1,998 research outputs found
Long Term Radiative Behavior of SGR 1900+14
The prolific magnetar SGR 1900+14 showed two outbursts in the last decade and
has been closely monitored in the X-rays to track the changes in its radiative
properties. We use archival Chandra and XMM-Newton observations of SGR 1900+14
to construct a history of its spectrum and persistent X-ray flux spanning a
period of about seven years. We show that the decline of its X-ray flux in
these two outburst episodes follows the same trend. The flux begins to decline
promptly and rapidly subsequent to the flares, then decreases gradually for
about 600 days, at which point it resumes a more rapid decline. Utilizing the
high quality spectral data in each epoch, we also study the spectral
coevolution of the source with its flux. We find that neither the magnetic
field strength nor the magnetospheric properties change over the period spanned
by the observations, while the surface temperature as well as the inferred
emitting area both decline with time following both outbursts. We also show
that the source reached the same minimum flux level in its decline from these
two subsequent outbursts, suggesting that this flux level may be its steady
quiescent flux.Comment: Accepted for publication in the Ap
Characteristic Variability Time Scales of Long Gamma-Ray Bursts
We determined the characteristic variability time scales (\Delta t_p) of 410
bright and long GRBs, by locating the peaks of their Power Density Spectra,
defined and calculated in the time domain. We found that the averaged
variability time scale decreases with the peak flux. This is consistent with
the time-dilation effect expected for the cosmological origin of GRBs. We also
found that the occurrence distribution of the characteristic variability time
scale shows bimodality, which might be interpreted as that the long GRB sample
is composed of two sub-classes with different variability time scales. However,
we found no difference for some other characteristics of these two sub-classes.Comment: 10 pages, 5 figures, corrected some typos and syntaxes, enlarged the
label fonts in fig.3 and fig.
Identification of the infrared counterpart of SGR 1935+2154 with the Hubble Space Telescope
We present deep Hubble Space Telescope observations of a new magnetar source,
the soft gamma-repeater SGR 1935+2154, discovered by Swift. We obtained three
epochs of observations: while the source was active in March 2015, during a
quiescent period in August 2015, and during a further active phase in May 2016.
Close to the center of the X-ray error region identified by Chandra we find a
faint (F140W(AB)=25.3) source, which fades by a factor of ~2 over the course of
5 months between the first two epochs of observations, before rebrightening
during the second active period. If this source is indeed the counterpart to
SGR 1935+2154 then it is amongst the faintest yet located for a magnetar. Our
observations are spaced over 1.3 years and enable us to place limits on the
source velocity of km s kpc; observations on
timescales of a decade can hence probe proper motion limits smaller than the
velocities observed for the majority of pulsars. The comparison of the
optical/IR and X-ray lightcurves of the source suggests that emission in the
two regimes is associated but not directly correlated, offering support for a
magnetospheric versus a fallback disc origin.Comment: 7 pages, 3 figures, accepted for publication in Ap
Fermi/GBM Results of Magnetars
Magnetars are magnetically powered rotating neutron stars with extreme magnetic fields (over 10(exp 14) Gauss). They were discovered in the X- and gamma-rays where they predominantly emit their radiation. Very few sources (roughly 18) have been found since their discovery in 1987. NASA's Fermi Gamma-ray Space Telescope was launched June 11,2009; since then the Fermi Gamma-ray Burst Monitor (GBM) recorded emission from four magnetar sources. Two of these were brand new sources, SGR J0501 +4516, discovered with Swift and extensively monitored with Swift and GBM, SGR J0418+5729, discovered with GBM and the Interplanetary Network (IPN). A third was SGR Jl550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP IEI547.0-5408), but exhibiting a very prolific outburst with over 400 events recorded in January 2009. In my talk I will give a short history of magnetars and describe how this, once relatively esoteric field, has emerged as a link between several astrophysical areas including Gamma-Ray Bursts. Finally, I will describe the exciting new results of Fermi in this field and the current status of our knowledge of the magnetar population properties and magnetic fields
Three Decades of High Energy Transients
Gamma-Ray Bursts are the most brilliant explosions in space. The first GRB was discovered on 1967, just over 40 years ago. It took several years and multiple generations of space and ground instruments to unravel some of the mysteries of this phenomenon. However, many questions remain open today. I will discuss the history, evolution and current status of the GRB field and its contributions in our understanding of the transient high energy sky. Finally, I will describe how GRBs can be utilized in future missions as tools, to probe the cosmic chemical evolution of the Universe Magnetars are magnetically powered rotating neutron stars with extreme magnetic fields (over 10(exp 14) Gauss). They were discovered in the X- and gamma-rays where they predominantly emit their radiation. Very few sources (roughly 24) have been found since their discovery in 1987. NASA's Fermi Gamma-ray Space Telescope was launched June 11, 2009; since then the Fermi Gamma-ray Burst Monitor (GBM) recorded emission from several magnetar sources. In total, six new sources were discovered between 2008 and 2011, with a synergy between Swift, RXTE, Fermi and the Interplanetary Network (IPN). I will give a short history of magnetars and describe how this, once relatively esoteric field, has emerged as a link between several astrophysical areas including Gamma-Ray Bursts
High-z Universe with Gamma Ray Bursts
Gamma-Ray Bursts (GRBs) are the most luminous explosions in space and trace the cosmic star formation history back to the first generations of stars. Their bright afterglows allow us to trace the abundances of heavy elements to large distances, thereby measuring cosmic chemical evolution. To date GRBs have been detected up to distances of z=8.23 and possibly even beyond z~9. This makes GRBs a unique and powerful tool to probe the high-z Universe up to the re-ionization era. We discuss the current status of the field, place it in context with other probes, and also discuss new mission concepts that have been planned to utilize GRBs as probes
Three Decades of Explosive High Energy Transients
Gamma-Ray Bursts are the most brilliant explosions in space. The first GRB was discovered on 1967, just 40 years ago. It took several years and multiple generations of space and ground instruments to unravel some of the mysteries of this phenomenon. However, many questions remain open today. I will discuss the history, evolution and current status of the GRB field and its contributions in our understanding of the transient high energy sky. Finally, I will describe how GRBs can be utilized in future missions as tools, to probe the cosmic chemical evolution of the Universe and the star formation rates
The Extreme Case of Magnetars
Magnetars are magnetically powered rotating neutron stars with extreme magnetic fields (over 10(exp 14) Gauss). They were discovered in the X- and gamma-rays where they predominantly emit their radiation. Very few sources (roughly 18) have been found since their discovery in 1987. NASA's Fermi Gamma-ray Space Telescope was launched June 11, 2009; since then the Fermi Gamma-ray Burst Monitor (GBM) recorded emission from four magnetar sources. Two of these were brand new sources, SGR J0501+4516, discovered with Swift and extensively monitored with Swift and GBM, SGR J0418+5729, discovered with GBM and the Interplanetary Network (IPN). A third was SGR J1550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP 1E1547.0-5408), but exhibiting a very prolific outburst with over 400 events recorded in January 2009. In my talk I will give a short history of magnetars and describe how this, once relatively esoteric field, has emerged as a link between several astrophysical areas including Gamma-Ray Bursts. Finally, I will describe the exciting new results of Fermi in this field and the current status of our knowledge of the magnetar population properties and magnetic fields
Probes of Diffusive Shock Acceleration using Gamma-Ray Burst Prompt Emission
The principal paradigm for gamma-ray bursts (GRBs) suggests that the prompt
transient gamma-ray signal arises from multiple shocks internal to the
relativistic expansion. This paper explores how GRB prompt emission spectra can
constrain electron (or ion) acceleration properties at the relativistic shocks
that pertain to GRB models. The array of possible high-energy power-law indices
in accelerated populations is highlighted, focusing on how spectra above 1 MeV
can probe the field obliquity in GRB internal shocks, and the character of
hydromagnetic turbulence in their environs. When encompassing the MeV-band
spectral break, fits to BATSE/EGRET burst data indicate that the preponderance
of electrons responsible for the prompt emission reside in an intrinsically
non-thermal population. This differs markedly from typical populations
generated in acceleration simulations; potential resolutions of this conflict
such as the action of self-absorption are mentioned. Spectral modeling also
suggests that the synchrotron mechanism is favored over synchrotron
self-Compton scenarios due to the latter's typically broad curvature near the
peak. Such diagnostics will be enhanced by the broadband spectral coverage of
bursts by the Fermi Gamma-Ray Space Telescope; the GBM will provide key
information on the lower energy portions of the non-thermal particle
population, while the LAT will constrain the power-law regime of particle
acceleration.Comment: 6 pages, 1 embedded figure, to appear in Proc. of the 6th Huntsville
Gamma-Ray Burst Symposium, eds. C. A. Meegan, N. Gehrels, and C. Kouveliotou
(AIP Conf. Proc., New York
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