13 research outputs found
Burst Tails from SGR J1550-5418 Observed with Rossi X-ray Timing Explorer
We present the results of our extensive search using the Bayesian block
method for long tails following short bursts from a magnetar, SGR J1550-5418,
over all RXTE observations of the source. We identified four bursts with
extended tails, most of which occurred during its 2009 burst active episode.
The durations of tails range between ~13 s and over 3 ks, which are much longer
than the typical duration of bursts. We performed detailed spectral and
temporal analysis of the burst tails. We find that the spectra of three tails
show a thermal nature with a trend of cooling throughout the tail. We compare
the results of our investigations with the properties of four other extended
tails detected from SGR 1900+14 and SGR 1806-20 and suggest a scenario for the
origin of the tail in the framework of the magnetar model.Comment: 10 pages, 7 figures, 4 tables, accepted for publication in Ap
Broadband Spectral Investigations of SGR J1550-5418 Bursts
We present the results of our broadband spectral analysis of 42 SGR
J1550-5418 bursts simultaneously detected with the Swift/X-ray Telescope (XRT)
and the Fermi/Gamma-ray Burst Monitor (GBM), during the 2009 January active
episode of the source. The unique spectral and temporal capabilities of the XRT
Windowed Timing mode have allowed us to extend the GBM spectral coverage for
these events down to the X-ray domain (0.5-10 keV). Our earlier analysis of the
GBM data found that the SGR J1550-5418 burst spectra were described equally
well with a Comptonized model or with two blackbody functions; the two models
were statistically indistinguishable. Our new broadband (0.5 - 200 keV)
spectral fits show that, on average, the burst spectra are better described
with two blackbody functions than with the Comptonized model. Thus, our joint
XRT/GBM analysis clearly shows for the first time that the SGR J1550-5418 burst
spectra might naturally be expected to exhibit a more truly thermalized
character, such as a two-blackbody or even a multi-blackbody signal. Using the
Swift and RXTE timing ephemeris for SGR J1550-5418 we construct the
distribution of the XRT burst counts with spin phase and find that it is not
correlated with the persistent X-ray emission pulse phase from SGR J1550-5418.
These results indicate that the burst emitting sites on the neutron star need
not be co-located with hot spots emitting the bulk of the persistent X-ray
emission. Finally, we show that there is a significant pulse phase dependence
of the XRT burst counts, likely demonstrating that the surface magnetic field
of SGR J1550-5418 is not uniform over the emission zone, since it is
anticipated that regions with stronger surface magnetic field could trigger
bursts more efficiently.Comment: accepted for publication in The Astrophysical Journa
Persistent Emission Properties of SGR J1935+2154 During Its 2020 Active Episode
We present detailed spectral and temporal characteristics of the persistent
X-ray emission of SGR J1935+2154 based on our XMM-Newton and Chandra
observations taken in the aftermath of its April 2020 burst storm, during which
hundreds of energetic X-ray bursts were emitted, including one associated with
an extraordinary fast radio burst. We clearly detect the pulsed X-ray emission
in the XMM-Newton data. An average spin-down rate of 1.610 s
s is obtained using our spin period measurement combined with three
earlier values reported from the same active episode. Our investigations of the
XMM-Newton and Chandra spectra with a variety of phenomenological and
physically-motivated models, concluded that the magnetic field topology of SGR
J1935+2154 is most likely highly non-dipolar. The spectral models indicate that
surface field strengths in somewhat localized regions substantially exceed the
polar value of 4.410 G inferred from a spin-down torque
associated with a rotating magnetic dipole.Comment: Accepted for publication in the ApJ Letter
Quasi-Periodic Peak Energy Oscillations in X-ray Bursts from SGR J1935+2154
Magnetars are young neutron stars powered by the strongest magnetic fields in
the Universe (10 G). Their transient X-ray emission usually manifests
as short (a few hundred milliseconds), bright, energetic ( 10
erg) X-ray bursts. Since its discovery in 2014, magnetar J1935+2154 has become
one of the most prolific magnetars, exhibiting very active bursting episodes,
and other fascinating events such as pulse timing anti-glitches and Fast Radio
Bursts. Here, we present evidence for possible 42 Hz (24 ms) quasi-periodic
oscillations in the spectrum peak energy (Ep) identified in a
unique burst detected with the Fermi Gamma-ray Burst Monitor in January 2022.
While quasi-periodic oscillations have been previously reported in the
intensity of magnetar burst lightcurves, quasi-periodic oscillations in the Ep
have not. We also find an additional event from the same outburst that appears
to exhibit similar character in Ep, albeit of lower statistical quality. For
these two exceptional transients, such Ep oscillations can be explained by
magnetospheric density and pressure perturbations. For burst-emitting plasma
consisting purely of pairs, these acoustic modes propagate along a
highly magnetized flux tube of length up to around neutron star
radii, with being lower if ions are present in the emission zone. Detailed
time-resolved analyses of other magnetar bursts are encouraged to evaluate the
rarity of these events and their underlying mechanisms
Burst and persistent emission properties during the recent active episode of the anomalous x-ray pulsar 1E 1841-045
Copyright American Astronomical SocietyThe Swift/Burst Alert Telescope detected the first burst from 1E 1841-045 in 2010 May with intermittent burst activity recorded through at least 2011 July. Here we present Swift and Fermi/Gamma-ray Burst Monitor observations of this burst activity and search for correlated changes to the persistent X-ray emission of the source. The T-90 durations of the bursts range between 18 and 140 ms, comparable to other magnetar burst durations, while the energy released in each burst ranges between (0.8-25) x 10(38) erg, which is on the low side of soft gamma repeater bursts. We find that the bursting activity did not have a significant effect on the persistent flux level of the source. We argue that the mechanism leading to this sporadic burst activity in 1E 1841-045 might not involve large-scale restructuring (either crustal or magnetospheric) as seen in other magnetar sources.Peer reviewedFinal Accepted Versio
Short gamma-ray bursts with extended emission observed with Swift/BAT and Fermi/GBM
Some short gamma-ray bursts (GRBs) are followed by longer extended emission (EE), lasting anywhere from similar to 10 to similar to 100 s. These short GRBs with EE can possess observational characteristics of both short and long GRBs (as represented by GRB 060614), and the traditional classification based on the observed duration places some of them in the long GRB class. While GRBs with EE pose a challenge to the compact-binary merger scenario, they may therefore provide an important link between short-and long-duration events. To identify the population of GRBs with EE regardless of their initial classifications, we performed a systematic search of short GRBs with EE using all available data (up to 2013 February) of both Swift/BAT and Fermi/GBM. The search identified 16 BAT and 14 GBM detected GRBs with EE, several of which are common events observed with both detectors. We investigated their spectral and temporal properties for both the spikes and the EE, and examined correlations among these parameters. Here we present the results of the systematic search as well as the properties of the identified events. Finally, their properties are also compared with short GRBs with EE observed with BATSE, identified through our previous search effort. We found several strong correlations among parameters, especially when all of the samples were combined. Based on our results, a possible progenitor scenario of two-component jet is discussed
Gamma-ray bursts with extended emission observed with BATSE
We present the results of our systematic search for extended emission components following initial short gamma-ray burst (GRB) spikes, using Burst and Transient Source Experiment (BATSE) observations. We performed the extended emission search for both short-and long-duration GRBs to unveil the BATSE population of a new hybrid class of GRBs similar to GRB 060614. For the identified bursts, we investigate temporal and spectral characteristics of their initial spikes as well as their extended emission. Our results reveal that the fraction of GRBs with extended emission is similar to 7 per cent of the total number of our BATSE sample. We find that the spectrum of the extended emission is, in general, softer than that of the initial spike, which is in accord with what has been observed in the prototypical bursts, GRB 060614. We also find that the energy fluence of the extended emission varies on a broad range from 0.1 to 40 times of the fluence of the initial spike. We discuss our results in the context of existing physical models, in particular within the two-component jet model
Fermi-GBM Observations of the SGR J1935+2154 Burst Forest
During 2020 April and May, SGR J1935+2154 emitted hundreds of short bursts
and became one of the most prolific transient magnetars. At the onset of the
active bursting period, a 130 s burst "forest," which included some bursts with
peculiar time profiles, were observed with the Fermi/Gamma-ray Burst Monitor
(GBM). In this Letter, we present the results of time-resolved spectral
analysis of this burst "forest" episode, which occurred on 2020 April 27. We
identify thermal spectral components prevalent during the entire 130 s episode;
high-energy maxima appear during the photon flux peaks, which are modulated by
the spin period of the source. Moreover, the evolution of the
spectral hardness (represented by or blackbody temperature)
within the lightcurve peaks is anti-correlated with the pulse phases
extrapolated from the pulsation observed within the persistent soft X-ray
emission of the source six hours later. Throughout the episode, the emitting
area of the high-energy (hotter) component is 1-2 orders of magnitude smaller
than that for the low-energy component. We interpret this with a geometrical
viewing angle scenario, inferring that the high-energy component likely
originates from a low-altitude hotspot located within closed toroidal magnetic
field lines.Comment: 23 pages, 8 figures, 1 table (machine-readable table provided
separately), Matches the published versio