arXiv subjects

S. Ganesh

Publications and source records attributed to S. Ganesh.

At least 37 records · Page 2Linked to original sources

arXiv2016

Primary black hole spin in OJ287 as determined by the General Relativity centenary flare

OJ287 is a quasi-periodic quasar with roughly 12 year optical cycles. It displays prominent outbursts which are predictable in a binary black hole model. The model predicted a major optical outburst in December 2015. We found that the outburst did occur within the expected time range, peaking on 2015 December 5 at magnitude 12.9 in the optical R-band. Based on Swift/XRT satellite measurements and optical polarization data, we find that it included a major thermal component. Its timing provides an accurate estimate for the spin of the primary black hole, chi = 0.313 +- 0.01. The present outburst also confirms the established general relativistic properties of the system such as the loss of orbital energy to gravitational radiation at the 2 % accuracy level and it opens up the possibility of testing the black hole no-hair theorem with a 10 % accuracy during the present decade.

astro-ph.HE↗

arXiv2015

pQCD approach to Charmonium regeneration in QGP at the LHC

We analyze the applicability of perturbative QCD (pQCD) approach to the issue of $J/ψ$ recombination at the Large Hadron Collider (LHC), and calculate the recombination cross section for $c\bar{c}$ recombination to form $J/ψ$ as a function of temperature. The charmonium wavefunction is obtained by employing a temperature dependent phenomenological potential between the $c\bar{c}$ pair. The temperature dependent formation time of charmonium is also employed in the current work. A set of coupled rate equations is established which incorporates color screening, gluonic dissociation, collisional damping and recombination of uncorrelated $c\bar{c}$ pair in the quark-gluon plasma (QGP) medium. The final $J/ψ$ suppression, thus determined as a function of centrality is compared with the ALICE experimental data at both mid and forward rapidity and CMS experimental data at mid rapidity obtained from the Large Hadron Collider (LHC) at center of mass energy $\sqrt{s_{NN}} = 2.76$ TeV. Keywords : Color screening, Recombination, Gluonic dissociation, Collisional damping, Survival probability, pQCD, Charmonium PACS numbers : 12.38.Mh, 12.38.Gc, 25.75.Nq, 24.10.Pa

hep-ph↗

arXiv2015

Unified Description of Charmonium Suppression in Quark-Gluon Plasma Medium at RHIC and LHC Energies

Recent experimental and theoretical studies suggest that the quarkonia suppression in a thermal QCD medium created at heavy ion collisions is a complex interplay of various physical processes. In this article we put together most of these processes in a unified way to calculate the charmonium survival probability (nuclear modification factor) at energies available at relativistic heavy ion collider (RHIC) and large hadron collider (LHC) experiments. We have included shadowing as the dominant cold nuclear matter (CNM) effect. Further, gluo-dissociation and collision damping has been included which provide width to the spectral function of charmonia in a thermal medium and causes the dissociation of charmonium along with usual colour screening. We include the colour screening using our recently proposed modified Chu and Matsui model. Furthermore we incorporate the recombination of uncorrelated charm and anti-charm quark for the regeneration of charmonium over the entire temporal evolution of QGP medium. Finally we do the feed-down correction from the excited states to calculate the survival probability of charmonium. We find that our unified model suitably describes the experimental nuclear modification data of $J/ψ$ at RHIC and LHC simultaneously.

hep-ph↗

arXiv2015

Temperature dependent formation-time approach for $Υ$ suppression at energies available at the CERN Large Hadraon Collider

We present here a comprehensive model to describe the bottomonium suppression data obtained from the CERN Large Hadron Collider (LHC) at center-of-mass energy of $\sqrt{s_{NN}}=2.76$ TeV. We employ a quasiparticle model (QPM) equation of state for the quark-gluon plasma (QGP) expanding under Bjorken's scaling law. The current model includes the modification of the formation time based on the temperature of the QGP, color screening during bottomonium production, gluon induced dissociation and collisional damping due to the imaginary part of the potential between the $b\bar b$ pair. We propose a method for determining the temperature-dependent formation time of bottomonia using the solution of the time-independent Schrödinger equation and compare it with another approach based on time-dependent Schrödinger wave equation simulation. We find that these two independent methods based on different axioms give similar results for the formation time. Cold nuclear matter effects and feed-down from higher resonance states of $Υ$ have also been included in the present work. The suppression of the bottomonium states at mid rapidity is determined as a function of centrality. The results compare closely with the recent centrality-dependent suppression data at the energies available at the CERN LHC in the mid rapidity region.

hep-ph↗

arXiv2015

A temperature dependent formation time approach for Υsuppression at LHC

We present here a model to describe the bottomonium suppression in Pb$+$Pb collisions at Large Hadron Collider (LHC), at $\sqrt{s_{NN}}=2.76$ TeV by using the quasi-particle model (QPM) equation of state (EOS) for the Quark-Gluon Plasma (QGP) expanding under Bjorken's hydrodynamical expansion. The current model includes the modification of the formation time based on the temperature of QGP, color screening during bottomonium production, gluon induced dissociation and collisional damping. The cold nuclear matter (CNM) effects and decay of higher resonances of bottomonium have also been included in the present work. The final suppression of the bottomonium states, at mid rapidity is calculated as a function of centrality. The results compare closely with the recent data at Large hadron Collider (LHC) in the mid rapidity region for various centrality bins. {\nd \it Keywords } : Color screening, Gluonic dissociation, Collisional damping, Survival probability, CNM effects\\ {\nd \it PACS numbers } : 12.38.Mh, 12.38.Gc, 25.75.Nq, 24.10.Pa

hep-ph↗

arXiv2014

Lately Exposed Amorphous Water Ice on Comet 49P/Arend-Rigaux

Comet 49P/ Arend-Rigaux, thought to be a low activity comet since the 1980's was found to be active in its recent apparitions. Recent analysis of the data obtained from Spitzer observation of the comet in 2006 compared with laboratory spectra has revealed amorphous water ice on the surface. In addition, in 2012 a jet was found to appear during its subsequent perihelion passage as witnessed during an observation carried out on 26th March 2012 using the PRL telescope at Mt. Abu. This confirms recent activity of Comet 49P/Arend-Rigaux due to the volatile subsurface materials exposed after several passages close to the Sun. Our result confirms the subsurface ices on cometary nuclei and insists for more observations for a better understanding.

astro-ph.EP↗

arXiv2013

Bottomonium suppression at $\sqrt{s_{NN}}=2.76$ TeV using model based on color screening and gluonic dissociation with collisional damping

We present a model to explain the bottomonium suppression in Pb+Pb collisions at mid rapidity obtained from Large Hadron Collider (LHC) energy, $\sqrt{s_{NN}}=2.76$ TeV. The model consists of two decoupled mechanisms namely, color screening during bottomonium production followed by gluon induced dissociation along with collisional damping. The quasi-particle model (QPM) is used as equation of state (EOS) for the Quark-Gluon Plasma (QGP) medium. The feed-down from higher $Υ$ states, such as $Υ(1P)$, $Υ(2S)$ and $Υ(2P)$, dilated formation times for bottomonium states and viscous effect of QGP medium are other ingredients included in the current formulation. We further assume that the QGP is expanding according to (1+1)-dimensional Bjorken's boost invariant scaling law. The net suppression (in terms of $p_T$ integrated survival probability) for bottomonium states at mid rapidity is obtained as a function of centrality and the result is then compared both quantitatively and qualitatively with the recent LHC experimental data in the mid rapidity region recently published by CMS collaboration. We find that the current model, based on the Debye color screening plus gluonic dissociation along with collisional damping, better describes the centrality dependence of bottomonium suppression at LHC energy as compared to color screening model alone. \vskip 0.5cm {\nd \it Keywords} : Color screening, Gluonic dissociation, Collisional damping, Survival probability {\nd \it PACS numbers} : 12.38.Mh, 12.38.Gc, 25.75.Nq, 24.10.Pa

hep-ph↗

arXiv2013

Efficient and Secure Routing Protocol for Wireless Sensor Networks through SNR based Dynamic Clustering Mechanisms

Advances in Wireless Sensor Network Technology (WSN) have provided the availability of small and low-cost sensor with capability of sensing various types of physical and environmental conditions, data processing and wireless communication. In WSN, the sensor nodes have a limited transmission range, and their processing and storage capabilities as well as their energy resources are limited. Triple Umpiring System (TUS) has already been proved its better performance on Wireless Sensor Networks. Clustering technique provides an effective way to prolong the lifetime of WSN. In this paper, we modified the Ad hoc on demand Distance Vector Routing (AODV) by incorporating Signal to Noise Ratio (SNR) based dynamic clustering. The proposed scheme Efficient and Secure Routing Protocol for Wireless Sensor Networks through SNR based dynamic Clustering mechanisms (ESRPSDC) can partition the nodes into clusters and select the Cluster Head (CH) among the nodes based on the energy and Non Cluster Head (NCH) nodes join with a specific CH based on SNR Values. Error recovery has been implemented during Inter cluster routing itself in order to avoid end-toend error recovery. Security has been achieved by isolating the malicious nodes using sink based routing pattern analysis. Extensive investigation studies using Global Mobile Simulator (GloMoSim) showed that this Hybrid ESRP significantly improves the Energy efficiency and Packet Reception Rate (PRR) compared to SNR unaware routing algorithms like Low Energy Aware Adaptive Clustering Hierarchy (LEACH) and Power- Efficient Gathering in Sensor Information Systems (PEGASIS).

cs.NI↗

arXiv2012

Precursor flares in OJ 287

We have studied three most recent precursor flares in the light curve of the blazar OJ 287 while invoking the presence of a precessing binary black hole in the system to explain the nature of these flares. Precursor flare timings from the historical light curves are compared with theoretical predictions from our model that incorporate effects of an accretion disk and post-Newtonian description for the binary black hole orbit. We find that the precursor flares coincide with the secondary black hole descending towards the accretion disk of the primary black hole from the observed side, with a mean z-component of approximately z_c = 4000 AU. We use this model of precursor flares to predict that precursor flare of similar nature should happen around 2020.96 before the next major outburst in 2022.

astro-ph.HE↗

arXiv2011

Rapid optical variability in blazar S5 0716+71 during 2010 March

We report rapid optical variability for the blazar S5 0716+71 during 2010 March 08-10 & 19-20 in the CCD observations made from Mt.Abu Infrared Observatory. The light curves are constructed for the duration longer than 3-hours each night, with very high temporal resolution(~ 45 seconds in R-band). During 2010 March 08 source smoothly decayed by about 0.15 mag in 2.88 hours, apart from a fast flicker lasting about 30 mins. S5 0716+71 brightened up during March 09 and 10 showing high activity while it was relatively faint (> 14 mag in R) albeit variable during March 19-20. During March 9 & 10, rapid flickers in the intensity modulate the long term intra-night (~ 3 hours) variation. The present observations suggest that the blazar S5 0716+71 showed night-to-night and intra-night variability at various time scales with 100% duty cycle for variation along with microvariability at significant levels. On night-to-night basis, the source exhibits mild bluer when brighter nature. The interaction of shocks with local inhomogeneities in the jet appears to cause intra-night variations while microvariations could be due to small scale perturbations intrinsic to the jet.

astro-ph.HE↗

arXiv2011

Optical Intraday Variability Studies of Ten Low Energy Peaked Blazars

We have carried out optical (R band) intraday variability (IDV) monitoring of a sample of ten bright low energy peaked blazars (LBLs). Forty photometric observations, of an average of ~ 4 hours each, were made between 2008 September and 2009 June using two telescopes in India. Measurements with good signal to noise ratios were typically obtained within 1-3 minutes, allowing the detection of weak, fast variations using N-star differential photometry. We employed both structure function and discrete correlation function analysis methods to estimate any dominant timescales of variability and found that in most of the cases any such timescales were longer than the duration of the observation. The calculated duty cycle of IDV in LBLs during our observing run is ~ 52%, which is low compared to many earlier studies; however, the relatively short periods for which each source was observed can probably explain this difference. We briefly discuss possible emission mechanisms for the observed variability.

astro-ph.CO↗

arXiv2010

Near opposition photometry of comet C/2007 N3 (Lulin)

Observations on comet C/2007 N3 (Lulin) were made at phase angles close to opposition ($1.7^{\circ}$ - $10^{\circ}$). Photometric observations were carried out during 2009 February 24-28, in the IHW blue and red continuum and $R$ broad band using photo-polarimeter mounted on the 1.2m telescope at Mt Abu IR Observatory. In all the bands, a significant linear increase in brightness with decreasing phase angle is detected for the above phase angle range. The phase coefficient ($β= 0.040\pm 0.001$ mag deg$^{-1}$ estimated in IHW red (6840Å) filter band) is found to be independent of wavelength. No non-linear opposition surge is observed for phase angle $>1.7^{\circ}$. The linear increase in brightness with decreasing phase angle in the range mentioned earlier can be explained using the shadow hiding model. The colour of the comet is found to be similar to the solar colour indicating the dominance of grains larger than $0.1μm$. A dip in the brightness of about 0.20 mag is seen at the phase angle $\sim 6.5^\circ$.

astro-ph.EP↗

arXiv2010

Photometry and spectroscopy of GRB 060526: A detailed study of the afterglow and host galaxy of a z=3.2 gamma-ray burst

Aims: With this paper we want to investigate the highly variable afterglow light curve and environment of gamma-ray burst (GRB) 060526 at $z=3.221$. Methods: We present one of the largest photometric datasets ever obtained for a GRB afterglow, consisting of multi-color photometric data from the ultraviolet to the near infrared. The data set contains 412 data points in total to which we add additional data from the literature. Furthermore, we present low-resolution high signal-to-noise spectra of the afterglow. The afterglow light curve is modeled with both an analytical model using broken power law fits and with a broad-band numerical model which includes energy injections. The absorption lines detected in the spectra are used to derive column densities using a multi-ion single-component curve-of-growth analysis from which we derive the metallicity of the host of GRB 060526. Results: The temporal behaviour of the afterglow follows a double broken power law with breaks at $t=0.090\pm0.005$ and $t=2.401\pm0.061$ days. It shows deviations from the smooth set of power laws that can be modeled by additional energy injections from the central engine, although some significant microvariability remains. The broadband spectral-energy distribution of the afterglow shows no significant extinction along the line of sight. The metallicity derived from \ion{S}{II} and \ion{Fe}{II} of [S/H] = --0.57 $\pm$0.25 and [Fe/H] = --1.09$\pm$0.24 is relatively high for a galaxy at that redshift but comparable to the metallicity of other GRB hosts at similar redshifts. At the position of the afterglow, no host is detected to F775W(AB) = 28.5 mag with the HST, implying an absolute magnitude of the host M(1500 Å)$>$--18.3 mag which is fainter than most long-duration hosts, although the GRB may be associated with a faint galaxy at a distance of 11 kpc.

astro-ph↗

arXiv2010

Quasi-Periodic Oscillations of ~ 15 minutes in the Optical Light Curve of the BL Lac S5 0716+714

Over the course of three hours on 27 December 2008 we obtained optical (R-band) observations of the blazar S5 0716+714 at a very fast cadence of 10 s. Using several different techniques we find fluctuations with an approximately 15-minute quasi-period to be present in the first portion of that data at a > 3 sigma confidence level. This is the fastest QPO that has been claimed to be observed in any blazar at any wavelength. While this data is insufficient to strongly constrain models for such fluctuations, the presence of such a short timescale when the source is not in a very low state seems to favor the action of turbulence behind a shock in the blazar's relativistic jet.

astro-ph.CO↗

arXiv2010

Real Time and Energy Efficient Transport Protocol for Wireless Sensor Networks

Reliable transport protocols such as TCP are tuned to perform well in traditional networks where packet losses occur mostly because of congestion. Many applications of wireless sensor networks are useful only when connected to an external network. Previous research on transport layer protocols for sensor networks has focused on designing protocols specifically targeted for sensor networks. The deployment of TCP/IP in sensor networks would, however, enable direct connection between the sensor network and external TCP/IP networks. In this paper we focus on the performance of TCP in the context of wireless sensor networks. TCP is known to exhibit poor performance in wireless environments, both in terms of throughput and energy efficiency. To overcome these problems we introduce a mechanism called TCP Segment Caching .We show by simulation that TCP Segment Caching significantly improves TCP Performance so that TCP can be useful e en in wireless sensor

cs.NI↗

arXiv2009

Automation of PRL's Astronomical Optical Polarimeter with a GNU/Linux based distributed control system

Physical Research Laboratory's (PRL) Optical Polarimeter has been used on various telescopes in India since its development in-house in the mid 1980s. To make the instrument more efficient and effective we have designed the acquisition and control system and written the software to run on the GNU/Linux Operating System. CCD cameras have been used, in place of eyepieces, which allow to observe fainter sources with smaller apertures. The use of smaller apertures provides dramatic gains in the signal-to-noise ratio. The polarimeter is now fully automated resulting in increased efficiency. With the advantage of networking being built-in at the operating system level in GNU/Linux, this instrument can now be controlled from anywhere on the PRL local area network which means that the observer can be stationed in Ahmedabad / Thaltej as well or via ssh anywhere on the internet. The current report provides an overview of the system as implemented.

astro-ph.IM↗

arXiv2009

Optical polarimetry and photometry of comet 17P/Holmes

Comet 17P/Holmes was observed for linear polarisation using the optical polarimeter mounted on the 1.2m telescope atop Gurushikhar peak near Mt. Abu during the period November-December 2007. Observations were conducted through the IHW narrow band (continuum) filters. During the observing run the phase angle was near $13^{\circ}$ at which the comet showed negative polarisation. On the basis of the observed polarisation data we find comet 17P/Holmes to be a typical comet with usual dust characteristics. We note that radial rate of change of brightness in coma in red band is higher than that in blue band; it has decreased by a factor of 3.6 and 2.5 respectively in red and blue bands during the November - December run, indicating relative increase in the abundance of smaller dust particles out ward. Radial brightness variation seen near the nucleus on November 6 is indicative of the presence of a blob or shocked region beyond 10" from the nucleus which has gradually smoothened by December 13. The brightness distribution is found steeper during November 5-7 as compared to on December 13.

astro-ph.EP↗

arXiv2009

Optical polarimetry of Comet NEAT C/2001 Q4

Comet NEAT C/2001 Q4 was observed for linear polarization using the optical polarimeter mounted at the 1.2m telescope at Mt. Abu Observatory, during the months of May and June 2004. Observations were conducted through the International Halley Watch narrow band (continuum) and B,V,R broad band filters. During the observing run the phase angle ranged from 85.6 deg in May to 55 deg in June. As expected, polarization increases with wavelength in this phase angle range. Polarization colour in the narrow bands changes at different epochs, perhaps related to cometary activity or molecular emission contamination. The polarization was also measured in the cometary coma at different locations along a line, in the direction of the tail. As expected, we notice minor decrease in the polarization as photocenter (nucleus) is traversed while brightness decreases sharply away from it. Based on these polarization observations we infer that the comet NEAT C/2001 Q4 has high polarization and a typical grain composition- mixture of silicates and organics.

astro-ph.EP↗