arXiv subjects

T. Kruhler

Publications and source records attributed to T. Kruhler.

14 recordsLinked to original sources

arXiv2018

Relativistic supernova 2009bb exploded close to an atomic gas cloud

The potential similarity of the powering mechanisms of relativistic SNe and GRBs allowed us to make a prediction that relativistic SNe are born in environments similar to those of GRBs, that is, ones which are rich in atomic gas. Here we embark on testing this hypothesis by analysing the properties of the host galaxy NGC 3278 of the relativistic SN 2009bb. This is the first time the atomic gas properties of a relativistic SN host are provided and the first time resolved 21 cm-hydrogen-line (HI) information is provided for a host of an SN of any type in the context of the SN position. We obtained radio observations with ATCA covering the HI line, and optical integral field unit spectroscopy observations with MUSE. The atomic gas distribution of NGC 3278 is not centred on the optical galaxy centre, but instead around a third of atomic gas resides in the region close to the SN position. This galaxy has a few times lower atomic and molecular gas masses than predicted from its SFR. SN 2009bb exploded close to the region with the highest SFR density and the lowest age (~5.5 Myr, corresponding to the initial mass of the progenitor star ~36 Mo). As for GRB hosts, the gas properties of NGC 3278 are consistent with a recent inflow of gas from the intergalactic medium, which explains the concentration of atomic gas close to the SN position and the enhanced SFR. Super-solar metallicity at the position of the SN (unlike for most GRBs) may mean that relativistic explosions signal a recent inflow of gas (and subsequent star formation), and their type (GRBs or SNe) is determined either i) by the metallicity of the inflowing gas, so that metal-poor gas results in a GRB explosion and metal-rich gas results in a relativistic SN explosion without an accompanying GRB, or ii) by the efficiency of gas mixing, or iii) by the type of the galaxy.

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arXiv2017

Serendipitous discovery of an optical emission line jet in NGC\,232

We report the detection of a highly collimated linear emission-line structure in the spiral galaxy NGC\,232 through the use of integral field spectroscopy data from the All-weather MUse Supernova Integral field Nearby Galaxies (AMUSING) survey. This jet--like feature extends radially from the nucleus and is primarily detected in [oiii]$λ$5007 without clear evidence of an optical continuum counterpart. The length of the radial structure projected on sky reaches $\sim 3$ kpc, which makes NGC\,232 the second longest emission-line jet reported. The ionized gas presents extreme [Oiii]/H$β$ and [Nii]/H$α$ line ratios, increasing along the jet-like structure. We discuss three possible scenarios to explain the observed structure: (i) direct ionization of in-falling material from the intergalactic medium by the AGN; (ii) photo-ionization by an un-detected optical counter-part of the radio jet and (iii) fast shocks ionization due to the lateral expansion of the radio jet across the ISM. Our analysis favors in-situ ionization.

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arXiv2017

A kilonova as the electromagnetic counterpart to a gravitational-wave source

Gravitational waves were discovered with the detection of binary black hole mergers and they should also be detectable from lower mass neutron star mergers. These are predicted to eject material rich in heavy radioactive isotopes that can power an electromagnetic signal called a kilonova. The gravitational wave source GW170817 arose from a binary neutron star merger in the nearby Universe with a relatively well confined sky position and distance estimate. Here we report observations and physical modelling of a rapidly fading electromagnetic transient in the galaxy NGC4993, which is spatially coincident with GW170817 and a weak short gamma-ray burst. The transient has physical parameters broadly matching the theoretical predictions of blue kilonovae from neutron star mergers. The emitted electromagnetic radiation can be explained with an ejected mass of 0.04 +/- 0.01 Msol, with an opacity of kappa <= 0.5 cm2/gm at a velocity of 0.2 +/- 0.1c. The power source is constrained to have a power law slope of beta = -1.2 +/- 0.3, consistent with radioactive powering from r-process nuclides. We identify line features in the spectra that are consistent with light r-process elements (90 < A < 140). As it fades, the transient rapidly becomes red, and emission may have contribution by a higher opacity, lanthanide-rich ejecta component. This indicates that neutron star mergers produce gravitational waves, radioactively powered kilonovae, and are a nucleosynthetic source of the r-process elements.

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arXiv2017

Late-time observations of the relativistic tidal disruption flare candidate Swift J1112.2-8238

We present late-time follow-up of the relativistic tidal disruption flare candidate Swift J1112.2-8238. We confirm the previously determined redshift of $z=0.8900\pm0.0005$ based on multiple emission line detections. {\em HST} imaging of the host galaxy indicates a complex and distorted morphology with at least two spatially distinct components. These are offset in velocity space by less than 350\,km\,s$^{-1}$ in VLT/X-Shooter observations, suggesting that the host is undergoing interaction with another galaxy. The transient position is consistent to 2.2$σ$ with the centre of a bulge-like component at a distance of 1.1$\pm$0.5\,kpc from its centre. Luminous, likely variable radio emission has also been observed, strengthening the similarities between Swift J1112.2-8238 and other previously identified relativistic tidal disruption flares. While the transient location is $\sim2σ$ from the host centroid, the disrupted nature of the host may provide an explanation for this. The tidal disruption model remains a good description for these events.

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arXiv2016

The Superluminous Transient ASASSN-15lh as a Tidal Disruption Event from a Kerr Black Hole

When a star passes within the tidal radius of a supermassive black hole, it will be torn apart. For a star with the mass of the Sun ($M_\odot$) and a non-spinning black hole with a mass $<10^8 M_\odot$, the tidal radius lies outside the black hole event horizon and the disruption results in a luminous flare. Here we report observations over a period of 10 months of a transient, hitherto interpreted as a superluminous supernova. Our data show that the transient rebrightened substantially in the ultraviolet and that the spectrum went through three different spectroscopic phases without ever becoming nebular. Our observations are more consistent with a tidal disruption event than a superluminous supernova because of the temperature evolution, the presence of highly ionised CNO gas in the line of sight and our improved localisation of the transient in the nucleus of a passive galaxy, where the presence of massive stars is highly unlikely. While the supermassive black hole has a mass $> 10^8 M_\odot$, a star with the same mass as the Sun could be disrupted outside the event horizon if the black hole were spinning rapidly. The rapid spin and high black hole mass can explain the high luminosity of this event.

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arXiv2015

GRB host galaxies with VLT/X-Shooter: properties at 0.8 < z < 1.3

Long gamma-ray bursts (LGRBs) are associated with the death of massive stars. Their host galaxies therefore represent a unique class of objects tracing star formation across the observable Universe. Indeed, recently accumulated evidence shows that GRB hosts do not differ substantially from general population of galaxies at high (z > 2) redshifts. However, it has been long recognised that the properties of z < 1.5 hosts, compared to general star-forming population, are unusual. To better understand the reasons for the supposed difference in LGRB hosts properties at z < 1.5, we obtained VLT/X- Shooter spectra of six hosts lying in the redshift range of 0.8 < z < 1.3. Some of these hosts have been observed before, yet we still lack well constrained information on their characteristics such as metallicity, dust extinction and star formation rate. We search for emission lines in the VLT/X-Shooter spectra of the hosts and measure their fluxes. We perform a detailed analysis, estimating host average extinction, star-formation rates, metallicities and electron densities where possible. Measured quantities of our hosts are compared to a larger sample of previously observed GRB hosts at z < 2. Star-formation rates and metallicities are measured for all the hosts analyzed in this paper and metallicities are well determined for 4 hosts. The mass-metallicity relation, the fundamental metallicity relation and SFRs derived from our hosts occupy similar parameter space as other host galaxies investigated so-far at the same redshift. We therefore conclude that GRB hosts in our sample support the found discrepancy between the properties of low-redshift GRB hosts and the general population of star- forming galaxies.

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arXiv2015

GRB 140606B / iPTF14bfu: Detection of shock-breakout emission from a cosmological gamma-ray burst?

We present optical and near-infrared photometry of GRB~140606B ($z=0.384$), and optical photometry and spectroscopy of its associated supernova (SN). The results of our modelling indicate that the bolometric properties of the SN ($M_{\rm Ni} = 0.4\pm0.2$~M$_{\odot}$, $M_{\rm ej} = 5\pm2$~M$_{\odot}$, and $E_{\rm K} = 2\pm1 \times 10^{52}$ erg) are fully consistent with the statistical averages determined for other GRB-SNe. However, in terms of its $γ$-ray emission, GRB~140606B is an outlier of the Amati relation, and occupies the same region as low-luminosity ($ll$) and short GRBs. The $γ$-ray emission in $ll$GRBs is thought to arise in some or all events from a shock-breakout (SBO), rather than from a jet. The measured peak photon energy ($E_{\rm p}\approx800$ keV) is close to that expected for $γ$-rays created by a SBO ($\gtrsim1$ MeV). Moreover, based on its position in the $M_{V,\rm p}$--$L_{\rm iso,γ}$~plane and the $E_{\rm K}$--$Γβ$~plane, GRB~140606B has properties similar to both SBO-GRBs and jetted-GRBs. Additionally, we searched for correlations between the isotropic $γ$-ray emission and the bolometric properties of a sample of GRB-SNe, finding that no statistically significant correlation is present. The average kinetic energy of the sample is $\bar{E}_{\rm K} = 2.1\times10^{52}$ erg. All of the GRB-SNe in our sample, with the exception of SN 2006aj, are within this range, which has implications for the total energy budget available to power both the relativistic and non-relativistic components in a GRB-SN event.

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arXiv2014

Detailed Afterglow Modeling and Host Galaxy Properties of the Dark GRB 111215A

Gamma-ray burst (GRB) 111215A was bright at X-ray and radio frequencies, but not detected in the optical or near-infrared (nIR) down to deep limits. We have observed the GRB afterglow with the Westerbork Synthesis Radio Telescope and Arcminute Microkelvin Imager at radio frequencies, with the William Herschel Telescope and Nordic Optical Telescope in the nIR/optical, and with the Chandra X-ray Observatory. We have combined our data with the Swift X-Ray Telescope monitoring, and radio and millimeter observations from the literature to perform broadband modeling, and determined the macro- and microphysical parameters of the GRB blast wave. By combining the broadband modeling results with our nIR upper limits we have put constraints on the extinction in the host galaxy. This is consistent with the optical extinction we have derived from the excess X-ray absorption, and higher than in other dark bursts for which similar modeling work has been performed. We also present deep imaging of the host galaxy with the Keck I telescope, Spitzer Space Telescope, and Hubble Space Telescope (HST), which resulted in a well-constrained photometric redshift, giving credence to the tentative spectroscopic redshift we obtained with the Keck II telescope, and estimates for the stellar mass and star formation rate of the host. Finally, our high resolution HST images of the host galaxy show that the GRB afterglow position is offset from the brightest regions of the host galaxy, in contrast to studies of optically bright GRBs.

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arXiv2014

A Trio of GRB-SNe: GRB 120729A, GRB 130215A / SN 2013ez and GRB 130831A / SN 2013fu

We present optical and near-infrared (NIR) photometry for three gamma-ray burst supernovae (GRB-SNe): GRB 120729A, GRB 130215A / SN 2013ez and GRB 130831A / SN 2013fu. In the case of GRB 130215A / SN 2013ez, we also present optical spectroscopy at t-t0=16.1 d, which covers rest-frame 3000-6250 Angstroms. Based on Fe II (5169) and Si (II) (6355), our spectrum indicates an unusually low expansion velocity of 4000-6350 km/s, the lowest ever measured for a GRB-SN. Additionally, we determined the brightness and shape of each accompanying SN relative to a template supernova (SN 1998bw), which were used to estimate the amount of nickel produced via nucleosynthesis during each explosion. We find that our derived nickel masses are typical of other GRB-SNe, and greater than those of SNe Ibc that are not associated with GRBs. For GRB 130831A / SN 2013fu, we use our well-sampled R-band light curve (LC) to estimate the amount of ejecta mass and the kinetic energy of the SN, finding that these too are similar to other GRB-SNe. For GRB 130215A, we take advantage of contemporaneous optical/NIR observations to construct an optical/NIR bolometric LC of the afterglow. We fit the bolometric LC with the millisecond magnetar model of Zhang & Meszaros (2001), which considers dipole radiation as a source of energy injection to the forward shock powering the optical/NIR afterglow. Using this model we derive an initial spin period of P=12 ms and a magnetic field of B=1.1 x 10^15 G, which are commensurate with those found for proposed magnetar central engines of other long-duration GRBs.

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arXiv2013

The Redshift Distribution of the TOUGH Survey

We present the redshift results from a Very Large Telescope program aimed at optimizing the legacy value of the Swift mission: to characterize a homogeneous, X-ray selected, sample of 69 GRB host galaxies. 19 new redshifts have been secured, resulting in a 83% (57/69) redshift completion, making the survey the most comprehensive in terms of redshift completeness of any sample to the full Swift depth, available to date. We present the cumulative redshift distribution and derive a conservative, yet small, associated uncertainty. We constrain the fraction of Swift GRBs at high redshift to a maximum of 10% (5%) for z > 6 (z > 7). The mean redshift of the host sample is assessed to be > 2.2. Using this more complete sample, we confirm previous findings that the GRB rate at high redshift (z > 3) appears to be in excess of predictions based on assumptions that it should follow conventional determinations of the star formation history of the universe, combined with an estimate of its likely metallicity dependence. This suggests that either star formation at high redshifts has been significantly underestimated, for example due to a dominant contribution from faint, undetected galaxies, or that GRB production is enhanced in the conditions of early star formation, beyond those usually ascribed to lower metallicity.

astro-ph.CO↗

arXiv2013

Discovery of the broad-lined Type Ic SN 2013cq associated with the very energetic GRB 130427A

Long-duration gamma-ray bursts (GRBs) at z < 1 are in most cases found to be accompanied by bright, broad-lined Type Ic supernovae (SNe Ic-BL). The highest-energy GRBs are mostly located at higher redshifts, where the associated SNe are hard to detect observationally. Here we present early and late observations of the optical counterpart of the very energetic GRB 130427A. Despite its moderate redshift z = 0.3399+/-0.0002, GRB 130427A is at the high end of the GRB energy distribution, with an isotropic-equivalent energy release of Eiso ~ 9.6x10^53 erg, more than an order of magnitude more energetic than other GRBs with spectroscopically confirmed SNe. In our dense photometric monitoring, we detect excess flux in the host-subtracted r-band light curve, consistent with what expected from an emerging SN, ~0.2 mag fainter than the prototypical SN 1998bw. A spectrum obtained around the time of the SN peak (16.7 days after the GRB) reveals broad undulations typical of SNe Ic-BL, confirming the presence of a SN, designated SN 2013cq. The spectral shape and early peak time are similar to those of the high expansion velocity SN 2010bh associated with GRB 100316D. Our findings demonstrate that high-energy long-duration GRBs, commonly detected at high redshift, can also be associated with SNe Ic-BL, pointing to a common progenitor mechanism.

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arXiv2010

Testing GRB models with the afterglow of GRB 090102

We present the observations of the afterglow of gamma-ray burst GRB 090102. Optical data taken by the TAROT, REM, GROND, together with publicly available data from Palomar, IAC and NOT telescopes, and X-ray data taken by the XRT instrument on board the Swift spacecraft were used. This event features an unusual light curve. In X-rays, it presents a constant decrease with no hint of temporal break from 0.005 to 6 days after the burst. In the optical, the light curve presents a flattening after 1 ks. Before this break, the optical light curve is steeper than that of the X-ray. In the optical, no further break is observed up to 10 days after the burst. We failed to explain these observations in light of the standard fireball model. Several other models, including the cannonball model were investigated. The explanation of the broad band data by any model requires some fine tuning when taking into account both optical and X-ray bands.

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arXiv2010

GRB 081008: from burst to afterglow and the transition phase in between

We present a multi-wavelength study of GRB 081008, at redshift 1.967, by Swift, ROTSE-III and GROND. Compared to other Swift GRBs, GRB 081008 has a typical gamma-ray isotropic equivalent energy output (10^53 erg) during the prompt phase, and displayed two temporally separated clusters of pulses. The early X-ray emission seen by the Swift/XRT was dominated by the softening tail of the prompt emission, producing multiple flares during and after the Swift/BAT detections. Optical observations that started shortly after the first active phase of gamma-ray emission showed two consecutive peaks. We interpret the first optical peak as the onset of the afterglow associated with the early burst activities. A second optical peak, coincident with the later gamma-ray pulses, imposes a small modification to the otherwise smooth lightcurve and thus suggests a minimal contribution from a probable internal component. We suggest the early optical variability may be from continuous energy injection into the forward shock front by later shells producing the second epoch of burst activities. These early observations thus provide a potential probe for the transition from prompt to the afterglow phase. The later lightcurve of GRB 081008 displays a smooth steepening in all optical bands and X-ray. The temporal break is consistent with being achromatic at the observed wavelengths. Our broad energy coverage shortly after the break constrains a spectral break within optical. However, the evolution of the break frequency is not observed. We discuss the plausible interpretations of this behavior.

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arXiv2008

OGLE2-TR-L9: An extrasolar planet transiting a fast-rotating F3 star

Context: Photometric observations for the OGLE-II microlens monitoring campaign have been taken in the period 1997-2000. All light curves of this campaign have recently been made public. Our analysis of these data has revealed 13 low-amplitude transiting objects among ~15700 stars in three Carina fields towards the galactic disk. One of these objects, OGLE2-TR-L9 (P~2.5 days), turned out to be an excellent transiting planet candidate. Aims: In this paper we report on our investigation of the true nature of OGLE2-TR-L9, by re-observing the photometric transit with the aim to determine the transit parameters at high precision, and by spectroscopic observations, to estimate the properties of the host star, and to determine the mass of the transiting object through radial velocity measurements. Methods: High precision photometric observations have been obtained in g', r', i', and z' band simultaneously, using the new GROND detector, mounted on the MPI/ESO 2.2m telescope at La Silla. Eight epochs of high-dispersion spectroscopic observations were obtained using the fiber-fed FLAMES/UVES Echelle spectrograph, mounted on ESO's Very Large Telescope at Paranal. Results: The photometric transit, now more than 7 years after the last OGLE-II observations, was re-discovered only ~8 minutes from its predicted time. The primary object is a fast rotating F3 star, with vsini=39.33+-0.38 km/s, T=6933+-58 K, log g = 4.25+-0.01, and [Fe/H] = -0.05+-0.20. The transiting object is an extrasolar planet with M_p=4.5+-1.5 M_Jup and R_p=1.61+-0.04 R_Jup. The rejection of possible blend scenarios was based on a quantitative analysis of the multi-color photometric data [abridged].

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