55 research outputs found
XMM-Newton view of Swift J1834.9-0846 and its Magnetar Wind Nebula
We report on the analysis of two XMM-Newton observations of the recently
discovered soft gamma repeater Swift J1834.9-0846, taken in September 2005 and
one month after the source went into outburst on 2011 August 7. We performed
timing and spectral analyses on the point source as well as on the extended
emission. We find that the source period is consistent with an extrapolation of
the Chandra ephemeris reported earlier and the spectral properties remained
constant. The source luminosity decreased to a level of 1.6x10^34 erg s^-1
following a decay trend of . Our spatial analysis of the
source environment revealed the presence of two extended emission regions
around the source. The first (Region A) is a symmetric ring around the point
source, starting at 25arcsec and extending to ~50arcsec. We argue that Region A
is a dust scattering halo. The second (Region B) has an asymmetrical shape
extending between 50arcsec and 150arcsec, and is detected both in the pre- and
post-outburst data. We argue that this region is a possible magnetar wind
nebula (MWN). The X-ray efficiency of the MWN with respect to the rotation
energy loss is substantially higher than those of rotation powered pulsars:
. The
higher efficiency points to a different energy source for the MWN of Swift
J1834.9-0846, most likely bursting activity of the magnetar, powered by its
high magnetic field, B=1.4x10^14 G.Comment: 10 pages, 10 figures, accepted for publication in Ap
Gendering entrepreneurship: A discursive analysis of a woman entrepreneur competition
[No abstract available
XMM-Newton Observations of Two Candidate Supernova Remnants
Candidate supernova remnants G23.5+0.1 and G25.5+0.0 were observed by
XMM-Newton in the course of a snap-shot survey of plerionic and composite SNRs
in the Galactic plane. In the field of G23.5+0.1, we detected an extended
source, ~3' in diameter, which we tentatively interpret as a pulsar-wind nebula
(PWN) of the middle-aged radio pulsar B1830-08. Our analysis suggests an
association between PSR B1830-08 and the surrounding diffuse radio emission. If
the radio emission is due to the SNR, then the pulsar must be significantly
younger than its characteristic age. Alternatively, the radio emission may come
from a relic PWN. In the field of G25.5+0.0, which contains the extended TeV
source HESS J1837-069, we detected the recently discovered young high-energy
pulsar J1838-0655 embedded in a PWN with extent of 1.3'. We also detected
another PWN candidate (AX J1837.3-0652) with an extent of 2' and unabsorbed
luminosity L_(2-10 keV) ~ 4 x 10^33 erg/s at d=7 kpc. The third X-ray source,
located within the extent of the HESS J1837-069, has a peculiar extended radio
counterpart, possibly a radio galaxy with a double nucleus or a microquasar. We
did not find any evidence of the SNR emission in the G25.5+0.0 field. We
provide detailed multiwavelength analysis and identifications of other field
sources and discuss robustness of the G25.5+0.0 and G23.5+0.1 classifications
as SNRs. (abstract abridged)Comment: 37 pages, 9 figures, submitted to Ap
Transit Timing Analysis in the HAT-P-32 system
We present the results of 45 transit observations obtained for the transiting
exoplanet HAT-P-32b. The transits have been observed using several telescopes
mainly throughout the YETI network. In 25 cases, complete transit light curves
with a timing precision better than min have been obtained. These light
curves have been used to refine the system properties, namely inclination ,
planet-to-star radius ratio , and the ratio between
the semimajor axis and the stellar radius . First analyses by
Hartman et al. (2011) suggest the existence of a second planet in the system,
thus we tried to find an additional body using the transit timing variation
(TTV) technique. Taking also literature data points into account, we can
explain all mid-transit times by refining the linear ephemeris by 21ms. Thus we
can exclude TTV amplitudes of more than min.Comment: MNRAS accepted; 13 pages, 10 figure
SGR 1806-20 distance and dust properties in molecular clouds by analysis of a flare x-ray echoes
The soft gamma repeater SGR 1806-20 is most famous for its giant flare from
2004, which yielded the highest gamma-ray flux ever observed on Earth. The
flare emphasized the importance of determining the distance to the SGR, thus
revealing the flare's energy output, with implications on SGRs energy budget
and giant flare rates. We analyze x-ray scattering echoes observed by Swift/XRT
following the 2006 August 6 intermediate burst of SGR 1806-20. Assuming
positions and opacities of the molecular clouds along the line-of-sight from
previous works, we derive direct constrains on the distance to SGR 1806-20,
setting a lower limit of 9.4 kpc and an upper limit of 18.6 kpc (90%
confidence), compared with a 6-15 kpc distance range by previous works. This
distance range matches an energy output of ~10^46 erg/s for the 2004 giant
flare. We further use, for the first time, the x-ray echoes in order to study
the dust properties in molecular clouds. Analyzing the temporal evolution of
the observed flux using a dust scattering model, which assumes a power-law size
distribution of the dust grains, we find a power-law index of
-3.3_{-0.7}^{+0.6} (1 sigma) and a lower limit of 0.1 micron (2 sigma) on the
dust maximal grain size, both conforming to measured dust properties in the
diffused interstellar medium (ISM). We advocate future burst follow-up
observations with Swift, Chandra and the planned NuSTAR telescopes, as means of
obtaining much superior results from such an analysis.Comment: 12 pages, 7 figures, 3 tables, submitted to MNRA
Rapid spectral variability of a giant flare from a magnetar in NGC 253
Magnetars are neutron stars with extremely strong magnetic fields (1013 to 1015 gauss)1,2, which episodically emit X-ray bursts approximately 100 milliseconds long and with energies of 1040 to 1041 erg. Occasionally, they also produce extremely bright and energetic giant flares, which begin with a short (roughly 0.2 seconds), intense flash, followed by fainter, longer-lasting emission that is modulated by the spin period of the magnetar3,4 (typically 2 to 12 seconds). Over the past 40 years, only three such flares have been observed in our local group of galaxies3–6, and in all cases the extreme intensity of the flares caused the detectors to saturate. It has been proposed that extragalactic giant flares are probably a subset7–11 of short γ-ray bursts, given that the sensitivity of current instrumentation prevents us from detecting the pulsating tail, whereas the initial bright flash is readily observable out to distances of around 10 to 20 million parsecs. Here we report X-ray and γ-ray observations of the γ-ray burst GRB 200415A, which has a rapid onset, very fast time variability, flat spectra and substantial sub-millisecond spectral evolution. These attributes match well with those expected for a giant flare from an extragalactic magnetar12, given that GRB 200415A is directionally associated13 with the galaxy NGC 253 (roughly 3.5 million parsecs away). The detection of three-megaelectronvolt photons provides evidence for the relativistic motion of the emitting plasma. Radiation from such rapidly moving gas around a rotating magnetar may have generated the rapid spectral evolution that we observe
SN 2009ip: Constraints on the Progenitor Mass-loss Rate
Some supernovae (SNe) show evidence for mass-loss events taking place prior to their explosions. Measuring their pre-outburst mass-loss rates provides essential information regarding the mechanisms that are responsible for these events. Here we present XMM-Newton and Swift X-ray observations taken after the latest, and presumably the final, outburst of SN 2009ip. We use these observations as well as new near-infrared and visible-light spectra and published radio and visible-light observations to put six independent order-of-magnitude constraints on the mass-loss rate of the SN progenitor prior to the explosion. Our methods utilize the X-ray luminosity, the bound-free absorption, the Hα luminosity, the SN rise time, free-free absorption, and the bolometric luminosity of the outburst detected prior to the explosion. Assuming spherical mass loss with a wind-density profile, we estimate that the effective mass-loss rate from the progenitor was between 10^(–3) and 10^(–2) M_☉ yr^(–1), over a few years prior to the explosion, with a velocity of ~10^3 km s^(–1). This mass-loss rate corresponds to a total circumstellar matter (CSM) mass of ~0.04 M_☉, within 6 × 10^(15) cm of the SN. We note that the mass-loss rate estimate based on the Hα luminosity is higher by an order of magnitude. This can be explained if the narrow-line Hα component is generated at radii larger than the shock radius, or if the CSM has an aspherical geometry. We discuss simple geometries which are consistent with our results
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