut fur extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching, Germany. ; International Centre for Radio Astronomy Research, Curtin University, GPO Box U1987, Perth, Western Australia 6845, Australia. ; Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Science, Nanjing 210008, China. ; Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK 2100 Copenhagen, Denmark. ; 1] Instituto de Astrofisica de Andalucia (IAA-CSIC), Glorieta de la Astronomia s/n, E-18008 Granada, Spain [2] Unidad Asociada Grupo Ciencia Planetarias UPV/EHU-IAA/CSIC, Departamento de Fisica Aplicada I, ETS Ingenieria, Universidad del Pais Vasco UPV/EHU, Alameda de Urquijo s/n, E-48013 Bilbao, Spain [3] Ikerbasque, Basque Foundation for Science, Alameda de Urquijo 36-5, E-48008 Bilbao, Spain. ; Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia. ; AIM (UMR 7158 CEA/DSM-CNRS-Universite Paris Diderot) Irfu/Service d'Astrophysique, Saclay, F-91191 Gif-sur-Yvette Cedex, France. ; Astrophysics Research Institute, Liverpool John Moores University, Liverpool Science Park, IC2 Building, 146 Brownlow Hill, Liverpool L3 5RF, UK. ; Space Science Office, ZP12, NASA/Marshall Space Flight Center, Huntsville, Alabama 35812, USA. ; 1] Scuola Normale Superiore, 7, I-56126 Pisa, Italy [2] INAF/IASF Bologna, via Gobetti 101, I-40129 Bologna, Italy. ; 1] Instituto de Astrofisica de Canarias (IAC), E-38200 La Laguna, Tenerife, Spain [2] Departamento de Astrofisica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain [3] New York University Abu Dhabi, PO Box 129188, Abu Dhabi, United Arab Emirates. ; INAF/IASF Milano, via E. Bassini 15, 20133 Milano, Italy. ; INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy. ; Isaac Newton Group of Telescopes, Apartado de Correos 321, E-38700 Santa Cruz de la Palma, Canary Islands, Spain. ; Thuringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany. ; Department of Physics, University of Warwick, Coventry CV4 7AL, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24776800" target="_blank"〉PubMed〈/a〉

Description: We present a 30-day monitoring campaign of the optical counterpart of the bright X-ray transient Swift J1745–26, starting only 19 min after the discovery of the source. We observe the system peaking at i '  ~ 17.6 on day six (MJD 561 92) to then decay at a rate of ~0.04 mag d –1 . We show that the optical peak occurs at least 3 d later than the hard X-ray (15–50 keV) flux peak. Our measurements result in an outburst amplitude greater than 4.3 mag, which favours an orbital period 21 h and a companion star with a spectral type later than ~A0. Spectroscopic observations taken with the Gran Telescopio de Canarias 10.4 m telescope reveal a broad (full width at half-maximum ~1100 km s –1 ), double-peaked Hα emission line from which we constrain the radial velocity semi-amplitude of the donor to be K 2  〉 250 km s –1 . The breadth of the line and the observed optical and X-ray fluxes suggest that Swift J1745–26 is a new black hole candidate located closer than ~7 kpc.

Description: MAXI J1659–152 was discovered on 2010 September 25 as a new X-ray transient, initially identified as a gamma-ray burst, but was later shown to be a new X-ray binary with a black hole as the most likely compact object. Dips in the X-ray light curves have revealed that MAXI J1659–152 is the shortest period black hole candidate identified to date. Here we present the results of a large observing campaign at radio, submillimetre, near-infrared (nIR), optical and ultraviolet (UV) wavelengths. We have combined this very rich data set with the available X-ray observations to compile a broad-band picture of the evolution of this outburst. We have performed broad-band spectral modelling, demonstrating the presence of a spectral break at radio frequencies and a relationship between the radio spectrum and X-ray states. Also, we have determined physical parameters of the accretion disc and put them into context with respect to the other parameters of the binary system. Finally, we have investigated the radio–X-ray and nIR/optical/UV–X-ray correlations up to ~3 yr after the outburst onset to examine the link between the jet and the accretion disc, and found that there is no significant jet contribution to the nIR emission when the source is in the soft or intermediate X-ray spectral state, consistent with our detection of the jet break at radio frequencies during these states.

Description: The spiral host galaxy of the Swift GRB 060505 at z  = 0.089 was the site of a puzzling long duration burst without an accompanying supernova. Studies of the burst environment by Thöne et al. suggested that this Gamma-ray Burst (GRB) came from the collapse of a massive star and that the GRB site was a region with properties different from the rest of the galaxy. We reobserved the galaxy in high spatial resolution using the VIMOS integral-field unit at the VLT with a spaxel size of 0.67 arcsec. Furthermore, we use long-slit high-resolution data from HIRES/Keck at two different slit positions covering the GRB site, the centre of the galaxy and an H ii region next to the GRB region. We compare the properties of different H ii regions in the galaxy with the GRB site and study the global and local kinematic properties of this galaxy. The resolved data show that the GRB site has the lowest metallicity in the galaxy with ~1/3 Z , but its specific star formation rate (SSFR) of 7.4 M  yr –1 / L / L * and age (determined by the Hα EW) are similar to other H ii regions in the host. The galaxy shows a gradient in metallicity and SSFR from the bulge to the outskirts as it is common for spiral galaxies. This gives further support to the theory that GRBs prefer regions of higher star formation and lower metallicity, which, in S-type galaxies, are more easily found in the spiral arms than in the centre. Kinematic measurements of the galaxy do not show evidence for large perturbations but a minor merger in the past cannot be excluded. This study confirms the collapsar origin of GRB 060505 but reveals that the properties of the H ii region surrounding the GRB were not unique to that galaxy. Spatially resolved observations are key to know the implications and interpretations of unresolved GRB hosts observations at higher redshifts.

Description: We present the results based on R -band polarimetric follow-up observations of the nearby (~10 Mpc) Type II-plateau SN 2012aw. Starting from ~10 d after the supernova (SN) explosion, these polarimetric observations cover ~90 d (during the plateau phase) and are distributed over nine epochs. To characterize the Milky Way interstellar polarization (ISP MW ), we have observed 14 field stars lying in a radius of 10° around the SN. We have also tried to subtract the host galaxy dust polarization component assuming that the dust properties in the host galaxy are similar to that observed for Galactic dust and the general magnetic field follow the large-scale structure of the spiral arms of a galaxy. After correcting the ISP MW , our analysis infer that SN 2012aw has maximum polarization of 0.85 ± 0.08 per cent but polarization angle does not show much variation with a weighted mean value of ~138°. However, if both ISP MW and host galaxy polarization components are subtracted from the observed polarization values of SN, maximum polarization of the SN becomes 0.68 ± 0.08 per cent. The distribution of Q and U parameters appears to follow a loop-like structure. The evolution of polarimetric light curve properties of this event is also compared with other well-studied core-collapse SNe of similar type.