Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the ultraviolet anomaly in NGC 5548 with X-ray spectroscopy

S. Mathur; A. Gupta; K. Page; R. W. Pogge; Y. Krongold; M. R. Goad; S. M. Adams; M. D. Anderson; P. Arévalo; A. J. Barth; C. Bazhaw; T. G. Beatty; M. C. Bentz; A. Bigley; S. Bisogni; G. A. Borman; T. A. Boroson; M. C. Bottorff; W. N. Brandt; A. A. Breeveld; J. E. Brown; J. S. Brown; E. M. Cackett; G. Canalizo; M. T. Carini; K. I. Clubb; J. M. Comerford; C. T. Coker; E. M. Corsini; D. M. Crenshaw; S. Croft; K. V. Croxall; E. Dalla Bontà; A. J. Deason; K. D. Denney; A. De Lorenzo-Caceres; G. De Rosa; M. Dietrich; R. Edelson; J. Ely; M. Eracleous; P. A. Evans; M. M. Fausnaugh; G. J. Ferland; A. V. Filippenko; K. Flatland; O. D. Fox; E. L. Gates; N. Gehrels; S. Geier; J. M. Gelbord; V. Gorjian; J. E. Greene; C. J. Grier; D. Grupe; P. B. Hall; C. B. Henderson; S. Hicks; E. Holmbeck; T. W. -S. Holoien; D. Horenstein; Keith Horne; T. Hutchison; M. Im; J. J. Jensen; C. A. Johnson; M. D. Joner; J. Jones; J. Kaastra; S. Kaspi; B. C. Kelly; P. L. Kelly; J. A. Kennea; M. Kim; S. Kim; S. C. Kim; A. King; S. A. Klimanov; C. S. Kochanek; K. T. Korista; G. A. Kriss; M. W. Lau; J. C. Lee; D. C. Leonard; M. Li; P. Lira; Z. Ma; F. MacInnis; E. R. Manne-Nicholas; M. A. Malkan; J. C. Mauerhan; R. McGurk; I. M. McHardy; C. Montouri; L. Morelli; A. Mosquera; D. Mudd; F. Muller-Sanchez; R. Musso; S. V. Nazarov; H. Netzer; M. L. Nguyen; R. P. Norris; J. A. Nousek; P. Ochner; D. N. Okhmat; B. Ou-Yang; A. Pancoast; I. Papadakis; J. R. Parks; L. Pei; B. M. Peterson; A. Pizzella; R. Poleski; J. -U. Pott; S. E. Rafter; H. -W. Rix; J. Runnoe; D. A. Saylor; J. S. Schimoia; K. Schnülle; S. G. Sergeev; B. J. Shappee; I. Shivvers; M. Siegel; G. V. Simonian; A. Siviero; A. Skielboe; G. Somers; M. Spencer; D. Starkey; D. J. Stevens; H. -I. Sung; J. Tayar; N. Tejos; C. S. Turner; P. Uttley; J. Van Saders; M. Vestergaard; L. Vican; S. Villanueva Jr; C. Villforth; Y. Weiss; J. -H. Woo; H. Yan; S. Young; H. Yuk; W. Zheng; W. Zhu; Y. Zu

doi:10.3847/1538-4357/aa832b

Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the ultraviolet anomaly in NGC 5548 with X-ray spectroscopy

S. Mathur, A. Gupta, K. Page, R. W. Pogge, Y. Krongold, M. R. Goad, S. M. Adams, M. D. Anderson, P. Arévalo, A. J. Barth, C. Bazhaw, T. G. Beatty, M. C. Bentz, A. Bigley, S. Bisogni, G. A. Borman, T. A. Boroson, M. C. Bottorff, W. N. Brandt, A. A. BreeveldJ. E. Brown, J. S. Brown, E. M. Cackett, G. Canalizo, M. T. Carini, K. I. Clubb, J. M. Comerford, C. T. Coker, E. M. Corsini, D. M. Crenshaw, S. Croft, K. V. Croxall, E. Dalla Bontà, A. J. Deason, K. D. Denney, A. De Lorenzo-Caceres, G. De Rosa, M. Dietrich, R. Edelson, J. Ely, M. Eracleous, P. A. Evans, M. M. Fausnaugh, G. J. Ferland, A. V. Filippenko, K. Flatland, O. D. Fox, E. L. Gates, N. Gehrels, S. Geier, J. M. Gelbord, V. Gorjian, J. E. Greene, C. J. Grier, D. Grupe, P. B. Hall, C. B. Henderson, S. Hicks, E. Holmbeck, T. W. -S. Holoien, D. Horenstein, Keith Horne, T. Hutchison, M. Im, J. J. Jensen, C. A. Johnson, M. D. Joner, J. Jones, J. Kaastra, S. Kaspi, B. C. Kelly, P. L. Kelly, J. A. Kennea, M. Kim, S. Kim, S. C. Kim, A. King, S. A. Klimanov, C. S. Kochanek, K. T. Korista, G. A. Kriss, M. W. Lau, J. C. Lee, D. C. Leonard, M. Li, P. Lira, Z. Ma, F. MacInnis, E. R. Manne-Nicholas, M. A. Malkan, J. C. Mauerhan, R. McGurk, I. M. McHardy, C. Montouri, L. Morelli, A. Mosquera, D. Mudd, F. Muller-Sanchez, R. Musso, S. V. Nazarov, H. Netzer, M. L. Nguyen, R. P. Norris, J. A. Nousek, P. Ochner, D. N. Okhmat, B. Ou-Yang, A. Pancoast, I. Papadakis, J. R. Parks, L. Pei, B. M. Peterson, A. Pizzella, R. Poleski, J. -U. Pott, S. E. Rafter, H. -W. Rix, J. Runnoe, D. A. Saylor, J. S. Schimoia, K. Schnülle, S. G. Sergeev, B. J. Shappee, I. Shivvers, M. Siegel, G. V. Simonian, A. Siviero, A. Skielboe, G. Somers, M. Spencer, D. Starkey, D. J. Stevens, H. -I. Sung, J. Tayar, N. Tejos, C. S. Turner, P. Uttley, J. Van Saders, M. Vestergaard, L. Vican, S. Villanueva Jr, C. Villforth, Y. Weiss, J. -H. Woo, H. Yan, S. Young, H. Yuk, W. Zheng, W. Zhu, Y. Zu

Research output: Contribution to journal › Article › peer-review

Abstract

During the Space Telescope and Optical Reverberation Mapping Project (STORM) observations of NGC 5548, the continuum and emission-line variability became de-correlated during the second half of the 6-month long observing campaign. Here we present Swift and Chandra X-ray spectra of NGC 5548 obtained as a part of the campaign. The Swift spectra show that excess flux (relative to a power-law continuum) in the soft X-ray band appears before the start of the anomalous emission-line behavior, peaks during the period of the anomaly, and then declines. This is a model-independent result suggesting that the soft excess is related to the anomaly. We divide the Swift data into on- and off-anomaly spectra to characterize the soft excess via spectral fitting. The cause of the spectral differences is likely due to a change in the intrinsic spectrum rather than being due to variable obscuration or partial covering. The Chandra spectra have lower signal-to-noise ratios, but are consistent with Swift data. Our preferred model of the soft excess is emission from an optically thick, warm Comptonizing corona, the effective optical depth of which increases during the anomaly. This model simultaneously explains all the three observations: the UV emission line flux decrease, the soft-excess increase, and the emission line anomaly.

Original language	English
Article number	55
Number of pages	9
Journal	Astrophysical Journal
Volume	846
Issue number	1
Early online date	31 Aug 2017
DOIs	https://doi.org/10.3847/1538-4357/aa832b
Publication status	Published - 1 Sept 2017

Keywords

Galaxies: active
Galaxies: individual (NGC 5548)
X-rays: galaxies
X-rays: individual (NGC 5548)

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10.3847/1538-4357/aa832b

Mathur-2017-Space-telescope-APJ-AAM
© 2017, American Astronomical Society. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at iopscience.iop.org / https://doi.org/10.3847/1538-4357/aa832b
Accepted author manuscript, 728 KB

Astronomy at St Andrews 2015-2018: Astronomy at St Andrews 2015-2018
Jardine, M. M. (PI), Cameron, A. C. (CoI), Cyganowski, C. J. (CoI), Horne, K. D. (CoI) & Wood, K. (CoI)
Science & Technology Facilities Council
1/04/15 → 31/03/18
Project: Standard

Cite this

Mathur, S., Gupta, A., Page, K., Pogge, R. W., Krongold, Y., Goad, M. R., Adams, S. M., Anderson, M. D., Arévalo, P., Barth, A. J., Bazhaw, C., Beatty, T. G., Bentz, M. C., Bigley, A., Bisogni, S., Borman, G. A., Boroson, T. A., Bottorff, M. C., Brandt, W. N., ... Zu, Y. (2017). Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the ultraviolet anomaly in NGC 5548 with X-ray spectroscopy. Astrophysical Journal, 846(1), Article 55. https://doi.org/10.3847/1538-4357/aa832b

@article{e2e2861b60874c6b9a7ef74061cda52b,

title = "Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the ultraviolet anomaly in NGC 5548 with X-ray spectroscopy",

abstract = "During the Space Telescope and Optical Reverberation Mapping Project (STORM) observations of NGC 5548, the continuum and emission-line variability became de-correlated during the second half of the 6-month long observing campaign. Here we present Swift and Chandra X-ray spectra of NGC 5548 obtained as a part of the campaign. The Swift spectra show that excess flux (relative to a power-law continuum) in the soft X-ray band appears before the start of the anomalous emission-line behavior, peaks during the period of the anomaly, and then declines. This is a model-independent result suggesting that the soft excess is related to the anomaly. We divide the Swift data into on- and off-anomaly spectra to characterize the soft excess via spectral fitting. The cause of the spectral differences is likely due to a change in the intrinsic spectrum rather than being due to variable obscuration or partial covering. The Chandra spectra have lower signal-to-noise ratios, but are consistent with Swift data. Our preferred model of the soft excess is emission from an optically thick, warm Comptonizing corona, the effective optical depth of which increases during the anomaly. This model simultaneously explains all the three observations: the UV emission line flux decrease, the soft-excess increase, and the emission line anomaly.",

keywords = "Galaxies: active, Galaxies: individual (NGC 5548), X-rays: galaxies, X-rays: individual (NGC 5548)",

author = "S. Mathur and A. Gupta and K. Page and Pogge, {R. W.} and Y. Krongold and Goad, {M. R.} and Adams, {S. M.} and Anderson, {M. D.} and P. Ar{\'e}valo and Barth, {A. J.} and C. Bazhaw and Beatty, {T. G.} and Bentz, {M. C.} and A. Bigley and S. Bisogni and Borman, {G. A.} and Boroson, {T. A.} and Bottorff, {M. C.} and Brandt, {W. N.} and Breeveld, {A. A.} and Brown, {J. E.} and Brown, {J. S.} and Cackett, {E. M.} and G. Canalizo and Carini, {M. T.} and Clubb, {K. I.} and Comerford, {J. M.} and Coker, {C. T.} and Corsini, {E. M.} and Crenshaw, {D. M.} and S. Croft and Croxall, {K. V.} and Bont{\`a}, {E. Dalla} and Deason, {A. J.} and Denney, {K. D.} and Lorenzo-Caceres, {A. De} and Rosa, {G. De} and M. Dietrich and R. Edelson and J. Ely and M. Eracleous and Evans, {P. A.} and Fausnaugh, {M. M.} and Ferland, {G. J.} and Filippenko, {A. V.} and K. Flatland and Fox, {O. D.} and Gates, {E. L.} and N. Gehrels and S. Geier and Gelbord, {J. M.} and V. Gorjian and Greene, {J. E.} and Grier, {C. J.} and D. Grupe and Hall, {P. B.} and Henderson, {C. B.} and S. Hicks and E. Holmbeck and Holoien, {T. W. -S.} and D. Horenstein and Keith Horne and T. Hutchison and M. Im and Jensen, {J. J.} and Johnson, {C. A.} and Joner, {M. D.} and J. Jones and J. Kaastra and S. Kaspi and Kelly, {B. C.} and Kelly, {P. L.} and Kennea, {J. A.} and M. Kim and S. Kim and Kim, {S. C.} and A. King and Klimanov, {S. A.} and Kochanek, {C. S.} and Korista, {K. T.} and Kriss, {G. A.} and Lau, {M. W.} and Lee, {J. C.} and Leonard, {D. C.} and M. Li and P. Lira and Z. Ma and F. MacInnis and Manne-Nicholas, {E. R.} and Malkan, {M. A.} and Mauerhan, {J. C.} and R. McGurk and McHardy, {I. M.} and C. Montouri and L. Morelli and A. Mosquera and D. Mudd and F. Muller-Sanchez and R. Musso and Nazarov, {S. V.} and H. Netzer and Nguyen, {M. L.} and Norris, {R. P.} and Nousek, {J. A.} and P. Ochner and Okhmat, {D. N.} and B. Ou-Yang and A. Pancoast and I. Papadakis and Parks, {J. R.} and L. Pei and Peterson, {B. M.} and A. Pizzella and R. Poleski and Pott, {J. -U.} and Rafter, {S. E.} and Rix, {H. -W.} and J. Runnoe and Saylor, {D. A.} and Schimoia, {J. S.} and K. Schn{\"u}lle and Sergeev, {S. G.} and Shappee, {B. J.} and I. Shivvers and M. Siegel and Simonian, {G. V.} and A. Siviero and A. Skielboe and G. Somers and M. Spencer and D. Starkey and Stevens, {D. J.} and Sung, {H. -I.} and J. Tayar and N. Tejos and Turner, {C. S.} and P. Uttley and Saders, {J. Van} and M. Vestergaard and L. Vican and {Villanueva Jr}, S. and C. Villforth and Y. Weiss and Woo, {J. -H.} and H. Yan and S. Young and H. Yuk and W. Zheng and W. Zhu and Y. Zu",

year = "2017",

month = sep,

day = "1",

doi = "10.3847/1538-4357/aa832b",

language = "English",

volume = "846",

journal = "Astrophysical Journal",

issn = "0004-637X",

publisher = "American Astronomical Society",

number = "1",

}

Mathur, S, Gupta, A, Page, K, Pogge, RW, Krongold, Y, Goad, MR, Adams, SM, Anderson, MD, Arévalo, P, Barth, AJ, Bazhaw, C, Beatty, TG, Bentz, MC, Bigley, A, Bisogni, S, Borman, GA, Boroson, TA, Bottorff, MC, Brandt, WN, Breeveld, AA, Brown, JE, Brown, JS, Cackett, EM, Canalizo, G, Carini, MT, Clubb, KI, Comerford, JM, Coker, CT, Corsini, EM, Crenshaw, DM, Croft, S, Croxall, KV, Bontà, ED, Deason, AJ, Denney, KD, Lorenzo-Caceres, AD, Rosa, GD, Dietrich, M, Edelson, R, Ely, J, Eracleous, M, Evans, PA, Fausnaugh, MM, Ferland, GJ, Filippenko, AV, Flatland, K, Fox, OD, Gates, EL, Gehrels, N, Geier, S, Gelbord, JM, Gorjian, V, Greene, JE, Grier, CJ, Grupe, D, Hall, PB, Henderson, CB, Hicks, S, Holmbeck, E, Holoien, TW-S, Horenstein, D, Horne, K, Hutchison, T, Im, M, Jensen, JJ, Johnson, CA, Joner, MD, Jones, J, Kaastra, J, Kaspi, S, Kelly, BC, Kelly, PL, Kennea, JA, Kim, M, Kim, S, Kim, SC, King, A, Klimanov, SA, Kochanek, CS, Korista, KT, Kriss, GA, Lau, MW, Lee, JC, Leonard, DC, Li, M, Lira, P, Ma, Z, MacInnis, F, Manne-Nicholas, ER, Malkan, MA, Mauerhan, JC, McGurk, R, McHardy, IM, Montouri, C, Morelli, L, Mosquera, A, Mudd, D, Muller-Sanchez, F, Musso, R, Nazarov, SV, Netzer, H, Nguyen, ML, Norris, RP, Nousek, JA, Ochner, P, Okhmat, DN, Ou-Yang, B, Pancoast, A, Papadakis, I, Parks, JR, Pei, L, Peterson, BM, Pizzella, A, Poleski, R, Pott, J-U, Rafter, SE, Rix, H-W, Runnoe, J, Saylor, DA, Schimoia, JS, Schnülle, K, Sergeev, SG, Shappee, BJ, Shivvers, I, Siegel, M, Simonian, GV, Siviero, A, Skielboe, A, Somers, G, Spencer, M, Starkey, D, Stevens, DJ, Sung, H-I, Tayar, J, Tejos, N, Turner, CS, Uttley, P, Saders, JV, Vestergaard, M, Vican, L, Villanueva Jr, S, Villforth, C, Weiss, Y, Woo, J-H, Yan, H, Young, S, Yuk, H, Zheng, W, Zhu, W & Zu, Y 2017, 'Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the ultraviolet anomaly in NGC 5548 with X-ray spectroscopy', Astrophysical Journal, vol. 846, no. 1, 55. https://doi.org/10.3847/1538-4357/aa832b

TY - JOUR

T1 - Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the ultraviolet anomaly in NGC 5548 with X-ray spectroscopy

AU - Mathur, S.

AU - Gupta, A.

AU - Page, K.

AU - Pogge, R. W.

AU - Krongold, Y.

AU - Goad, M. R.

AU - Adams, S. M.

AU - Anderson, M. D.

AU - Arévalo, P.

AU - Barth, A. J.

AU - Bazhaw, C.

AU - Beatty, T. G.

AU - Bentz, M. C.

AU - Bigley, A.

AU - Bisogni, S.

AU - Borman, G. A.

AU - Boroson, T. A.

AU - Bottorff, M. C.

AU - Brandt, W. N.

AU - Breeveld, A. A.

AU - Brown, J. E.

AU - Brown, J. S.

AU - Cackett, E. M.

AU - Canalizo, G.

AU - Carini, M. T.

AU - Clubb, K. I.

AU - Comerford, J. M.

AU - Coker, C. T.

AU - Corsini, E. M.

AU - Crenshaw, D. M.

AU - Croft, S.

AU - Croxall, K. V.

AU - Bontà, E. Dalla

AU - Deason, A. J.

AU - Denney, K. D.

AU - Lorenzo-Caceres, A. De

AU - Rosa, G. De

AU - Dietrich, M.

AU - Edelson, R.

AU - Ely, J.

AU - Eracleous, M.

AU - Evans, P. A.

AU - Fausnaugh, M. M.

AU - Ferland, G. J.

AU - Filippenko, A. V.

AU - Flatland, K.

AU - Fox, O. D.

AU - Gates, E. L.

AU - Gehrels, N.

AU - Geier, S.

AU - Gelbord, J. M.

AU - Gorjian, V.

AU - Greene, J. E.

AU - Grier, C. J.

AU - Grupe, D.

AU - Hall, P. B.

AU - Henderson, C. B.

AU - Hicks, S.

AU - Holmbeck, E.

AU - Holoien, T. W. -S.

AU - Horenstein, D.

AU - Horne, Keith

AU - Hutchison, T.

AU - Im, M.

AU - Jensen, J. J.

AU - Johnson, C. A.

AU - Joner, M. D.

AU - Jones, J.

AU - Kaastra, J.

AU - Kaspi, S.

AU - Kelly, B. C.

AU - Kelly, P. L.

AU - Kennea, J. A.

AU - Kim, M.

AU - Kim, S.

AU - Kim, S. C.

AU - King, A.

AU - Klimanov, S. A.

AU - Kochanek, C. S.

AU - Korista, K. T.

AU - Kriss, G. A.

AU - Lau, M. W.

AU - Lee, J. C.

AU - Leonard, D. C.

AU - Li, M.

AU - Lira, P.

AU - Ma, Z.

AU - MacInnis, F.

AU - Manne-Nicholas, E. R.

AU - Malkan, M. A.

AU - Mauerhan, J. C.

AU - McGurk, R.

AU - McHardy, I. M.

AU - Montouri, C.

AU - Morelli, L.

AU - Mosquera, A.

AU - Mudd, D.

AU - Muller-Sanchez, F.

AU - Musso, R.

AU - Nazarov, S. V.

AU - Netzer, H.

AU - Nguyen, M. L.

AU - Norris, R. P.

AU - Nousek, J. A.

AU - Ochner, P.

AU - Okhmat, D. N.

AU - Ou-Yang, B.

AU - Pancoast, A.

AU - Papadakis, I.

AU - Parks, J. R.

AU - Pei, L.

AU - Peterson, B. M.

AU - Pizzella, A.

AU - Poleski, R.

AU - Pott, J. -U.

AU - Rafter, S. E.

AU - Rix, H. -W.

AU - Runnoe, J.

AU - Saylor, D. A.

AU - Schimoia, J. S.

AU - Schnülle, K.

AU - Sergeev, S. G.

AU - Shappee, B. J.

AU - Shivvers, I.

AU - Siegel, M.

AU - Simonian, G. V.

AU - Siviero, A.

AU - Skielboe, A.

AU - Somers, G.

AU - Spencer, M.

AU - Starkey, D.

AU - Stevens, D. J.

AU - Sung, H. -I.

AU - Tayar, J.

AU - Tejos, N.

AU - Turner, C. S.

AU - Uttley, P.

AU - Saders, J. Van

AU - Vestergaard, M.

AU - Vican, L.

AU - Villanueva Jr, S.

AU - Villforth, C.

AU - Weiss, Y.

AU - Woo, J. -H.

AU - Yan, H.

AU - Young, S.

AU - Yuk, H.

AU - Zheng, W.

AU - Zhu, W.

AU - Zu, Y.

PY - 2017/9/1

Y1 - 2017/9/1

N2 - During the Space Telescope and Optical Reverberation Mapping Project (STORM) observations of NGC 5548, the continuum and emission-line variability became de-correlated during the second half of the 6-month long observing campaign. Here we present Swift and Chandra X-ray spectra of NGC 5548 obtained as a part of the campaign. The Swift spectra show that excess flux (relative to a power-law continuum) in the soft X-ray band appears before the start of the anomalous emission-line behavior, peaks during the period of the anomaly, and then declines. This is a model-independent result suggesting that the soft excess is related to the anomaly. We divide the Swift data into on- and off-anomaly spectra to characterize the soft excess via spectral fitting. The cause of the spectral differences is likely due to a change in the intrinsic spectrum rather than being due to variable obscuration or partial covering. The Chandra spectra have lower signal-to-noise ratios, but are consistent with Swift data. Our preferred model of the soft excess is emission from an optically thick, warm Comptonizing corona, the effective optical depth of which increases during the anomaly. This model simultaneously explains all the three observations: the UV emission line flux decrease, the soft-excess increase, and the emission line anomaly.

AB - During the Space Telescope and Optical Reverberation Mapping Project (STORM) observations of NGC 5548, the continuum and emission-line variability became de-correlated during the second half of the 6-month long observing campaign. Here we present Swift and Chandra X-ray spectra of NGC 5548 obtained as a part of the campaign. The Swift spectra show that excess flux (relative to a power-law continuum) in the soft X-ray band appears before the start of the anomalous emission-line behavior, peaks during the period of the anomaly, and then declines. This is a model-independent result suggesting that the soft excess is related to the anomaly. We divide the Swift data into on- and off-anomaly spectra to characterize the soft excess via spectral fitting. The cause of the spectral differences is likely due to a change in the intrinsic spectrum rather than being due to variable obscuration or partial covering. The Chandra spectra have lower signal-to-noise ratios, but are consistent with Swift data. Our preferred model of the soft excess is emission from an optically thick, warm Comptonizing corona, the effective optical depth of which increases during the anomaly. This model simultaneously explains all the three observations: the UV emission line flux decrease, the soft-excess increase, and the emission line anomaly.

KW - Galaxies: active

KW - Galaxies: individual (NGC 5548)

KW - X-rays: galaxies

KW - X-rays: individual (NGC 5548)

U2 - 10.3847/1538-4357/aa832b

DO - 10.3847/1538-4357/aa832b

M3 - Article

SN - 0004-637X

VL - 846

JO - Astrophysical Journal

JF - Astrophysical Journal

IS - 1

M1 - 55

ER -

Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the ultraviolet anomaly in NGC 5548 with X-ray spectroscopy

Abstract

Keywords

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Astronomy at St Andrews 2015-2018: Astronomy at St Andrews 2015-2018

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