The GRB 030328 host: another case of a blue starburst galaxy

We present for the first time the detection of the GRB 030328 host galaxy in four optical bands equivalent to UBRI. The host galaxy spectral energy distribution is consistent with a low extinction (E(B-V) < 0.21) starburst galaxy. The restframe B-band magnitude of the host is M_B ~ -20.4Comment: 4 pages, 2 figures, accepted for publication in Il nuovo cimento (4th Workshop Gamma-Ray Bursts in the Afterglow Era, Rome, 18-22 October 2004

A young stellar environment for the superluminous supernova PTF12dam

The progenitors of super luminous supernovae (SLSNe) are still a mystery. Hydrogen-poor SLSN hosts are often highly star-forming dwarf galaxies and the majority belongs to the class of extreme emission line galaxies hosting young and highly star-forming stellar populations. Here we present a resolved long-slit study of the host of the hydrogen-poor SLSN PTF12dam probing the kpc environment of the SN site to determine the age of the progenitor. The galaxy is a "tadpole" with uniform properties and the SN occurred in a star-forming region in the head of the tadpole. The galaxy experienced a recent star-burst superimposed on an underlying old stellar population. We measure a very young stellar population at the SN site with an age of ~3 Myr and a metallicity of 12+log(O/H)=8.0 at the SN site but do not observe any WR features. The progenitor of PTF12dam must have been a massive star of at least 60 M_solar and one of the first stars exploding as a SN in this extremely young starburst.Comment: submitted to MNRAS letters. 5 pages, 3 figures, supplementary material: 2 figures, 2 table

A spectroscopic look at the gravitationally lensed type Ia SN 2016geu at z=0.409

The spectacular success of type Ia supernovae (SNe Ia) in SN-cosmology is based on the assumption that their photometric and spectroscopic properties are invariant with redshift. However, this fundamental assumption needs to be tested with observations of high-z SNe Ia. To date, the majority of SNe Ia observed at moderate to large redshifts (0.4 < z < 1.0) are faint, and the resultant analyses are based on observations with modest signal-to-noise ratios that impart a degree of ambiguity in their determined properties. In rare cases however, the Universe offers a helping hand: to date a few SNe Ia have been observed that have had their luminosities magnified by intervening galaxies and galaxy clusters acting as gravitational lenses. In this paper we present long-slit spectroscopy of the lensed SNe Ia 2016geu, which occurred at a redshift of z=0.409, and was magnified by a factor of ~55 by a galaxy located at z=0.216. We compared our spectra, which were obtained a couple weeks to a couple months past peak light, with the spectroscopic properties of well-observed, nearby SNe Ia, finding that SN 2016geu's properties are commensurate with those of SNe Ia in the local universe. Based primarily on the velocity and strength of the Si II 6355 absorption feature, we find that SN 2016geu can be classified as a high-velocity, high-velocity gradient and "core-normal" SN Ia. The strength of various features (measured though their pseudo-equivalent widths) argue against SN 2016geu being a faint, broad-lined, cool or shallow-silicon SN Ia. We conclude that the spectroscopic properties of SN 2016geu imply that it is a normal SN Ia, and when taking previous results by other authors into consideration, there is very little, if any, evolution in the observational properties of SNe Ia up to z~0.4. [Abridged]Comment: 12 pages, 5 figures, 4 tables. Submitted to MNRAS. Comments welcome

Multi-wavelength analysis of the field of the dark burst GRB 031220

We have collected and analyzed data taken in different spectral bands (from X-ray to optical and infrared) of the field of GRB031220 and we present results of such multiband observations. Comparison between images taken at different epochs in the same filters did not reveal any strong variable source in the field of this burst. X-ray analysis shows that only two of the seven Chandra sources have a significant flux decrease and seem to be the most likely afterglow candidates. Both sources do not show the typical values of the R-K colour but they appear to be redder. However, only one source has an X-ray decay index (1.3 +/- 0.1) that is typical for observed afterglows. We assume that this source is the best afterglow candidate and we estimate a redshift of 1.90 +/- 0.30. Photometric analysis and redshift estimation for this object suggest that this GRB can be classified as a Dark Burst and that the obscuration is the result of dust extinction in the circum burst medium or inside the host galaxy.Comment: 7 pages, 5 figures, accepted for publication on A&

Near-infrared follow-up to the May 2008 activation of SGR 1627-41

On 28 May 2008, the Swift satellite detected the first reactivation of SGR 1627-41 since its discovery in 1998. Following this event we began an observing campaign in near infrared wavelengths to search for a possible counterpart inside the error circle of this SGR, which is expected to show flaring activity simultaneous to the high energy flares or at least some variability as compared to the quiescent state. For the follow-up we used the 0.6m REM robotic telescope at La Silla Observatory, which allowed a fast response within 24 hours and, through director discretionary time, the 8.2m Very Large Telescope at Paranal Observatory. There, we observed with NACO to produce high angular resolution imaging with the aid of adaptive optics. These observations represent the fastest near infrared observations after an activation of this SGR and the deepest and highest spatial resolution observations of the Chandra error circle. 5 sources are detected in the immediate vicinity of the most precise X-ray localisation of this source. For 4 of them we do not detect variability, although the X-ray counterpart experimented a significant decay during our observation period. The 5th source is only detected in one epoch, where we have the best image quality, so no variability constrains can be imposed and remains as the only plausible counterpart. We can impose a limit of Ks > 21.6 magnitudes to any other counterpart candidate one week after the onset of the activity. Our adaptive optics imaging, with a resolution of 0.2" provides a reference frame for subsequent studies of future periods of activity.Comment: Accepted for publication in A&

The earliest spectroscopy of the GRB 030329 afterglow with 6-m telescope

The earliest BTA (SAO RAS 6-m telescope) spectroscopic observations of the GRB 030329 optical transient (OT) are presented, which almost coincide in time with the "first break" ($t\sim 0.5$ day after the GRB) of the OT light curve. The beginning of spectral changes are seen as early as $\sim 10-12$ hours after the GRB. So, the onset of the spectral changes for $t<1$ day indicates that the contribution from Type Ic supernova (SN) into the OT optical flux can be detected earlier. The properties of early spectra of GRB 030329/SN 2003dh can be consistent with a shock moving into a stellar wind formed from the pre-SN. Such a behavior (similar to that near the UV shock breakout in SNe) can be explained by the existence of a dense matter in the immediate surroundings of massive stellar GRB/SN progenitor). The urgency is emphasized of observation of early GRB/SN spectra for solving a question that is essential for understanding GRB physical mechanism: {\it Do all} long-duration gamma-ray bursts are caused by (or physically connected to) {\it ordinary} core-collapse supernovae? If clear association of normal/ordinary core-collapse SNe (SN Ib/c, and others SN types) and GRBs would be revealed in numbers of cases, we may have strong observational limits for gamma-ray beaming and for real energetics of the GRB sources.Comment: 4 pages, 5 figures. Proceedings of the 4th Workshop "Gamma-Ray Bursts in the Afterglow Era", Roma, 2004 October 18-22, eds. L. Piro, L. Amati, S. Covino, and B. Gendre. Il Nuovo Cimento, in pres

The host of the Type I SLSN 2017egm: A young, sub-solar metallicity environment in a massive spiral galaxy

Here we present an integral-field study of the massive, high-metallicity spiral NGC 3191, the host of SN 2017egm, the closest SLSN Type I to date. We use data from PMAS/CAHA and the public MaNGA survey to shed light on the properties of the SLSN site and the origin of star-formation in this non-starburst spiral galaxy. We map the physical properties different \ion{H}{II} regions throughout the galaxy and characterize their stellar populations using the STARLIGHT fitting code. Kinematical information allows to study a possible interaction with its neighbouring galaxy as the origin of recent star formation activity which could have caused the SLSN. NGC 3191 shows intense star-formation in the western part with three large SF regions of low metallicity. The central regions of the host have a higher metallicity, lower specific star-formation rate and lower ionization. Modeling the stellar populations gives a different picture: The SLSN region has two dominant stellar populations with different ages, the youngest one with an age of 2-10 Myr and lower metallicity, likely the population from which the SN progenitor originated. Emission line kinematics of NGC 3191 show indications of interaction with its neighbour MCG+08-19-017 at $\sim$45 kpc, which might be responsible for the recent starburst. In fact, this galaxy pair has in total hosted 4 SNe, 1988B (Type Ia), SN 2003ds (Type Ic in MCG+08-19-017), PTF10bgl (SLSN-Type II) and 2017egm, underlying the enhanced SF in both galaxies due to interaction. Our study shows that one has to be careful interpreting global host and even gas properties without looking at the stellar population history of the region. SLSNe seem to still be consistent with massive stars ($>$ 20 M$_\odot$) requiring low ($< 0.6Z_{\odot}$) metallicity and those environments can also occur in massive, late-type galaxies but not necessarily starbursts.Comment: Accepted for publication in A&A, 13 pages, 11 figures, 7 tables. Abstract has been reduced to match arXiv form requirement

Multiwavelength chase of GRB 031220 afterglow

Several gamma ray bursts (GRBs) with X-ray afterglow do not show any optical-IR afterglow. The nature of this class of events, the so-called Dark Bursts, is still not clear. The optical absorption could be due to the interstellar dust or to the high redshift of the event. Or, more simply, the non-detection of the optical transient should be due to the delay in the observation or to the rapid energy decaying of these events. High spatial resolution X-ray observations are the most promising tool to investigate on such kind of events. We have collected and analyzed X-ray data and images taken in different spectral bands (optical and infrared) for GRB 031220 and we present the results of the analysis of multiband observations on the field of this burst. Comparison between images taken at different epochs in the same filters did not reveal any strongly variable sources. Photometric analysis and photometric redshift estimation of all possible afterglow candidates suggest that this GRB can be classifie d as a Dark Burst