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Title: Slow-blue nuclear hypervariables in PanSTARRS-1

We discuss 76 large amplitude transients (Δm > 1.5) occurring in the nuclei of galaxies, nearly all with no previously known active galactic nucleus (AGN). They have been discovered as part of the Pan-STARRS1 (PS1) 3π survey, by comparison with Sloan Digital Sky Survey (SDSS) photometry a decade earlier, and then monitored with the Liverpool Telescope, and studied spectroscopically with the William Herschel Telescope (WHT). Based on colours, light-curve shape, and spectra, these transients fall into four groups. A few are misclassified stars or objects of unknown type. Some are red/fast transients and are known or likely nuclear supernovae. A few are either radio sources or erratic variables and so likely blazars. However the majority (~66 per cent) are blue and evolve slowly, on a time-scale of years. Spectroscopy shows them to be AGN at z ~0.3 – 1.4, which must have brightened since the SDSS photometry by around an order of magnitude. It is likely that these objects were in fact AGN a decade ago, but too weak to be recognized by SDSS; they could then be classed as ‘hypervariable’ AGN. By searching the SDSS Stripe 82 quasar database, we find 15 similar objects. We discuss several possible explanationsmore » for these slow-blue hypervariables – (i) unusually luminous tidal disruption events; (ii) extinction events; (iii) changes in accretion state; and (iv) large amplitude microlensing by stars in foreground galaxies. A mixture of explanations (iii) and (iv) seems most likely. As a result, both hold promise of considerable new insight into the AGN phenomenon.« less
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [5] ;  [5] ;  [6] ;  [7] ;  [8] ;  [8] ;  [8] ;  [8] ;  [8] ;  [8] ;  [8] ;  [9] ;  [4] more »;  [5] ;  [5] ;  [1] ;  [5] ;  [5] ;  [3] « less
  1. Univ. of Edinburgh (United Kingdom)
  2. Univ. of Maryland, College Park, MD (United States)
  3. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)
  4. Durham Univ. (United Kingdom)
  5. Queen's Univ., Belfast, Northern Ireland (United Kingdom)
  6. Queen's Univ., Belfast, Northern Ireland (United Kingdom); Univ. of Cambridge (United Kingdom)
  7. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  8. Univ. of Hawaii, Honolulu, HI (United States)
  9. Princeton Univ., Princeton, NJ (United States)
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Volume: 463; Journal Issue: 1; Journal ID: ISSN 0035-8711
Publisher:
Royal Astronomical Society
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; accretion; accretion discs; gravitational lensing: micro; galaxies: active; galaxies: nuclei; quasars: general
OSTI Identifier:
1349095

Lawrence, A., Bruce, A. G., MacLeod, C., Gezari, S., Elvis, M., Ward, M., Smartt, S. J., Smith, K. W., Wright, D., Fraser, M., Marshall, P., Kaiser, N., Burgett, W., Magnier, E., Tonry, J., Chambers, K., Wainscoat, R., Waters, C., Price, P., Metcalfe, N., Valenti, S., Kotak, R., Mead, A., Inserra, C., Chen, T. W., and Soderberg, A.. Slow-blue nuclear hypervariables in PanSTARRS-1. United States: N. p., Web. doi:10.1093/mnras/stw1963.
Lawrence, A., Bruce, A. G., MacLeod, C., Gezari, S., Elvis, M., Ward, M., Smartt, S. J., Smith, K. W., Wright, D., Fraser, M., Marshall, P., Kaiser, N., Burgett, W., Magnier, E., Tonry, J., Chambers, K., Wainscoat, R., Waters, C., Price, P., Metcalfe, N., Valenti, S., Kotak, R., Mead, A., Inserra, C., Chen, T. W., & Soderberg, A.. Slow-blue nuclear hypervariables in PanSTARRS-1. United States. doi:10.1093/mnras/stw1963.
Lawrence, A., Bruce, A. G., MacLeod, C., Gezari, S., Elvis, M., Ward, M., Smartt, S. J., Smith, K. W., Wright, D., Fraser, M., Marshall, P., Kaiser, N., Burgett, W., Magnier, E., Tonry, J., Chambers, K., Wainscoat, R., Waters, C., Price, P., Metcalfe, N., Valenti, S., Kotak, R., Mead, A., Inserra, C., Chen, T. W., and Soderberg, A.. 2016. "Slow-blue nuclear hypervariables in PanSTARRS-1". United States. doi:10.1093/mnras/stw1963. https://www.osti.gov/servlets/purl/1349095.
@article{osti_1349095,
title = {Slow-blue nuclear hypervariables in PanSTARRS-1},
author = {Lawrence, A. and Bruce, A. G. and MacLeod, C. and Gezari, S. and Elvis, M. and Ward, M. and Smartt, S. J. and Smith, K. W. and Wright, D. and Fraser, M. and Marshall, P. and Kaiser, N. and Burgett, W. and Magnier, E. and Tonry, J. and Chambers, K. and Wainscoat, R. and Waters, C. and Price, P. and Metcalfe, N. and Valenti, S. and Kotak, R. and Mead, A. and Inserra, C. and Chen, T. W. and Soderberg, A.},
abstractNote = {We discuss 76 large amplitude transients (Δm > 1.5) occurring in the nuclei of galaxies, nearly all with no previously known active galactic nucleus (AGN). They have been discovered as part of the Pan-STARRS1 (PS1) 3π survey, by comparison with Sloan Digital Sky Survey (SDSS) photometry a decade earlier, and then monitored with the Liverpool Telescope, and studied spectroscopically with the William Herschel Telescope (WHT). Based on colours, light-curve shape, and spectra, these transients fall into four groups. A few are misclassified stars or objects of unknown type. Some are red/fast transients and are known or likely nuclear supernovae. A few are either radio sources or erratic variables and so likely blazars. However the majority (~66 per cent) are blue and evolve slowly, on a time-scale of years. Spectroscopy shows them to be AGN at z ~0.3 – 1.4, which must have brightened since the SDSS photometry by around an order of magnitude. It is likely that these objects were in fact AGN a decade ago, but too weak to be recognized by SDSS; they could then be classed as ‘hypervariable’ AGN. By searching the SDSS Stripe 82 quasar database, we find 15 similar objects. We discuss several possible explanations for these slow-blue hypervariables – (i) unusually luminous tidal disruption events; (ii) extinction events; (iii) changes in accretion state; and (iv) large amplitude microlensing by stars in foreground galaxies. A mixture of explanations (iii) and (iv) seems most likely. As a result, both hold promise of considerable new insight into the AGN phenomenon.},
doi = {10.1093/mnras/stw1963},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 1,
volume = 463,
place = {United States},
year = {2016},
month = {9}
}