122 research outputs found
Long Gamma-Ray Burst Host Galaxies and their Environments
In this book-chapter we first briefly discuss some basic observational issues
related to what a GRB host galaxy is (whether they are operationally well
defined as a class) and sample completeness. We then describe some of the early
studies of GRB hosts starting with statistical studies of upper limits done
prior to the first detections, the first host detection after the BeppoSAX
breakthrough and leading up to the current Swift era. Finally, we discuss the
status of efforts to construct a more complete sample of GRBs based on Swift
and end with an outlook. We only consider the host galaxies of long-duration
GRBs.Comment: 31 pages, 14 figures; Chapter 13 in "Gamma-Ray Bursts", eds. C.
Kouveliotou, R. A. M. J. Wijers, S. E. Woosley, Cambridge University Press,
201
Gamma-Ray Bursts and Afterglow Polarisation
Polarimetry of Gamma-Ray Burst (GRB) afterglows in the last few years has
been considered one of the most effective tool to probe the geometry,
energetic, dynamics and the environment of GRBs. We report some of the most
recent results and discuss their implications and future perspectives.Comment: 6 pages, 4 figures. Proceeding for the "Interacting Binaries:
Accretion, Evolution and Outcome" worshop held in Cefalu' (Italy) in July
200
Constraints on the relative sizes of intervening Mg II-absorbing clouds and quasar emitting regions
Context: A significantly higher incidence of strong (rest equivalent width
W_r > 1 {\AA}) intervening Mg II absorption is observed along gamma-ray burst
(GRB) sight-lines relative to those of quasar sight-lines. A geometrical
explanation for this discrepancy has been suggested: the ratio of the beam size
of the source to the characteristic size of a Mg II absorption system can
influence the observed Mg II equivalent width, if these two sizes are
comparable. Aims: We investigate whether the differing beam sizes of the
continuum source and broad-line region of Sloan Digital Sky Survey (SDSS)
quasars produce a discrepancy between the incidence of strong Mg II absorbers
illuminated by the quasar continuum region and those of absorbers illuminated
by both continuum and broad-line region light. Methods: We perform a
semi-automated search for strong Mg II absorbers in the SDSS Data Release 7
quasar sample. The resulting strong Mg II absorber catalog is available online.
We measure the sight-line number density of strong Mg II absorbers superimposed
on and off the quasar C IV 1550 {\AA} and C III] 1909 {\AA} emission lines.
Results: We see no difference in the sight-line number density of strong Mg II
absorbers superimposed on quasar broad emission lines compared to those
superimposed on continuum-dominated spectral regions. This suggests that the Mg
II-absorbing clouds typically observed as intervening absorbers in quasar
spectra are larger than the beam sizes of both the continuum-emitting regions
and broad line-emitting regions in the centers of quasars, corresponding to a
lower limit of the order of 10^17} cm for the characteristic size of a Mg II
absorbing cloud.Comment: 10 pages, 5 figures. Edit: fixed a missing cross-referenc
The Optically Unbiased GRB Host (TOUGH) survey. IV. Lyman-alpha emitters
We report the results of a spectroscopic search for Lyman-alpha emission from
gamma-ray burst host galaxies. Based on the well-defined TOUGH sample of 69
X-ray selected Swift GRBs, we have targeted the hosts of a subsample of 20 GRBs
known from afterglow spectroscopy to be in the redshift range 1.8-4.5. We
detect Lya emission from 7 out of the 20 hosts, with the typical limiting
3sigma line flux being 8E-18 erg/cm2/s, corresponding to a Lya luminosity of
6E41 erg/s at z=3. The Lya luminosities for the 7 hosts in which we detect Lya
emission are in the range (0.6-2.3)E42 erg/s corresponding to star-formation
rates of 0.6-2.1 Msun/yr (not corrected for extinction). The rest-frame Lya
equivalent widths (EWs) for the 7 hosts are in the range 9-40A. For 6 of the 13
hosts for which Lya is not detected we place fairly strong 3sigma upper limits
on the EW (<20A), while for others the EW is either unconstrained or has a less
constraining upper limit. We find that the distribution of Lya EWs is
inconsistent with being drawn from the Lya EW distribution of bright Lyman
break galaxies at the 98.3% level, in the sense that the TOUGH hosts on average
have larger EWs than bright LBGs. We can exclude an early indication, based on
a smaller, heterogeneous sample of pre-Swift GRB hosts, that all GRB hosts are
Lya emitters. We find that the TOUGH hosts on average have lower EWs than the
pre-Swift GRB hosts, but the two samples are only inconsistent at the 92%
level. The velocity centroid of the Lya line is redshifted by 200-700 km/s with
respect to the systemic velocity, similar to what is seen for LBGs, possibly
indicating star-formation driven outflows from the host galaxies. There seems
to be a trend between the Lya EW and the optical to X-ray spectral index of the
afterglow (beta_OX), hinting that dust plays a role in the observed strength
and even presence of Lya emission. [ABRIDGED]Comment: ApJ accepted (v2: minor changes in the Subject headings and reference
list
GRBs as Probes of Massive Stars Near and Far
Long-duration gamma-ray bursts are the manifestations of massive stellar
death. Due to the immense energy release they are detectable from most of the
observable universe. In this way they allow us to study the deaths of single
(or binary) massive stars possibly throughout the full timespan massive stars
have existed in the Universe. GRBs provide a means to infer information about
the environments and typical galaxies in which massive stars are formed. Two
main obstacles remain to be crossed before the full potential of GRBs as probes
of massive stars can be harvested: i) we need to build more complete and well
understood samples in order not to be fooled by biases, and ii) we need to
understand to which extent GRBs may be intrinsically biased in the sense that
they are only formed by a limited subset of massive stars defined by most
likely a restricted metallicity interval. We describe the status of an ongoing
effort to build a more complete sample of long-duration GRBs with measured
redshifts. Already now we can conclude that the environments of GRB progenitors
are very diverse with metallicities ranging from solar to a hundredth solar and
extinction ranging from none to A_V>5 mag. We have also identified a sightline
with significant escape of Lyman continuum photons and another with a clear
2175AA extinction bump.Comment: Invited review - in "Massive Stars as Cosmic Engines", IAU Symp. 250
(Kauai), ed. F. Bresolin, P. A. Crowther, and J. Puls (Cambridge University
Press), p. 443-456. Typos and refs correcte
Rapid formation of large dust grains in the luminous supernova SN 2010jl
The origin of dust in galaxies is still a mystery. The majority of the
refractory elements are produced in supernova explosions but it is unclear how
and where dust grains condense and grow, and how they avoid destruction in the
harsh environments of star-forming galaxies. The recent detection of 0.1-0.5
solar masses of dust in nearby supernova remnants suggests in situ dust
formation, while other observations reveal very little dust in supernovae the
first few years after explosion. Observations of the bright SN 2010jl have been
interpreted as pre-existing dust, dust formation or no dust at all. Here we
report the rapid (40-240 days) formation of dust in its dense circumstellar
medium. The wavelength dependent extinction of this dust reveals the presence
of very large (> 1 micron) grains, which are resistant to destructive
processes. At later times (500-900 days), the near-IR thermal emission shows an
accelerated growth in dust mass, marking the transition of the supernova from a
circumstellar- to an ejecta-dominated source of dust. This provides the link
between the early and late dust mass evolution in supernovae with dense
circumstellar media.Comment: 62 pages, 13 figures, 1 table. Author version of the Letter to
Nature, published online July 9 2014 (Nature, 511, 7509, pp. 326-329 (2014)),
prior to the final editorial changes to conform to Journal style; includes
Methods and Extended Data Figures and the Supplementary Information. See
published version
http://www.nature.com/nature/journal/v511/n7509/full/nature13558.htm
Helium in natal HII regions: the origin of the X-ray absorption in gamma-ray burst afterglows
Soft X-ray absorption in excess of Galactic is observed in the afterglows of
most gamma-ray bursts (GRBs), but the correct solution to its origin has not
been arrived at after more than a decade of work, preventing its use as a
powerful diagnostic tool. We resolve this long-standing problem and find that
He in the GRB's host HII region is responsible for most of the absorption. We
show that the X-ray absorbing column density (N_Hx) is correlated with both the
neutral gas column density and with the optical afterglow extinction (Av). This
correlation explains the connection between dark bursts and bursts with high
N_Hx values. From these correlations we exclude an origin of the X-ray
absorption which is not related to the host galaxy, i.e. the intergalactic
medium or intervening absorbers are not responsible. We find that the
correlation with the dust column has a strong redshift evolution, whereas the
correlation with the neutral gas does not. From this we conclude that the
column density of the X-ray absorption is correlated with the total gas column
density in the host galaxy rather than the metal column density, in spite of
the fact that X-ray absorption is typically dominated by metals. The strong
redshift evolution of N_Hx/Av is thus a reflection of the cosmic metallicity
evolution of star-forming galaxies. We conclude that the absorption of X-rays
in GRB afterglows is caused by He in the HII region hosting the GRB. While dust
is destroyed and metals are stripped of all of their electrons by the GRB to
great distances, the abundance of He saturates the He-ionising UV continuum
much closer to the GRB, allowing it to remain in the neutral or singly-ionised
state. Helium X-ray absorption explains the correlation with total gas, the
lack of strong evolution with redshift as well as the absence of dust, metal or
hydrogen absorption features in the optical-UV spectra.Comment: 10 pages, 4 figures, submitted to Ap
Polarimetry of the superluminous supernova LSQ14mo: no evidence for significant deviations from spherical symmetry
We present the first polarimetric observations of a Type I superluminous
supernova (SLSN). LSQ14mo was observed with VLT/FORS2 at five different epochs
in the V band, with the observations starting before maximum light and spanning
26 days in the rest frame (z=0.256). During this period, we do not detect any
statistically significant evolution (< 2) in the Stokes parameters. The
average values we obtain, corrected for interstellar polarisation in the
Galaxy, are Q = -0.01% ( 0.15%) and U = - 0.50% ( 0.14%). This low
polarisation can be entirely due to interstellar polarisation in the SN host
galaxy. We conclude that, at least during the period of observations and at the
optical depths probed, the photosphere of LSQ14mo does not present significant
asymmetries, unlike most lower-luminosity hydrogen-poor SNe Ib/c.
Alternatively, it is possible that we may have observed LSQ14mo from a special
viewing angle. Supporting spectroscopy and photometry confirm that LSQ14mo is a
typical SLSN I. Further studies of the polarisation of Type I SLSNe are
required to determine whether the low levels of polarisation are a
characteristic of the entire class and to also study the implications for the
proposed explosion models.Comment: ApJ Letters, 4 Figures, 3 Tables. The previous version was accepted.
This version contains minor modifications to match proofs (as much as
possible
SN 2007uy - metamorphosis of an aspheric Type Ib explosion
The supernovae of Type Ibc are rare and the detailed characteristics of these
explosions have been studied only for a few events. Unlike Type II SNe, the
progenitors of Type Ibc have never been detected in pre-explosion images. So,
to understand the nature of their progenitors and the characteristics of the
explosions, investigation of proximate events are necessary. Here we present
the results of multi-wavelength observations of Type Ib SN 2007uy in the nearby
( 29.5 Mpc) galaxy NGC 2770. Analysis of the photometric observations
revealed this explosion as an energetic event with peak absolute R band
magnitude , which is about one mag brighter than the mean value
() derived for well observed Type Ibc events. The SN is highly
extinguished, E(B-V) = 0.630.15 mag, mainly due to foreground material
present in the host galaxy. From optical light curve modeling we determine that
about 0.3 M radioactive Ni is produced and roughly 4.4
M material is ejected during this explosion with liberated energy
erg, indicating the event to be an energetic one.
Through optical spectroscopy, we have noticed a clear aspheric evolution of
several line forming regions, but no dependency of asymmetry is seen on the
distribution of Ni inside the ejecta. The SN shock interaction with the
circumburst material is clearly noticeable in radio follow-up, presenting a
Synchrotron Self Absorption (SSA) dominated light curve with a contribution of
Free Free Absorption (FFA) during the early phases. Assuming a WR star, with
wind velocity \ga 10^3 {\rm km s}^{-1}, as a progenitor, we derive a lower
limit to the mass loss rate inferred from the radio data as \dot{M} \ga
2.4\times10^{-5} M, yr, which is consistent with the results
obtained for other Type Ibc SNe bright at radio frequencies.Comment: 22 pages, 13 figures, accepted for publication in MNRA
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