LOFAR detections of low-frequency radio recombination lines towards Cassiopeia A

A. Asgekar; J. B. R. Oonk; S. Yatawatta; R. J. van Weeren; J. P. McKean; G. White; N. Jackson; J. Anderson; I. M. Avruch; F. Batejat; R. Beck; M. E. Bell; M. R. Bell; I. van Bemmel; M. J. Bentum; G. Bernardi; P. Best; L. Birzan; A. Bonafede; R. Braun; F. Breitling; R. H. van de Brink; J. Broderick; W. N. Brouw; M. Brueggen; H. R. Butcher; W. van Cappellen; B. Ciardi; J. E. Conway; F. de Gasperin; E. de Geus; A. de Jong; M. de Vos; S. Duscha; J. Eisloeffel; H. Falcke; R. A. Fallows; C. Ferrari; W. Frieswijk; M. A. Garrett; J. -M. Griessmeier; T. Grit; A. W. Gunst; T. E. Hassall; G. Heald; J. W. T. Hessels; M. Hoeft; M. Iacobelli; H. Intema; E. Juette; A. Karastergiou; J. Kohler; V. I. Kondratiev; M. Kuniyoshi; G. Kuper; C. Law; J. van Leeuwen; P. Maat; G. Macario; G. Mann; S. Markoff; D. McKay-Bukowski; M. Mevius; J. C. A. Miller-Jones; J.D. Mol; R. Morganti; D. D. Mulcahy; H. Munk; M. J. Norden; E. Orru; H. Paas; M. Pandey-Pommier; V. N. Pandey; R. Pizzo; A. G. Polatidis; W. Reich; H. Rottgering; B. Scheers; A. Schoenmakers; J. Sluman; O. Smirnov; C. Sobey; M. Steinmetz; M. Tagger; Y. Tang; C. Tasse; R. Vermeulen; C. Vocks; R. A. M. J. Wijers; M. W. Wise; O. Wucknitz; P. Zarka

doi:10.1051/0004-6361/201221001

LOFAR detections of low-frequency radio recombination lines towards Cassiopeia A

A. Asgekar^*, J. B. R. Oonk, S. Yatawatta, R. J. van Weeren, J. P. McKean, G. White, N. Jackson, J. Anderson, I. M. Avruch, F. Batejat, R. Beck, M. E. Bell, M. R. Bell, I. van Bemmel, M. J. Bentum, G. Bernardi, P. Best, L. Birzan, A. Bonafede, R. BraunF. Breitling, R. H. van de Brink, J. Broderick, W. N. Brouw, M. Brueggen, H. R. Butcher, W. van Cappellen, B. Ciardi, J. E. Conway, F. de Gasperin, E. de Geus, A. de Jong, M. de Vos, S. Duscha, J. Eisloeffel, H. Falcke, R. A. Fallows, C. Ferrari, W. Frieswijk, M. A. Garrett, J. -M. Griessmeier, T. Grit, A. W. Gunst, T. E. Hassall, G. Heald, J. W. T. Hessels, M. Hoeft, M. Iacobelli, H. Intema, E. Juette, A. Karastergiou, J. Kohler, V. I. Kondratiev, M. Kuniyoshi, G. Kuper, C. Law, J. van Leeuwen, P. Maat, G. Macario, G. Mann, S. Markoff, D. McKay-Bukowski, M. Mevius, J. C. A. Miller-Jones, J.D. Mol, R. Morganti, D. D. Mulcahy, H. Munk, M. J. Norden, E. Orru, H. Paas, M. Pandey-Pommier, V. N. Pandey, R. Pizzo, A. G. Polatidis, W. Reich, H. Rottgering, B. Scheers, A. Schoenmakers, J. Sluman, O. Smirnov, C. Sobey, M. Steinmetz, M. Tagger, Y. Tang, C. Tasse, R. Vermeulen, C. Vocks, R. A. M. J. Wijers, M. W. Wise, O. Wucknitz, P. Zarka

^*Corresponding author for this work

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Abstract

Cassiopeia A was observed using the low-band antennas of the LOw Frequency ARray (LOFAR) with high spectral resolution. This allowed a search for radio recombination lines (RRLs) along the line-of-sight to this source. Five carbon alpha RRLs were detected in absorption between 40 and 50 MHz with a signal-to-noise ratio of >5 from two independent LOFAR data sets. The derived line velocities (v(LSR) similar to -50 km s(-1)) and integrated optical depths (similar to 13 s(-1)) of the RRLs in our spectra, extracted over the whole supernova remnant, are consistent within each LOFAR data set and with those previously reported. For the first time, we are able to extract spectra against the brightest hotspot of the remnant at frequencies below 330 MHz. These spectra show significantly higher (15-80 percent) integrated optical depths, indicating that there is small-scale angular structure of the order of similar to 1 pc in the absorbing gas distribution over the face of the remnant. We also place an upper limit of 3 x 10(-4) on the peak optical depths of hydrogen and helium RRLs. These results demonstrate that LOFAR has the desired spectral stability and sensitivity to study faint recombination lines in the decameter band.

Original language	English
Article number	L11
Number of pages	5
Journal	Astronomy & astrophysics
Volume	551
DOIs	https://doi.org/10.1051/0004-6361/201221001
Publication status	Published - Mar-2013

Keywords

ISM: clouds
radio lines: ISM
ISM: individual objects: Cassiopeia A
CARBON
MHZ
REGIONS

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10.1051/0004-6361/201221001

LOFAR detections of low-frequency radio recombination lines towards Cassiopeia AFinal publisher's version, 160 KBLicence: Unspecified

http://adsabs.harvard.edu/abs/2013A%26A...551L..11A

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Asgekar, A., Oonk, J. B. R., Yatawatta, S., van Weeren, R. J., McKean, J. P., White, G., Jackson, N., Anderson, J., Avruch, I. M., Batejat, F., Beck, R., Bell, M. E., Bell, M. R., van Bemmel, I., Bentum, M. J., Bernardi, G., Best, P., Birzan, L., Bonafede, A., ... Zarka, P. (2013). LOFAR detections of low-frequency radio recombination lines towards Cassiopeia A. Astronomy & astrophysics, 551, [L11]. https://doi.org/10.1051/0004-6361/201221001

@article{c3152027cf4f4b849356d3501801824b,

title = "LOFAR detections of low-frequency radio recombination lines towards Cassiopeia A",

abstract = "Cassiopeia A was observed using the low-band antennas of the LOw Frequency ARray (LOFAR) with high spectral resolution. This allowed a search for radio recombination lines (RRLs) along the line-of-sight to this source. Five carbon alpha RRLs were detected in absorption between 40 and 50 MHz with a signal-to-noise ratio of >5 from two independent LOFAR data sets. The derived line velocities (v(LSR) similar to -50 km s(-1)) and integrated optical depths (similar to 13 s(-1)) of the RRLs in our spectra, extracted over the whole supernova remnant, are consistent within each LOFAR data set and with those previously reported. For the first time, we are able to extract spectra against the brightest hotspot of the remnant at frequencies below 330 MHz. These spectra show significantly higher (15-80 percent) integrated optical depths, indicating that there is small-scale angular structure of the order of similar to 1 pc in the absorbing gas distribution over the face of the remnant. We also place an upper limit of 3 x 10(-4) on the peak optical depths of hydrogen and helium RRLs. These results demonstrate that LOFAR has the desired spectral stability and sensitivity to study faint recombination lines in the decameter band.",

keywords = "ISM: clouds, radio lines: ISM, ISM: individual objects: Cassiopeia A, CARBON, MHZ, REGIONS",

author = "A. Asgekar and Oonk, {J. B. R.} and S. Yatawatta and {van Weeren}, {R. J.} and McKean, {J. P.} and G. White and N. Jackson and J. Anderson and Avruch, {I. M.} and F. Batejat and R. Beck and Bell, {M. E.} and Bell, {M. R.} and {van Bemmel}, I. and Bentum, {M. J.} and G. Bernardi and P. Best and L. Birzan and A. Bonafede and R. Braun and F. Breitling and {van de Brink}, {R. H.} and J. Broderick and Brouw, {W. N.} and M. Brueggen and Butcher, {H. R.} and {van Cappellen}, W. and B. Ciardi and Conway, {J. E.} and {de Gasperin}, F. and {de Geus}, E. and {de Jong}, A. and {de Vos}, M. and S. Duscha and J. Eisloeffel and H. Falcke and Fallows, {R. A.} and C. Ferrari and W. Frieswijk and Garrett, {M. A.} and Griessmeier, {J. -M.} and T. Grit and Gunst, {A. W.} and Hassall, {T. E.} and G. Heald and Hessels, {J. W. T.} and M. Hoeft and M. Iacobelli and H. Intema and E. Juette and A. Karastergiou and J. Kohler and Kondratiev, {V. I.} and M. Kuniyoshi and G. Kuper and C. Law and {van Leeuwen}, J. and P. Maat and G. Macario and G. Mann and S. Markoff and D. McKay-Bukowski and M. Mevius and Miller-Jones, {J. C. A.} and J.D. Mol and R. Morganti and Mulcahy, {D. D.} and H. Munk and Norden, {M. J.} and E. Orru and H. Paas and M. Pandey-Pommier and Pandey, {V. N.} and R. Pizzo and Polatidis, {A. G.} and W. Reich and H. Rottgering and B. Scheers and A. Schoenmakers and J. Sluman and O. Smirnov and C. Sobey and M. Steinmetz and M. Tagger and Y. Tang and C. Tasse and R. Vermeulen and C. Vocks and Wijers, {R. A. M. J.} and Wise, {M. W.} and O. Wucknitz and P. Zarka",

year = "2013",

month = mar,

doi = "10.1051/0004-6361/201221001",

language = "English",

volume = "551",

journal = "Astronomy & astrophysics",

issn = "0004-6361",

publisher = " EDP Sciences",

}

Asgekar, A, Oonk, JBR, Yatawatta, S, van Weeren, RJ, McKean, JP, White, G, Jackson, N, Anderson, J, Avruch, IM, Batejat, F, Beck, R, Bell, ME, Bell, MR, van Bemmel, I, Bentum, MJ, Bernardi, G, Best, P, Birzan, L, Bonafede, A, Braun, R, Breitling, F, van de Brink, RH, Broderick, J, Brouw, WN, Brueggen, M, Butcher, HR, van Cappellen, W, Ciardi, B, Conway, JE, de Gasperin, F, de Geus, E, de Jong, A, de Vos, M, Duscha, S, Eisloeffel, J, Falcke, H, Fallows, RA, Ferrari, C, Frieswijk, W, Garrett, MA, Griessmeier, J-M, Grit, T, Gunst, AW, Hassall, TE, Heald, G, Hessels, JWT, Hoeft, M, Iacobelli, M, Intema, H, Juette, E, Karastergiou, A, Kohler, J, Kondratiev, VI, Kuniyoshi, M, Kuper, G, Law, C, van Leeuwen, J, Maat, P, Macario, G, Mann, G, Markoff, S, McKay-Bukowski, D, Mevius, M, Miller-Jones, JCA, Mol, JD, Morganti, R, Mulcahy, DD, Munk, H, Norden, MJ, Orru, E, Paas, H, Pandey-Pommier, M, Pandey, VN, Pizzo, R, Polatidis, AG, Reich, W, Rottgering, H, Scheers, B, Schoenmakers, A, Sluman, J, Smirnov, O, Sobey, C, Steinmetz, M, Tagger, M, Tang, Y, Tasse, C, Vermeulen, R, Vocks, C, Wijers, RAMJ, Wise, MW, Wucknitz, O & Zarka, P 2013, 'LOFAR detections of low-frequency radio recombination lines towards Cassiopeia A', Astronomy & astrophysics, vol. 551, L11. https://doi.org/10.1051/0004-6361/201221001

TY - JOUR

T1 - LOFAR detections of low-frequency radio recombination lines towards Cassiopeia A

AU - Asgekar, A.

AU - Oonk, J. B. R.

AU - Yatawatta, S.

AU - van Weeren, R. J.

AU - McKean, J. P.

AU - White, G.

AU - Jackson, N.

AU - Anderson, J.

AU - Avruch, I. M.

AU - Batejat, F.

AU - Beck, R.

AU - Bell, M. E.

AU - Bell, M. R.

AU - van Bemmel, I.

AU - Bentum, M. J.

AU - Bernardi, G.

AU - Best, P.

AU - Birzan, L.

AU - Bonafede, A.

AU - Braun, R.

AU - Breitling, F.

AU - van de Brink, R. H.

AU - Broderick, J.

AU - Brouw, W. N.

AU - Brueggen, M.

AU - Butcher, H. R.

AU - van Cappellen, W.

AU - Ciardi, B.

AU - Conway, J. E.

AU - de Gasperin, F.

AU - de Geus, E.

AU - de Jong, A.

AU - de Vos, M.

AU - Duscha, S.

AU - Eisloeffel, J.

AU - Falcke, H.

AU - Fallows, R. A.

AU - Ferrari, C.

AU - Frieswijk, W.

AU - Garrett, M. A.

AU - Griessmeier, J. -M.

AU - Grit, T.

AU - Gunst, A. W.

AU - Hassall, T. E.

AU - Heald, G.

AU - Hessels, J. W. T.

AU - Hoeft, M.

AU - Iacobelli, M.

AU - Intema, H.

AU - Juette, E.

AU - Karastergiou, A.

AU - Kohler, J.

AU - Kondratiev, V. I.

AU - Kuniyoshi, M.

AU - Kuper, G.

AU - Law, C.

AU - van Leeuwen, J.

AU - Maat, P.

AU - Macario, G.

AU - Mann, G.

AU - Markoff, S.

AU - McKay-Bukowski, D.

AU - Mevius, M.

AU - Miller-Jones, J. C. A.

AU - Mol, J.D.

AU - Morganti, R.

AU - Mulcahy, D. D.

AU - Munk, H.

AU - Norden, M. J.

AU - Orru, E.

AU - Paas, H.

AU - Pandey-Pommier, M.

AU - Pandey, V. N.

AU - Pizzo, R.

AU - Polatidis, A. G.

AU - Reich, W.

AU - Rottgering, H.

AU - Scheers, B.

AU - Schoenmakers, A.

AU - Sluman, J.

AU - Smirnov, O.

AU - Sobey, C.

AU - Steinmetz, M.

AU - Tagger, M.

AU - Tang, Y.

AU - Tasse, C.

AU - Vermeulen, R.

AU - Vocks, C.

AU - Wijers, R. A. M. J.

AU - Wise, M. W.

AU - Wucknitz, O.

AU - Zarka, P.

PY - 2013/3

Y1 - 2013/3

N2 - Cassiopeia A was observed using the low-band antennas of the LOw Frequency ARray (LOFAR) with high spectral resolution. This allowed a search for radio recombination lines (RRLs) along the line-of-sight to this source. Five carbon alpha RRLs were detected in absorption between 40 and 50 MHz with a signal-to-noise ratio of >5 from two independent LOFAR data sets. The derived line velocities (v(LSR) similar to -50 km s(-1)) and integrated optical depths (similar to 13 s(-1)) of the RRLs in our spectra, extracted over the whole supernova remnant, are consistent within each LOFAR data set and with those previously reported. For the first time, we are able to extract spectra against the brightest hotspot of the remnant at frequencies below 330 MHz. These spectra show significantly higher (15-80 percent) integrated optical depths, indicating that there is small-scale angular structure of the order of similar to 1 pc in the absorbing gas distribution over the face of the remnant. We also place an upper limit of 3 x 10(-4) on the peak optical depths of hydrogen and helium RRLs. These results demonstrate that LOFAR has the desired spectral stability and sensitivity to study faint recombination lines in the decameter band.

AB - Cassiopeia A was observed using the low-band antennas of the LOw Frequency ARray (LOFAR) with high spectral resolution. This allowed a search for radio recombination lines (RRLs) along the line-of-sight to this source. Five carbon alpha RRLs were detected in absorption between 40 and 50 MHz with a signal-to-noise ratio of >5 from two independent LOFAR data sets. The derived line velocities (v(LSR) similar to -50 km s(-1)) and integrated optical depths (similar to 13 s(-1)) of the RRLs in our spectra, extracted over the whole supernova remnant, are consistent within each LOFAR data set and with those previously reported. For the first time, we are able to extract spectra against the brightest hotspot of the remnant at frequencies below 330 MHz. These spectra show significantly higher (15-80 percent) integrated optical depths, indicating that there is small-scale angular structure of the order of similar to 1 pc in the absorbing gas distribution over the face of the remnant. We also place an upper limit of 3 x 10(-4) on the peak optical depths of hydrogen and helium RRLs. These results demonstrate that LOFAR has the desired spectral stability and sensitivity to study faint recombination lines in the decameter band.

KW - ISM: clouds

KW - radio lines: ISM

KW - ISM: individual objects: Cassiopeia A

KW - CARBON

KW - MHZ

KW - REGIONS

U2 - 10.1051/0004-6361/201221001

DO - 10.1051/0004-6361/201221001

M3 - Article

SN - 0004-6361

VL - 551

JO - Astronomy & astrophysics

JF - Astronomy & astrophysics

M1 - L11

ER -