arXiv subjects

Biswajit Paul

Publications and source records attributed to Biswajit Paul.

At least 145 records · Page 8Linked to original sources

arXiv2013

Average spectral properties of galactic X-ray binaries with 3 years of MAXI data

The energy spectra of X-ray binaries (XRBs) have been investigated during the last few decades with many observatories in different energy bands and with different energy resolutions. However, these studies are carried out in selected states of XRBs like during outbursts, transitions, quiescent states, and are always done in limited time windows of pointed observations. It is now possible to investigate the long term averaged spectra of a large number of X-ray binaries with the all sky monitor MAXI, which also has a broad energy band. Here we present the average spectral behaviour of a few representative XRBs. The long term averaged spectrum of Cyg X-1 is described by a sum of two power-laws having $Γ_{1}$ ~ 2.8 and $Γ_{2}$ ~ 1.2, along with a multi color disk blackbody having an inner disk temperature of 0.5 keV, GX 301-2 is described by a power-law with a high energy cut-off at $E_{c}$ ~ 15 keV and a blackbody component at 0.2 keV and that of Aql X-1 is described by a multi color disk blackbody at 2 keV and a power-law of $Γ$ ~ 2.2. We have also constructed the combined X-ray spectrum of the X-ray binaries in the Milky Way, which can be compared to the XRBs spectra of other galaxies observed with Chandra and XMM-Newton. These measurements are also relevant to investigate the X-ray interaction with the ISM and its contribution to the ionising X-ray background in the early universe.

astro-ph.HE↗

arXiv2013

BRST symmetry and $W$-algebra in higher derivative models

In this paper we discuss the (anti-)BRST symmetries and $W$-algebra of higher derivative theories of relativistic particles satisfying general gauge conditions. Using this formalism, the connection between the (anti-)BRST symmetries and $W$-algebra for the rigid relativistic particle is established. Incidentally, the full $W$-algebra emerges only when the anti-BRST transformations are considered in tandem with the BRST ones. Further, the BRST symmetry is made finite and coordinate-dependent. We show that such finite coordinate-dependent BRST symmetry changes the BRST invariant gauge-fixing fermion within the functional integration. This is exploited to connect two different arbitrary gauge conditions.

hep-th↗

arXiv2013

Revisiting SWJ2000.6+3210 : A persistent Be X-ray pulsar ?

We present a detailed timing and spectral analysis of the Be X-ray binary SWJ2000.6+3210 discovered by the BAT Galactic plane survey. Two Suzaku observations of the source made at six months interval, reveal pulsations at ~ 890s for both observations with a much weaker pulse fraction in the second one. Pulsations are clearly seen in the energy band of 0.3-10 keV of XIS for both observations and at high energies up to 40 keV for the second observation. The broad band X-ray spectrum is consistent with a powerlaw and high energy cutoff model along with a hot blackbody component. No change in spectral parameters is detected between the observations. We have also analyzed several short observations of the source with Swift/XRT and detected only a few percent variation in flux around a mean value of 3:5 *10^{-11} erg cm^{-2} s^{-1}. The results indicates that SWJ2000.6+3210 is a member of persistent Be X-ray binaries which have the same broad characteristics as this source.

astro-ph.HE↗

arXiv2013

ASTROSAT: Some Key Science Prospects

ASTROSAT is an astronomy satellite designed for simultaneous multi-wavelength studies in the Optical/UV and a broad X-ray energy range. With four X-ray instruments and a pair of UV-Optical telescopes, ASTROSAT will provide unprecendented opportunity for simultaneous multi-wavelength observations, which is of immense value in study of highly variable sources, especially X-ray binaries and Active Galactic Nuclei. The Large Area X-ray Proportional Counters (LAXPC) of ASTROSAT, which has the largest effective area in the hard X-ray band compared to all previous X-ray missions, will enable high time resolution X-ray measurements in the 2-80 keV band with moderate energy resolution. Here we give a brief summary of the payload characteristics of ASTROSAT and discuss some of the main science topics that will be addressed with the LAXPC, and with simultaneous observations with the UVIT telescopes, with particular emphasis on X-ray binaries and compact objects. The possibility of aiding gravitational wave experiments is also briefly mentioned.

astro-ph.HE↗

arXiv2013

Simulating GHZ Correlations Relaxing Physical Constraints

Violation of Bell inequality (or, Bell-type inequalities) by nonlocal correlations is justified by relaxation of at least one of the plausible physical constraints used to model such inequality. Based on this fact, in this letter we present a procedure to simulate three-qubit GHZ correlation relaxing two constraints, determinism and no signaling simultaneously. We have also derived the minimum amount of indeterminism and signaling to be introduced in a system. The corresponding number of signaling and local bits of mutual information needed to communicate are also provided and thus we are able to focus on utility of relaxation of these two constraints as useful resources.

quant-ph↗

arXiv2013

Pulse phase dependent variations of the cyclotron absorption features of the accreting pulsars A 0535+26, XTE J1946+274 and 4U 1907+09 with Suzaku

We have performed a detailed pulse phase resolved spectral analysis of the cyclotron resonant scattering features (CRSF) of the two Be/X-ray pulsars A0535+26 and XTE J1946+274 and the wind accreting HMXB pulsar 4U 1907+09 using Suzaku observations. The CRSF parameters vary strongly over the pulse phase and can be used to map the magnetic field and a possible deviation form the dipole geometry in these sources. It also reflects the conditions at the accretion column and the local environment over the changing viewing angles. The pattern of variation with pulse phase are obtained with more than one continuum spectral models for each source, all of which give consistent results. Care is also taken to perform the analysis over a stretch of data having constant spectral characteristics and luminosity to ensure that the results reflect the variations due to the changing viewing angle alone. For A0535+26 and XTE J1946+274 which show energy dependent dips in their pulse profiles, a partial covering absorber is added in the continuum spectral models to take into account an additional absorption at those phases by the accretion stream/column blocking our line of sight.

astro-ph.HE↗

arXiv2013

Gauge symmetry and Virasoro algebra in quantum charged rigid membrane -- a first order formalism

The quantum charged rigid membrane model, which is a higher derivative theory has been considered to explore its gauge symmetries using a recently developed first order formalism \cite{BMP}. Hamiltonian analysis has been performed and the gauge symmetry of the model is identified as reparametrisation symmetry. First class constraints are shown to have a truncated Virasoro algebraic structure. An exact correspondence between the higher derivative theory and the first order formalism has been shown from the point of view of equations of motion.

hep-th↗

arXiv2013

Timing and Spectral properties of Be/X-ray pulsar EXO 2030+375 during a Type I outburst

We present results from a study of broadband timing and spectral properties of EXO 2030+375 using a Suzaku observation. Pulsations with a period of 41.41 s and strong energy dependent pulse profiles were clearly detected up to ~100 keV. Narrow dips are seen in the profiles up to ~70 keV. Presence of prominent dips at several phases in the profiles up to such high energy ranges were not seen before. At higher energies, these dips gradually disappeared and the profile appeared single-peaked. The 1.0-200.0 keV broad-band spectrum is found to be well described by a partial covering high energy cut-off power-law model. Several low energy emission lines are also detected in the pulsar spectrum. We fitted the spectrum using neutral as well as partially ionized absorbers along with above continuum model yielding similar parameter values. The partial covering with partially ionized absorber resulted into marginally better fit. The spectral fitting did not require any cyclotron feature in the best fit model. To investigate the changes in spectral parameters at dips, we carried out pulse-phase-resolved spectroscopy. During the dips, the value of additional column density was estimated to be high compared to other pulse phases. While using partially ionized absorber, the value of ionization parameter is also higher at the dips. This may be the reason for the presence of dips up to higher energies. No other spectral parameters show any systematic variation with pulse phases of the pulsar.

astro-ph.HE↗

arXiv2012

Pulse phase resolved spectroscopy of Vela X-1 with Suzaku

We present a detailed pulse phase resolved spectral analysis of the persistent high mass X-ray binary pulsar Vela X-1 observed with Suzaku during June 2008. The pulse profiles exhibit both intensity and energy dependence with multiple peaks at low energies and double peaks at higher energies. The source shows some spectral evolution over the duration of the observation and care has been taken to average over data with minimum spectral variability for the analysis. We model the continuum with a phenomenological partial covering high energy cutoff model and a more physical partial covering thermal Comptonization model (CompTT) excluding the time ranges having variable hardness ratio and intensity dependence. For both the models we detect a cyclotron resonant scattering feature (CRSF) and its harmonic at ~ 25 keV and ~ 50 keV. Both the CRSF fundamental and harmonics parameters are strongly variable over the pulse phase, with the ratio of the two line energies deviating from the classical value of 2. The continuum parameters also show significant variation over the pulse phase and give us some idea about the changing physical conditions that is seen with the changing viewing angle at different pulse phases and obscuration by the accretion stream at some pulse phases.

astro-ph.HE↗

arXiv2012

Investigation of variability of iron emission lines in Centaurus X-3

We present the results obtained from a study of the variability of iron emission lines in the high mass X-ray binary pulsar Cen X-3 during the eclipse, eclipse-egress and out-of-eclipse phases using XMM-Newton observations. Three iron emission lines at 6.4 keV, 6.7 keV, and 6.97 keV are clearly detected in the spectrum of the pulsar during the entire observations, irrespective of different binary phases. The properties of these emission lines are investigated at different intensity levels. The flux level and equivalent width of the emission lines change during the eclipse, eclipse-egress and out-of-eclipse orbital phases. Based on the results obtained from the time resolved spectral analysis, it is understood that the most probable emitting region of 6.4 keV fluorescent line is very close to the neutron star whereas the other two lines are produced in a region that is far from the neutron star, probably in the highly photo-ionized wind of the companion star or in the accretion disk corona.

astro-ph.SR↗

arXiv2012

Simultaneous X-ray and optical observations of thermonuclear bursts in the LMXB EXO 0748-676

We report the detection of a large number of optical bursts in the Low Mass X-ray Binary (LMXB) EXO 0748-676 simultaneous with the thermonuclear X-ray bursts. The X-ray and the optical bursts are detected in a long observation of this source with the XMM-Newton observatory. This has increased the number of thermonuclear X-ray bursts in the LMXBs with simultaneous optical detection by several factors. The optical bursts are found to have a linear rise followed by a slow, somewhat exponential decay. Most of the optical bursts have longer rise and decay timescale compared to the corresponding X-ray bursts. We have determined the X-ray and optical excess photon counts in the bursts that allow us to look at the optical to X-ray burst fluence ratio for each burst and the ratio as a function of the X-ray burst intensity and as a function of the orbital phase. The delay between the onset of the X-ray bursts and the onset of the optical bursts have also been measured and is found to have an average value of 3.25 seconds. We do not find any convincing evidence of orbital phase dependence of the following parameters: X-ray to optical delay, rise time of the optical bursts, and optical to X-ray burst intensity ratio as would be expected if the optical bursts were produced by reprocessing from the surface of the secondary star that is facing the compact star. On the other hand, if the optical bursts are produced by reprocessing of the X-rays in the accretion disk, the onset of the bursts is not expected to have a sharp, linear shape as is observed in a few of the bursts in EXO 0748-676. We emphasise the fact that simultaneous optical observations of the X-ray bursts in multiple wavelength bands will enable further detailed investigations of the reprocessing phenomena, including any non-linear effect of the X-ray irradiation.

astro-ph.HE↗

arXiv2012

Gauge invariances of higher derivative Maxwell-Chern-Simons field theory -- a new Hamiltonian approach

A new method of abstracting the independent gauge invariances of higher derivative systems, recently introduced in [1], has been applied to higher derivative field theories. This has been discussed taking the extended Maxwell-Chern-Simons model as an example. A new Hamiltonian analysis of the model is provided. This Hamiltonian analysis has been used to construct the independent gauge generator. An exact mapping between the Hamiltonian gauge transformations and the U(1) symmetries of the action has been established.

hep-th↗

arXiv2011

Timing and broad band spectroscopy of 1A 1118-61 with Suzaku

We present a timing and broad-band pulse phase resolved spectral analysis of the transient Be X-ray binary pulsar 1A 1118-61 observed during its outburst in January 2009 using Suzaku observations. Suzaku observations were made twice, once at the peak of the outburst, and once 13 days later at its declining phase.Pulse profiles from both observations exhibit strong energy dependence with several peaks at low energies and a single peak above ~10 keV. A weak, narrow peak is detected at the main dip of the pulse profiles from both observations in the energy bands below 3 keV, indicating the presence of a phase dependent soft excess in the source continuum. The broad-band energy spectrum of the pulsar could be fitted well with a partial covering cutoff power-law model and a narrow iron fluorescence line. We also detect a broad cyclotron feature at ~50 keV from both observations which is a feature common for accretion powered pulsars with high magnetic field strengths. Pulse phase-resolved spectral analysis shows an increase in the absorption column density of the partial covering component, as well as variation in the covering fraction at the dips of the pulse profiles, that naturally explains the energy dependence of the same. The cyclotron line parameters also show significant variation with pulse phase with a ~ 10 keV variation in the cyclotron line energy and a variation in depth by a factor of three. This can be explained either as the effect of different viewing angles of the dipole field at different pulse phases, or a more complex underlying magnetic field geometry

astro-ph.HE↗

arXiv2011

RXTE-ASM light curves of Cen X-3

In Paul, Raichur and Mukherjee (2005) we had reported a spectral mode change in the X-ray binary pulsar Cen X-3 using the then available ASM light curves of Cen X-3. Being mindful of the fact that instrument calibration or other issues like gain changes, software issues etc. might give rise to some of the artifacts, we had used the ASM light curves of three other X-ray binary pulsars namely Her X-1, SMC X-1 and Vela X-1 for comparison for the same observation times. In light of the recent finding of Müller et al. (2011); which reports the non-detection of such features in the current ASM light curves available on the HEASARC website and with other instruments like MAXI, SWIFT and INTEGRAL, we would like to point out the inconsistency between the ASM ligthcurves available in 2005 and now. This information will be very useful for other users of ASM light curves.

astro-ph.HE↗

arXiv2011

Transient High Mass X-ray Binaries

High Mass X-ray Binaries (HMXBs) are interesting objects that provide a wide range of observational probes to the nature of the two stellar components, accretion process, stellar wind and orbital parameters of the systems. A large fraction of the transient HMXBs are found to be Be/X-ray binaries in which the companion Be star with its circumstellar disk governs the outburst. These outbursts are understood to be due to the sudden enhanced mass accretion to the neutron star and is likely to be associated with changes in the circumstellar disk of the companion. In the recent years, another class of transient HMXBs have been found which have supergiant companions and show shorter bursts. X-ray, infrared and optical observations of these objects provide vital information regarding these systems. Here we review some key observational properties of the transient HMXBs and also discuss some important recent developments from studies of this class of sources. The X-ray properties of these objects are discussed in some detail whereas the optical and infrared properties are briefly discussed.

astro-ph.HE↗

arXiv2011

Gauge symmetry and W-algebra in higher derivative systems

The problem of gauge symmetry in higher derivative Lagrangian systems is discussed from a Hamiltonian point of view. The number of independent gauge parameters is shown to be in general {\it{less}} than the number of independent primary first class constraints, thereby distinguishing it from conventional first order systems. Different models have been considered as illustrative examples. In particular we show a direct connection between the gauge symmetry and the W-algebra for the rigid relativistic particle.

hep-th↗

arXiv2011

Pulse profile stability of the Crab pulsar

We present an X-ray timing analysis of the Crab pulsar, PSR B0531+21, using the archival RXTE data. We have investigated the stability of the Crab pulse profile, in soft (2-20 keV) and hard (30-100 keV) X-ray energies, over the last decade of RXTE operation. The analysis includes measurement of the separation between the two pulse peaks; and intensity and the widths of the two peaks. We did not find any significant time dependency in the pulse shape. The two peaks are stable in phase, intensity and widths, for the last ten years. The first pulse is relatively stronger at soft X-rays. The first pulse peak is narrower than the second peak, in both, soft- and hard X-ray energies. Both the peaks show a slow rise and a steeper fall. The ratio of the pulsed photons in the two peaks is also constant in time.

astro-ph.HE↗

arXiv2011

Timing and spectral studies of the transient X-ray pulsar GX 304-1 during an outburst

We present the timing and spectral properties of the transient X-ray pulsar GX 304-1 during its recent outburst in 2010 August, using observations carried out with the Proportional Counter Array (PCA) instrument on-board the Rossi X-ray Timing Explorer (RXTE) satellite. We detected strong intensity and energy dependent variations in the pulse profiles during the outburst. The pulse profile showed significant evolution over the outburst. It showed complex structures consisting of a main peak with steps on both sides during the start of the outburst. On some days, a sharp dip like feature was seen which disappeared at the end of the outburst; when the profile evolved into a sinusoidal shape. At low energies, the pulse profiles appeared complex, consisting of multiple peaks and a narrow minimum. The amplitude of the second brightest peak in low energies decreased with energy, and above 12 keV, the shape of the pulse profile changed to a single broad peak with a dip like feature. The dip had energy dependence, both in phase and in width. We detected Quasi-periodic Oscillations (QPO) at 0.125 Hz with a harmonic. The QPO feature had a low rms value of 2.9% and it showed a positive energy dependence up to 40 keV with the rms value increasing to 9% at 40 keV. The QPO frequency decreased from 0.128 Hz to 0.108 Hz in 12 days. During most of the outburst, the 3-30 keV spectrum of GX 304-1 can be well fitted with a partial covering power-law model with a high energy cut-off and iron fluorescent line emission. For a few of the observations carried out during the decay of the outburst, the partial covering absorption component is found to change to single component absorption. We also found that the partial covering and high energy cut-off parameters vary significantly with the pulse phase.

astro-ph.HE↗