0ptical observations of GRB afterglows: GRB 970508 and GRB 980326 revisited

Since January 1997, we have monitored 15 GRB fields, detecting 6 optical/IR afterglows. For GRB 970508, we derive a power-law decay exponent alpha = -1.19 (R-band). The luminosity of the host galaxy L relative to the characteristic luminosity L^{star} is in the range 0.06--0.15, i.e. a dwarf galaxy. For GRB 980326, we derive a power-law decay exponent alpha = -1.7, taking into account the new upper limit for the host as R > 27.3 provided by Bloom and Kulkarni (1998). This implies one of the fastest GRB optical decays ever measured. The fact that only about 50% of optical transients have been found within the gamma/X-ray error boxes, suggest that either considerable intrinsic absorption is present or that some optical transients display a very fast decline. We also propose that the secondary maximum detected on 17 Apr 1998 could be explained in the context of the SN-like light curves 2-3 weeks after the GRB, as recently suggested by Woosley (1999).Comment: Accepted for publication in Astronomy and Astrophysics Supplement Series (special issue on "Gamma-ray bursts in the afterglow era"). 2 pages and 2 postscript figure

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.Comment: 3 pages, no figures. To appear in the proceedings of the October 2000 Rome Workshop on ``Gamma-Ray Bursts in the Afterglow Era'

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

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.Comment: 16 pages, Accepted into Proceedings of AstroRob Malaga 200

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$\sigma$) in the Stokes parameters. The average values we obtain, corrected for interstellar polarisation in the Galaxy, are Q = -0.01% ($\pm$ 0.15%) and U = - 0.50% ($\pm$ 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

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.Comment: 15 pages, 7 figures. Accepted for publication in the Special issue "Robotic Astronomy" of Advances in Astronomy. It includes two iterations with the referee

IAA : Información y actualidad astronómica (13)

Sumario : Las galaxias anfitrionas de los GRBs.-- Marte: una historia de descubrimientos.-- Programa Ramón y Cajal: ¿recuperación o catapulta de cerebros?.-- CHARLAS CON...Fernando Cornet.-- El problema de la distancia a las Pléyades.-- Un bólido sobre nuestras cabezas.-- Actividades IAA.-- Agenda.Esta revista se publica con la ayuda de la Acción Especial DIS 2003-10261-E del Programa Nacional de Difusión y divulgación de la Ciencia y la Tecnología, del Ministerio de Ciencia y Tecnología.N