Astronomy, Astrophysics and Space Engineering

The 2010 outburst of the transient neutron star low-mass X-ray binary IGR J17480-2446 has exhibited a series of unique X-ray bursts as well as millihertz (mHz) quasi-periodic oscillations (QPOs) related to these bursts. It has been recently proposed that these are type-II bursts, powered by the gravitational energy. This implies that the current nuclear-burning-based model of mHz QPOs is not correct, and this timing feature cannot be used as a tool to measure the neutron star parameters. We report the analysis of the Rossi X-Ray Timing Explorer data of IGR J17480-2446 to show that the burst properties of this source are quite different from the properties of the type-II bursts observed from the rapid burster and GRO J1744-28. For example, the inferred ratio (~50-90) of the non-burst fluence to burst fluence is consistent with the thermonuclear origin of IGR J17480-2446 bursts and is significantly different from this ratio (lsim4) for type-II bursts. Our results suggest that the bursts and the mHz QPOs from IGR J17480-2446 are powered by the nuclear energy.

We study the spectral-state evolution of the Terzan 5 transient neutron star low-mass X-ray binary IGR J17480-2446, and how the best-fitting spectral parameters and burst properties evolved with these states, using the Rossi X-ray Timing Explorer data. As reported by other authors, this is the second source that showed transitions between atoll state and 'Z' state. We find large-scale hysteresis in the almost 'C'-like hardness-intensity track of the source in the atoll state. This discovery is likely to provide a missing piece of the jigsaw puzzle involving various types of hardness-intensity tracks from 'q' shaped for Aquila X-1, 4U 1608-52 and many black holes to 'C' shaped for many atoll sources. Furthermore, the regular pulsations, a diagonal transition between soft and hard states, and the large-scale hysteresis observed from IGR J17480-2446 argue against some of the previous suggestions involving magnetic field about atolls and millisecond pulsars. Our results also suggest that the nature of spectral evolution throughout an outburst does not, at least entirely, depend on the peak luminosity of the outburst. Besides, the source took at least a month to trace the softer banana state, as opposed to a few hours to a day, which is typical for an atoll source. In addition, while the soft colour usually increases with intensity in the softer portion of an atoll source, IGR J17480-2446 showed an opposite behaviour. From the detailed spectral fitting, we conclude that a blackbody+power-law model is the simplest one, which describes the source continuum spectra well throughout the outburst. We find that these two spectral components were plausibly connected to each other, and they worked together to cause the source-state evolution. Spectral parameters smoothly changed as IGR J17480-2446 transitioned between the atoll state and 'Z' state, and thermonuclear bursts disappeared in the softer parts of 'Z' tracks. Finally, based on the burst properties, we suggest that IGR J17480-2446 is somewhat an analogue of the only other clock-like burster GS 1826-238, and the former showed much smaller burst intervals plausibly because it is a pulsar.

The HI 21 cm transition line is expected to be an important probe into the cosmic dark ages and epoch of reionization. Foreground source removal is one of the principal challenges for the detection of this signal. This paper investigates the extragalactic point source contamination and how accurately bright sources ( 1 Jy) must be removed in order to detect 21 cm emission with upcoming radio telescopes such as the Murchison Widefield Array (MWA). We consider the residual contamination in 21 cm maps and power spectra due to position errors in the sky-model for bright sources, as well as frequency independent calibration errors. We find that a source position accuracy of 0.1 arcsec will suffice for detection of the HI power spectrum. For calibration errors, 0.05 % accuracy in antenna gain amplitude is required in order to detect the cosmic signal. Both sources of subtraction error produce residuals that are localized to small angular scales, k ⊥ 0.05 Mpc −1 , in the two-dimensional power spectrum.

In the context of the VLA-COSMOS Deep project additional VLA A array observations at 1.4 GHz were obtained for the central degree of the COSMOS field and combined with the existing data from the VLA-COSMOS Large project. A newly constructed Deep mosaic with a resolution of 2.5 ′′ was used to search for sources down to 4σ with 1σ ≈ 12 µJy/beam in the central 50 ′ ×50 ′ . This new catalog is combined with the catalog from the Large project (obtained at 1.5 ′′ ×1.4 ′′ resolution) to construct a new Joint catalog. All sources listed in the new Joint catalog have peak flux densities of ≥5σ at 1.5 ′′ and/or 2.5 ′′ resolution to account for the fact that a significant fraction of sources at these low flux levels are expected to be slighty resolved at 1.5 ′′ resolution. All properties listed in the Joint catalog such as peak flux density, integrated flux density and source size are determined in the 2.5 ′′ resolution Deep image. In addition, the Joint catalog contains 43 newly identified multi-component sources.

Observations of the HI 21cm transition line promises to be an important probe into the cosmic dark ages and epoch of reionization. One of the challenges for the detection of this signal is the accuracy of the foreground source removal. This paper investigates the extragalactic point source contamination and how accurately the bright sources ( 1 Jy) should be removed in order to reach the desired RMS noise and be able to detect the 21cm transition line. Here, we consider position and flux errors in the global sky-model for these bright sources as well as the frequency independent residual calibration errors. The synthesized beam is the only frequency dependent term included here. This work determines the level of accuracy for the calibration and source removal schemes and puts forward constraints for the design of the cosmic reionization data reduction scheme for the upcoming low frequency arrays like MWA,PAPER, etc. We show that in order to detect the reionization signal the bright sources need to be removed from the data-sets with a positional accuracy of ∼ 0.1 arc-second. Our results also demonstrate that the efficient foreground source removal strategies can only tolerate a frequency independent antenna based mean residual calibration error of 0.2% in amplitude or 0.2 degree in phase, if they are constant over each days of observations (6 hours). In future papers we will extend this analysis to the power spectral domain and also include the frequency dependent calibration errors and direction dependent errors (ionosphere, primary beam, etc).

We present an analysis of the radio properties of large samples of Lyman Break Galaxies (LBGs) at z ∼ 3, 4, and 5 from the COSMOS field. The median stacking analysis yields a statistical detection of the z ∼ 3 LBGs (U-band dropouts), with a 1.4 GHz flux density of 0.90 ± 0.21µJy. The stacked emission is unresolved, with a size < 1", or a physical size < 8kpc. The total star formation rate implied by this radio luminosity is 31 ± 7 M ⊙ year −1 , based on the radio-FIR correlation in low redshift star forming galaxies. The star formation rate derived from a similar analysis of the UV luminosities is 17 M ⊙ year −1 , without any correction for UV dust attenuation. The simplest conclusion is that the dust attenuation factor is 1.8 at UV wavelengths. However, this factor is considerably ⋆ Based on observations in the COSMOS Legacy Survey including those taken on the HST, Keck, NRAO-VLA, Subaru, KPNO 4m, CTIO 4m, and CFHT 3.6m.

We use the 2011 Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data of the 401-Hz accreting pulsar and burster IGR J17498−2921 to perform timing analysis and time-resolved spectroscopy of 12 thermonuclear X-ray bursts. We confirm previously reported burst oscillations from this source with a much higher significance (8.8σ ). We note that the bursts can be divided into three groups: big photospheric radius expansion (PRE) bursts are about 10 times more luminous than medium bursts, while the latter are about 10 times more luminous than small bursts. The PCA field of view of these observations contains several known bursters, and hence some of the observed bursts might not be from IGR J17498−2921. The oscillations during big bursts at the known pulsar frequency show that these bursts were definitely from IGR J17498−2921. We find that at least several of the other bursts were also likely originated from IGR J17498−2921. Spectral analysis reveals that the luminosity differences among various bursts are primarily due to differences in normalizations, and not temperatures, even when we consider the effects of colour factor. This shows burning on a fraction of the stellar surface for those small and medium bursts, which originated from IGR J17498−2921. The low values of the upper limits of burst oscillation amplitude for these bursts suggest a small angle between the spin axis and the magnetic axis. We find indications of the PRE nature of a medium burst, which likely originated from IGR J17498−2921. If true, then, to the best of our knowledge, this is the first time that two PRE bursts with a peak count rate ratio of as high as ≈12 have been detected from the same source.

Burst oscillations during the rising phases of thermonuclear X-ray bursts are usually believed to originate from
flame spreading on the neutron star surface. However, the decrease of fractional oscillation amplitude with rise time,
which provides a main observational support for the flame spreading model, have so far been reported from only a
few bursts. Moreover, the non-detection and intermittent detections of rise oscillations from many bursts are not yet
understood considering the flame spreading scenario. Here, we report the decreasing trend of fractional oscillation
amplitude from an extensive analysis of a large sample of Rossi X-ray Timing Explorer Proportional Counter Array
bursts from 10 neutron star low-mass X-ray binaries. This trend is 99.99% significant for the best case, which
provides, to the best of our knowledge, by far the strongest evidence of such a trend. Moreover, it is important to
note that an opposite trend is not found in any of the bursts. The concave shape of the fractional amplitude profiles
for all the bursts suggests latitude-dependent flame speeds, possibly due to the effects of the Coriolis force. We also
systematically study the roles of low fractional amplitude and low count rate for non-detection and intermittent
detections of rise oscillations, and attempt to understand them within the flame spreading scenario. Our results
support a weak turbulent viscosity for flame spreading, and imply that burst rise oscillations originate from an
expanding hot spot, thus making these oscillations a more reliable tool to constrain the neutron star equations of
state.

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 analyses 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.

The 2011 outburst of Swift J1822.3–1606 was extraordinary; periodic modulations at the spin period of the underlying neutron star were clearly visible, remarkably similar to what is observed during the decaying tail of magnetar giant flares. We investigated the temporal characteristics of X-ray emission during the early phases of the outburst. We performed a periodicity search with the spectral hardness ratio (HR) and found a coherent signal near the spin period of the neutron star, but with a lag of about 3 radians. Therefore, the HR is strongly anti-correlated with the X-ray intensity, which is also seen in the giant flares. We studied the time evolution of the pulse profile and found that it evolves from a complex morphology to a much simpler shape within about a month. Pulse profile simplification also takes place during the giant flares, but on a much shorter timescale of about a few minutes. We found that the amount of energy emitted during the first 25 days of the outburst is comparable to what was detected in minutes during the decaying tail of giant flares. Based on these similarities, we suggest that the triggering mechanisms of the giant flares and the magnetar outbursts are likely the same. We propose that the trapped fireball that develops in the magnetosphere at the onset of the outburst radiates away efficiently in minutes in magnetars exhibiting giant flares, while in other magnetars, such as Swift J1822.3–1606, the efficiency of radiation of the fireball is not as high and, therefore, lasts much longer.

Extended emission episodes with intensity above the pre-burst level are observed following magnetar bursts from a number of soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs). Such extended tail emission were observed subsequent to two events detected from AXP 4U 0142+61. We investigated in detail the evolution of spectral and temporal properties during these two tail segments using RXTE/PCA observations, and report distinct variations both in the spectral and temporal behavior throughout the tails. In particular, sudden enhancement of pulsation amplitude in conjunction with bursts, and smooth decline of X-ray emission (cooling) during the tail were observed in both cases. We suggest that an inefficiently radiating trapped fireball formed during the burst, which can heat up the stellar surface, is able to explain the tail properties and its energetics. We also present the episodic detection of absorption and emission features during tails. One possible mechanism that has been proposed to give rise to such spectral lines is the proton/ion cyclotron resonance process which has been suggested to offer a valuable tool in probing the complex magnetic field of magnetars. Subject headings: pulsars: individual (4U 0142+61) – stars: magnetars – stars: neutron – X-rays: stars

Two energetic hard X-ray bursts from the rotation-powered pulsar PSR J1119−6127 recently triggered the Fermi and Swift space observatories. We have performed in-depth spectral and temporal analyses of these two events. Our extensive searches in both observatories' data for lower luminosity bursts uncovered 10 additional events from the source. We report here on the timing and energetics of the 12 bursts from PSR J1119−6127 during its burst active phase on 2016 July 26 and 28. We also found a spectral softer X-ray flux enhancement in a post-burst episode, which shows evidence of cooling. Here we discuss the implications of these results on the nature of this unusual high-field radio pulsar, which firmly place it within the typical magnetar population.

In this paper, I document the strategy and results of my attempts at modelling and understanding the nature of multipath error in navigation satellites. I shall be discussing my python code and the math used in the python code to study the signal error. I would also briefly discuss some fundamental concepts associated with navigation satellite as and when required.

In this technical report, I describe the details of the code that I had written to fit a curve for a set of observational data points using the Givens Rotation method of performing QR factorization. This document is structured in a manner where I first describe what Givens Rotation is, then the complete sequence of how I used Givens Rotation to find the R factor and, finally, how I use the R factor to fit a curve that matches the measured data points.

We have compiled the most comprehensive burst sample from magnetar 4U 0142+61, comprising 27 bursts from its three burst-active episodes in 2011, 2012 and the latest one in 2015 observed with Swift/BAT and Fermi /GBM. Bursts from 4U 0142+61 morphologically resemble typical short bursts from other magnetars. However, 4U 0142+61 bursts are less energetic compared to the bulk of magnetar bursts. We uncovered an extended tail emission following a burst on 2015 February 28, with a thermal nature, cooling over a timescale of several minutes. During this tail emission, we also uncovered pulse peak phase aligned X-ray bursts , which could originate from the same underlying mechanism as that of the extended burst tail, or an associated and spatially coincident but different mechanism.

Plasma accreted onto the surface of a neutron star can ignite due to unstable thermonuclear burning and produce a bright flash of X-ray emission called a Type-I X-ray burst. Such events are very common; thousands have been observed to date from over a hundred accreting neutron stars. The intense, often Eddington-limited, radiation generated in these thermonuclear explosions can have a discernible effect on the surrounding accretion flow that consists of an accretion disk and a hot electron corona. Type-I X-ray bursts can there-B N. Degenaar