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263 results on '"Sridhar, S. S."'

101. LOFAR 150-MHz observations of the Boötes field: catalogue and source counts

Author

Williams, W. L., van Weeren, R. J., Röttgering, H. J. A., Best, P., Dijkema, T. J., de Gasperin, F., Hardcastle, M. J., Heald, G., Prandoni, I., Sabater, J., Shimwell, T. W., Tasse, C., van Bemmel, I. M., Brüggen, M., Brunetti, G., Conway, J. E., Enßlin, T., Engels, D., Falcke, H., Ferrari, C., Haverkorn, M., Jackson, N., Jarvis, M. J., Kapińska, A. D., Mahony, E. K., Miley, G. K., Morabito, L. K., Morganti, R., Orrú, E., Retana-Montenegro, E., Sridhar, S. S., Toribio, M. C., White, G. J., Wise, M. W., Zwart, J. T. L., Williams, W. L., van Weeren, R. J., Röttgering, H. J. A., Best, P., Dijkema, T. J., de Gasperin, F., Hardcastle, M. J., Heald, G., Prandoni, I., Sabater, J., Shimwell, T. W., Tasse, C., van Bemmel, I. M., Brüggen, M., Brunetti, G., Conway, J. E., Enßlin, T., Engels, D., Falcke, H., Ferrari, C., Haverkorn, M., Jackson, N., Jarvis, M. J., Kapińska, A. D., Mahony, E. K., Miley, G. K., Morabito, L. K., Morganti, R., Orrú, E., Retana-Montenegro, E., Sridhar, S. S., Toribio, M. C., White, G. J., Wise, M. W., and Zwart, J. T. L.

Abstract

We present the first wide area (19 deg2), deep (≈120-150 μJy beam-1), high-resolution (5.6 × 7.4 arcsec) LOFAR High Band Antenna image of the Boötes field made at 130-169 MHz. This image is at least an order of magnitude deeper and 3-5 times higher in angular resolution than previously achieved for this field at low frequencies. The observations and data reduction, which includes full direction-dependent calibration, are described here. We present a radio source catalogue containing 6 276 sources detected over an area of 19 deg2, with a peak flux density threshold of 5σ. As the first thorough test of the facet calibration strategy, introduced by van Weeren et al., we investigate the flux and positional accuracy of the catalogue. We present differential source counts that reach an order of magnitude deeper in flux density than previously achieved at these low frequencies, and show flattening at 150-MHz flux densities below 10 mJy associated with the rise of the low flux density star-forming galaxies and radio-quiet AGN.

102. Low-frequency observations of the Giant Radio Galaxy NGC 6251

Author

Cantwell, T M, Bray, J D, Croston, Judith, Scaife, A M M, Mulcahy, D D, Best, P N, Brüggen, M, Brunetti, G, Callingham, J R, Clarke, A O, Hardcastle, M J, Harwood, J J, Heald, G, Heesen, V, Iacobelli, M, Jamrozy, M, Morganti, R, Orrú, E, O'Sullivan, S P, Riseley, C J, Röttgering, H J A, Shulevski, A, Sridhar, S S, Tasse, C, Van Eck, C L, Cantwell, T M, Bray, J D, Croston, Judith, Scaife, A M M, Mulcahy, D D, Best, P N, Brüggen, M, Brunetti, G, Callingham, J R, Clarke, A O, Hardcastle, M J, Harwood, J J, Heald, G, Heesen, V, Iacobelli, M, Jamrozy, M, Morganti, R, Orrú, E, O'Sullivan, S P, Riseley, C J, Röttgering, H J A, Shulevski, A, Sridhar, S S, Tasse, C, and Van Eck, C L

Abstract

We present LOFAR observations at 150 MHz of the borderline FRI/FRII giant radio galaxy NGC 6251. This paper presents the most sensitive and highest resolution images of NGC 6251 at these frequencies to date, revealing for the first time a low-surface-brightness extension to the northern lobe, and a possible backflow associated with the southern lobe. The integrated spectra of components of NGC 6251 are consistent with previous measurements at higher frequencies, similar to results from other LOFAR studies of nearby radio galaxies. We find the outer structures of NGC 6251 to be either at equipartition or slightly electron dominated, similar to those of FRII sources rather than FRIs, but this conclusion remains tentative because of uncertainties associated with the geometry and the extrapolation of X-ray measurements to determine the external pressure distribution on the scale of the outer lobes. We place lower limits on the ages of the extension of the northern lobe and the backflow of the southern lobe of t ≳ 250 Myr and t ≳ 210 Myr, respectively. We present the first detection of polarization at 150 MHz in NGC 6251. Taking advantage of the high Faraday resolution of LOFAR, we place an upper limit on the magnetic field in the group of B<0.2(ΛB/10kpc)−0.5μG for a coherence scale of ΛB<60kpc and B<13μG~forΛB=240 kpc.

103. The LOFAR Two-metre Sky Survey - II. First data release

Author

Shimwell, T. W., Tasse, C., Hardcastle, M. J., Mechev, A. P., Williams, W. L., Best, P. N., Röttgering, H. J. A., Callingham, J. R., Dijkema, T. J., de Gasperin, F., Hoang, D. N., Hugo, B., Mirmont, M., Oonk, J. B. R., Prandoni, I., Rafferty, D., Sabater, J., Smirnov, O., van Weeren, R. J., White, G. J., Atemkeng, M., Bester, L., Bonnassieux, E., Brüggen, M., Brunetti, G., Chyży, K. T., Cochrane, R., Conway, J. E., Croston, J. H., Danezi, A., Duncan, K., Haverkorn, M., Heald, G. H., Iacobelli, M., Intema, H. T., Jackson, N., Jamrozy, M., Jarvis, M. J., Lakhoo, R., Mevius, M., Miley, G. K., Morabito, L., Morganti, R., Nisbet, D., Orrú, E., Perkins, S., Pizzo, R. F., Schrijvers, C., Smith, D. J. B., Vermeulen, R., Wise, M. W., Alegre, L., Bacon, D. J., van Bemmel, I. M., Beswick, R. J., Bonafede, A., Botteon, A., Bourke, S., Brienza, M., Calistro Rivera, G., Cassano, R., Clarke, A. O., Conselice, C. J., Dettmar, R. J., Drabent, A., Dumba, C., Emig, K. L., Enßlin, T. A., Ferrari, C., Garrett, M. A., Génova-Santos, R. T., Goyal, A., Gürkan, G., Hale, C., Harwood, J. J., Heesen, V., Hoeft, M., Horellou, C., Jackson, C., Kokotanekov, G., Kondapally, R., Kunert- Bajraszewska, M., Mahatma, V., Mahony, E. K., Mandal, S., McKean, J. P., Merloni, A., Mingo, B., Miskolczi, A., Mooney, S., Nikiel- Wroczyński, B., O'Sullivan, S. P., Quinn, J., Reich, W., Roskowiński, C., Rowlinson, A., Savini, F., Saxena, A., Schwarz, D. J., Shulevski, A., Sridhar, S. S., Stacey, H. R., Urquhart, S., van der Wiel, M. H. D., Varenius, E., Webster, B., Wilber, A., Shimwell, T. W., Tasse, C., Hardcastle, M. J., Mechev, A. P., Williams, W. L., Best, P. N., Röttgering, H. J. A., Callingham, J. R., Dijkema, T. J., de Gasperin, F., Hoang, D. N., Hugo, B., Mirmont, M., Oonk, J. B. R., Prandoni, I., Rafferty, D., Sabater, J., Smirnov, O., van Weeren, R. J., White, G. J., Atemkeng, M., Bester, L., Bonnassieux, E., Brüggen, M., Brunetti, G., Chyży, K. T., Cochrane, R., Conway, J. E., Croston, J. H., Danezi, A., Duncan, K., Haverkorn, M., Heald, G. H., Iacobelli, M., Intema, H. T., Jackson, N., Jamrozy, M., Jarvis, M. J., Lakhoo, R., Mevius, M., Miley, G. K., Morabito, L., Morganti, R., Nisbet, D., Orrú, E., Perkins, S., Pizzo, R. F., Schrijvers, C., Smith, D. J. B., Vermeulen, R., Wise, M. W., Alegre, L., Bacon, D. J., van Bemmel, I. M., Beswick, R. J., Bonafede, A., Botteon, A., Bourke, S., Brienza, M., Calistro Rivera, G., Cassano, R., Clarke, A. O., Conselice, C. J., Dettmar, R. J., Drabent, A., Dumba, C., Emig, K. L., Enßlin, T. A., Ferrari, C., Garrett, M. A., Génova-Santos, R. T., Goyal, A., Gürkan, G., Hale, C., Harwood, J. J., Heesen, V., Hoeft, M., Horellou, C., Jackson, C., Kokotanekov, G., Kondapally, R., Kunert- Bajraszewska, M., Mahatma, V., Mahony, E. K., Mandal, S., McKean, J. P., Merloni, A., Mingo, B., Miskolczi, A., Mooney, S., Nikiel- Wroczyński, B., O'Sullivan, S. P., Quinn, J., Reich, W., Roskowiński, C., Rowlinson, A., Savini, F., Saxena, A., Schwarz, D. J., Shulevski, A., Sridhar, S. S., Stacey, H. R., Urquhart, S., van der Wiel, M. H. D., Varenius, E., Webster, B., and Wilber, A.

Abstract

The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing sensitive, high-resolution 120–168 MHz survey of the entire northern sky for which observations are now 20% complete. We present our first full-quality public data release. For this data release 424 square degrees, or 2% of the eventual coverage, in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45°00'00" to 57°00'00") were mapped using a fully automated direction-dependent calibration and imaging pipeline that we developed. A total of 325 694 sources are detected with a signal of at least five times the noise, and the source density is a factor of ∼10 higher than the most sensitive existing very wide-area radio-continuum surveys. The median sensitivity is S 144 MHz = 71 µJy beam−1 and the point-source completeness is 90% at an integrated flux density of 0.45 mJy. The resolution of the images is 6" and the positional accuracy is within 0.2". This data release consists of a catalogue containing location, flux, and shape estimates together with 58 mosaic images that cover the catalogued area. In this paper we provide an overview of the data release with a focus on the processing of the LOFAR data and the characteristics of the resulting images. In two accompanying papers we provide the radio source associations and deblending and, where possible, the optical identifications of the radio sources together with the photometric redshifts and properties of the host galaxies. These data release papers are published together with a further ∼20 articles that highlight the scientific potential of LoTSS.

104. LOFAR, VLA, AND CHANDRA observations of the Toothbrush galaxy cluster

Author

van Weeren, R. J., Brunetti, G., Brüggen, M., Andrade-Santos, F., Ogrean, G. A., Williams, W. L., Röttgering, H. J. A., Dawson, W. A., Forman, W. R., Gasperin, F. de, Hardcastle, M. J., Jones, C., Miley, G. K., Rafferty, D. A., Rudnick, L., Sabater, J., Sarazin, C. L., Shimwell, T. W., Bonafede, A., Best, P. N., Bîrzan, L., Cassano, R., Chyży, K. T., Croston, J. H., Dijkema, T. J., Enßlin, T., Ferrari, C., Heald, G., Hoeft, M., Horellou, C., Jarvis, M. J., Kraft, R. P., Mevius, M., Intema, H. T., Murray, S. S., Orrú, E., Pizzo, R., Sridhar, S. S., Simionescu, A., Stroe, A., Tol, S. van der, White, G. J., van Weeren, R. J., Brunetti, G., Brüggen, M., Andrade-Santos, F., Ogrean, G. A., Williams, W. L., Röttgering, H. J. A., Dawson, W. A., Forman, W. R., Gasperin, F. de, Hardcastle, M. J., Jones, C., Miley, G. K., Rafferty, D. A., Rudnick, L., Sabater, J., Sarazin, C. L., Shimwell, T. W., Bonafede, A., Best, P. N., Bîrzan, L., Cassano, R., Chyży, K. T., Croston, J. H., Dijkema, T. J., Enßlin, T., Ferrari, C., Heald, G., Hoeft, M., Horellou, C., Jarvis, M. J., Kraft, R. P., Mevius, M., Intema, H. T., Murray, S. S., Orrú, E., Pizzo, R., Sridhar, S. S., Simionescu, A., Stroe, A., Tol, S. van der, and White, G. J.

Abstract

We present deep LOFAR observations between 120 and 181 MHz of the "Toothbrush" (RX J0603.3+4214), a cluster that contains one of the brightest radio relic sources known. Our LOFAR observations exploit a new and novel calibration scheme to probe 10 times deeper than any previous study in this relatively unexplored part of the spectrum. The LOFAR observations, when combined with VLA, GMRT, and Chandra X-ray data, provide new information about the nature of cluster merger shocks and their role in re-accelerating relativistic particles. We derive a spectral index of $\alpha =-0.8\pm 0.1$ at the northern edge of the main radio relic, steepening toward the south to $\alpha \approx -2$. The spectral index of the radio halo is remarkably uniform ($\alpha =-1.16$, with an intrinsic scatter of $\leq 0.04$). The observed radio relic spectral index gives a Mach number of ${ \mathcal M }={2.8}_{-0.3}^{+0.5}$, assuming diffusive shock acceleration. However, the gas density jump at the northern edge of the large radio relic implies a much weaker shock (${ \mathcal M }\approx 1.2$, with an upper limit of ${ \mathcal M }\approx 1.5$). The discrepancy between the Mach numbers calculated from the radio and X-rays can be explained if either (i) the relic traces a complex shock surface along the line of sight, or (ii) if the radio relic emission is produced by a re-accelerated population of fossil particles from a radio galaxy. Our results highlight the need for additional theoretical work and numerical simulations of particle acceleration and re-acceleration at cluster merger shocks.

105. The LOFAR Two-metre Sky Survey – I. Survey Description and Preliminary Data Release

Author

Shimwell, T. W., Röttgering, H. J. A., Best, P. N., Williams, W. L., Dijkema, T.J., de Gasperin, F., Hardcastle, M. J., Heald, G. H., Hoang, D. N., Horneffer, A., Intema, H., Mahony, E. K., Mandal, S., Mechev, A. P., Morabito, L., Oonk, J. B. R., Rafferty, D., Retana-Montenegro, E., Sabater, J., Tasse, C., van Weeren, R. J., Brüggen, M., Brunetti, G., Chyży, K. T., Conway, J. E., Haverkorn, M., Jackson, N., Jarvis, M. J., McKean, J. P., Miley, G. K., Morganti, R., White, G. J., Wise, M. W., van Bemmel, I. M., Beck, R., Brienza, M., Bonafede, A., Calistro Rivera, G., Cassano, R., Clarke, A. O., Cseh, D., Deller, A., Drabent, A., van Driel, W., Engels, D., Falcke, H., Ferrari, C., Fröhlich, S., Garrett, M. A., Harwood, J. J., Heesen, V., Hoeft, M., Horellou, C., Israel, F. P., Kapińska, A. D., Kunert-Bajraszewska, M., McKay, D. J., Mohan, N. R., Orrú, E., Pizzo, R. F., Prandoni, I., Schwarz, D. J., Shulevski, A., Sipior, M., Smith, D. J. B., Sridhar, S. S., Steinmetz, M., Stroe, A., Varenius, E., van der Werf, P. P., Zensus, J. A., Zwart, J. T. L., Shimwell, T. W., Röttgering, H. J. A., Best, P. N., Williams, W. L., Dijkema, T.J., de Gasperin, F., Hardcastle, M. J., Heald, G. H., Hoang, D. N., Horneffer, A., Intema, H., Mahony, E. K., Mandal, S., Mechev, A. P., Morabito, L., Oonk, J. B. R., Rafferty, D., Retana-Montenegro, E., Sabater, J., Tasse, C., van Weeren, R. J., Brüggen, M., Brunetti, G., Chyży, K. T., Conway, J. E., Haverkorn, M., Jackson, N., Jarvis, M. J., McKean, J. P., Miley, G. K., Morganti, R., White, G. J., Wise, M. W., van Bemmel, I. M., Beck, R., Brienza, M., Bonafede, A., Calistro Rivera, G., Cassano, R., Clarke, A. O., Cseh, D., Deller, A., Drabent, A., van Driel, W., Engels, D., Falcke, H., Ferrari, C., Fröhlich, S., Garrett, M. A., Harwood, J. J., Heesen, V., Hoeft, M., Horellou, C., Israel, F. P., Kapińska, A. D., Kunert-Bajraszewska, M., McKay, D. J., Mohan, N. R., Orrú, E., Pizzo, R. F., Prandoni, I., Schwarz, D. J., Shulevski, A., Sipior, M., Smith, D. J. B., Sridhar, S. S., Steinmetz, M., Stroe, A., Varenius, E., van der Werf, P. P., Zensus, J. A., and Zwart, J. T. L.

Abstract

The LOFAR Two-metre Sky Survey (LoTSS) is a deep 120-168MHz imaging survey that will eventually cover the entire northern sky. Each of the 3170 pointings will be observed for 8 hrs, which, at most declinations, is sufficient to produce ~5'' resolution images with a sensitivity of ~100 µJy/beam and accomplish the main scientific aims of the survey, which are to explore the formation and evolution of massive black holes, galaxies, clusters of galaxies and large-scale structure. Owing to the compact core and long baselines of LOFAR, the images provide excellent sensitivity to both highly extended and compact emission. For legacy value, the data are archived at high spectral and time resolution to facilitate subarcsecond imaging and spectral line studies. In this paper we provide an overview of the LoTSS. We outline the survey strategy, the observational status, the current calibration techniques, a preliminary data release, and the anticipated scientific impact. The preliminary images that we have released were created using a fully automated but direction-independent calibration strategy and are significantly more sensitive than those produced by any existing large-area low-frequency survey. In excess of 44,000 sources are detected in the images that have a resolution of 25'', typical noise levels of less than 0.5 mJy/beam, and cover an area of over 350 square degrees in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45°00'00'' to 57°00'00'').

106. The LOFAR Two-metre Sky Survey – I. Survey Description and Preliminary Data Release

Author

Shimwell, T. W., Röttgering, H. J. A., Best, P. N., Williams, W. L., Dijkema, T.J., de Gasperin, F., Hardcastle, M. J., Heald, G. H., Hoang, D. N., Horneffer, A., Intema, H., Mahony, E. K., Mandal, S., Mechev, A. P., Morabito, L., Oonk, J. B. R., Rafferty, D., Retana-Montenegro, E., Sabater, J., Tasse, C., van Weeren, R. J., Brüggen, M., Brunetti, G., Chyży, K. T., Conway, J. E., Haverkorn, M., Jackson, N., Jarvis, M. J., McKean, J. P., Miley, G. K., Morganti, R., White, G. J., Wise, M. W., van Bemmel, I. M., Beck, R., Brienza, M., Bonafede, A., Calistro Rivera, G., Cassano, R., Clarke, A. O., Cseh, D., Deller, A., Drabent, A., van Driel, W., Engels, D., Falcke, H., Ferrari, C., Fröhlich, S., Garrett, M. A., Harwood, J. J., Heesen, V., Hoeft, M., Horellou, C., Israel, F. P., Kapińska, A. D., Kunert-Bajraszewska, M., McKay, D. J., Mohan, N. R., Orrú, E., Pizzo, R. F., Prandoni, I., Schwarz, D. J., Shulevski, A., Sipior, M., Smith, D. J. B., Sridhar, S. S., Steinmetz, M., Stroe, A., Varenius, E., van der Werf, P. P., Zensus, J. A., Zwart, J. T. L., Shimwell, T. W., Röttgering, H. J. A., Best, P. N., Williams, W. L., Dijkema, T.J., de Gasperin, F., Hardcastle, M. J., Heald, G. H., Hoang, D. N., Horneffer, A., Intema, H., Mahony, E. K., Mandal, S., Mechev, A. P., Morabito, L., Oonk, J. B. R., Rafferty, D., Retana-Montenegro, E., Sabater, J., Tasse, C., van Weeren, R. J., Brüggen, M., Brunetti, G., Chyży, K. T., Conway, J. E., Haverkorn, M., Jackson, N., Jarvis, M. J., McKean, J. P., Miley, G. K., Morganti, R., White, G. J., Wise, M. W., van Bemmel, I. M., Beck, R., Brienza, M., Bonafede, A., Calistro Rivera, G., Cassano, R., Clarke, A. O., Cseh, D., Deller, A., Drabent, A., van Driel, W., Engels, D., Falcke, H., Ferrari, C., Fröhlich, S., Garrett, M. A., Harwood, J. J., Heesen, V., Hoeft, M., Horellou, C., Israel, F. P., Kapińska, A. D., Kunert-Bajraszewska, M., McKay, D. J., Mohan, N. R., Orrú, E., Pizzo, R. F., Prandoni, I., Schwarz, D. J., Shulevski, A., Sipior, M., Smith, D. J. B., Sridhar, S. S., Steinmetz, M., Stroe, A., Varenius, E., van der Werf, P. P., Zensus, J. A., and Zwart, J. T. L.

Abstract

The LOFAR Two-metre Sky Survey (LoTSS) is a deep 120-168MHz imaging survey that will eventually cover the entire northern sky. Each of the 3170 pointings will be observed for 8 hrs, which, at most declinations, is sufficient to produce ~5'' resolution images with a sensitivity of ~100 µJy/beam and accomplish the main scientific aims of the survey, which are to explore the formation and evolution of massive black holes, galaxies, clusters of galaxies and large-scale structure. Owing to the compact core and long baselines of LOFAR, the images provide excellent sensitivity to both highly extended and compact emission. For legacy value, the data are archived at high spectral and time resolution to facilitate subarcsecond imaging and spectral line studies. In this paper we provide an overview of the LoTSS. We outline the survey strategy, the observational status, the current calibration techniques, a preliminary data release, and the anticipated scientific impact. The preliminary images that we have released were created using a fully automated but direction-independent calibration strategy and are significantly more sensitive than those produced by any existing large-area low-frequency survey. In excess of 44,000 sources are detected in the images that have a resolution of 25'', typical noise levels of less than 0.5 mJy/beam, and cover an area of over 350 square degrees in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45°00'00'' to 57°00'00'').

107. LOFAR, VLA, AND CHANDRA observations of the Toothbrush galaxy cluster

Author

van Weeren, R. J., Brunetti, G., Brüggen, M., Andrade-Santos, F., Ogrean, G. A., Williams, W. L., Röttgering, H. J. A., Dawson, W. A., Forman, W. R., Gasperin, F. de, Hardcastle, M. J., Jones, C., Miley, G. K., Rafferty, D. A., Rudnick, L., Sabater, J., Sarazin, C. L., Shimwell, T. W., Bonafede, A., Best, P. N., Bîrzan, L., Cassano, R., Chyży, K. T., Croston, J. H., Dijkema, T. J., Enßlin, T., Ferrari, C., Heald, G., Hoeft, M., Horellou, C., Jarvis, M. J., Kraft, R. P., Mevius, M., Intema, H. T., Murray, S. S., Orrú, E., Pizzo, R., Sridhar, S. S., Simionescu, A., Stroe, A., Tol, S. van der, White, G. J., van Weeren, R. J., Brunetti, G., Brüggen, M., Andrade-Santos, F., Ogrean, G. A., Williams, W. L., Röttgering, H. J. A., Dawson, W. A., Forman, W. R., Gasperin, F. de, Hardcastle, M. J., Jones, C., Miley, G. K., Rafferty, D. A., Rudnick, L., Sabater, J., Sarazin, C. L., Shimwell, T. W., Bonafede, A., Best, P. N., Bîrzan, L., Cassano, R., Chyży, K. T., Croston, J. H., Dijkema, T. J., Enßlin, T., Ferrari, C., Heald, G., Hoeft, M., Horellou, C., Jarvis, M. J., Kraft, R. P., Mevius, M., Intema, H. T., Murray, S. S., Orrú, E., Pizzo, R., Sridhar, S. S., Simionescu, A., Stroe, A., Tol, S. van der, and White, G. J.

Abstract

We present deep LOFAR observations between 120 and 181 MHz of the "Toothbrush" (RX J0603.3+4214), a cluster that contains one of the brightest radio relic sources known. Our LOFAR observations exploit a new and novel calibration scheme to probe 10 times deeper than any previous study in this relatively unexplored part of the spectrum. The LOFAR observations, when combined with VLA, GMRT, and Chandra X-ray data, provide new information about the nature of cluster merger shocks and their role in re-accelerating relativistic particles. We derive a spectral index of $\alpha =-0.8\pm 0.1$ at the northern edge of the main radio relic, steepening toward the south to $\alpha \approx -2$. The spectral index of the radio halo is remarkably uniform ($\alpha =-1.16$, with an intrinsic scatter of $\leq 0.04$). The observed radio relic spectral index gives a Mach number of ${ \mathcal M }={2.8}_{-0.3}^{+0.5}$, assuming diffusive shock acceleration. However, the gas density jump at the northern edge of the large radio relic implies a much weaker shock (${ \mathcal M }\approx 1.2$, with an upper limit of ${ \mathcal M }\approx 1.5$). The discrepancy between the Mach numbers calculated from the radio and X-rays can be explained if either (i) the relic traces a complex shock surface along the line of sight, or (ii) if the radio relic emission is produced by a re-accelerated population of fossil particles from a radio galaxy. Our results highlight the need for additional theoretical work and numerical simulations of particle acceleration and re-acceleration at cluster merger shocks.

108. LOFAR Facet Calibration

Author

Weeren, R. J. van, Williams, W. L., Hardcastle, M. J., Shimwell, T. W., Rafferty, D. A., Sabater, J., Heald, G., Sridhar, S. S., Dijkema, T. J., Brunetti, G., Brüggen, M., Andrade-Santos, F., Ogrean, G. A., Röttgering, H. J. A., Dawson, W. A., Forman, W. R., Gasperin, F. de, Jones, C., Miley, G. K., Rudnick, L., Sarazin, C. L., Bonafede, A., Best, P. N., Bîrzan, L., Cassano, R., Chyży, K. T., Croston, J. H., Ensslin, T., Ferrari, C., Hoeft, M., Horellou, C., Jarvis, M. J., Kraft, R. P., Mevius, M., Intema, H. T., Murray, S. S., Orrú, E., Pizzo, R., Simionescu, A., Stroe, A., Tol, S. van der, White, G. J., Weeren, R. J. van, Williams, W. L., Hardcastle, M. J., Shimwell, T. W., Rafferty, D. A., Sabater, J., Heald, G., Sridhar, S. S., Dijkema, T. J., Brunetti, G., Brüggen, M., Andrade-Santos, F., Ogrean, G. A., Röttgering, H. J. A., Dawson, W. A., Forman, W. R., Gasperin, F. de, Jones, C., Miley, G. K., Rudnick, L., Sarazin, C. L., Bonafede, A., Best, P. N., Bîrzan, L., Cassano, R., Chyży, K. T., Croston, J. H., Ensslin, T., Ferrari, C., Hoeft, M., Horellou, C., Jarvis, M. J., Kraft, R. P., Mevius, M., Intema, H. T., Murray, S. S., Orrú, E., Pizzo, R., Simionescu, A., Stroe, A., Tol, S. van der, and White, G. J.

Abstract

LOFAR, the Low-Frequency Array, is a powerful new radio telescope operating between 10 and 240 MHz. LOFAR allows detailed sensitive high-resolution studies of the low-frequency radio sky. At the same time LOFAR also provides excellent short baseline coverage to map diffuse extended emission. However, producing high-quality deep images is challenging due to the presence of direction-dependent calibration errors, caused by imperfect knowledge of the station beam shapes and the ionosphere. Furthermore, the large data volume and presence of station clock errors present additional difficulties. In this paper we present a new calibration scheme, which we name facet calibration, to obtain deep high-resolution LOFAR High Band Antenna images using the Dutch part of the array. This scheme solves and corrects the direction-dependent errors in a number of facets that cover the observed field of view. Facet calibration provides close to thermal noise limited images for a typical 8 hr observing run at resolution, meeting the specifications of the LOFAR Tier-1 northern survey.

109. A plethora of diffuse steep spectrum radio sources in Abell 2034 revealed by LOFAR

Author

Shimwell, T. W., Luckin, J., Brüggen, M., Brunetti, G., Intema, H. T., Owers, M. S., Röttgering, H. J. A., Stroe, A., van Weeren, R. J., Williams, W. L., Cassano, R., de Gasperin, F., Heald, G. H., Hoang, D. N., Hardcastle, M. J., Sridhar, S. S., Sabater, J., Best, P. N., Bonafede, A., Chyży, K. T., Enßlin, T. A., Ferrari, C., Haverkorn, M., Hoeft, M., Horellou, C., McKean, J. P., Morabito, L. K., Orrù, E., Pizzo, R., Retana-Montenegro, E., White, G. J., Shimwell, T. W., Luckin, J., Brüggen, M., Brunetti, G., Intema, H. T., Owers, M. S., Röttgering, H. J. A., Stroe, A., van Weeren, R. J., Williams, W. L., Cassano, R., de Gasperin, F., Heald, G. H., Hoang, D. N., Hardcastle, M. J., Sridhar, S. S., Sabater, J., Best, P. N., Bonafede, A., Chyży, K. T., Enßlin, T. A., Ferrari, C., Haverkorn, M., Hoeft, M., Horellou, C., McKean, J. P., Morabito, L. K., Orrù, E., Pizzo, R., Retana-Montenegro, E., and White, G. J.

Abstract

With Low-Frequency Array (LOFAR) observations, we have discovered a diverse assembly of steep spectrum emission that is apparently associated with the intra cluster medium (ICM) of the merging galaxy cluster Abell 2034. Such a rich variety of complex emission associated with the ICM has been observed in few other clusters. This not only indicates that Abell 2034 is a more interesting and complex system than previously thought but it also demonstrates the importance of sensitive and high-resolution, low-frequency observations. These observations can reveal emission from relativistic particles which have been accelerated to sufficient energy to produce observable emission or have had their high energy maintained by mechanisms in the ICM. The most prominent feature in our maps is a bright bulb of emission connected to two steep spectrum filamentary structures, the longest of which extends perpendicular to the merger axis for 0.5 Mpc across the south of the cluster. The origin of these objects is unclear, with no shock detected in the X-ray images and no obvious connection with cluster galaxies or AGNs. We also find that the X-ray bright region of the cluster coincides with a giant radio halo with an irregular morphology and a very steep spectrum. In addition, the cluster hosts up to three possible radio relics, which are misaligned with the cluster X-ray emission. Finally, we have identified multiple regions of emission with a very steep spectral index that seem to be associated with either tailed radio galaxies or a shock.

110. The LOFAR Two-metre Sky Survey

Author

Shimwell, T. W., Tasse, C., Hardcastle, M. J., Mechev, A. P., Williams, W. L., Best, P. N., Röttgering, H. J. A., Callingham, J. R., Dijkema, T. J., de Gasperin, F., Hoang, D. N., Hugo, B., Mirmont, M., Oonk, J. B. R., Prandoni, I., Rafferty, D., Sabater, J., Smirnov, O., van Weeren, R. J., White, G. J., Atemkeng, M., Bester, L., Bonnassieux, E., Brüggen, M., Brunetti, G., Chyży, K. T., Cochrane, R., Conway, J. E., Croston, J. H., Danezi, A., Duncan, K., Haverkorn, M., Heald, G. H., Iacobelli, M., Intema, H. T., Jackson, N., Jamrozy, M., Jarvis, M. J., Lakhoo, R., Mevius, M., Miley, G. K., Morabito, L., Morganti, R., Nisbet, D., Orrú, E., Perkins, S., Pizzo, R. F., Schrijvers, C., Smith, D. J. B., Vermeulen, R., Wise, M. W., Alegre, L., Bacon, D. J., van Bemmel, I. M., Beswick, R. J., Bonafede, A., Botteon, A., Bourke, S., Brienza, M., Calistro Rivera, G., Cassano, R., Clarke, A. O., Conselice, C. J., Dettmar, R. J., Drabent, A., Dumba, C., Emig, K. L., Enßlin, T. A., Ferrari, C., Garrett, M. A., Génova-Santos, R. T., Goyal, A., Gürkan, G., Hale, C., Harwood, J. J., Heesen, V., Hoeft, M., Horellou, C., Jackson, C., Kokotanekov, G., Kondapally, R., Kunert-Bajraszewska, M., Mahatma, V., Mahony, E. K., Mandal, S., McKean, J. P., Merloni, A., Mingo, B., Miskolczi, A., Mooney, S., Nikiel-Wroczyński, B., O’Sullivan, S. P., Quinn, J., Reich, W., Roskowiński, C., Rowlinson, A., Savini, F., Saxena, A., Schwarz, D. J., Shulevski, A., Sridhar, S. S., Stacey, H. R., Urquhart, S., van der Wiel, M. H. D., Varenius, E., Webster, B., and Wilber, A.

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111. Rucaparib or Physician's Choice in Metastatic Prostate Cancer.

Author

Fizazi, K., Piulats, J. M., Reaume, M. N., Ostler, P., MeDermott, R., Gingerich, J. R., Pintus, E., Sridhar, S. S., Bambury, R. M., Emmenegger, U., Lindberg, H., Morris, D., Nole, F., Staffurth, J., Redfern, C., Siez, M. I., Abida, W., Daugaard, G., Heidenreich, A., and Krieger, L.

Abstract

BACKGROUND In a phase 2 study, rucaparib, an inhibitor of poly(ADP-ribose) polymerase (PARP), showed a high level of activity in patients who had metastatic, castration-resistant prostate cancer associated with a deleterious BRCA alteration. Data are needed to confirm and expand on the findings of the phase 2 study. METHODS In this randomized, controlled, phase 3 trial, we enrolled patients who had metastatic, castration-resistant prostate cancer with a BRCA1, BRCA2, or ATM alteration and who had disease progression after treatment with a second-generation androgen-receptor pathway inhibitor (ARPI). We randomly assigned the patients in a 2:1 ratio to receive oral rucaparib (600 mg twice daily) or a physician’s choice control (docetaxel or a second-generation ARPI [abiraterone acetate or enzalutamide]). The primary outcome was the median duration of imaging-based progression-free survival according to independent review. RESULTS Of the 4855 patients who had undergone prescreening or screening, 270 were assigned to receive rucaparib and 135 to receive a control medication (intention-to-treat population); in the two groups, 201 patients and 101 patients, respectively, had a BRCA alteration. At 62 months, the duration of imaging-based progression-free survival was significantly longer in the rucaparib group than in the control group, both in the BRCA subgroup (median, 11.2 months and 6.4 months, respectively; hazard ratio, 0.50; 95% confidence interval [CI], 0.36 to 0.69) and in the intention-to-treat group (median, 10.2 months and 6.4 months, respectively; hazard ratio, 0.61; 95% CI, 0.47 to 0.80; P<0.001 for both comparisons). In an exploratory analysis in the ATM subgroup, the median duration of imaging-based progression-free survival was 8.1 months in the rucaparib group and 6.8 months in the control group (hazard ratio, 0.95; 95% CI, 0.59 to 1.52). The most frequent adverse events with rucaparib were fatigue and nausea. CONCLUSIONS The duration of imaging-based progression-free survival was significantly longer with rucaparib than with a control medication among patients who had metastatic, castration-resistant prostate cancer with a BRCA alteration. [ABSTRACT FROM AUTHOR]

Published
2023
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112. Avelumab Maintenance Therapy for Advanced or Metastatic Urothelial Carcinoma.

Author

Powles, T., Park, S. H., Voog, E., Caserta, C., Valderrama, B. P., Gurney, H., Kalofonos, H., Radulović, S., Demey, W., Ullén, A., Loriot, Y., Sridhar, S. S., Tsuchiya, N., Kopyltsov, E., Sternberg, C. N., Bellmunt, J., Aragon-Ching, J. B., Petrylak, D. P., Laliberte, R., and Wang, J.

Subjects
*TRANSITIONAL cell carcinoma, *PROGRESSION-free survival, *PROGRAMMED death-ligand 1, *DISEASE progression, *CONTROL groups
Abstract

BACKGROUND Platinum-based chemotherapy is standard-of-care first-line treatment for advanced urothelial carcinoma. However, progression-free survival and overall survival are limited by chemotherapy resistance. METHODS In a phase 3 trial, we randomly assigned patients with unresectable locally advanced or metastatic urothelial cancer who did not have disease progression with first-line chemotherapy (four to six cycles of gemcitabine plus cisplatin or carboplatin) to receive best supportive care with or without maintenance avelumab. The primary end point was overall survival, assessed among all patients who underwent randomization (overall population) and among those with tumors positive for programmed cell death ligand 1 (PD-L1). Secondary end points included progressionfree survival and safety. RESULTS Among all 700 patients who underwent randomization, the addition of maintenance avelumab to best supportive care significantly prolonged overall survival as compared with best supportive care alone (control). Overall survival at 1 year was 71.3% in the avelumab group and 58.4% in the control group (median overall survival, 21.4 months vs. 14.3 months; hazard ratio for death, 0.69; 95% confidence interval [Cl], 0.56 to 0.86; P = 0.001). Avelumab also significantly prolonged overall survival in the PD-Ll-positive population; overall survival at 1 year was 79.1% in the avelumab group and 60.4% in the control group (hazard ratio, 0.56; 95% Cl, 0.40 to 0.79; P<0.001). The median progression-free survival was 3.7 months in the avelumab group and 2.0 months in the control group in the overall population (hazard ratio for disease progression or death, 0.62; 95% Cl, 0.52 to 0.75) and 5.7 months and 2.1 months, respectively, in the PD-Ll-positive population (hazard ratio, 0.56; 95% Cl, 0.43 to 0.73). The incidence of adverse events from any cause was 98.0% in the avelumab group and 77.7% in the control group; the incidence of adverse events of grade 3 or higher was 47.4% and 25.2%, respectively. CONCLUSIONS Maintenance avelumab plus best supportive care significantly prolonged overall survival, as compared with best supportive care alone, among patients with urothelial cancer who had disease that had not progressed with first-line chemotherapy. (Funded by Pfizer and Merck [Darmstadt, Germany]; JAVELIN Bladder 100 ClinicalTrials.gov number, NCT02603432). [ABSTRACT FROM AUTHOR]

Published
2020
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113. Review on Heart Sound Analysis Technique

Author

More Monali, U., Shastri Aparana, R., Kacprzyk, Janusz, Series editor, Sathiakumar, Swamidoss, editor, Awasthi, Lalit Kumar, editor, Masillamani, M. Roberts, editor, and Sridhar, S S, editor

Published
2014
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138. Policy-Based Energy Management in Smart Homes

Author

Anandalakshmi, T. K., Sathiakumar, S., Parameswaran, N., Kacprzyk, Janusz, Series editor, Sathiakumar, Swamidoss, editor, Awasthi, Lalit Kumar, editor, Masillamani, M. Roberts, editor, and Sridhar, S S, editor

Published
2014
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145. A Review Paper on IEEE 802.11 WLAN

Author

Singh, Vikram, Awasthi, Lalit Kumar, Kacprzyk, Janusz, Series editor, Sathiakumar, Swamidoss, editor, Awasthi, Lalit Kumar, editor, Masillamani, M. Roberts, editor, and Sridhar, S S, editor

Published
2014
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148. Secure Text Steganography

Author

Akhilandeswari, P., George, Jabin G., Kacprzyk, Janusz, Series editor, Sathiakumar, Swamidoss, editor, Awasthi, Lalit Kumar, editor, Masillamani, M. Roberts, editor, and Sridhar, S S, editor

Published
2014
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