Showing papers by "A. J. Castro-Tirado published in 2010"

The Afterglows of Swift-era Gamma-ray Bursts. I. Comparing pre-Swift and Swift-era Long/Soft (Type II) GRB Optical Afterglows

Abstract: We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to 2009 September, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A, and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host-galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z = 1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, are weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) is very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at 1 day after the GRB in the z = 1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without, reveals no indication that the former are statistically significantly more luminous. Furthermore, we propose the existence of an upper ceiling on afterglow luminosities and study the luminosity distribution at early times, which was not accessible before the advent of the Swift satellite. Most GRBs feature afterglows that are dominated by the forward shock from early times on. Finally, we present the first indications of a class of long GRBs, which form a bridge between the typical high-luminosity, high-redshift events and nearby low-luminosity events (which are also associated with spectroscopic supernovae) in terms of energetics and observed redshift distribution, indicating a continuous distribution overall.

Grb 090313 and the origin of optical peaks in gamma-ray burst light curves: implications for lorentz factors and radio flares

Abstract: A.M. acknowledges funding from the Particle Physics and Astronomy Research Council (PPARC). C.G.M. is grateful for financial support from the Royal Society and Research Councils (UK). A.G. acknowledges founding from the Slovenian Research Agency and from the Centre of Excellence for Space Sciences and Technologies SPACE-SI, an operation partly financed by the European Union, European Regional Development Fund and Republic of Slovenia, Ministry of Higher Education, Science and Technology. I.d.G.-M. is partially supported by Ministerio de Ciencia e Innovaci´on (Spain), grant AYA2008-06189-C03 (including FEDER funds), and by Consejer´ia de Innovaci´on, Ciencia y Empresa of Junta deAndaluc´ia (Spain). The Liverpool Telescope is operated by Liverpool John Moores University at the Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. The Faulkes Telescopes, now owned by Las Cumbres Observatory, are operated with support from the Dill Faulkes Educational Trust. This work is partially based on observations carried out with the IRAM Plateau de Bure Interferometer and observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut f¨ur Astronomie Heidelberg and the Instituto de Astrof´isica de Andaluc´ia (CSIC). IRAM is supported by INSU/CNRS (France),MPG (Germany), and IGN (Spain). We thank Calar Alto Observatory for allocation of director’s discretionary time to this program. We also thank M.R Zapatero-Osorio for the acquisition and reduction of NOT data. The research of J.G. and A.J.C.T. is supported by the Spanish programmes AYA2007-63677, AYA2008-03467/ESP, and AYA2009-14000-C03-01. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.

VLT/X-shooter spectroscopy of the GRB 090926A afterglow

Abstract: Aims. The aim of this paper is to study the environment and intervening absorbers of the gamma-ray burst GRB090926A through analyzing optical spectra of its afterglow. Methods. We analyzed medium-resolution spectroscopic observations (R = 10 000, corresponding to 30 km s(-1), S/N = 15-30 and wavelength range 3000-25 000) of the optical afterglow of GRB090926A, taken with X-shooter at the VLT similar to 22 h after the GRB trigger. Results. The spectrum shows that the ISM in the GRB host galaxy at z = 2.1071 is rich in absorption features, with two components contributing to the line profiles. In addition to the ground state lines, we detect C II, OI, Si II, FeII, and Ni II-excited absorption features, which we used to derive information on the distance between the host absorbing gas and the site of the GRB explosion. The distance of component I is found to be 2.40 +/- 0.15 kpc, while component II is located far away from the GRB, possibly at similar to 5 kpc. These values are compatible with those found for other GRBs. The hydrogen column density associated to GRB 090926A is log N-H/cm(-2) = 21.60 +/- 0.07, and the metallicity of the host galaxy is in the range [X/H] = -2.5 to -1.9 with respect to the solar values, i.e., among the lowest values ever observed for a GRB host galaxy. A comparison with galactic chemical evolution models has suggested that the host of GRB090926A is likely to be a dwarf-irregular galaxy. No emission lines were detected, but a Ha flux in emission of 9 x 10(-18) erg s(-1) cm(-2) (i.e., a star-formation rate of 2 M-circle dot yr(-1)), which is typical of many GRB hosts, would have been detected in our spectra, and thus emission lines are well within the reach of X-shooter. We put an upper limit to the H molecular fraction of the host galaxy ISM, which is f < 7x10(-7). The continuum has been fitted assuming a power-law spectrum, with a spectral index of beta = 0.89(-0.02)(+0.02) . The best fit does essentially not require any intrinsic extinction because EB-V < 0.01 mag adopting a SMC extinction curve. Finally, the line of sight of GRB090926A presents four weak intervening absorption systems in the redshift range 1.24 < z < 1.95.

GRB 090313 and the Origin of Optical Peaks in GRB Light Curves: Implications for Lorentz Factors and Radio Flares

Abstract: We use a sample of 19 Gamma Ray Bursts (GRBs) that exhibit single-peaked optical light curves to test the standard fireball model by investigating the relationship between the time of the onset of the afterglow and the temporal rising index. Our sample includes GRBs and X-ray flashes for which we derive a wide range of initial Lorentz factors ($40 < \Gamma < 450$). Using plausible model parameters the typical frequency of the forward shock is expected to lie close to the optical band; within this low typical frequency framework, we use the optical data to constrain $\epsilon_e$ and show that values derived from the early time light curve properties are consistent with published typical values derived from other afterglow studies. We produce expected radio light curves by predicting the temporal evolution of the expected radio emission from forward and reverse shock components, including synchrotron self-absorption effects at early time. Although a number of the GRBs in this sample do not have published radio measurements, we demonstrate the effectiveness of this method in the case of {\it Swift} GRB 090313, for which millimetric and centrimetric observations were available, and conclude that future detections of reverse-shock radio flares with new radio facilities such as the EVLA and ALMA will test the low frequency model and provide constraints on magnetic models.

Unveiling the Origin of Grb 090709A: Lack of Periodicity in a Reddened Cosmological Long-Duration Gamma-Ray Burst

Abstract: We present broadband (gamma-ray, X-ray, near-infrared, optical, and radio) observations of the Swift gamma-ray burst (GRB) 090709A and its afterglow in an effort to ascertain the origin of this high-energy transient. Previous analyses suggested that GRB090709A exhibited quasi-periodic oscillations with a period of 8.06s, a trait unknown in long-duration GRBs but typical of flares from soft gamma-ray repeaters. When properly accounting for the underlying shape of the power-density spectrum of GRB090709A, we find no conclusive (>3σ) evidence for the reported periodicity. In conjunction with the location of the transient (far from the Galactic plane and absent any nearby host galaxy in the local universe) and the evidence for extinction in excess of the Galactic value, we consider a magnetar origin relatively unlikely. A long-duration GRB, however, can account for the majority of the observed properties of this source. GRB090709A is distinguished from other long-duration GRBs primarily by the large amount of obscuration from its host galaxy (AK,obs ≳ 2mag). © 2010. The American Astronomical Society. All rights reserved..

GRB 021004: Tomography of a gamma-ray burst progenitor and its host galaxy

Abstract: Aims. We analyse the distribution of matter around the progenitor star of gamma-ray burst GRB 021004 and the properties of its host galaxy with high-resolution echelle and near-infrared spectroscopy. Methods. Observations were taken by the 8.2 m Very Large Telescope with the Ultraviolet and Visual Echelle spectrograph (UVES) and the Infrared Spectrometer And Array Camera (ISAAC) between 10 and 14 h after the onset of the event. Results. We report the first detection of emission lines from a GRB host galaxy in the near-infrared, detecting Hα and the [O III] doublet. These allow us to independently measure the systemic redshift (z = 2.3304 ± 0.0005), which is not contaminated by absorption as the Lyα line is, and infer the host galaxy properties. From the visual echelle spectroscopy, we find several absorptionline groups spanning a range of about 3000 km s −1 in velocity relative to the redshift of the host galaxy. The absorption profiles are very complex with both velocity-broadened components extending over several 100 km s −1 and narrow lines with velocity widths of only ∼20 km s −1 . By analogy with QSO absorption line studies, the relative velocities, widths, and degrees of ionization of the lines (“line-locking”, “ionization-velocity correlation”) show that the progenitor had both an extremely strong radiation field and several distinct mass-loss phases (winds). Conclusions. These results are consistent with GRB progenitors being massive stars, such as luminous blue variables (LBVs) or Wolf-Rayet stars, providing a detailed picture of the spatial and velocity structure of the GRB progenitor star at the time of explosion. −

Challenging gamma-ray burst models through the broadband dataset of GRB 060908

Abstract: Context. Multiwavelength observations of gamma-ray burst prompt and afterglow emission are a key tool to separate the various possible emission processes and scenarios proposed to interpret the complex gamma-ray burst phenomenology. Aims. We collected a large dataset on GRB 060908 in order to carry out a comprehensive analysis of the prompt emission as well as the early and late afterglow. Methods. Data from Swift-BAT, -XRT and -UVOT together with data from a number of different ground-based optical/near-infrared and millimeter telescopes allowed us to follow the afterglow evolution after about a minute from the high-energy event down to the host galaxy limit. We discuss the physical parameters required to model these emissions. Results. The prompt emission of GRB 060908 was characterised by two main periods of activity, spaced by a few seconds of low intensity, with a tight correlation between activity and spectral hardness. Observations of the afterglow began less than one minute after the high-energy event, when it was already in a decaying phase, and it was characterised by a rather flat optical/near-infrared spectrum which can be interpreted as due to a hard energy-distribution of the emitting electrons. On the other hand, the X-ray spectrum of the afterglow could be fit by a rather soft electron distribution. Conclusions. GRB 060908 is a good example of a gamma-ray burst with a rich multi-wavelength set of observations. The availability of this dataset, built thanks to the joint efforts of many different teams, allowed us to carry out stringent tests for various interpretative scenarios, showing that a satisfactorily modelling of this event is challenging. In the future, similar efforts will enable us to obtain optical/near-infrared coverage comparable in quality and quantity to the X-ray data for more events, therefore opening new avenues to progress gamma-ray burst research.

GRB 021004: Tomography of a gamma-ray burst progenitor and its host galaxy

Abstract: We analyse the distribution of matter around the progenitor star of gamma-ray burst GRB 021004 as well as the properties of its host galaxy with high-resolution echelle as well as near-infrared spectroscopy. Observations were taken by the 8.2m Very Large Telescope with the Ultraviolet and Visual Echelle spectrograph (UVES) and the Infrared Spectrometer And Array Camera (ISAAC) between 10 and 14 hours after the onset of the event. We report the first detection of emission lines from a GRB host galaxy in the near-infrared, detecting H-alpha and the [O III] doublet. These allow an independent measurement of the systemic redshift (z = 2.3304 +/- 0.0005) which is not contaminated by absorption as the Ly-alpha line is, and the deduction of properties of the host galaxy. From the visual echelle spectroscopy, we find several absorption line groups spanning a range of about 3,000 km/s in velocity relative to the redshift of the host galaxy. The absorption profiles are very complex with both velocity-broadened components extending over several 100 km/s and narrow lines with velocity widths of only 20 km/s. By analogy with QSO absorption line studies, the relative velocities,widths, and degrees of ionization of the lines ("line-locking", "ionization--velocity correlation") show that the progenitor had both an extremely strong radiation field and several distinct mass loss phases (winds). These results are consistent with GRB progenitors being massive stars, such as Luminous Blue Variables (LBVs) or Wolf--Rayet stars, providing a detailed picture of the spatial and velocity structure of the GRB progenitor star at the time of explosion. The host galaxy is a prolific star-forming galaxy with a SFR of about 40 solar masses per year.

Challenging GRB models through the broadband dataset of GRB060908

Abstract: Context: Multiwavelength observations of gamma-ray burst prompt and afterglow emission are a key tool to disentangle the various possible emission processes and scenarios proposed to interpret the complex gamma-ray burst phenomenology. Aims: We collected a large dataset on GRB060908 in order to carry out a comprehensive analysis of the prompt emission as well as the early and late afterglow. Methods: Data from Swift-BAT, -XRT and -UVOT together with data from a number of different ground-based optical/NIR and millimeter telescopes allowed us to follow the afterglow evolution from about a minute from the high-energy event down to the host galaxy limit. We discuss the physical parameters required to model these emissions. Results: The prompt emission of GRB060908 was characterized by two main periods of activity, spaced by a few seconds of low intensity, with a tight correlation between activity and spectral hardness. Observations of the afterglow began less than one minute after the high-energy event, when it was already in a decaying phase, and it was characterized by a rather flat optical/NIR spectrum which can be interpreted as due to a hard energy-distribution of the emitting electrons. On the other hand, the X-ray spectrum of the afterglow could be fit by a rather soft electron distribution. Conclusions: GRB060908 is a good example of a gamma-ray burst with a rich multi-wavelength set of observations. The availability of this dataset, built thanks to the joint efforts of many different teams, allowed us to carry out stringent tests for various interpretative scenarios showing that a satisfactorily modeling of this event is challenging. In the future, similar efforts will enable us to obtain optical/NIR coverage comparable in quality and quantity to the X-ray data for more events, therefore opening new avenues to progress gamma-ray burst research.

Simultaneous polarization monitoring of supernovae SN 2008D/XT 080109 and SN 2007uy: isolating geometry from dust

Abstract: Context. The possible existence of a continuum encompassing the diversity of explosive stellar deaths, ranging from ordinary supernovae (SNe; lacking any sign of a relativistic outflow) to relativistic hypernovae associated with energetic long duration gamma-ray bursts (GRBs), is under intense debate. In this context, the supernova SN 2008D associated with the X-ray transient (XT) 080109 could represent a paradigmatic case, since it might exemplify a potential borderline transition event. Optical polarimetric studies could contribute to shed light on the different interpretations given in the literature for this supernova (hereafter, SN 2008D/XT 080109). Aims. The main aim is to infer geometric information of SN 2008D/XT 080109 through the study of the evolution of its linear optical polarization. We also report the polarization evolution of SN 2007uy, and discuss the properties of the host galaxy interstellar medium (ISM) towards the XT. The final goal is to compare the polarization properties, and therefore the geometries, of both SNe. Methods. We present a V-band linear polarization monitoring campaign carried out for SN 2008D/XT 080109 and SN 2007uy, which shone for weeks contemporaneously in NGC 2770. This fortunate coincidence brought us the opportunity to observe both objects simultaneously, and most importantly, with identical instrumental setups. The observations span 74.9 days, starting 3.6 days after the XT and are distributed in 11 visits. In addition we performed observations in the millimetre (mm) range in order to identify the dominant origin of the observed polarization. Results. We report positive linear polarization detections at several epochs for SN 2008D/XT 080109 at a level of ∼1%. For SN 2007uy the measured polarization is around ∼1.5%. In both cases the observed linear polarization seems dominated by the host galaxy interstellar polarization (HGIP), especially for the case of SN 2007uy. SN 2007uy shows Stokes parametres consistent with no time evolution, which could be described by the HGIP plus a constant eccentricity expansion on the sky plane. Over the course of our observations of SN 2007uy, we find that its total polarization signal does not change by more than 0.29% with a 90% confidence interval. Despite the dominant HGIP, a statistical analysis of the distribution of the SN 2008D/XT 080109 Stokes parametres suggests that it could show a possible intrinsic variable polarization component. Moreover, assuming the polarization signal from SN 2007uy is constant, we find that the temporal evolution of the intrinsic SN 2008D/XT 080109 polarization could be explained by an aspherical axisymmetric expansion with variable eccentricity, although other more complex geometric scenarios are also compatible with the data. We come to the same result even if we make no assumption on the SN 2007uy Stokes parametres, although at a lower significance level. Conclusions. We conclude that the data seem to suggest a potential symmetry axis for SN 2008D/XT 080109, which is reinforced when SN 2007uy is assumed to have constant Stokes parametres and used as reference star. We suggest that at least the projected, if not the intrinsic, geometry of SN 2008D/XT 080109 and SN 2007uy could be different.

Robotic Autonomous Observatories: A Historical Perspective

Abstract: This paper presents a historical introduction to the field of Robotic Astronomy, from the point of view of a scientist working in this field for more than a decade. The author discusses the basic definitions, the differing telescope control operating systems, observatory managers, as well as a few current scientific applications.

Four Years of Real-Time GRB Followup by BOOTES-1B (2005–2008)

Abstract: Four years of BOOTES-1B GRB follow-up history are summarised for the first time in the form of a table. The successfully followed events are described case by case. Further, the data are used to show the GRB trigger rate in Spain on a per-year basis, resulting in an estimate of 18 triggers and about 51 hours of telescope time per year for real-time triggers. These numbers grow to about 22 triggers and 77 hours per year if we include also the GRBs observable within 2 hours after the trigger.

Detection of the high z GRB 080913 and its implications on progenitors and energy extraction mechanisms

Abstract: Aims. We present multiwavelength observations of one of the most distant gamma-ray bursts detected so far, GRB 080913. Based on these observations, we consider whether it could be classified as a short-duration GRB and discuss the implications for the progenitor nature and energy extraction mechanisms. Methods. Multiwavelength X-ray, near IR and millimetre observations were made between 20.7 h and ∼16.8 days after the event. Results. Whereas a very faint afterglow was seen at the 3.5m CAHA telescope in the nIR, the X-ray afterglow was clearly detected in both Swift and XMM-Newton observations. An upper limit is reported in the mm range. We have modeled the data assuming a collimated θ0 3 ◦ blast wave with an energy injection at ∼0.5 days carrying 5 ∼ 10 52 erg or approximately 12 times the initial energy of the blast wave. We find that GRB 080913 shares many of the gamma-ray diagnostics with the more recent burst GRB 090423 for being classified as short had they ocurred at low redshift. If the progenitor were a compact binary merger, it is likely composed by a NS and BH. The Blandford-Znajek (BZ) mechanism is the preferred one to extract energy from the central, maximally-rotating BH. Both the magnetic field close to the event horizon (B )a nd the BH mass (Mbh) are restricted within a relatively narrow range, such that (B/3 × 10 16 G)(Mbh/7 M� ) ∼ 1. Similar constraints on the central BH hold for collapsar-like progenitor systems if the BZ-mechanism works for the system at hand.

Is the plateau state in GRS 1915+105 equivalent to canonical hard states?

Abstract: GRS 1915+105 is a very peculiar black hole binary that exhibits accretion-related states that are not observed in any other stellar-mass black hole system. One of these states, however - referred to as the plateau state - may be related to the canonical hard state of black hole X-ray binaries. Both the plateau and hard state are associated with steady, relatively lower X-ray emission and flat/inverted radio emission, that is sometimes resolved into compact, self-absorbed jets. However, while generally black hole binaries quench their jets when the luminosity becomes too high, GRS 1915+105 seems to sustain them despite the fact that it accretes at near- or super-Eddington rates. In order to investigate the relationship between the plateau and the hard state, we fit two multiwavelength observations using a steady-state outflow-dominated model, developed for hard-state black hole binaries. The data sets consist of quasi-simultaneous observations in radio, near-infrared and X-ray bands. Interestingly, we find both significant differences between the two plateau states, as well as between the best-fitting model parameters and those representative of the hard state. We discuss our interpretation of these results, and the possible implications for GRS 1915+105's relationship to canonical black hole candidates.

Is the plateau state in GRS 1915+105 equivalent to canonical hard states?

Abstract: GRS1915+105 is a very peculiar black hole binary that exhibits accretion-related states that are not observed in any other stellar-mass black hole system One of these states, however -- referred to as the plateau state -- may be related to the canonical hard state of black hole X-ray binaries Both the plateau and hard state are associated with steady, relatively lower X-ray emission and flat/inverted radio emission, that is sometimes resolved into compact, self-absorbed jets However, while generally black hole binaries quench their jets when the luminosity becomes too high, GRS1915+105 seems to sustain them despite the fact that it accretes at near- or super-Eddington rates In order to investigate the relationship between the plateau and the hard state, we fit two multi-wavelength observations using a steady-state outflow-dominated model, developed for hard state black hole binaries The data sets consist of quasi-simultaneous observations in radio, near-infrared and X-ray bands Interestingly, we find both significant differences between the two plateau states, as well as between the best-fit model parameters and those representative of the hard state We discuss our interpretation of these results, and the possible implications for GRS 1915+105's relationship to canonical black hole candidates

Study of envelope velocity evolution of core-collapse type Ib-c supernovae from observations of XRF 080109 / SN 2008D and GRB 060218 / SN 2006aj with BTA

Abstract: Results of modeling the spectra of two supernovae SN2008D and SN2006aj related to the X-ray flash XRF 080109 and gamma-ray burst GRB/XRF 060218, respectively, are studied The spectra were obtained with the 6-meter BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences in 648 and 2761 days after the explosion of SN2008D, and in 255 and 355 days after the explosion of SN2006aj The spectra were interpreted in the Sobolev approximation with the SYNOW code An assumption about the presence of envelopes around the progenitor stars is confirmed by an agreement between the velocities of lines interpreted as hydrogen and helium, and the empiric power-law velocity drop with time for the envelopes of classic core-collapse supernovae Detection of a P Cyg profile of the Hβ line in the spectra of optical afterglows of GRBs can be a determinative argument in favor of this hypothesis

Four Years of Realtime GRB Followup by BOOTES-1B (2005-2008)

Abstract: Four years of BOOTES-1B GRB follow-up history are summarised for the first time in the form of a table. The successfully followed events are described case by case. Further, the data are used to show the GRB trigger rate in Spain on a per-year basis, resulting in an estimate of 18 triggers and about 51 h of telescope time per year for real time triggers. These numbers grow to about 22 triggers and 77 h per year if we include also the GRBs observable within 2 hours after the trigger.

Study of Envelope Velocity Evolution of Type Ib-c Core-Collapse Supernovae from Observations of XRF 080109 / SN 2008D and GRB 060218 / SN 2006aj with BTA

Abstract: Results of modeling the spectra of two supernovae SN 2008D and SN 2006aj related to the X-ray flash XRF 080109 and gamma-ray burst GRB / XRF 060218, respectively, are studied. The spectra were obtained with the 6-meter BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences in 6.48 and 27.61 days after the explosion of SN 2008D, and in 2.55 and 3.55 days after the explosion of SN 2006aj. The spectra were interpreted in the Sobolev approximation with the SYNOW code. An assumption about the presence of envelopes around the progenitor stars is confirmed by an agreement between the velocities of lines interpreted as hydrogen and helium, and the empiric power-law velocity drop with time for the envelopes of classic core-collapse supernovae. Detection of a P Cyg profile of the H-beta line in the spectra of optical afterglows of GRBs can be a determinative argument in favor of this hypothesis.

A tale of two GRB-SNe at a common redshift of z = 0.54

Abstract: We present ground-based and HST optical observations of the optical transients (OTs) of long-duration Gamma Ray Bursts (GRBs) 060729 and 090618, both at a redshift of z = 0.54. For GRB 060729, bumps are seen in the optical light curves (LCs), and the late-time broadband spectral energy distributions (SEDs) of the OT resemble those of local type Ic supernovae (SNe). For GRB 090618, the dense sampling of our optical observations has allowed us to detect well-defined bumps in the optical LCs, as well as a change in colour, that are indicative of light coming from a core-collapse SN. The accompanying SNe for both events are individually compared with SN1998bw, a known GRB-supernova, and SN1994I, a typical type Ic supernova without a known GRB counterpart, and in both cases the brightness and temporal evolution more closely resemble SN1998bw. We also exploit our extensive optical and radio data for GRB 090618, as well as the publicly-available SWIFT -XRT data, and discuss the properties of the afterglow at early times. In the context of a simple jet-like model, the afterglow of GRB 090618 is best explained by the presence of a jet-break at t-to > 0.5 days. We then compare the rest-frame, peak V -band absolute magnitudes of all of the GRB and X-Ray Flash (XRF)-associated SNe with a large sample of local type Ibc SNe, concluding that, when host extinction is considered, the peak magnitudes of the GRB/XRF-SNe cannot be distinguished from the peak magnitudes of non-GRB/XRF SNe.

Design, Manufacturing, and Commissioning of BIRCAM (Bootes InfraRed CAMera)

Abstract: This paper covers the various aspect of design, manufacturing and commissioning of the infrared camera BIRCAM, installed at BOOTES-IR, the 60 cm robotic infrared telescope at Sierra Nevada Observatory (OSN, Granada, Spain). We describe how we achieved a quality astronomical image, moving from the scientific requirements.

Recent GRBs Observed with the 1.23 m CAHA Telescope and the Status of Its Upgrade

Abstract: We report on optical observations of Gamma-Ray Bursts (GRBs) followed up by our collaboration with the 1.23 m telescope located at the Calar Alto observatory. The 1.23 m telescope is an old facility, currently undergoing upgrades to enable fully autonomous response to GRB alerts. We discuss the current status of the control system upgrade of the 1.23 m telescope. The upgrade is being done by our group based on the Remote Telescope System, 2nd Version (RTS2), which controls the available instruments and interacts with the EPICS database of Calar Alto. (Our group is called ARAE (Robotic Astronomy & High-Energy Astrophysics) and is based on members of IAA (Instituto de Astrofisica de Andalucia). Currently the ARAE group is responsible to develop the BOOTES network of robotic telescopes (Jelinek et al. 2009).) Currently the telescope can run fully autonomously or under observer supervision using RTS2. The fast reaction response mode for GRB reaction (typically with response times below 3 minutes from the GRB onset) still needs some development and testing. The telescope is usually operated in legacy interactive mode, with periods of supervised autonomous runs under RTS2. We show the preliminary results of several GRBs followed up with observer intervention during the testing phase of the 1.23 m control software upgrade.

ERRATUM: “LOW-RESOLUTION SPECTROSCOPY OF GAMMA-RAY BURST OPTICAL AFTERGLOWS: BIASES IN THE SWIFT SAMPLE AND CHARACTERIZATION OF THE ABSORBERS*” (2009, ApJS, 185, 526)

Abstract: In this paper, Figure 14 is incomplete due to an error during production. We here provide the missing sub-figures.

Searching for differences in Swift's intermediate GRBs

Abstract: Gamma-ray bursts are usually classified through their high-energy emission into short-duration and long-duration bursts, which presumably reflect two different types of progenitors. However, it has been shown on statistical grounds that a third, intermediate population is needed in this classification scheme, although an extensive study of the properties of this class has so far not been done. The large amount of follow-up studies generated during the Swift era allows us to have a suficient sample to attempt a study of this third population through the properties of their prompt emission and their afterglows. Our study is focused on a sample of GRBs observed by Swift during its first four years of operation. The sample contains those bursts with measured redshift since this allows us to derive intrinsic properties. Intermediate bursts are less energetic and have dimmer afterglows than long GRBs, especially when considering the X-ray light curves, which are on average one order of magnitude fainter than long bursts. There is a less significant trend in the redshift distribution that places intermediate bursts closer than long bursts. Except for this, intermediate bursts show similar properties to long bursts. In particular, they follow the Epeak vs. Eiso correlation and have, on average, positive spectral lags with a distribution similar to that of long bursts. Like long GRBs, they normally have an associated supernova, although some intermediate bursts have shown no supernova component. This study shows that intermediate bursts are different from short bursts and, in spite of sharing many properties with long bursts, there are some differences between them as well. We suggest that the physical difference between intermediate and long bursts could be that for the first the ejecta are thin shells while for the latter they are thick shells.

Host galaxy of the dark gamma-ray burst GRB 051008

Abstract: We have discovered and studied the host galaxy of the “dark” gamma-ray burst GRB051008, a burst for which no optical afterglow has been detected. We studied the properties and determined the redshift of the host galaxy and analyzed its neighborhood. We perform a comparative analysis of the properties of GRB051008 and its host galaxy with the properties of other known dark gamma-ray bursts. We analyze the causes of the lack of optical afterglow in this gamma-ray burst.

OCTOCAM: A fast multichannel imager and spectrograph for the 10.4m GTC

Abstract: OCTOCAM is a multi-channel imager and spectrograph that has been proposed for the 10.4m GTC telescope. It will use dichroics to split the incoming light to produce simultaneous observations in 8 different bands, ranging from the ultraviolet to the near-infrared. The imaging mode will have a field of view of 2' x 2' in u, g, r, i, z, J, H and Ks bands, whereas the long-slit spectroscopic mode will cover the complete range from 4,000 to 23,000 {\AA} with a resolution of 700 - 1,700 (depending on the arm and slit width). An additional mode, using an image slicer, will deliver a spectral resolution of over 3,000. As a further feature, it will use state of the art detectors to reach high readout speeds of the order of tens of milliseconds. In this way, OCTOCAM will be occupying a region of the time resolution - spectral resolution - spectral coverage diagram that is not covered by a single instrument in any other observatory, with an exceptional sensitivity.

Simultaneous polarization monitoring of the X-ray flash XRF080109/SN2008D and SN2007uy: isolating geometry from dust

Abstract: Context. There is a general consensus that Long Gamma-Ray Bursts (GRBs), including X-ray Flashes (XRFs), are created by the explosion of massive stars. However little is still known about the geometry of such stellar explosions. In this paper we study the optical polarimetric properties of an XRF dominated by the associated hypernova, in other words, an XRF with no contaminating afterglow. The final scope of this study is to shed light on the still uncertain picture of the GRBs’ expansion geometry. Aims. The main aim is to investigate the evolution of the linear optical polarization of the X-ray flash XRF 080109 /SN 2008D. As a secondary product, we also report the polarization evolution of SN 2007uy, and discuss the properties of the host galaxy interstellar medium (ISM) towards the XRF. Methods. We present a V-band linear polarization monitoring campaign carried out for the X-ray flash XRF 080109/SN 2008D and SN 2007uy, which shone for weeks contemporaneously in NGC 2770. This fortunate coincidence brought us the opportunity to observe both objects simultaneously, and most importantly, with identical instrumental setups. The observations span 7 4.9 days, starting 3.6 days after the X-ray flash and are distributed in 11 visits . In addition we performed observations in the millimetre (mm) range in order to identify the dominant origin of the observed polarization. Results. We report positive linear polarization detections at sever al epochs for XRF 080109/SN 2008 at a level of∼1%. For SN 2007uy the measured polarization is around∼ 1.5%. In both cases the observed linear polarization seems dominated by the host galaxy interstellar polarization (HGIP), especially for the case of SN 2 007uy. Dust emission at 1.2 mm detected at and around the XRF position supports this scenario. Despite the dominant HGIP, a statistical analysis of the distribution of the XRF 080109/SN 2008D Stokes parametres suggests that it could show a possible intrinsic variable polarization component. Moreover we show that the temporal evolution of the intrinsic XRF 080109/SN 2008D polarization could be explained by an aspherical axisymmetric expansion with variable eccentricity, although other more complex geometric scenarios are also compatible. In contrast, the SN 2007uy polarization could be described by the HGIP plus a constant eccentricity expansion on the plane of the sky. We suggest that at least the projected, if not the intrinsic, geometry of XRF 080109/SN 2008D and SN 2007uy could be different.