GRB 101225A - a new class of GRBs?

AbstractThe Christmas burst, GRB 101225A, was one of the most controversial bursts in the last few years. Its exceptionally long duration but bright X-ray emission showing a thermal component followed by a strange afterglow with a thermal SED lead to two different interpretations. We present here our model ascribing this strange event to a new type of GRB progenitor consisting of a neutron star and an evolved main-sequence star in a very faint galaxy at redshift 0.33 while Campana et al. (2011) proposed a Galactic origin. New observations at several wavelengths might resolve the question between the two models in the near future.

GRB 070311: a direct link between the prompt emission and the afterglow

We present prompt gamma-ray, early NIR/optical, late optical and X-ray observations of the peculiar GRB 070311 discovered by INTEGRAL, in order to gain clues on the mechanisms responsible for the prompt gamma-ray pulse as well as for the early and late multi-band afterglow of GRB 070311. We fitted with empirical functions the gamma-ray and optical light curves and scaled the result to the late time X-rays. The H-band light curve taken by REM shows two pulses peaking 80 and 140 s after the peak of the gamma-ray burst and possibly accompanied by a faint gamma-ray tail. Remarkably, the late optical and X-ray afterglow underwent a major rebrightening between 3x10^4 and 2x10^5 s after the burst …

GRB 101225A - an unusual stellar death on Christmas Day

The unusual gamma-ray burst GRB 101225A from a helium star/neutron star merger at redshift 0.33

Collimation and asymmetry of the hot blast wave from the recurrent nova V745 Scorpii

The recurrent symbiotic nova V745 Sco exploded on 2014 February 6 and was observed on February 22 and 23 by the Chandra X-ray Observatory Transmission Grating Spectrometers. By that time the supersoft source phase had already ended and Chandra spectra are consistent with emission from a hot, shock-heated circumstellar medium with temperatures exceeding 10^7K. X-ray line profiles are more sharply peaked than expected for a spherically-symmetric blast wave, with a full width at zero intensity of approximately 2400 km/s, a full width at half maximum of 1200 +/- 30 km/s and an average net blueshift of 165 +/- 10 km/s. The red wings of lines are increasingly absorbed toward longer wavelengths by…

GRB 101225A: an unusual stellar death on Christmas Day

X-RAY SPECTROSCOPIC DIAGNOSIS OF A WIND-COLLIMATED BLAST WAVE AND METAL-RICH EJECTA FROM THE 2006 EXPLOSION OF RS OPHIUCHI

Chandra HETG observations of RS Ophiuchi at day 13.9 of the 2006 outburst reveal a rich spectrum of emission lines from abundant ions formed over a wide temperature range (∼ 3 × 10 6 to 60 × 10 6 K) indicative of shock heating of the circumstellar medium by the expanding blast wave. Lines are asymmetric and strongly broadened (v ∼ 2400 km s −1 at zero intensity). Using simple analytical model profiles, we show how the lines are shaped by differential absorption in the red giant wind and explosion ejecta, and that shock heating to multimillion degree temperatures appears to have occurred preferentially in the direction perpendicular to the line of sight. We conclude that the asymmetric natur…

The unusual γ-ray burst GRB 101225A from a helium star/neutron star merger at redshift 0.33

Long Gamma-Ray Bursts (GRBs) are the most dramatic examples of massive stellar deaths, usually associated with supernovae. They release ultra-relativistic jets producing non-thermal emission through synchrotron radiation as they interact with the surrounding medium. Here we report observations of the peculiar GRB 101225A (the "Christmas burst"). Its gamma-ray emission was exceptionally long and followed by a bright X-ray transient with a hot thermal component and an unusual optical couuterpart. During the first 10 days, the optical emission evolved as an expanding, cooling blackbody after which an additional component, consistent with a faint supernova, emerged. We determine its distance to…

Optical and X-ray Observations of M31N 2007-12b: An Extragalactic Recurrent Nova with a Detected Progenitor?

We report combined optical and X-ray observations of nova M31N 2007-12b. Optical spectroscopy obtained 5 days after the 2007 December outburst shows evidence of very high ejection velocities (FWHM H$\alpha \simeq 4500$ km s$^{-1}$). In addition, Swift X-ray data show that M31N 2007-12b is associated with a Super-Soft Source (SSS) which appeared between 21 and 35 days post-outburst and turned off between then and day 169. Our analysis implies that $M_{\rm WD} \ga 1.3 $M$_{\odot}$ in this system. The optical light curve, spectrum and X-ray behaviour are consistent with those of a recurrent nova. Hubble Space Telescope observations of the pre-outburst location of M31N 2007-12b reveal the prese…

Swift Observations of GRB 070110: An Extraordinary X-Ray Afterglow Powered by the Central Engine

We present a detailed analysis of Swift multi-wavelength observations of GRB 070110 and its remarkable afterglow. The early X-ray light curve, interpreted as the tail of the prompt emission, displays a spectral evolution already seen in other gamma-ray bursts. The optical afterglow shows a shallow decay up to ~2 d after the burst, which is not consistent with standard afterglow models. The most intriguing feature is a very steep decay in the X-ray flux at ~20 ks after the burst, ending an apparent plateau. The abrupt drop of the X-ray light curve rules out an external shock as the origin of the plateau in this burst and implies long-lasting activity of the central engine. The temporal and s…

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

We present multiwavelength observations of one of the most distant gamma-ray bursts detected so far, GRB080913. 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 wa…

GRB 061121: Broadband Spectral Evolution through the Prompt and Afterglow Phases of a Bright Burst

Swift triggered on a precursor to the main burst of GRB 061121 (z=1.314), allowing observations to be made from the optical to gamma-ray bands. Many other telescopes, including Konus-Wind, XMM-Newton, ROTSE and the Faulkes Telescope North, also observed the burst. The gamma-ray, X-ray and UV/optical emission all showed a peak ~75s after the trigger, although the optical and X-ray afterglow components also appear early on - before, or during, the main peak. Spectral evolution was seen throughout the burst, with the prompt emission showing a clear positive correlation between brightness and hardness. The Spectral Energy Distribution (SED) of the prompt emission, stretching from 1eV up to 1MeV…