2008 (IPP)
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Item X-ray emission from active galactic nuclei with intermediate mass black holes(2008-12) Dewangan, Gulab ChandWe present a systematic X-ray study of eight active galactic nuclei (AGNs) with intermediate mass black holes (MBH ∼ 8 − 95 × 104 M⊙) based on 12 XMM-Newton observations. The sample includes the two prototype AGNs in this class – NGC 4395 and POX 52 and six other AGNs discovered with the Sloan Digitized Sky Survey. These AGNs show some of the strongest X-ray variability with the normalized excess variances being the largest and the power density break time scales being the shortest observed among radio-quiet AGNs. The excess variance – luminosity correlation appears to depend on both the BH mass and the Eddington luminosity ratio. The break time scale – black hole mass relations for AGN with IMBHs are consistent with that observed for massive AGNs. We find that the FWHM of the Hβ/Hα line is uncorrelated with the BH mass, but shows strong anticorrelation with the Eddington luminosity ratio. Four AGNs show clear evidence for soft X-ray excess emission (kTin ∼ 150 −200 eV). X-ray spectra of three other AGNs are consistent with the presence of the soft excess emission. NGC 4395 with lowest L/LEdd lacks the soft excess emission. Evidently small black mass is not the primary driver of strong soft X-ray excess emission from AGNs. The X-ray spectral properties and optical-to-X-ray spectral energy distributions of these AGNs are similar to those of Seyfert 1 galaxies. The observed X-ray/UV properties of AGNs with IMBHs are consistent with these AGNs being low mass extension of more massive AGNs; those with high Eddington luminosity ratio looking more like narrow-line Seyfert 1s while those with low L/LEdd looking more like broad-line Seyfert 1s.Item Type IIP Supernova SN 2004et: A Multi-Wavelength Study in X-Ray, Optical and Radio(2008-06) Bhattacharya, DipankarContext. We explore the physics behind one of the brightest radio afterglows ever, GRB 030329, at late times when the jet is non- relativistic. Aims. We determine the physical parameters of the blast wave and its surroundings, in particular the index of the electron energy distribution, the energy of the blast wave, and the density (structure) of the circumburst medium. We then compare our results with those from image size measurements. Methods. We observed the GRB030329 radio afterglow with the Westerbork Synthesis Radio Telescope and the Giant Metrewave Radio Telescope at frequencies from 325 MHz to 8.4 GHz, spanning a time range of 268-1128 days after the burst. We modeled all the available radio data and derived the physical parameters. Results. The index of the electron energy distribution is p = 2.1, the circumburst medium is homogeneous, and the transition to the non-relativistic phase happens at tNR ∼ 80 days. The energy of the blast wave and density of the surrounding medium are comparable to previous findings. Conclusions. Our findings indicate that the blast wave is roughly spherical at tNR, and they agree with the implications from the VLBI studies of image size evolution. It is not clear from the presented dataset whether we have seen emission from the counter jet or not. We predict that the Low Frequency Array will be able to observe the afterglow of GRB030329 and many other radio afterglows, constraining the physics of the blast wave during its non-relativistic phase even further.Item Two new diagnostics of dark energy(2008-11-03) Sahni, Varun; Starobinsky, A. A.We introduce two new diagnostics of dark energy (DE). The first, Om, is a combination of the Hubble parameter and the cosmological redshift and provides a null test of dark energy being a cosmological constant Λ. Namely, if the value of Om(z) is the same at different redshifts, then DE ≡ Λ, exactly. The slope of Om(z) can differentiate between different models of dark energy even if the value of the matter density is not accurately known. For DE with an unevolving equation of state, a positive slope of Om(z) is suggestive of Phantom (w < −1) while a negative slope indicates Quintessence (w > −1). The second diagnostic – acceleration probe ¯ q – is the mean value of the deceleration parameter over a small redshift range. It can be used to determine the cosmological redshift at which the universe began to accelerate, again without reference to the current value of the matter density. We apply the Om and ¯ q diagnostics to the Union data set of type Ia supernovae combined with recent data from the cosmic microwave background (WMAP5) and baryon acoustic oscillations.Item Towards a robust estimate of the merger rate evolution using near-IR photometry(2008-04-01) Rawat, A.; Kembhavi, A.K.We use a combination of deep, high angular resolution imaging data from the CDFS (HST/ACS GOODS survey) and ground based near-IR Ks images to derive the evolution of the galaxy major merger rate in the redshift range 0.2 ≤ z ≤ 1.2. We select galaxies on the sole basis of their J-band rest-frame, absolute magnitude, which is a good tracer of the stellar mass. We find steep evolution with redshift, with the merger rate ∝ (1 + z)3.43±0.49 for optically selected pairs, and ∝ (1 + z)2.18±0.18 for pairs selected in the near-IR. Our result is unlikely to be affected by luminosity evolution which is relatively modest when using restframe J band selection. The apparently more rapid evolution that we find in the visible is likely caused by biases relating to incompleteness and spatial resolution affecting the ground based near IR photometry, underestimating pair counts at higher redshifts in the near-IR. The major merger rate was ∼5.6 times higher at z ∼ 1.2 than at the current epoch. Overall 41%×(0.5Gyr/τ ) of all galaxies with MJ ≤ −19.5 have undergone a major merger in the last ∼ 8Gyr, where τ is the merger timescale. Interestingly, we find no effect on the derived major merger rate due to the presence of the large scale structure at z = 0.735 in the CDFS.Item Time-delay interferometry and the relativistic treatment of LISA optical links(2008-08-20) Dhurandhar, SanjeevLISA is a joint spae mission of the ESA and NASA for deteting low frequeny gravitational radiation in the band 10−5 −1 Hz. In order to attain the requisite sensitivity for LISA, the laser frequeny noise must be suppressed below the other seondary noises su h asthe optial path noise, a eleration noise et. This is ahieved beause of the redundan y in the data, more spe i ally, by ombining six appropriately time-delayed data streams ontain ingfrational Doppler shifts - time delay interferometry (TDI). The orbits of the spa eraft are omputed in the gravitational eld of the Sun and Earth in the Newtonian framework, while the optial links are treated fully general relativisti ally and thus, e ets suh as the Sagna, Shapiro delay, et. are automatially in orporated. We show that in the model of LISA that we onsider here, there are symmetries inherent in the physis, whih may be used e e tively to suppress the residual laser frequen y noise and simplify the algebrai approa h to TDI.Item Some earliest ancient astronomical observatories in Kashmir (India)(2008-03) Iqbal, NaseerWe identify some ancient observatories in the north-west belt of Kashmir (India) and predict that the Site Bumai Sopore as the oldest one in this region belonging to the upper Paleolithic period. All the sites fall in the respective periods of Neolithic, Paleolithic and upper Paleolithic. Detail practices of state-regulated the Meteor impact, supernova, change of seasons in a year and others. This paper reports the earliest structures that support those carvings.Item Reconstructing cosmological matter perturbations using standard candles and rulers(2008-01-31) Alam, Ujjaini; Sahni, Varun; Starobinsky, A. A.For a large class of dark energy (DE) models, for which the effective gravitational constant is a constant and there is no direct exchange of energy between DE and dark matter (DM), knowledge of the expansion history suffices to reconstruct the growth factor of linearized density perturbations in the non-relativistic matter component on scales much smaller than the Hubble distance. In this paper we develop a nonparametric method for extracting information about the perturbative growth factor from data pertaining to the luminosity or angular size distances. A comparison of the reconstructed density contrast with observations of large scale structure and gravitational lensing can help distinguish DE models such as the cosmological constant and quintessence from models based on modified gravity theories as well as models in which DE and DM are either unified, or interact directly. We show that for current SNe data, the linear growth factor at z = 0.3 can be constrained to 5%, and the linear growth rate to 6%. With future SNe data, such as expected from the JDEM mission, we may be able to constrain the growth factor to 2−3% and the growth rate to 3−4% at z = 0.3 with this unbiased, model-independent reconstruction method. For future BAO data which would deliver measurements of both the angular diameter distance and Hubble parameter, it should be possible to constrain the growth factor at z = 2.5 to 9%. These constraints grow tighter with the errors on the datasets. With a large quantity of data expected in the next few years, this method can emerge as a competitive tool for distinguishing between different models of dark energy.Item Rapidly Flaring Afterglow of the Very Bright and Energetic GRB 070125(2008-01-08) Updike, A. C.We report on multi-wavelength observations, ranging from X-ray to radio wave bands, of the IPN-localized gamma-ray burst GRB 070125. Spectroscopic observations reveal the presence of absorption lines due to O I, Si II, and C IV, implying a likely redshift of z = 1.547. The well-sampled light curves, in particular from 0.5 to 4 days after the burst, suggest a jet break at 3.7 days, corresponding to a jet opening angle of ∼7.0◦ , and implying an intrinsic GRB energy in the 1–10,000 keV band of around Eγ = (6.3 − 6.9) × 1051 erg (based on the fluences measured by the gamma-ray detectors of the IPN network). GRB070125 is among the brightest afterglows observed to date. The spectral energy distri- bution implies a host extinction of AV < 0.9 mag. Two rebrightening episodes are observed, one with excellent time coverage, showing an increase in flux of 56% in ∼8000 seconds. The evolution of the afterglow light curve is achromatic at all times. Late-time observations of the afterglow do not show evidence for emission from an underlying host galaxy or supernova. Any host galaxy would be subluminous, consistent with current GRB host-galaxy samples. Evidence for strong Mg II absorption features is not found, which is perhaps surprising in view of the relatively high redshift of this burst and the high likelihood for such features along GRB-selected lines of sight.Item Properties of warm absorbers in active galaxies: a systematic stability curve analysis(2008-10-14) Chakravorty, Susmita; Kembhavi, A.K.Signatures of warm absorbers are seen in soft X-ray spectra of about half of all Seyfert1 galaxies observed and in some quasars and blazars. We use the thermal equilibrium curve to study the influence of the shape of the ionizing continuum, density and the chemical composition of the absorbing gas on the existence and nature of the warm absorbers. We describe circumstances in which a stable warm absorber can exist as a multiphase medium or one with continuous variation in pressure. In particular we find the following results: i) the warm absorber exists only if the spectral index of the X-ray power-law ionizing continuum α > 0.2 and has a multiphase nature if α ∼ 0.8, which interestingly is the spectral index formost of the observed Seyfert 1 galaxies; ii) thermal and ionization states of highly dense warm absorbers are sensitive to their density if the ionizing continuum is sufficiently soft, i.e. dominated by the ultraviolet iii) absorbing gas with super Solar metallicity is more likely to have a multiphase nature; iv) the nature of the warm absorber is significantly influenced by the absence of iron and associated elements which are produced in the later stages of star formation history in supernovae of type Ia.Item Probable meteor impact crater in Kashmir Vally (India)(2008-03) Iqbal, NaseerDal lake in Srinagar Kashmir (India) which falls towards south is a lake surrounded by mountains on its three sides with a latitude of 340 2` north and longitude 740 4` east, is a probable meteor impact crater, almost Basin shaped and is spread over an area of 12 sq k ms. In this paper we report some preliminary bservations about it and invite the attention of international community of scientists towards its existence and studies and to establish finally whether or not it is a meteor impact crater.