Searcharxiv⌕ Search

arXiv subjects

Alberto J. Castro-Tirado

Publications and source records attributed to Alberto J. Castro-Tirado.

54 records · Page 3Linked to original sources
arXiv2013

The 2011 October Draconids outburst. I. Orbital elements, meteoroid fluxes and 21P/Giacobini-Zinner delivered mass to Earth

On October 8th, 2011 the Earth crossed the dust trails left by comet 21P/Giacobini-Zinner during its XIX and XX century perihelion approaches with the comet being close to perihelion. The geometric circumstances of that encounter were thus favorable to produce a meteor storm, but the trails were much older than in the 1933 and 1946 historical encounters. As a consequence the 2011 October Draconid display exhibited several activity peaks with Zenithal Hourly Rates of about 400 meteors per hour. In fact, if the display had been not forecasted, it could have passed almost unnoticed as was strongly attenuated for visual observers due to the Moon. This suggests that most meteor storms of a similar nature could have passed historically unnoticed under unfavorable weather and Moon observing conditions. The possibility of obtaining information on the physical properties of cometary meteoroids penetrating the atmosphere under low-geocentric velocity encounter circumstances motivated us to set up a special observing campaign. Added to the Spanish Fireball Network wide-field all-sky and CCD video monitoring, other high-sensitivity 1/2" black and white CCD video cameras were attached to modified medium-field lenses for obtaining high resolution orbital information. The trajectory, radiant, and orbital data of 16 October Draconid meteors observed at multiple stations are presented. The results show that the meteors appeared from a geocentric radiant located at R.A.=263.0+-0.4 deg. and Dec.=+55.3+-0.3 deg. that is in close agreement with the radiant predicted for the 1873-1894 and the 1900 dust trails. The estimated mass of material from 21P/Giacobini-Zinner delivered to Earth during the six-hours outburst was around 950+-150 kg.

astro-ph.EP↗
arXiv2012

The Highly Energetic Expansion of SN2010bh Associated with GRB 100316D

We present the spectroscopic and photometric evolution of the nearby (z = 0.059) spectroscopically confirmed type Ic supernova, SN 2010bh, associated with the soft, long-duration gamma-ray burst (X-ray flash) GRB 100316D. Intensive follow-up observations of SN 2010bh were performed at the ESO Very Large Telescope (VLT) using the X-shooter and FORS2 instruments. Owing to the detailed temporal coverage and the extended wavelength range (3000--24800 A), we obtained an unprecedentedly rich spectral sequence among the hypernovae, making SN 2010bh one of the best studied representatives of this SN class. We find that SN 2010bh has a more rapid rise to maximum brightness (8.0 +/- 1.0 rest-frame days) and a fainter absolute peak luminosity (L_bol~3e42 erg/s) than previously observed SN events associated with GRBs. Our estimate of the ejected (56)Ni mass is 0.12 +/- 0.02 Msun. From the broad spectral features we measure expansion velocities up to 47,000 km/s, higher than those of SNe 1998bw (GRB 980425) and 2006aj (GRB 060218). Helium absorption lines He I lambda5876 and He I 1.083 microm, blueshifted by ~20,000--30,000 km/s and ~28,000--38,000 km/s, respectively, may be present in the optical spectra. However, the lack of coverage of the He I 2.058 microm line prevents us from confirming such identifications. The nebular spectrum, taken at ~186 days after the explosion, shows a broad but faint [O I] emission at 6340 A. The light-curve shape and photospheric expansion velocities of SN 2010bh suggest that we witnessed a highly energetic explosion with a small ejected mass (E_k ~ 1e52 erg and M_ej ~ 3 Msun). The observed properties of SN 2010bh further extend the heterogeneity of the class of GRB supernovae.

astro-ph.HE↗
arXiv2012

BOOTES Observation of GRB 080603B

We report on multicolor photometry of long GRB080603B afterglow from BOOTES-1B and BOOTES-2. The optical afterglow has already been reported to present a break in the optical lightcurve at 0.12+/-0.2 days after the trigger. We construct the lightcurve and the spectral energy distribution and discuss the nature of the afterglow.

astro-ph.HE↗
arXiv2010

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

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 Å 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.

astro-ph.IM↗
arXiv2010

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

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.

astro-ph.HE↗
arXiv2010

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

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.

astro-ph.HE↗
arXiv2010

Recent GRBs observed with the 1.23m CAHA telescope and the status of its upgrade

We report on optical observations of Gamma-Ray Bursts (GRBs) followed up by our collaboration with the 1.23m telescope located at the Calar Alto observatory. The 1.23m 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 1.23m telescope. The upgrade is being done by the ARAE our group, based on members of IAA (Instituto de Astrofiisica de Andalucia). Currently the ARAE group is responsible to develop the BOOTES network of robotic telescopes based on the Remote Telescope System, 2nd Version (RTS2), which controls the available instruments and interacts with the EPICS database of Calar Alto. 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 1.23m control software upgrade.

astro-ph.IM↗
arXiv2006

The bright optical flash from GRB 060117

We present a discovery and observation of an extraordinarily bright prompt optical emission of the GRB 060117 obtained by a wide-field camera atop the robotic telescope FRAM of the Pierre Auger Observatory from 2 to 10 minutes after the GRB. We found rapid average temporal flux decay of alpha = -1.7 +- 0.1 and a peak brightness R = 10.1 mag. Later observations by other instruments set a strong limit on the optical and radio transient fluxes, unveiling an unexpectedly rapid further decay. We present an interpretation featuring a relatively steep electron-distribution parameter p ~ 3.0 and providing a straightforward solution for the overall fast decay of this optical transient as a transition between reverse and forward shock.

astro-ph↗
arXiv2003

A very energetic supernova associated with the gamma-ray burst of 29 March 2003

Over the past five years evidence has mounted that long-duration (> 2 s) gamma-ray bursts (GRBs)--the most brilliant of all astronomical explosions--signal the collapse of massive stars in our Universe. This evidence was originally based on the probable association of one unusual GRB with a supernova, but now includes the association of GRBs with regions of massive star formation in distant galaxies, the appearance of supernova-like 'bumps' in the optical afterglow light curves of several bursts and lines of freshly synthesized elements in the spectra of a few X-ray afterglows. These observations support, but do not yet conclusively demonstrate, the idea that long-duration GRBs are associated with the deaths of massive stars, presumably arising from core collapse. Here we report evidence that a very energetic supernova (a hypernova) was temporally and spatially coincident with a GRB at redshift z = 0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs, thereby favouring the 'collapsar' model.

astro-ph↗
arXiv2001

Follow-up observations from observatories based in Spain

We present a review of the follow-up observations carried out from observatories located in Spain; Calar-Alto, Izanha and Roque de Los Muchachos. It summarizes the observations carried out by our group for 27 GRBs occurred in the period 1999-2000, spanning from GRB 990123 to GRB 001007.

astro-ph↗
arXiv2001

Observations and theoretical models of gamma-ray bursts

GRBs have remained a puzzle for many high-energy astrophysicists since their discovery in 1967. With the advent of the X-ray satellites BeppoSAX and RossiXTE, it has been possible to carry out deep multi-wavelength observations of the counterparts associated with the long GRBs class just within a few hours of occurence, thanks to the observation of the fading X-ray emission that follows the more energetic gamma-ray photons once the GRB event has ended. The fact that this emission (the afterglow) extends at longer wavelengths, has led to the discovery optical/IR/radio counterparts in 1997-2000, greatly improving our understanding of these sources. Now it is widely accepted that GRBs originate at cosmological distances with energie releases of 10^51-10^53 ergs. About 25 host galaxies have been detected so far for long-duration GRBs. The observed afterglow satisfies the predictions of the "standard" relativistic fireball model, and the central engines that power these extraordinary events are thought to be the collapse of massive stars rather than the merging of compact objects as previously also suggested. Short GRBs still remain a mystery as no counterparts have been detected.

astro-ph↗
arXiv2000

Multifrequency studies of Gamma-Ray bursts: towards the understanding of the mystery

GRBs have remained a puzzle for many high-energy astrophysicists since their discovery in 1967. With the advent of the X-ray satellites BeppoSAX and RossiXTE, it has been possible to carry out deep multi-wavelength observations of the counterparts associated with the GRBs just within a few hours of occurence, thanks to the observation of the fading X-ray emission that follows the more energetic gamma-ray photons once the GRB event has ended. The fact that this emission (the afterglow) extends at longer wavelengths, has led to the discovery of the first optical/IR/radio counterparts in 1997-99, greatly improving our understanding of these sources. Now it is widely accepted that GRBs originate at cosmological distances. The observed afterglow satisfies the predictions of the "standard" relativistic fireball model, and the central engines that power these extraordinary events are thought to be the collapse of massive stars or the merging of compact objects.

astro-ph↗
arXiv1999

Cosmic gamma-ray bursts: the most energetic phenomenon in the Universe

Gamma-Ray Bursts (GRBs) have remained a puzzle for many high-energy astrophysicists since their discovery in 1967. With the advent of the X-ray satellites BeppoSAX and RossiXTE, it has been possible to carry out deep multi-wavelength observations of the counterparts associated with the GRBs just within a few hours of occurence, thanks to the observation of the fading X-ray emission that follows the more energetic gamma-ray photons once the GRB event has ended. The fact that this emission (the afterglow) extends at longer wavelengths, has led to the discovery of the first optical/IR/radio counterparts in 1997-98, greatly improving our understanding of these sources. Now it is widely accepted that GRBs originate at cosmological distances but while the observed afterglow satisfies the predictions of the relativistic fireball models, the central engines that power these extraordinary events remain still unknown. Detailed results for nine selected GRBs are presented as well as a summary of the GRB counterparts and host galaxies found so far.

astro-ph↗
arXiv1998

Multiwavelength observations of gamma-ray bursts: Towards the understanding of the mystery

Since their discovery in 1973, Gamma-Ray Bursts (GRBs) have remained for many years one of the most elusive mysteries in High Energy-Astrophysics. The main problem regarding the nature of GRBs has usually been the lack of knowledge of their distance scale. About 300 GRBs are detected annually by BATSE in the full sky, but only a few of them can be localized accurately to less than half a degree. For many years, follow-up observations by other satellites and ground-based telescopes were conducted, but no counterparts at other wavelengths were found. The breakthrough took place in 1997, thanks to the observation by BeppoSAX and RossiXTE of the fading X-ray emission that follows the more energetic gamma-ray photons once the GRB event has ended. This emission (the afterglow) extends at longer wavelengths, and the good accuracy in the position determination by BeppoSAX has led to the discovery of the first optical counterparts -for GRB 970228, GRB 970508, and GRB 971214-, greatly improving our understanding of these puzzling sources. Now it is widely accepted that most bursts originate at cosmological distances but the final solution of the GRB problem is still far away.

astro-ph↗
arXiv1998

Archival search for recurrent activity at the position the gamma-ray burst GRB 970228 optical counterpart

We have examined 8004 plates at the Harvard College Observatory Plate Collection searching for optical transient emission from the gamma-ray burst GRB 970228. This is the first archival search carried out so far for a gamma-ray burst with known transient optical emission. The total exposure time amounts to ~1.1 yr. No convincing optical activity was found above 12.5 mag at the expected position of the GRB 970228 optical counterpart.

astro-ph↗
arXiv1997

Hubble Space Telescope Imaging of the Optical Transient Associated with GRB970508

We report on Hubble Space Telescope (HST) observations of the optical transient (OT) discovered in the error box of the gamma-ray burst GRB970508. The object was imaged on 1997 June 2 with the Space Telescope Imaging Spectrograph (STIS) and Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). The observations reveal a point-like source with R = 23.1 +- 0.2 and H = 20.6 +- 0.3, in agreement with the power-law temporal decay seen in ground-based monitoring. Unlike the case of GRB970228, no nebulosity is detected surrounding the OT of GRB970508. We set very conservative upper limits of R ~ 24.5 and H ~ 22.2 on the brightness of any underlying extended source. If this subtends a substantial fraction of an arcsecond, then the R band limit is ~25.5. In combination with Keck spectra that show Mg I absorption and [O II] emission at a redshift of z = 0.835, our observations suggest that the OT is located in a star-forming galaxy with total luminosity one order of magnitude lower than the knee of the galaxy luminosity function, L*. Such galaxies are now thought to harbor the majority of star formation at z ~ 1; therefore, these observations may provide support for a link between GRBs and star formation.

astro-ph↗
arXiv1997

GRANAT/WATCH catalogue of cosmic gamma-ray bursts: December 1989 to September 1994

We present the catalogue of gamma-ray bursts observed with the WATCH all-sky monitor on board the GRANAT satellite during the period December 1989 to September 1994. The cosmic origin of 95 bursts comprising the catalogue is confirmed either by their localization with WATCH or by their detection with other GRB experiments. For each burst its time history and information on its intensity in the two energy ranges 8-20 keV and 20-60 keV are presented. Most events show hardening of the energy spectrum near the burst peak. In part of the bursts an X-ray precursor or a tail is seen at 8-20 keV. We have determined the celestial positions of the sources of 47 bursts. Their localization regions (at 3-sigma confidence level) are equivalent in area to circles with radii ranging from 0.2 to 1.6 deg. The burst sources appear isotropically distributed on the sky on large angular scales.

astro-ph↗