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Title: Slow-blue nuclear hypervariables in PanSTARRS-1

Journal Article · · Monthly Notices of the Royal Astronomical Society
 [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)
+ Show Author Affiliations

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.

Research Organization:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Organization:
USDOE
Grant/Contract Number:
AC02-76SF00515
OSTI ID:
1349095
Journal Information:
Monthly Notices of the Royal Astronomical Society, Vol. 463, Issue 1; ISSN 0035-8711
Publisher:
Royal Astronomical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 32 works
Citation information provided by
Web of Science

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Cited By (12)

A population of highly energetic transient events in the centres of active galaxies journal November 2017
A new class of flares from accreting supermassive black holes journal January 2019
Results of a systematic search for outburst events in 1.4 million galaxies journal October 2018
The ‘Big Dipper’: the nature of the extreme variability of the AGN SDSS J2232−0806 journal February 2019
The Vanishing and Appearing Sources during a Century of Observations Project. I. USNO Objects Missing in Modern Sky Surveys and Follow-up Observations of a “Missing Star” journal December 2019
New Physical Insights about Tidal Disruption Events from a Comprehensive Observational Inventory at X-Ray Wavelengths journal April 2017
Extreme Variability Quasars from the Sloan Digital Sky Survey and the Dark Energy Survey journal February 2018
A Mid-IR Selected Changing-look Quasar and Physical Scenarios for Abrupt AGN Fading journal August 2018
A Forward Modeling Approach to AGN Variability--Method Description and Early Applications journal September 2019
New physical insights about Tidal Disruption Events from a comprehensive observational inventory at X-ray wavelengths text January 2016
A forward modelling approach to AGN variability -- Method description and early applications text January 2019
The Vanishing & Appearing Sources during a Century of Observations project: I. USNO objects missing in modern sky surveys and follow-up observations of a "missing star" text January 2019

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Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
accretion
accretion discs
gravitational lensing: micro
galaxies: active
galaxies: nuclei
quasars: general