3 research outputs found
The optical rebrightening of GRB100814A: an interplay of forward and reverse shocks?
We present a wide dataset of -ray, X-ray, UVOIR, and radio observations of the Swift GRB100814A. At the end of the slow decline phase of the X-ray and optical afterglow, this burst shows a sudden and prominent rebrightening in the optical band only, followed by a fast decay in both bands. The optical rebrightening also shows chromatic evolution. Such a puzzling behaviour cannot be explained by a single component model. We discuss other possible interpretations, and we find that a model that incorporates a long-lived reverse shock and forward shock fits the temporal and
spectral properties of GRB100814 the best
Relativistic jet activity from the tidal disruption of a star by a massive black hole
Supermassive black holes have powerful gravitational fields with
strong gradients that can destroy stars that get too close1,2, producing
a bright flare in ultraviolet and X-ray spectral regions from
stellar debris that forms an accretion disk around the black hole3–7.
The aftermath of this process may have been seen several times over
the past two decades in the form of sparsely sampled, slowly fading
emission from distant galaxies8–14, but the onset of the stellar disruption
event has not hitherto been observed. Here we report
observations of a bright X-ray flare from the extragalactic transient
Swift J164449.31573451. This source increased in brightness in
the X-ray band by a factor of at least 10,000 since 1990 and by a
factor of at least 100 since early 2010. We conclude that we have
captured the onset of relativistic jet activity from a supermassive
black hole. A companion paper15 comes to similar conclusions on
the basis of radio observations. This event is probably due to the
tidal disruption of a star falling into a supermassive black hole, but
the detailed behaviour differs from current theoretical models of
such events
Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the UV anomaly in NGC 5548 with X-Ray Spectroscopy
During the Space Telescope and Optical Reverberation Mapping Project (STORM)
observations of NGC 5548, the continuum and emission-line variability became decorrelated
during the second half of the 6-month long observing campaign. Here we
present Swift and Chandra X-ray spectra of NGC 5548 obtained as a part of the campaign.
The Swift spectra show that excess flux (relative to a power-law continuum) in
the soft X-ray band appears before the start of the anomalous emission-line behavior,
peaks during the period of the anomaly, and then declines. This is a model-independent
result suggesting that the soft excess is related to the anomaly. We divide the Swift data
into on- and off-anomaly spectra to characterize the soft excess via spectral fitting.
The cause of the spectral differences is likely due to a change in the intrinsic spectrum
rather than being due to variable obscuration or partial covering. The Chandra spectra
have lower signal-to-noise ratios, but are consistent with Swift data. Our preferred
model of the soft excess is emission from an optically thick, warm Comptonizing
corona, the effective optical depth of which increases during the anomaly. This model
simultaneously explains all the three observations: the UV emission line flux decrease,
the soft-excess increase, and the emission line anomaly