Magnetar

About: Magnetar is a research topic. Over the lifetime, 2905 publications have been published within this topic receiving 106806 citations.

Phase-resolved x-ray spectra of magnetars and the coronal outflow model

Abstract: We test a model recently proposed for the persistent hard X-ray emission from magnetars. In the model, hard X-rays are produced by a decelerating electron-positron flow in the closed magnetosphere. The flow decelerates as it radiates its energy away via resonant scattering of soft X-rays, then it reaches the top of the magnetic loop and annihilates there. We test the model against observations of three magnetars: 4U 0142+61, 1RXS J1708-4009, and 1E 1841-045. We find that the model successfully fits the observed phase-resolved spectra. We derive constraints on the angle between the rotational and magnetic axes of the neutron star, the object inclination to the line of sight, and the size of the active twisted region filled with the plasma flow. Using the fit of the hard X-ray component of the magnetar spectrum, we revisit the remaining soft X-ray component. We find that it can be explained by a modified two-temperature blackbody model. The hotter blackbody is consistent with a hot spot covering 1%-10% of the neutron star surface. Such a hot spot is expected at the base of the magnetospheric e ± outflow, as some particles created in the e ± discharge flow back and bombard the stellar surface.

Observations of energetic high magnetic field pulsars with the fermi large area telescope

Abstract: We report the detection of γ-ray pulsations from the high-magnetic-field rotation-powered pulsar PSR J1119 6127 using data from the Fermi Large Area Telescope. The γ-ray light curve of PSR J1119 6127 shows a single, wide peak offset from the radio peak by 0.43±0.02 in phase. Spectral analysis suggests a power law of index 1.0 ± 0.3 +0.4 −0.2 with an energy cut-off at 0.8 ± 0.2 +2.0 −0.5 GeV. The first uncertainty is statistical and the second is systematic. We discuss the emission models of PSR J1119 6127 and demonstrate that despite the object’s high surface magnetic field—near that of magnetars—the field strength and structure in the γ-ray emitting zone are apparently similar to those of typical young pulsars. Additionally, we present upper limits on the γ-ray pulsed emission for the magnetically active PSR J1846 0258 in the supernova remnant Kesteven 75 and two other energetic high-B pulsars, PSRs J1718 3718 and J1734 3333. We explore possible explanations for the non-detection of these three objects, including peculiarities in their emission geometry. Subject headings: gamma rays: stars — pulsars: general — pulsars: individual (PSR J1119 6127, PSR J1718 3718, PSR J1734 3333, PSR J1846 0258)

Discovery of a transient gamma-ray counterpart to FRB 131104

Abstract: We report our discovery in Swift satellite data of a transient gamma-ray counterpart (3.2$\sigma$ confidence) to the fast radio burst FRB131104, the first such counterpart to any FRB. The transient has duration $T_{90} \gtrsim 100$s and fluence $S_\gamma\approx 4\times 10^{-6}$ erg cm$^{-2}$, increasing the energy budget for this event by more than a billion times; at the nominal $z\approx 0.55$ redshift implied by its dispersion measure, the burst's gamma-ray energy output is $E_\gamma \approx 5\times 10^{51}$ erg. The observed radio to gamma-ray fluence ratio for FRB131104 is consistent with a lower limit we derive from Swift observations of another FRB, which is not detected in gamma-rays, and with an upper limit previously derived for the brightest gamma-ray flare from SGR 1806-20, which was not detected in the radio. X-ray, ultraviolet, and optical observations beginning two days after the FRB do not reveal any associated afterglow, supernova, or transient; Swift observations exclude association with the brightest 65% of Swift gamma-ray burst X-ray afterglows, while leaving the possibility of an associated supernova at much more than 10% the FRB's nominal distance, $D\gtrsim 320$ Mpc, largely unconstrained. Transient high-luminosity gamma-ray emission arises most naturally in a relativistic outflow or shock breakout, as for example from magnetar flares, gamma-ray bursts, relativistic supernovae, and some types of galactic nuclear activity. Our discovery thus bolsters the case for an extragalactic origin for some FRBs and suggests that future rapid-response observations might identify long-lived counterparts, resolving the nature of these mysterious phenomena and realizing their promise as probes of cosmology and fundamental physics.

Timing Noise in SGR 1806-20

Abstract: We have phase connected a sequence of RXTE PCA observations of SGR 1806-20 covering 178 days. We find a simple secular spin-down model does not adequately fit the data. The period derivative varies gradually during the observations between 8.1 and 11.7 * 10^-11 s/s (at its highest, ~40% larger than the long term trend), while the average burst rate as seen with BATSE drops throughout the time interval. The phase residuals give no compelling evidence for periodicity, but more closely resemble timing noise as seen in radio pulsars. The magnitude of the timing noise, however, is large relative to the noise level typically found in radio pulsars. Combining these results with the noise levels measured for some AXPs, we find all magnetar candidates have \Delta_8 values larger than those expected from a simple extrapolation of the correlation found in radio pulsars. We find that the timing noise in SGR 1806-20 is greater than or equal to the levels found in some accreting systems (e.g., Vela X-1, 4U 1538-52 and 4U 1626-67), but the spin-down of SGR 1806-20 has thus far maintained coherence over 6 years. Alternatively, an orbital model with a period P_orb = 733 days provides a statistically acceptable fit to the data. If the phase residuals are created by Doppler shifts from a gravitationally bound companion, then the allowed parameter space for the mass function (small) and orbital separation (large) rule out the possibility of accretion from the companion sufficient to power the persistent emission from the SGR.

NuSTAR OBSERVATIONS OF X-RAY BURSTS FROM THE MAGNETAR 1E 1048.1−5937

Abstract: We report the detection of eight bright X-ray bursts from the 6.5 s magnetar 1E 1048.1−5937, during a 2013 July observation campaign with the Nuclear Spectroscopic Telescope Array. We study the morphological and spectral properties of these bursts and their evolution with time. The bursts resulted in count rate increases by orders of magnitude, sometimes limited by the detector dead time, and showed blackbody spectra with kT ~ 6–8 keV in the T_(90) duration of 1–4 s, similar to earlier bursts detected from the source. We find that the spectra during the tail of the bursts can be modeled with an absorbed blackbody with temperature decreasing with flux. The burst flux decays followed a power law of index 0.8–0.9. In the burst tail spectra, we detect a ~13 keV emission feature, similar to those reported in previous bursts from this source as well as from other magnetars observed with the Rossi X-ray Timing Explorer. We explore possible origins of the spectral feature such as proton cyclotron emission, which implies a magnetic field strength of B ~ 2 × 10^(15) G in the emission region. However, the consistency of the energy of the feature in different objects requires further explanation.