D. Svinkin

GRB 091024A AND THE NATURE OF ULTRA-LONG GAMMA-RAY BURSTS

We present a broadband study of gamma-ray burst (GRB) 091024A within the context of other ultra-long-duration GRBs. An unusually long burst detected by Konus-Wind (KW), Swift, and Fermi, GRB 091024A has prompt emission episodes covering ~1300 s, accompanied by bright and highly structured optical emission captured by various rapid-response facilities, including the 2 m autonomous robotic Faulkes North and Liverpool Telescopes, KAIT, S-LOTIS, and the Sonoita Research Observatory. We also observed the burst with 8 and 10 m class telescopes and determine the redshift to be z = 1.0924 ± 0.0004. We find no correlation between the optical and γ-ray peaks and interpret the optical light curve as being of external origin, caused by the reverse and forward shock of a highly magnetized jet (RB ≈ 100-200). Low-level emission is detected throughout the near-background quiescent period between the first two emission episodes of the KW data, suggesting continued central-engine activity; we discuss the implications of this ongoing emission and its impact on the afterglow evolution and predictions. We summarize the varied sample of historical GRBs with exceptionally long durations in gamma-rays (gsim1000 s) and discuss the likelihood of these events being from a separate population; we suggest ultra-long GRBs represent the tail of the duration distribution of the long GRB population.

GRB 130925A: an ultralong gamma ray burst with a dust-echo afterglow, and implications for the origin of the ultralong GRBs

This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. PAE, JPO, KW and APB acknowledge UK Space Agency support. The Konus-Wind experiment is partially supported by a Russian Space Agency contract, RFBR grants 12-02-00032a and 13-02-12017 ofi-m. DNB and JAK acknowledge support from NASA contract NAS5-00136. This work includes observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, in the island of La Palma. This work was partially supported by the Spanish Ministry project AYA2012-29727-C03-01.

Constraining the energy budget of GRB 080721

We follow the bright, highly energetic afterglow of Swift-discovered GRB 080721 at z = 2.591 out to 36 d or 3 x 10(6) s since the trigger in the optical and X-ray bands. We do not detect a break in the late-time light curve inferring a limit on the opening angle of theta(j) >= 7 degrees.3 and setting tight constraints on the total energy budget of the burst of E-gamma >= 9.9 x 10(51) erg within the fireball model. To obey the fireball model closure relations, the gamma-ray burst (GRB) jet must be expanding into a homogeneous surrounding medium and likely lies behind a significant column of dust. The energy constraint we derive can be used as an observational input for models of the progenitors of long GRBs: we discuss how such high collimation-corrected energies could be accommodated with certain parameters of the standard massive star core-collapse models. We can, however, most probably rule out a magnetar progenitor for this GRB which would require 100 per cent efficiency to reach the observed total energy.

A MISSING-LINK IN THE SUPERNOVA–GRB CONNECTION: THE CASE OF SN 2012ap

Gamma-ray bursts (GRBs) are characterized by ultra-relativistic outflows, while supernovae are generally characterized by non-relativistic ejecta. GRB afterglows decelerate rapidly, usually within days, because their low-mass ejecta rapidly sweep up a comparatively larger mass of circumstellar material. However, supernovae with heavy ejecta can be in nearly free expansion for centuries. Supernovae were thought to have non-relativistic outflows except for a few relativistic ones accompanied by GRBs. This clear division was blurred by SN 2009bb, the first supernova with a relativistic outflow without an observed GRB. However, the ejecta from SN 2009bb was baryon loaded and in nearly free expansion for a year, unlike GRBs. We report the first supernova discovered without a GRB but with rapidly decelerating mildly relativistic ejecta, SN 2012ap. We discovered a bright and rapidly evolving radio counterpart driven by the circumstellar interaction of the relativistic ejecta. However, we did not find any coincident GRB with an isotropic fluence of more than one-sixth of the fluence from GRB 980425. This shows for the first time that central engines in SNe Ic, even without an observed GRB, can produce both relativistic and rapidly decelerating outflows like GRBs.

GROND coverage of the main peak of gamma-ray burst 130925A

Aims. Prompt or early optical emission in gamma-ray bursts (GRBs) is notoriously difficult to measure, and observations of the dozen cases show a large variety of properties. Yet, such early emission promises to help us achieve a better understanding of the GRB emission process(es). Methods. We performed dedicated observations of the ultra-long duration (T90 about 7000 s) Swift GRB 130925A in the optical/nearinfrared with the 7-channel Gamma-Ray burst Optical and Near-infrared Detector (GROND) at the 2.2 m MPG/ESO telescope. Results. We detect an optical/near-infrared flare with an amplitude of nearly 2 mag which is delayed with respect to the keV−MeV prompt emission by about 300−400 s. The decay time of this flare is shorter than the duration of the flare (500 s) or its delay. Conclusions. While we cannot offer a straightforward explanation, we discuss the implications of the flare properties and suggest ways toward understanding it.

A search for giant flares from soft gamma-ray repeaters in nearby galaxies in the Konus-WIND short burst sample

The knowledge of the rate of soft gamma-ray repeater (SGR) giant flares is important for understanding the giant flare mechanism and the SGR energy budget in the framework of the magnetar model. We estimate the upper limit to the rate using the results of an extensive search for extragalactic soft gamma-repeater giant flares (GFs) among 140 short gamma-ray bursts detected between 1994 and 2010 by Konus-Wind using InterPlanetary Network (IPN) localizations and temporal parameters. We show that Konus-Wind and the IPN are capable of detecting GFs with energies of 2.3×10 46 erg (which is the energy of the GF from SGR 1806 20 assuming a distance of 15 kpc) at distances of up to � 30 Mpc and GFs with energies of . 10 45 erg (which is the energy of the GF from SGR 0526 66) at distances of up to � 6 Mpc. Using a sample of 1896 nearby galaxies we found that only two bursts, GRB 051103 and GRB 070201, have a low chance coincidence probability between an IPN localization and a nearby galaxy. We found the upper limit to the fraction of GFs among short GRBs with fluence above � 5×10 7 erg cm 2 to be < 8% (95% confidence level). Assuming that the number of active SGRs in nearby galaxies is proportional to their core-collapse supernova rate, we derived the one-sided 95% upper limit to the rate of GFs with energy output similar to the GF from SGR 1806 20 to be (0.6–1.2) × 10 4 Q 1.5 46 yr 1 per SGR, where Q46 is the GF energy output in 10 46 erg.

GRB 051008: a long, spectrally hard dust-obscured GRB in a Lyman-break galaxy at z ≈ 2.8

We present observations of the dark gamma-ray burst GRB 051008 provided by Swift/BAT, Swift/XRT, Konus-WIND, INTEGRAL/SPI-ACS in the high-energy domain and the Shajn, Swift/UVOT, Tautenburg, NOT, Gemini and Keck I telescopes in the optical and near-infrared bands. The burst was detected only in gamma- and X-rays and neither a prompt optical nor a radio afterglow was detected down to deep limits. We identified the host galaxy of the burst, which is a typical Lyman-break galaxy (LBG) with R-magnitude of 24.06 ± 0.10 mag. A redshift of the galaxy of z=2.77^(+0.15)_(−0.20) is measured photometrically due to the presence of a clear, strong Lyman-break feature. The host galaxy is a small starburst galaxy with moderate intrinsic extinction (A_V = 0.3) and has a star formation rate of ∼60 M_⊙ yr^(−1) typical for LBGs. It is one of the few cases where a GRB host has been found to be a classical LBG. Using the redshift we estimate the isotropic-equivalent radiated energy of the burst to be E_(iso) = (1.15 ± 0.20) × 10^(54) erg. We also provide evidence in favour of the hypothesis that the darkness of GRB 051008 is due to local absorption resulting from a dense circumburst medium.

THE INTERPLANETARY NETWORK RESPONSE TO LIGO GW150914

We have performed a blind search for a gamma-ray transient of arbitrary duration and energy spectrum around the time of the LIGO gravitational-wave event GW150914 with the six-spacecraft interplanetary network (IPN). Four gamma-ray bursts were detected between 30 hr prior to the event and 6.1 hr after it, but none could convincingly be associated with GW150914. No other transients were detected down to limiting 15–150 keV fluences of roughly 5 ×10−8–5 × 10−7 erg cm−2. We discuss the search strategies and temporal coverage of the IPN on the day of the event and compare the spatial coverage to the region where GW150914 originated. We also report the negative result of a targeted search for the Fermi-GBM event reported in conjunction with GW150914.

Investigation of Primordial Black Hole Bursts using Interplanetary Network Gamma-ray Bursts

NASA [NNX09AU03G, NNX10AU34G, NNX11AP96G, NNX13AP09G, NNG04GM50G, NNG06GE69G, NNX07AQ22G, NNX08AC90G, NNX08AX95G, NNX09AR28G, NNX08AN23G, NNX09AO97G, NNX12AD68G, NNX06AI36G, NNX08AB84G, NNX08AZ85G, NNX09AV61G, NNX10AR12G, NNX07AR71G, NAG5-3500]; JPL [1282043, Y503559, NNX12AE41G, NNX13AI54G, NNX15AE60G, NNX07AH52G, NAG5-13080, NAG5-7766, NAG5-9126, NAG5-10710, NNG06GI89G]; Laboratory Directed Research and Development program at the Los Alamos National Laboratory (LANL); Russian Space Agency contract and RFBR [15-02-00532, 13-02-12017-ofi-m]

Studies of cosmic gamma-ray bursts and soft gamma repeaters in the Russian-American Konus-Wind experiment

The studies of the cosmic gamma-ray bursts and soft gamma repeaters that have been performed in the Russian-American Konus-Wind experiment during the last several years have been summarized. The experiment has been continuously performed using the Konus Russian scientific instrument on the Wind American spacecraft since 1994 under the optimal interplanetary space conditions in the absence of noise caused by the Earth’s radiation belts and the shadowing of detectors. Two high-sensitivity detectors have constantly observed the entire celestial sphere and recorded detailed time and spectral characteristics of bursts in a wide range of energies (20 keV–15 MeV). The Konus-Wind data have been widely used in the present-day multiwave studies of gamma-ray bursts.