Chandra LETGS spectroscopy of the Quasar MR2251-178 and its warm absorber

We present an analysis of our Chandra Low Energy Transmission Grating Spectrometer (LETGS) observation of the quasar MR2251-178. The warm absorber of MR2251-178 is well described by a hydrogen column density, N_H~2x10^21 cm^-2, and an ionization parameter log(xi)~0.6. We find in the spectrum weak evidence for narrow absorption lines from Carbon and Nitrogen which indicate that the ionized material is in outflow. We note changes (in time) of the absorption structure in the band (0.6-1) keV (around the UTAs plus the OVII and OVIII K-edges) at different periods of the observation. We measure a (0.1-2) keV flux of 2.58x10^-11 ergs cm^-2 s^-1. This flux implies that the nuclear source of MR2251-178 is in a relatively low state. No significant variability is seen in the light curve. We do not find evidence for an extra cold material in the line of sight, and set an upper limit of N_H~1.2x10^20 cm^-2. The X-ray spectrum does not appear to show evidence for dusty material, though an upper limit in the neutral carbon and oxygen column densities can only be set to N_CI~2x10^19 cm^-2 and N_OI~9x10^19 cm^-2, respectively.Comment: 42 pages, 12 figures, Accepted in Apj. Typo in abstract (ver2): "We do not find evidence for an extra...

Comments on black holes I: The possibility of complementarity

We comment on a recent paper of Almheiri, Marolf, Polchinski and Sully who argue against black hole complementarity based on the claim that an infalling observer 'burns' as he approaches the horizon. We show that in fact measurements made by an infalling observer outside the horizon are statistically identical for the cases of vacuum at the horizon and radiation emerging from a stretched horizon. This forces us to follow the dynamics all the way to the horizon, where we need to know the details of Planck scale physics. We note that in string theory the fuzzball structure of microstates does not give any place to 'continue through' this Planck regime. AMPS argue that interactions near the horizon preclude traditional complementarity. But the conjecture of 'fuzzball complementarity' works in the opposite way: the infalling quantum is absorbed by the fuzzball surface, and it is the resulting dynamics that is conjectured to admit a complementary description.Comment: 34 pages, 6 figures, v3: clarifications & references adde

The information paradox: A pedagogical introduction

The black hole information paradox is a very poorly understood problem. It is often believed that Hawking's argument is not precisely formulated, and a more careful accounting of naturally occurring quantum corrections will allow the radiation process to become unitary. We show that such is not the case, by proving that small corrections to the leading order Hawking computation cannot remove the entanglement between the radiation and the hole. We formulate Hawking's argument as a `theorem': assuming `traditional' physics at the horizon and usual assumptions of locality we will be forced into mixed states or remnants. We also argue that one cannot explain away the problem by invoking AdS/CFT duality. We conclude with recent results on the quantum physics of black holes which show the the interior of black holes have a `fuzzball' structure. This nontrivial structure of microstates resolves the information paradox, and gives a qualitative picture of how classical intuition can break down in black hole physics.Comment: 38 pages, 7 figures, Latex (Expanded form of lectures given at CERN for the RTN Winter School, Feb 09), typo correcte

What can the information paradox tell us about the early Universe?

In recent years we have come to understand how the information paradox is resolved in string theory. The huge entropy $S_{bek}={A\over 4G}$ of black holes is realized by an explicit set of horizon sized `fuzzball' wavefunctions. The wavefunction of a collapsing shell spreads relatively quickly over this large phase space of states, invalidating the classical black hole geometry the shell would have created. We argue that a related effect may occur in the early Universe. When matter is crushed to high densities we can access a similarly large phase space of gravitational `fuzzball' solutions. While we cannot estimate specific quantities at this point, a qualitative analysis suggests that spreading over phase space creates an extra `push' expanding the Universe to larger volumes.Comment: 6 pages, 3 figures (Essay awarded second prize in the Gravity Research Foundation essay competition 2012

An X-ray view of Mrk 705: A borderline narrow-line Seyfert 1 galaxy

Mrk 705 exhibits optical properties of both narrow- and broad-line Seyfert 1 galaxies. We examine the X-ray properties of this borderline object utilising proprietary and public data from Chandra, ASCA, ROSAT and RXTE, spanning more than twelve years. Though long-term flux variability from the pointed observations appears rather modest (about 3 times), we do find examples of rare large amplitude outbursts in the RXTE monitoring data. There is very little evidence of long-term spectral variability as the low- and high-energy spectra appear constant with time. A 6.4 keV emission line is detected in the ASCA spectra of Mrk 705, but not during the later, higher flux state Chandra observation. However, the upper limit on the equivalent width of a line in the Chandra spectrum is consistent with a constant-flux emission line and a brighter continuum, suggesting that the line is emitted from distant material such as the putative torus. Overall, the X-ray properties of Mrk 705 appear typical of BLS1 activity.Comment: 7 pages, 7 figures. Accepted for publication in A&A (Research Note

Aspidella: un fósil de cuerpo blando ediacárico de la Arenisca de Jodhpur (Supergrupo de Marwar), área de Sursagar, Jodhpur, Rajasthan occidental, India

This paper describes well-preserved Aspidella remains, the Ediacaran body fossils from the Jodhpur Sandstone of the Marwar Supergroup in Sursagar area, Jodhpur, western Rajasthan, India. They show distinct morphological features previously described in other famous Ediacaran fossil sites, such as the Fermuse Formation of Newfoundland, South Australia and White Sea of RussiaSe describen en este trabajo los restos bien conservados de Aspidella, fósiles de cuerpo blando ediacáricos de la Arenisca de Jodhpur (Supergrupo de Marwar) el área de Sursagar, Jodhpur, al oeste de Rajasthan, India. Éstos muestran características morfológicas características descritas anteriormente en otros famosos yacimientos fósiles ediacáricos, como los de la Formación de Fermuse (Terranova), Australia meridional y el Mar Blanco de Rusia

Steel Industry-Wastes as New Materials for Road Construction

A large number of steel plants have been set up in India and they are producing several million tonnes of iron and steel. However, the production of iron and steel is always associated with the generation of waste materials like air cooled slag, steel slag, granulated slag and flyash etc. These materials are posing serious problems of disposal and causing environmental pollution. Road Construction is one such sector where these materials can be utilised in bulk. CRRI started a few projects sponsored by Steel Authority of India Limited (SAIL), and all these materials were tested on a big scale in CRRI laboratory. Based on the success of laboratory results, various combinations were tried in the field and finally a road was constructed. This road has been monitored regularly for surface unevenness and pavement structural strength. This paper gives the results of extensive laboratory investigations and performance of the road

Role of Shrubs in Rangeland Based Livestock Production System in Western Rajasthan, India

Rangeland covers ~ 51% of the terrestrial surface of the Earth, and supports half of the world‟s livestock. More than 80 % of forage consumed by domestic livestock is supplied by rangelands in Africa and Asia. Hot arid regions of India cover an area of 31.7 million hectares and out of which Rajasthan state constitutes ~ 61.8 % of the entire area. The crop production in this area is low, unstable and risky. Livestock sustains arid farming systems by virtue of their potential to reduce risk, alleviate poverty, important providers of nutrients and traction for growing crops in smallholder systems and the imparting sustainability of household. The hot arid region of Rajasthan has about 29.08 million livestock. Pastures and grazing lands, residential area and wayside grazing lands, crop by-products and residues, fodder crops etc. are the major feed resources. For the small ruminants and camels, the rangelands are the major source of feed supply. Shrubs are vital component of rangeland vegetation and cover \u3e 70 % of desert landscapes from Aravalli to the international border of the Indian part of Thar desert. They are an important source of feed and assure feed availability in a drought situation. They have remarkable morpho-physiological adaptations to different land forms and survive under harsh edapho-climatic conditions. During recent past, a rapid decline population of browse shrubs is noticed due to their over exploitation, destruction of natural habitat, expending irrigation facilities, increasing agricultural mechanization and changes in land use pattern. In the present paper key species, fodder production and nutritive value of shrubs of hot arid rangelands are discussed