2008 (IPP)

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Giant Radio Jet Ejected by An Ultramassive Black Hole in a Single-Lobed Radio Galaxy
(2008-01) Bagchi, Joydeep
We report the discovery of a very unusual, highly asymmetric radio galaxy whose radio jet, the largest yet detected, emits strongly polarized synchrotron radiation and can be traced all the way from the galactic nucleus to the hot spot located ∼ 440 kpc away. This jet emanates from an extremely massive black-hole (> 109 M⊙) and forms a strikingly compact radio lobe. No radio lobe is detected on the side of the counter-jet, even though it is similar to the main jet in brightness up to a scale of tens of kilo parsecs. Thus, contrary to the nearly universal trend, the brightness asymmetry in this radio galaxy increases with distance from the nucleus. With several unusual properties, including a predominantly toroidal magnetic ﬁeld, this Fanaroﬀ-Riley type II mega-jet is an exceptionally useful laboratory for testing the role of magnetic ﬁeld in jet stabilization and radio lobe formation.
APSIS - an Artificial Planetary System in Space to probe extra-dimensional gravity and MOND
(2008-01) Sahni, Varun; Shtanov, Yuri
A proposal is made to test Newton’s inverse-square law using the perihelion shift of test masses (planets) in free fall within a spacecraft located at the Earth–Sun L2 point. Such an Artiﬁcial Planetary System In Space (APSIS) will operate in a dragfree environment with controlled experimental conditions and minimal interference from terrestrial sources of contamination. We demonstrate that such a space experiment can probe the presence of a ‘hidden’ ﬁfth dimension on the scale of a micron, if the perihelion shift of a ‘planet’ can be measured to sub-arc-second accuracy. Some suggestions for spacecraft design are made.
Modelling interstellar extinction and polarization with spheroidal grains
(2008-01) Voshchinnikov, N. V.; Das, H.K.
We calculate the wavelength dependence of the ratio of the linear polarization degree to extinction (polarizing eﬃciency) P(λ)/A(λ) from the ultraviolet to ear-infrared. The prolate and oblate particles with aspect ratios from a/b = 1.1 up to 10 are assumed to be rotating and partially aligned with the mechanism of paramagnetic relaxation (Davis-Greenstein). Size/shape/orientation eﬀects are analyzed. It is found that the wavelength dependence of P(λ)/A(λ) is mainly determined by the particle composition and size whereas the values of P(λ)/A(λ) depend on the particle shape, degree and direction of alignment.
Constrained semi-analytical models of Galactic outflows
(2008-01) Samui, Saumyadip; Subramanian, Kandaswamy; Srianand, R.
We present semi-analytic models of galactic outﬂows that are constrained by available ob- servations on high redshift star formation and reionization. Galactic outﬂows are modeled in a manner akin to models of stellar wind blown bubbles. Large scale outﬂows can generically escape from low mass halos (M . 109 M ) for a wide range of model parameters while this is not the case in high mass halos (M & 1011 M ). The ﬂow generically accelerates within the halo virial radius, then starts to decelerate, and traverses well into the intergalactic medium (IGM), before freezing to the Hubble ﬂow. The acceleration phase can result in shell fragmentation due to the Rayleigh-Taylor instability, although the ﬁnal outﬂow radius is not signiﬁcantly altered. The gas phase metallicity of the outﬂow and within the galaxy are computed assuming uniform instantaneous mixing. Ionization states of different metal species are calculated and used to examine the detectability of metal lines from the outﬂows. The global inﬂuence of galactic outﬂows is also investigated using porosity weighted averages and probability density functions of various physical quantities. Models with only atomic cooled halos signiﬁcantly ﬁll the IGM at z 3 with metals (with 2:5 & [Z=Z ] & 3:7), the actual extent depending on the efﬁciency of winds, the initial mass function (IMF) and the fractional mass that goes through star formation. The reionization history has a signiﬁcant effect on the volume ﬁlling factor, due to radiative feedback. In these models, a large fraction of outﬂows at z 3 are supersonic, hot (T 105K) and have low density, making metal lines difﬁcult to detect. They may also result in signiﬁcant perturbations in the IGM gas on scales probed by the Lyman- forest. On the contrary, models including molecular cooled halos with a normal mode of star formation can potentially volume ﬁll the universe at z 8 without drastic dynamic effects on the IGM, thereby setting up a possible metallicity ﬂoor ( 4:0 [Z=Z ] 3:6). The order unity ﬂuctuations at z 8 that becomes the mildly non-linear ﬂuctuations traced by Lyman- forest at z < 4 will then have this metallicity. Interestingly, molecular cooled halos with a “top-heavy” mode of star formation are not very successful in establishing the metallicity ﬂoor because of the additional radiative feedback, that they induce.
Kinematic alpha effect in isotropic turbulence simulations
(2008-01) Sur, Sharanya; Brandenburg, Axel; Subramanian, Kandaswamy
Using numerical simulations at moderate magnetic Reynolds numbers up to 220 it is shown that in the kinematic regime, isotropic helical turbulence leads to an alpha effect and a turbulent diffusivitywhose values are independent of the magnetic Reynolds number,Rm, provided Rm exceeds unity. These turbulent coefﬁcients are also consistent with expectations from the ﬁrst order smoothing approximation. For small values of Rm, alpha and turbulent diffusivity are proportional to Rm. Over ﬁnite time intervals meaningful values of alpha and turbulent diffusivity can be obtained even when there is small-scale dynamo action that produces strong magnetic ﬂuctuations. This suggests that small-scale dynamo-generated ﬁelds do not make a correlated contribution to the mean electromotive force.
Detailed study of the GRB 030329 radio afterglow deep into the non-relativistic phase
(2008-01) Horst, A. J. van der; Kamble, A.; Resmi, L.; et al.
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
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.
Photometric and Spectroscopic study of a highly reddened type Ia supernova SN 2003hx in NGC 2076
(2008-01-28) Misra, Kuntal; Sahu, D. K.
We present UBV RI CCD photometry and optical spectra of the type Ia supernova SN 2003hx which appeared in the galaxy NGC 2076, obtained till ∼ 146 days after the epoch of B band maximum. The supernova reached at maximum brightness in B band on JD 245 2893 ± 1.0 with an apparent magnitude of 14.92 ± 0.01 mag which was estimated by making template ﬁts to the light curves. SN 2003hx is an example of a highly reddened supernova with E(B −V ) = 0.56 ± 0.23. We estimate Rv = 1.97 ± 0.54 which indicates the small size of dust particles as compared to their galactic counterparts. The luminosity decline rate is ∆m15(B) = 1.17 ± 0.12 mag and the absolute B band magnitude obtained from the luminosity versus decline rate relation (Phillips et al. 1999) is MB max = -19.20 ± 0.18 mag. The peak bolometric luminosity indicates that ∼ 0.66 M⊙ mass of 56 Ni was ejected by the supernova. The spectral evolution indicates the supernova to be a normal type Ia event.
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.
MHD modes of solar wind flow tubes
(2008-02) Chandra, Suresh
Nakariakov & Roberts (1995) and Nakariakov et al. (1996) investigated the linear mag- netosonic waves trapped within solar wind ow tubes by accounting for a slab having boundaries at x = d and extended up to in nity in y and z directions. They obtained dispersion relations for sausage and kink surface waves in incompressible plasma. Following the approach of Nakariakov & Roberts (1995), we have obtained dispersion relations for sausage and kink surface waves in a compressible plasma. Values of the parameter a !=kCAo are found to vary in the ranges 0.755 0.849 and 1.080 1.356 for the sausage waves and in the ranges 0.850 0.882 and 1.358 1.538 for the kink waves in the compressible plasma. It shows an interesting feature that the sausage and kink surface waves are exclusive from each other.
Molecular hydrogen in high-redshift damped lyman-alpha systems: the VLT/UVES database
(2008-02) Noterdaeme, P.; Srianand, R.
Aims. We present the current status of ongoing searches for molecular hydrogen in high-redshift (1.8 < zabs ≤ 4.2) Damped Lyman-α systems (DLAs) capitalising on observations performed with the ESO Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES). Methods. We identify 77 DLAs/strong sub-DLAs, with log N(Hi) ≥ 20 and zabs > 1.8, which have data that include redshifted H2 Lyman and/or Werner-band absorption lines. This sample of Hi, H2 and metal line measurements, performed in an homogeneous manner, is more than twice as large as our previous sample (Ledoux et al. 2003) considering every system in which searches for H2 could be completed so far, including all non-detections. Results. H2 is detected in thirteen of the systems, which have molecular fractions of values between f ≃ 5 × 10−7 and f ≃ 0.1, where f = N(H2)/(2N(H2) + N(Hi)). Upper limits are measured for the remaining 64 systems with detection limits of typically log N(H2) ∼ 14.3, corresponding to log f < −5. We ﬁnd that about 35% of the DLAs with metallicities relative to solar [X/H] ≥ −1.3 (i.e., 1/20th solar), with X = Zn, S or Si, have molecular fractions log f > −4.5, while H2 is detected – regardless of the molecular fraction – in ∼ 50% of them. In contrast, only about 4% of the [X/H] < −1.3 DLAs have log f > −4.5. We show that the presence of H2 does not strongly depend on the total neutral hydrogen column density, although the probability of ﬁnding log f > −4.5 is higher for log N(Hi) ≥ 20.8 than below this limit (19% and 7% respectively). The overall H2 detection rate in log N(Hi) ≥ 20 DLAs is found to be about 16% (10% considering only log f > −4.5 detections) after correction for a slight bias towards large N(Hi). There is a strong preference for H2-bearing DLAs to have signiﬁcant depletion factors, [X/Fe] > 0.4. In addition, all H2-bearing DLAs have column densities of iron into dust grains larger than log N(Fe)dust ∼ 14.7, and about 40% of the DLAs above this limit have detected H2 lines with log f > −4.5. This demonstrates the importance of dust in governing the detectability of H2 in DLAs. Our extended sample supports neither the redshift evolution of the detection fraction of H2-bearing DLAs nor that of the molecular fraction in systems with H2 detections over the redshift range 1.8 < zabs ≤ 3.
Probable meteor impact crater in Kashmir Vally (India)
(2008-03) Iqbal, Naseer
Dal 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.
Some earliest ancient astronomical observatories in Kashmir (India)
(2008-03) Iqbal, Naseer
We 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.
Hard Electron Energy Distribution in the Relativistic Shocks of GRB Afterglows
(2008-04) Resmi, L.; Bhattacharya, Dipankar
Particle acceleration in relativistic shocks is not a very well understood subject. Owing to that diﬃculty, radiation spectra from relativistic shocks, such as those in GRB afterglows, have been often modelled by making assumptions about the underlying electron distribution. One such assumption is a relatively soft distribution of the particle energy, which need not be true always, as is obvious from observations of several GRB afterglows. In this paper, we describe modiﬁcations to the afterglow standard model to accommodate energy spectra which are ‘hard’. We calculate the overall evolution of the synchrotron and compton ﬂux arising from such a distribution. We also model two afterglows, GRB010222 and GRB020813, under this assumption and estimate the physical parameters.
First detection of CO in a high-redshift damped Lyman - Alpha system
(2008-04) Srianand, R.
We present the ﬁrst detection of carbon monoxide (CO) in a damped Lyman-α system (DLA) at zabs =2.41837 toward SDSS J143912.04+111740.5. We also detected H2 and HD molecules. The measured total column densities (in log units) of H i, H2, and CO are 20.10±0.10, 19.38±0.10, and 13.89±0.02, respectively. The molecular fraction, f = 2N(H2)/(N(H i)+2N(H2)) = 0.27+0.10 −0.08, is the highest among all known DLAs. The abundances relative to solar of S, Zn, Si, and Fe are −0.03±0.12, +0.16±0.11, −0.86±0.11, and −1.32±0.11, respectively, indicating a high metal enrichment and a depletion pattern onto dust-grains similar to the cold ISM of our Galaxy. The measured N(CO)/N(H2) = 3×10−6 is much less than the conventional CO/H2 ratio used to convert the CO emission into gaseous mass but is consistent with what is measured along translucent sightlines in the Galaxy. The CO rotational excitation temperatures are higher than those measured in our Galactic ISM for similar kinetic temperature and density. Using the C i ﬁne structure absorption lines, we show that this is a consequence of the excitation being dominated by radiative pumping by the cosmic microwave background radiation (CMBR). From the CO excitation temperatures, we derive TCMBR = 9.15±0.72 K, while 9.315±0.007 K is expected from the hot big-bang theory. This is the most precise high-redshift measurement of TCMBR and the ﬁrst conﬁrmation of the theory using molecular transitions at high redshift.
Modeling the interstellar aromatic infrared bands with co-added spectra of PAHs
(2008-04) Pathak, Amit; Rastogi, Shantanu
Aims. The observed variations in pro les of the interstellar aromatic infrared bands correlate with the object type and are indicative of PAH populations existing in di erent sources. Spectroscopic studies of PAHs can provide tools for interpreting the variations accompanying the AIBs. As the observed spectra results from a mix of possible species in the region, we try to model this composite spectra by co-adding emissions from PAHs in di erent size groups. Methods. Theoretical IR data of PAHs having 10 to 96 carbon atoms is used to obtain emission spectra. The models are taken in size groups made up of small, medium, and large PAHs. Results. The models show a good pro le match with observations for the 7.7 m complex having sub-features at 7.6 and 7.8 m. The 7.6 m sub-feature dominates in the spectra of medium-sized PAH cations, matching observations from UV-rich interstellar environments. The 7.8 m component is more intense in the spectra of large PAH cations (model III), correlating with observations from benign astrophysical regions. A possible interpretation of the observations of C H out-of-plane bend modes and the weak outliers on the blue side of the intense 11.2 m band is proposed. The models provide pointers to possible PAH populations in di erent regions
Complex light-curve of the afterglow of GRB071010A
(2008-04) Covino, S.; Avanzo, P. D.
We present and discuss the results of an extensive observational campaign devoted to GRB071010A, a long-duration gamma-ray burst detected by the Swift satellite. This event was followed for almost a month in the optical/near-infrared (NIR) with various telescopes starting from about 2min after the high-energy event. Swift -XRT observations started only later at about 0.4 d. The light-curve evolution allows us to single out an initial rising phase with a maximum at about 7min, possibly the afterglow onset in the context of the standard reball model, which is then followed by a smooth decay interrupted by a sharp rebrightening at about 0.6 d. The rebrightening was visible in both the optical/NIR and X-rays and can be interpreted as an episode of discrete energy injection, although various alternatives are possible. A steepening of the afterglow light curve is recorded at about 1 d. The entire evolution of the optical/NIR afterglow is consistent with being achromatic.
Automated classification of sloan digital sky survey (SDSS) stellar spectra using artificial neural networks
(2008-04) Bazarghan, M.; Gupta, Ranjan
Automated techniques have been developed to automate the process of classiﬁcation of objects or their analysis. The large datasets provided by upcoming spectroscopic surveys with dedicated telescopes urges scientists to use these automated techniques for analysis of such large datasets which are now available to the community. Sloan Digital Sky Survey (SDSS) is one of such surveys releasing massive datasets. We use Probabilistic Neural Network (PNN) for automatic classiﬁcation of about 5000 SDSS spectra into 158 spectral type of a reference library ranging from O type to M type stars.
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.
Not one bit of de sitter information
(2008-04-02) Parikh, Maulik; Schaar, Jan Pieter van der
We formulate the information paradox in de Sitter space in terms of the no-cloning principle of quantum mechanics. We show that energy conservation puts an upper bound on the maximum entropy available to any de Sitter observer. Combined with a general result on the average information in a quantum subsystem, this guarantees that an observer in de Sitter space cannot obtain even a single bit of information from the de Sitter horizon, thereby preventing any observable violations of the quantum no-cloning principle, in support of observer complementarity.