Long Gamma-ray Bursts Host Research Articles

A fast-cadenced search for gamma-ray burst orphan afterglows with the Deeper, Wider, Faster programme

ABSTRACT The relativistic outflows that produce long gamma-ray bursts (LGRBs) can be described by a structured jet model where prompt $\gamma$-ray emission is restricted to a narrow region in the jet’s core. Viewing the jet off-axis from the core, a population of afterglows without an associated GRB detection can be predicted. In this work, we conduct an archival search for these ‘orphan’ afterglows (OAs) with minute-cadence, deep ($g\sim 23$) data from the Dark Energy Camera (DECam) taken as part of the Deeper, Wider, Faster programme (DWF). We introduce a method to select fast-evolving OA candidates within DWF data that comprises a machine learning model, based on a realistic synthetic population of OAs. Using this classifier, we recover 51 OA candidates. Of these candidates, 42 are likely flare events from M-class stars. The remaining nine possess quiescent, coincident sources in archival data with angular profiles consistent with a star and are inconsistent with the expected population of LGRB host galaxies. We therefore conclude that these are likely Galactic events. We calculate an upper limit on the rate of OAs down to $g\lt 22$ AB mag of 7.46 deg$^{-2}$yr$^{-1}$ using our criteria and constrain possible jet structures. We also place an upper limit of the characteristic angle between the $\gamma$-ray-emitting region and the jet’s half-opening angle. For a smooth power law and a power law with core jet model, respectively, these values are $58.3^{\circ }$ and $56.6^{\circ }$, for a power-law index of 0.8 and $75.3^{\circ }$ and $76.8^{\circ }$ for a power-law index of 1.2.

Accessing the Host Galaxies of Long Gamma-Ray Bursts with Next-generation Telescopes

We present a method to estimate the detection expectations of host galaxies of long gamma-ray bursts (LGRBs) in the grizJHKL bands. It is found that given the same limiting magnitude mgrizJHKL,lim in each band, the z band produces the largest number of overall LGRB hosts and low-mass hosts (M * ≤ 108 M ⊙) at mgrizJHKL,lim≳26 mag. For the detection of high-redshift LGRB hosts (redshift ≥5), it is recommended to prioritize the L band, due to its good performance at both low and high limiting magnitudes. We specifically estimate the expectation of LGRB host detection with mgrizJHKL,lim=28 mag, which the James Webb Space Telescope can partially attain. We find that there may exist 116, 259, 277, 439, 266, 294, 274, and 316 LGRB hosts, including 0.54, 31, 28, 143, 12, 20, 14, and 35 low-mass ones in the grizJHKL bands and 13, 14, 15, 14, and 15 high-redshift ones in the zJHKL bands, for 15 yr Swift LGRBs with S ≥ 10−6 erg cm−2. The results show that the study of LGRB hosts under next-generation observational conditions holds significant potential, especially for low-mass host studies. However, it appears that the deeper sensitivities of galaxy telescopes may not significantly enhance statistical studies of high-redshift hosts. Strategies aimed at increasing the number of distant LGRB hosts may require the expansion of high-redshift LGRB detections.

Localized Fast Radio Bursts Are Consistent with Magnetar Progenitors Formed in Core-collapse Supernovae

Abstract With the localization of fast radio bursts (FRBs) to galaxies similar to the Milky Way and the detection of a bright radio burst from SGR J1935+2154 with energy comparable to extragalactic radio bursts, a magnetar origin for FRBs is evident. By studying the environments of FRBs, evidence for magnetar formation mechanisms not observed in the Milky Way may become apparent. In this Letter, we use a sample of FRB host galaxies and a complete sample of core-collapse supernova (CCSN) hosts to determine whether FRB progenitors are consistent with a population of magnetars born in CCSNe. We also compare the FRB hosts to the hosts of hydrogen-poor superluminous supernovae (SLSNe-I) and long gamma-ray bursts (LGRBs) to determine whether the population of FRB hosts is compatible with a population of transients that may be connected to millisecond magnetars. After using a novel approach to scale the stellar masses and star formation rates of each host galaxy to be statistically representative of z = 0 galaxies, we find that the CCSN hosts and FRBs are consistent with arising from the same distribution. Furthermore, the FRB host distribution is inconsistent with the distribution of SLSNe-I and LGRB hosts. With the current sample of FRB host galaxies, our analysis shows that FRBs are consistent with a population of magnetars born through the collapse of giant, highly magnetic stars.

The FRB 121102 Host Is Atypical among Nearby Fast Radio Bursts

Abstract We search for host galaxy candidates of nearby fast radio bursts (FRBs), FRB 180729.J1316+55, FRB 171020, FRB 171213, FRB 180810.J1159+83, and FRB 180814.J0422+73 (the second repeating FRB). We compare the absolute magnitudes and the expected host dispersion measure DMhost of these candidates with that of the first repeating FRB, FRB 121102, as well as those of long gamma-ray bursts (LGRBs) and superluminous supernovae (SLSNe), the proposed progenitor systems of FRB 121102. We find that while the FRB 121102 host is consistent with those of LGRBs and SLSNe, the nearby FRB host candidates, at least for FRB 180729.J1316+55, FRB 171020, and FRB 180814.J0422+73, either have a smaller DMhost or are fainter than FRB 121102 host, as well as the hosts of LGRBs and SLSNe. In order to avoid the uncertainty in estimating DMhost due to the line-of-sight effect, we propose a galaxy-group-based method to estimate the electron density in the intergalactic regions, and hence, DMIGM. The result strengthens our conclusion. We conclude that the host galaxy of FRB 121102 is atypical, and LGRBs and SLSNe are likely not the progenitor systems of at least most nearby FRB sources. The recently reported two FRB hosts differ from the host of FRB 121102 and also the host candidates suggested in this paper. This is consistent with the conclusion of our paper and suggests that the FRB hosts are very diverse.

Are long gamma-ray bursts biased tracers of star formation? Clues from the host galaxies of the Swift/BAT6 complete sample of bright LGRBs

Aims. Long gamma-ray bursts (LGRB) have been proposed as promising tracers of star formation owing to their association with the core-collapse of massive stars. Nonetheless, previous studies we carried out at z < 1 support the hypothesis that the conditions necessary for the progenitor star to produce an LGRB (e.g. low metallicity), were challenging the use of LGRBs as star-formation tracers, at least at low redshift. The goal of this work is to characterise the population of host galaxies of LGRBs at 1 < z < 2, investigate the conditions in which LGRBs form at these redshifts and assess their use as tracers of star formation. Methods. We performed a spectro-photometric analysis to determine the stellar mass, star formation rate, specific star formation rate and metallicity of the complete, unbiased host galaxy sample of the Swift/BAT6 LGRB sample at 1 < z < 2. We compared the distribution of these properties to the ones of typical star-forming galaxies from the MOSDEF and COSMOS2015 Ultra Deep surveys, within the same redshift range. Results. We find that, similarly to z < 1, LGRBs do not directly trace star formation at 1 < z < 2, and they tend to avoid high-mass, high-metallicity host galaxies. We also find evidence for an enhanced fraction of starbursts among the LGRB host sample with respect to the star-forming population of galaxies. Nonetheless we demonstrate that the driving factor ruling the LGRB efficiency is metallicity. The LGRB host distributions can be reconciled with the ones expected from galaxy surveys by imposing a metallicity upper limit of logOH ∼ 8.55. We can determine upper limits on the fraction of super-solar metallicity LGRB host galaxies of ∼20%, 10% at z < 1, 1 < z < 2, respectively. Conclusions. Metallicity rules the LGRB production efficiency, which is stifled at Z ≳ 0.7 Z⊙. Under this hypothesis we can expect LGRBs to trace star formation at z > 3, once the bulk of the star forming galaxy population are characterised by metallicities below this limit. The role played by metallicity can be explained by the conditions necessary for the progenitor star to produce an LGRB. The moderately high metallicity threshold found is in agreement with the conditions necessary to rapidly produce a fast-rotating Wolf-Rayet stars in close binary systems, and could be accommodated by single star models under chemically homogeneous mixing with very rapid rotation and weak magnetic coupling.

Dwarf galaxies as hosts of stellar explosions: gas kinematics and abundances in 3D

AbstractThe hosts of long Gamma-ray bursts (GRBs) are places of intense star-formation, which, at low redshift, are primarily low-mass dwarf starburst galaxies. Spatially resolved studies of these galaxies are still sparse, even more so at high spectral resolution where we can probe gas kinematics, in- and outflows and differences in abundance between different components. Here we present the first high resolution IFU sample of six low redshift GRB hosts, all dwarf starbursts. All galaxies in our sample show evidence for excess emission or broad emission components, with velocities of 100-200 km s−1. For GRB 030329, outflowing gas had also been observed in absorption in spectra of the GRB afterglow. The high velocity emission is usually blue shifted, connected to the brightest star-forming regions and more metal rich than the narrow component associated with the emission of the general host ISM. This gives strong indications that the excess emission/broad component is indeed associated to a starburst wind as observed in many field star-burst galaxies and a sign for the intense ongoing star-formation in those galaxies.

The chemical enrichment of long gamma-ray bursts nurseries up to z = 2

Aims. We investigate the existence of a metallicity threshold for the production of long gamma-ray bursts (LGRBs). Methods. We used the host galaxies of the Swift/BAT6 sample of LGRBs. We considered the stellar mass, star formation rate (SFR), and metallicity determined from the host galaxy photometry and spectroscopy up to z = 2 and used them to compare the distribution of host galaxies to that of field galaxies in the mass-metallicity and fundamental metallicity relation plane. Results. We find that although LGRBs also form in galaxies with relatively large stellar masses, the large majority of host galaxies have metallicities below log (O/H) ~ 8.6. The extension to z = 2 results in a good sampling of stellar masses also above Log(M∗/M⊙) ~ 9.5 and provides evidence that LGRB host galaxies do not follow the fundamental metallicity relation. As shown by the comparison with dedicated numerical simulations of LGRB host galaxy population, these results are naturally explained by the existence of a mild (~0.7 Z⊙) threshold for the LGRB formation. The present statistics does not allow us to discriminate between different shapes of the metallicity cutoff, but the relatively high metallicity threshold found in this work is somewhat in disagreement to most of the standard single-star models for LGRB progenitors.

Taking stock of superluminous supernovae and long gamma-ray burst host galaxy comparison using a complete sample of LGRBs

Long gamma-ray bursts (LGRBs) and superluminous supernovae (SLSNe) are both explosive transients with very massive progenitor stars. Clues about the nature of the progenitors can be found by investigating environments in which such transients occur. While studies of LGRB host galaxies have a long history, dedicated observational campaigns have only recently resulted in a high enough number of photometrically and spectroscopically observed SLSN hosts to allow statistically significant analysis of their properties. In this paper we make a comparison of the host galaxies of hydrogen-poor (H-poor) SLSNe and the Swift/BAT6 sample of LGRBs. In contrast to previous studies we use a complete sample of LGRBs and we address a special attention to the comparison methodology and the selection of SLSN sample whose data have been compiled from the available literature. At intermediate redshifts (0.3 < z < 0.7) the two classes of transients select galaxies whose properties (stellar mass, luminosity, star-formation rate, specific star-formation rate and metallicity) do not differ on average significantly. Moreover, the host galaxies of both classes of objects follow the fundamental metallicity relation and the fundamental plane of metallicity. In contrast to previous studies we show that at intermediate redshifts the emission line equivalent widths of the two populations are essentially the same and that the previous claims regarding the higher fraction of SLSN hosts among the extreme emission line galaxies with respect to LGRBs are mostly due to a larger fraction of strong-line emitters among SLSN hosts at z < 0.3, where samples of LGRB hosts are small and poorly defined.

Are long gamma-ray bursts biased tracers of star formation? Clues from the host galaxies of theSwift/BAT6 complete sample of bright LGRBs

Long gamma-ray bursts (LGRBs) are associated with the deaths of massive stars and could thus be a potentially powerful tool to trace cosmic star formation. However, especially at low redshifts (z < 1.5) LGRBs seem to prefer particular types of environment. Our aim is to study the host galaxies of a complete sample of bright LGRBs to investigate the impact of the environment on GRB formation. We study host galaxy spectra of the Swift/BAT6 complete sample of 14 z < 1 bright LGRBs. We use the detected nebular emission lines to measure the dust extinction, star formation rate (SFR) and nebular metallicity (Z) of the hosts and supplement the data set with previously measured stellar masses M$_{\star}$. The distributions of the obtained properties and their interrelations (e.g. mass-metallicity and SFR-M$_{\star}$ relations) are compared to samples of field star-forming galaxies.We find that LGRB hosts at z < 1 have on average lower SFRs than if they were direct star-formation tracers. By directly comparing metallicity distributions of LGRB hosts and star-forming galaxies, we find a good match between the two populations up to Z $\sim 8.4-8.5$, after which the paucity of metal-rich LGRB hosts becomes apparent. The LGRB host galaxies of our complete sample are not inconsistent with the mass-metallicity relation at similar mean redshift and stellar masses. The cutoff against high metallicities (and high masses) can explain the low SFR values of LGRB hosts. We find a hint of increased incidence of starburst galaxies in the Swift/BAT6 z < 1 sample with respect to that of a field star-forming population. Given that the SFRs are low on average, the latter is ascribed to low stellar masses. Nevertheless the limits on the completeness and metallicity availability of current surveys, coupled with the limited number of LGRB host galaxies, prevent us from reaching more quantitative conclusions.

GRB host galaxies with VLT/X-Shooter: properties at 0.8 &lt; z &lt; 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 recognized 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 Very Large Telescope (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 (SFR). 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, SFRs, 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. SFRs and metallicities are measured for all the hosts analysed in this paper and metallicities are well determined for four 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.

A method for quantifying the gamma-ray burst bias. Application in the redshift range of 0–1.1

Long Gamma Ray Bursts (LGRBs) are related to the final stages of evolution of massive stars. As such, they should follow the star formation rate (SFR) of galaxies. We can use them to probe for star-forming galaxies (SFGs) in the distant universe following this assumption. The relation between the rate of LGRBs in a given galaxy and its SFR (that we call the LGRB "bias") may be complex, as we have indications that the LGRB hosts are not perfect analogues to the general population of SFGs. In this work, we try to quantify the dependence of the LGRB bias on physical parameters of their host galaxy such as the SFR or the stellar mass. We propose an empirical method based on the comparison of stellar mass functions (and SFR distributions) of LGRB hosts and of SFGs in order to find how the bias depends on the stellar mass or the SFR. By applying this method to a sample of LGRB hosts at redshifts lower than 1.1, where the properties of SFGs are well established, and where the properties of LGRB host galaxies can be deduced from observations (for stellar masses larger than 10**9.25 Msun and SFR larger than 1.8 Msun / yr), we find that the LGRB bias depends on both the stellar mass and SFR. We find that the bias decreases with the SFR, i.e. we see no preference for highly SFGs, once taken into account the larger number of massive stars in galaxies with larger SFR. We do not find any trend with the specific star formation rate (SSFR) but the dynamical range in SSFR in our study is narrow. Although through an indirect method, we relate these trends to a possible decrease of the LGRBs rate / SFR ratio with the metallicity. The method we propose suggests trends that may be useful to constrain models of LGRB progenitors, showing a clear decrease of the LGRB bias with the metallicity. This is promising for the future as the number of LGRB hosts studied will increase.

Simulating high-z gamma-ray burst host galaxies

We investigate the nature of high-z host galaxies of long Gamma-Ray Bursts (LGRBs) by means of state-of-the-art numerical simulations of cosmic structure formation and evolution of galaxies. We combine results from different runs with various box sizes and resolutions. By assigning to each simulated galaxy the probability to host a LGRB, assumed to be proportional to the mass of young stars, we provide a full description of the physical properties of high-z LGRB host galaxy population. We find that LGRBs at z>6 are hosted in galaxies with typical star formation rates SFR \sim 0.03-0.3 Msun yr^{-1}, stellar masses M \sim 10^{6-8} Msun, and metallicities Z \sim 0.01-0.1 Zsun. Furthermore, the ratio between their doubling time and the corresponding cosmic time seems to be universally equal to ~0.1-0.3, independently from the redshift. The distribution of their UV luminosity places LGRB hosts in the faint-end of the galaxy luminosity function, well below the current capabilities of space- or ground-based optical facilities. This is in line with recent reports of non-detection of LGRB hosts using extremely deep HST and VLT observations. In conclusion, high-z LGRBs are found to trace the position of those faint galaxies that are thought to be the major actors in the re-ionization of the Universe.

SN 2008jb: A “LOST” CORE-COLLAPSE SUPERNOVA IN A STAR-FORMING DWARF GALAXY AT ∼10 Mpc

We present the discovery and follow-up observations of SN 2008jb, a core-collapse supernova in the dwarf irregular galaxy ESO 302-14 at 9.6 Mpc. This transient was missed by galaxy-targeted surveys and was only found in archival optical images obtained by CRTS and ASAS. It was detected shortly after explosion and reached a bright optical maximum, Vmax = 13.6 mag (M_Vmax ~ -16.5). The shape of the light curve shows a plateau of 100 days, followed by a drop of 1.4 mag in V-band to a decline with the approximate Co 56 decay slope, consistent with 0.04 Msun of Ni 56 synthesized in the explosion. A spectrum obtained 2 years after explosion shows a broad, boxy Halpha emission line, which is unusual for type IIP supernovae. We detect the supernova in archival Spitzer and WISE images obtained 8-14 months after explosion, which show clear signs of warm dust emission. The dwarf irregular host galaxy has a low gas-phase oxygen abundance, 12 + log(O/H) = 8.2 (~1/5 Solar), similar to those of the SMC and the hosts of long gamma-ray bursts and luminous core-collapse supernovae. We study the host environment using GALEX FUV, R-band, and Halpha images and find that the supernova occurred in a large star-formation complex. The morphology of the Halpha emission appears as a large shell (R = 350 pc) surrounding the FUV and optical emission. We estimate an age of ~9 Myr and a total mass of ~2 x 10^5 Msun for the star-formation complex. These properties are consistent with the expanding Halpha supershells observed in well-studied nearby dwarf galaxies, which are tell-tale signs of feedback from the cumulative effect of massive star winds and supernovae. The age estimated for the star-forming region suggests a relatively high-mass progenitor star with initial mass of ~20 Msun. We discuss the implications of these findings in the study of core-collapse supernova progenitors. (Abridged)

The extinction properties of long gamma-ray burst host galaxies from H and He i recombination lines★

In this paper we show how a self-consistent treatment of hydrogen and helium emission line fluxes of the hosts of long gamma-ray bursts can result in improved understanding of the dust properties in these galaxies. In particular, we find that even with modest signal to noise spectroscopy we can differentiate different values for R_V, the ratio of total to selective extinction. The inclusion of Paschen and Brackett lines, even at low signal to noise, greatly increase the accuracy of the derived reddening. This method is often associated with strong systematic errors, caused by the need for multiple instruments to cover the wide wavelength range, the requirement to separate stellar hydrogen absorption from the nebular emission, and because of the dependancy of the predicted line fluxes on the electron temperature. We show how these three systematic errors can be negated, by using suitable instrumentation (in particular X-shooter on the Very Large Telescope) and wide wavelength coverage. We demonstrate this method using an extensive optical and near-infrared spectroscopic campaign of the host galaxy of gamma-ray burst 060218 (SN 2006aj), obtained with FORS1, UVES and ISAAC on the VLT, covering a broad wavelength range with both high and low spectral resolution. We contrast our findings of this source with X-shooter data of a star forming region in the host of GRB 100316D, and show the improvement over existing published fluxes of long GRB hosts.

The nature of long-GRB host galaxies from chemical abundances

Gamma-ray bursts (GRBs) are the most energetic events after the Big Bang and they have been observed up to very high redshift. By means of measures of chemical abundances now available for the galaxies hosting such events,thought to originate from the explosion of very powerful supernovae (Type Ib/c), we have the opportunity to study the nature of these host galaxies. The aim of this paper is to identify the hosts of Long GRBs (LGRBs) observed both at low and high redshift to see whether the hosts can be galaxies of the same type observed at different cosmic epochs. We adopt detailed chemical evolution models for galaxies of different morphological type (ellipticals, spirals, irregulars) which follow the time evolution of the abundances of several chemical elements (H, He, $\alpha$-elements, Fe), and compare the results with the observed abundances and abundance ratios in galaxies hosting LGRBs. We find that the abundances and abundance ratios predicted by models devised for typical irregular galaxies can well fit the abundances in the hosts both at high and low redshift. We also find that the predicted Type Ib/c supernova rate for irregulars is in good agreement with observations. Models for spirals and particularly ellipticals do not fit the high-redshift hosts of LGRBs (DLA systems) nor the low redshift hosts: in particular, ellipticals cannot possibly be the hosts of gamma-ray-bursts at low redshift since they do not show any star formation, and therefore no supernovae Ib/c. We conclude that the observed abundance and abundance ratios in LGRBs hosts suggest that these hosts are irregular galaxies both at high and low redshift thus showing that the host galaxies belong to in an evolutionary sequence.

THE HOST GALAXIES OF SHORT-DURATION GAMMA-RAY BURSTS: LUMINOSITIES, METALLICITIES, AND STAR FORMATION RATES

The association of some short-duration gamma-ray bursts (GRBs) with elliptical galaxies established that their progenitors, unlike those of long GRBs, belong to an old stellar population. However, the majority of short GRBs appear to occur in star forming galaxies, raising the possibility that some progenitors are related to recent star formation activity. Here, we present optical spectroscopy of these hosts and measure their luminosities, star formation rates, and metallicities. We find luminosities of LB ≈ 0.1-1.5 L *, star formation rates of SFR ≈ 0.2-6 M ☉ yr–1, and metallicities of 12 + log(O/H) ≈ 8.5-8.9 (Z ≈ 0.6-1.6 Z ☉). A detailed comparison to the hosts of long GRBs reveals systematically higher luminosities, lower specific star formation rates (SFR/LB ) by about an order of magnitude, and higher metallicities by about 0.6 dex. The Kolmogorov-Smirnov probability that the short and long GRB hosts are drawn from the same underlying galaxy distribution is only ~10–3. Short GRB hosts exhibit excellent agreement with the specific star formation rates and the luminosity-metallicity relation of field galaxies at z ~ 0.1-1. We thus conclude that short GRB hosts are not dominated by young stellar populations like long GRB hosts. Instead, short GRB hosts appear to be drawn uniformly from the underlying field galaxy distribution, indicating that the progenitors have a wide age distribution of several Gyr.