P. Jakobsson

Paris Diderot University, Lutetia Parisorum, Île-de-France, France

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Publications (371)718.91 Total impact

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    ABSTRACT: We present the first reported case of the simultaneous metallicity determination of a gamma-ray burst (GRB) host galaxy, from both afterglow absorption lines as well as strong emission-line diagnostics. Using spectroscopic and imaging observations of the afterglow and host of the long-duration GRB121024A at z = 2.30, we give one of the most complete views of a GRB host/environment to date. We observe a strong damped Ly-alpha absorber (DLA) with a hydrogen column density of log N(HI) = 21.80+/-0.15, H_2 absorption in the Lyman-Werner bands (molecular fraction of log(f) ~ -1.4; fourth solid detection of molecular hydrogen in a GRB-DLA), the nebular emission lines H-alpha, H-beta, [OII], [OIII] and [NII], as well as a large variety of metal absorption lines. We find a GRB host galaxy that is highly star-forming (SFR ~ 40 Msolar/yr), with a dust-corrected metallicity along the line of sight of [Zn/H]corr = -0.5+/-0.2 ([O/H] ~ -0.3 from emission lines), and a depletion factor of refractory elements of [Zn/Fe] = 0.85+/-0.04. The molecular gas is separated by 400 km/s from the gas that is excited by the GRB (implying a fairly massive host, in agreement with the derived stellar mass of log(Mstellar/Msolar) = 9.9+/-0.2). Including emission line analysis, we isolate and characterise three different gas-phases within the star-forming host galaxy. Our main result is that the metallicity determinations from both absorption and emission lines are consistent, which is encouraging for the comparison of GRB host metallicities at different redshifts.
    09/2014;
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    ABSTRACT: Context. Gamma-ray burst (GRBs) afterglows probe sightlines to star-forming regions in distant star-forming galaxies. Here we present a study of the peculiar afterglow spectrum of the z = 0.889 Swift GRB 140506A. Aims. Our aim is to understand the origin of the very unusual properties of the absorption along the line-of-sight. Methods. We analyse spectroscopic observations obtained with the X-shooter spectrograph mounted on the ESO/VLT at two epochs 8.8 h and 33 h after the burst as well as imaging from the GROND instrument. We also present imaging and spectroscopy of the host galaxy obtained with the Magellan telescope. Results. The underlying afterglow appears to be a typical afterglow of a long-duration GRB. However, the material along the line-of- sight has imprinted very unusual features on the spectrum. Firstly, there is a very broad and strong flux drop below 8000 AA (4000 AA in the rest frame), which seems to be variable between the two spectroscopic epochs. We can reproduce the flux-drops both as a giant 2175 AA extinction bump and as an effect of multiple scattering on dust grains in a dense environment. Secondly, we detect absorption lines from excited H i and He i. We also detect molecular absorption from CH+ . Conclusions. We interpret the unusual properties of these spectra as reflecting the presence of three distinct regions along the line-of-sight: the excited He i absorption originates from an H ii-region, whereas the Balmer absorption must originate from an associated photodissociation region. The strong metal line and molecular absorption and the dust extinction must originate from a third, cooler region along the line-of-sight. The presence of (at least) three separate regions is reflected in the fact that the different absorption components have different velocities relative to the systemic redshift of the host galaxy.
    09/2014;
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    ABSTRACT: The reionisation of the universe is thought to have ended around z~6, as inferred from spectroscopy of distant bright background sources such as quasars (QSO) and gamma-ray burst (GRB) afterglows. Furthermore, spectroscopy of a GRB afterglow provides insight in its host galaxy, which is often too dim and distant to study otherwise. We present the high S/N VLT/X-shooter spectrum of GRB130606A at z=5.913. We aim to measure the degree of ionisation of the IGM between 5.02<z<5.84, and to study the chemical abundance pattern and dust content of its host galaxy. We measure the flux decrement due to IGM absorption at Ly$\alpha$, $\beta$ and $\gamma$ wavelength regions. The hydrogen and metal absorption lines formed in the host galaxy are fitted with Voigt profiles to obtain column densities. Our measurements of the Ly$\alpha$-forest optical depth are consistent with previous measurements of QSOs, but have smaller uncertainty than these. The Ly$\alpha$ red-damping-wing analysis yields a neutral fraction $x_{HI}<0.03$ (3$\sigma$). We obtain column density measurements of several elements. The ionisation corrections due to the GRB is estimated to be negligible (<0.03 dex), but larger corrections may apply due to pre-existing radiation field (up to 0.3 dex based on sub-DLA studies). Our measurements confirm that the Universe is already predominantly ionised over the redshift range probed in this work, but was slightly more neutral at z>5.6. GRBs are useful probes of the IGM ionisation state of the early Universe, but because of internal scatter we need a larger statistical sample to draw robust conclusions. The high [Si/Fe] in the host can be due to dust depletion, alpha-element enhancement or a combination. The very high value of [Al/Fe]=2.40+/-0.78 might be connected to the stellar population history. We estimate the host metallicity to be -1.5<[M/H]<-1.2 (3%-6% of solar). [truncated]
    09/2014;
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    Zach Cano, Pall Jakobsson
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    ABSTRACT: In this paper we demonstrate, in principle, how gamma-ray burst supernovae (GRB-SNe) can be used to measure the Hubble constant, H_0. Using two statistical data-fitting procedures, a linear-least squares (LLS) method and a Monte-Carlo (MC) method, we first present a statistically significant luminosity--decline relationship of GRB-SNe in filters UBVRI, and then provide constraints on H_0. Using SN 1998bw, and a fiducial distance to its host galaxy of 37 Mpc, we constrain H_0 to the range 61--69 km/s/Mpc. In our analysis, we adopt conservative errors of 20% in the SN magnitudes. The subsequent errors in H_0 derived from the MC method are of order 2--4 km/s/Mpc, and roughly ten times larger using the LLS method. Interestingly, the weakest luminosity--decline relation is seen in the B-band; however the B-band (and V-band) data provide one of the tightest constraints on H_0 of all the filters. Finally, as GRB-SNe arise from massive star progenitors, whose lifetimes are of order several million years, they are likely to occur at earlier times in the universe than SNe Ia, as the latter require at least one white-dwarf star in a binary system, which forms only after a few billion years. This suggests that with suitable instrumentation and facilities, GRB-SNe can be found at larger redshifts/earlier times in the universe than SNe Ia, and eventually providing useful constraints on the fundamental cosmological parameters in the early universe.
    09/2014;
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    ABSTRACT: 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.
    08/2014;
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    ABSTRACT: Luminous infrared galaxies and submillimeter galaxies contribute significantly to stellar mass assembly and the frequency of GRBs in these systems provides an important test of the connection between the gamma-ray burst rate and that of overall cosmic star-formation. We present sensitive 3 GHz radio observations using the Karl G. Jansky Very Large Array of 31 uniformly-selected GRB host galaxies spanning a redshift range from 0 < z < 2.5, providing the first fully dust- and sample-unbiased measurement of the fraction of GRBs originating from the Universe's most bolometrically luminous galaxies. Four galaxies are detected, with inferred radio star-formation rates ranging between 50-300 Msun/yr. Three of the four detections correspond to events consistent with being optically-obscured "dark" bursts. Our overall detection fraction implies that between 5-25% of GRBs between 0.5 < z < 2.5 occur in galaxies with S_3GHz > 10 uJy, corresponding to SFR > 50 Msun/yr at z~1 or > 250 Msun/yr at z~2. Similar galaxies contribute approximately 10-30% of all cosmic star-formation, so our results are consistent with a GRB rate which is not strongly biased with respect to the total star-formation rate of a galaxy. However, all four radio-detected hosts have modest stellar masses (~few x 10^10 Msun), significantly lower than IR/submillimeter-selected field galaxies of similar luminosities. We suggest that GRBs may be suppressed in metal-rich environments but independently are enhanced in intense starbursts, producing a strong efficiency dependence on mass but little net dependence on bulk galaxy star-formation rate.
    07/2014;
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    ABSTRACT: Following the photometric observations of the counterpart of GRB 140512A (Pagani et al. GCN 16249) from the 2.5 m NOT (+ALFOSC) reported by de Ugarte Postigo et al. (GCN 16253) we obtained spectroscopic data. Observations consisted in 2x1800s exposures using Grism #4, which covers the range from 3800 to 9100. The mean observing epoch was May 13, 3:18:50 UT (7.78 hrs after the burst). The spectrum presents absorption features consistent with FeII and MgII at a common redshift of z=0.725, which we consider the most probable redshift for this event. http://gcn.gsfc.nasa.gov/gcn/gcn3/16310.gcn3
    GRB Coordinates Network, Circular Service, 16310. 05/2014;
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    ABSTRACT: We imaged the field of GRB 140516A (Bernardini et al. GCNC 16285) with the 2.5m Nordic Optical telescope equipped with ALFOSC. The observations were carried out in the R-band on May 16.89163-16.97005 UT (0.88-2.77 hours post burst) with a total exposure time of 13x300s. We did not detect any objects brighter than R=24.5 (3 sigma Vega limit calibrated against USNO B1.0) consistent with the enhanced XRT position (Osborne et al. GCNC 16289). http://gcn.gsfc.nasa.gov/gcn/gcn3/16290.gcn3
    GRB Coordinates Network, Circular Service, 16290. 05/2014;
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    ABSTRACT: We have observed the afterglow of GRB 140515A (D'Avanzo et al., GCN 16267) with the 2.5m NOT telescope. Observations consisted of 5x300s imaging in the z-band and have an average epoch of 12.10 hr after the burst. The images reveal the optical afterglow detected by Chornock et al. (GCN 16269) and Fong et al. (GCN 16274) at a magnitude of z(AB) = 22.15+/-0.15, as compared with SDSS stars. This indicates a decay with a slope of alpha ~ -0.9 (where F_nu~t^alpha) as compared with the photometry of Fong et al. (GCN 16274). Further observations are ongoing. http://gcn.gsfc.nasa.gov/gcn/gcn3/16278.gcn3
    GRB Coordinates Network, Circular Service, 16278. 05/2014;
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    ABSTRACT: 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.
    05/2014;
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    ABSTRACT: Observations of the afterglows of long gamma-ray bursts (GRBs) allow the study of star-forming galaxies across most of cosmic history. Here we present observations of GRB 111008A, from which we can measure metallicity, chemical abundance patterns, dust-to-metals ratio (DTM), and extinction of the GRB host galaxy at z = 5.0. The host absorption system is a damped Lyα absorber with a very large neutral hydrogen column density of and a metallicity of [S/H] = –1.70 ± 0.10. It is the highest-redshift GRB with such a precise metallicity measurement. The presence of fine-structure lines confirms the z = 5.0 system as the GRB host galaxy and makes this the highest redshift where Fe II fine-structure lines have been detected. The afterglow is mildly reddened with AV = 0.11 ± 0.04 mag, and the host galaxy has a DTM that is consistent with being equal to or lower than typical values in the Local Group.
    The Astrophysical Journal 04/2014; 785(2):150. · 6.73 Impact Factor
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    ABSTRACT: The spiral host galaxy of 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 Th\"one et al. (2008) suggested that this 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 (IFU) 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 center of the galaxy and an HII region next to the GRB region. We compare the properties of different HII 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 around 1/3 Z_solar, but its specific SFR (SSFR) of 7.4 M_solar/yr/L/L* and age (determined by the Halpha EW) are similar to other HII 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 GRB060505 but reveals that the properties of the HII 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.
    04/2014; 441(3).
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    ABSTRACT: A significant proportion ($\sim30\%$) of the short-duration gamma-ray bursts (SGRBs) localised by Swift have no detected host galaxy coincident with the burst location to deep limits, and also no high-likelihood association with proximate galaxies on the sky. These SGRBs may represent a population at moderately high redshifts ($z\gtrsim1$), for which the hosts are faint, or a population where the progenitor has been kicked far from its host or is sited in an outlying globular cluster. We consider the afterglow and host observations of three 'hostless' bursts (GRBs 090305A, 091109B and 111020A), coupled with a new observational diagnostic to aid the association of SGRBs with putative host galaxies to investigate this issue. Considering the well localised SGRB sample, 7/25 SGRBs can be classified as 'hostless' by our diagnostic. Statistically, however, the proximity of these seven SGRBs to nearby galaxies is higher than is seen for random positions on the sky. This suggests that the majority of 'hostless' SGRBs have likely been kicked from proximate galaxies at moderate redshift. Though this result still suggests only a small proportion of SGRBs will be within the AdLIGO horizon for NS-NS or NS-BH inspiral detection ($z\sim0.1$), in the particular case of GRB 111020A a plausible host candidate is at $z=0.02$.
    Monthly Notices of the Royal Astronomical Society 02/2014; 437(2). · 5.52 Impact Factor
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    ABSTRACT: At low redshift, a handful of gamma-ray bursts (GRBs) have been discovered with peak luminosities ($L_{\rm iso} < 10^{48.5}~\rm{erg\,s}^{-1}$) substantially lower than the average of the more distant ones ($L_{\rm iso} > 10^{49.5}~\rm{erg\,s}^{-1}$). The properties of several low-luminosity (low-$L$) GRBs indicate that they can be due to shock break-out, as opposed to the emission from ultrarelativistic jets. Owing to this, it is highly debated how both populations are connected, and whether there is a continuum between them. The burst at redshift $z=0.283$ from 2012 April 22 is one of the very few examples of intermediate-$L$ GRBs with a $\gamma$-ray luminosity of $L\sim10^{48.9}~\rm{erg\,s}^{-1}$ that have been detected up to now. Together with the robust detection of its accompanying supernova SN 2012bz, it has the potential to answer important questions on the origin of low- and high-$L$ GRBs and the GRB-SN connection. We carried out a spectroscopy campaign using medium- and low-resolution spectrographs at 6--10-m class telescopes, covering the time span of 37.3 days, and a multi-wavelength imaging campaign from radio to X-ray energies over a duration of $\sim270$ days. Furthermore, we used a tuneable filter centred at H$\alpha$ to map star formation in the host galaxy and the surrounding galaxies. We used these data to extract and model the properties of different radiation components and incorporate spectral-energy-distribution fitting techniques to extract the properties of the host galaxy. Modelling the light curve and spectral energy distribution from the radio to the X-rays revealed the blast-wave to expand with an initial Lorentz factor of $\Gamma_0\sim60$, low for a high-$L$ GRB, and that the afterglow had an exceptional low peak luminosity-density of $\lesssim2\times10^{30}~\rm{erg\,s}^{-1}\,\rm{Hz}^{-1}$ in the sub-mm. [Abridged]
    01/2014;
  • Z. Cano, D. Xu, D. Malesani, P. Jakobsson, T. Pursimo
    11/2013;
  • 11/2013;
  • 11/2013;
  • 11/2013;
  • 11/2013;
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    ABSTRACT: We investigate the possible use of photon dispersion mechanisms in cosmology. In particular, we consider ordinary dispersion in a cold electron plasma, as well as recently proposed photon dispersion due to vacuum quantum fluctuations. We also consider dispersion due to a finite photon mass, for compar-ison. The dispersion time delay of radiation from extragalactic sources such as gamma-ray bursts (GRBs), their afterglows and flares in active galactic nuclei is estimated for the various mechanisms and the results compared. Finally it is shown how the delay can be used in a new cosmological test to differentiate between world models.

Publication Stats

3k Citations
718.91 Total Impact Points

Institutions

  • 2014
    • Paris Diderot University
      Lutetia Parisorum, Île-de-France, France
  • 1999–2014
    • University of Iceland
      • Science Institute
      Reikiavik, Capital Region, Iceland
  • 2012
    • Ikerbasque - Basque Foundation for Science
      Bilbo, Basque Country, Spain
    • Max Planck Institute for Extraterrestrial Physics
      Arching, Bavaria, Germany
  • 2002–2012
    • University of Copenhagen
      • • Dark Cosmology Centre (DARK)
      • • Niels Bohr Institute
      København, Capital Region, Denmark
  • 2011
    • The University of Warwick
      • Department of Physics
      Warwick, ENG, United Kingdom
  • 2006–2011
    • University of Hertfordshire
      • Centre for Astrophysics Research (CAR)
      Hatfield, ENG, United Kingdom
    • Thüringer Landessternwarte Tautenburg
      Tautenburg, Thuringia, Germany
  • 2003–2007
    • University of Leicester
      • Department of Physics and Astronomy
      Leicester, ENG, United Kingdom
    • Aarhus University
      • Department of Physics and Astronomy
      Aarhus, Central Jutland, Denmark
  • 2005
    • Space Telescope Science Institute
      Baltimore, Maryland, United States