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To appear in the Astrophysical Journal Letters
Preprint typeset using LATEX style emulateapj v. 04/20/08
THE SUDDEN DEATH OF THE NEAREST QUASAR
Kevin Schawinski,1,2,3, Daniel A. Evans,4,5,6, Shanil Virani,2,3,7, C. Megan Urry,2,3,7, William C. Keel,8,9,
Priyamvada Natarajan,2,3,7, Chris J. Lintott,10,11, Anna Manning,8,9, Paolo Coppi,2,3,7, Sugata Kaviraj,10, 12,
Steven P. Bamford,13, Gyula I. G. Jo´zsa,14,15, Michael Garrett,14,16,17, Hanny van Arkel,14, Pamela Gay,18 and
Lucy Fortson19
To appear in the Astrophysical Journal Letters
ABSTRACT
Galaxy formation is significantly modulated by energy output from supermassive black holes at the
centers of galaxies which grow in highly efficient luminous quasar phases. The timescale on which black
holes transition into and out of such phases is, however, unknown. We present the first measurement
of the shutdown timescale for an individual quasar using X-ray observations of the nearby galaxy
IC 2497, which hosted a luminous quasar no more than 70,000 years ago that is still seen as a light
echo in ‘Hanny’s Voorwerp’, but whose present-day radiative output is lower by at least 2 and more
likely by over 4 orders of magnitude. This extremely rapid shutdown provides new insights into the
physics of accretion in supermassive black holes, and may signal a transition of the accretion disk to
a radiatively inefficient state.
Subject headings: (galaxies:) quasars: general; (galaxies:) quasars: individual (IC 2497)
1. INTRODUCTION
The discovery of the object known as “Hanny’s Voor-
werp”20 (the Voorwerp hereafter) by a citizen scientist
participating in the Galaxy Zoo project (Lintott et al.
2008, 2009) permits the first direct probe of a quasar’s
Electronic address: kevin.schawinski@yale.edu
1 Einstein Fellow
2 Department of Physics, Yale University, New Haven, CT 06511,
U.S.A.
3 Yale Center for Astronomy and Astrophysics, Yale University,
P.O. Box 208121, New Haven, CT 06520, U.S.A.
4 Massachusetts Institute of Technology, Kavli Institute for As-
trophysics and Space Research, 77 Massachusetts Avenue, Cam-
bridge, MA 02139, USA
5 Harvard-Smithsonian Center for Astrophysics, 60 Garden
Street, Cambridge, MA 02138, USA
6 Elon University, Elon, NC 27244, USA
7 Department of Astronomy, Yale University, New Haven, CT
06511, USA
8 Department of Physics and Astronomy, University of Alabama,
Box 870324,Tuscaloosa, AL 35487, USA
9 Visiting Astronomer, Kitt Peak National Observatory, NOAO,
operated by AURA under cooperative agreement with the US NSF
10 Astrophysics Department, University of Oxford, Oxford, OX1
3RH, UK
11 Adler Planetarium, 1300 S. Lakeshore Drive, Chicago, IL
60605
12 Blackett Laboratory, Imperial College London, London SW7
2AZ, UK
13 Centre for Astronomy & Particle Theory, University of Not-
tingham, University Park, Nottingham NG7 2RD, UK
14 Netherlands Institute for Radio Astronomy, Postbus 2, 7990
AA Dwingeloo, The Netherlands
15 Argelander-Institut fu¨r Astronomie, Auf dem Hu¨gel 71, 53121
Bonn, Germany
16 Leiden Observatory, University of Leiden, P.O. Box 9513, 2300
RA Leiden, The Netherlands
17 Centre for Astrophysics and Supercomputing, Swinburne Uni-
versity of Technology, Hawthorn, 3122 Victoria, Australia
18 Southern Illinois University Edwardsville, IL, USA
19 School of Physics and Astronomy, 116 Church Street S.E.,
University of Minnesota/Twin Cities, Minneapolis, MN 55455,
USA
20 Voorwerp is the Dutch word for object. The object’s
name was coined by the members of the Galaxy Zoo fo-
rum who named it after the discoverer, Hanny van Arkel
(http://www.galaxyzooforum.org).
variability for an individual source on timescales signifi-
cantly longer than human lifetimes (Lintott et al. 2009).
The Voorwerp is a large (11×16 kiloparsec) cloud of ion-
ized gas 45,000-70,000 lightyears away from the nucleus
of the galaxy IC 2497, embedded in a larger reservoir of
atomic hydrogen (Jo´zsa et al. 2009), with a mass of sev-
eral times 109M⊙ (see Figure 1). The optical spectrum
of the Voorwerp is dominated by a powerful [O iii] λ5007
emission line and shows little detectable continuum. The
presence of other emission lines with high ionization po-
tentials, such as [He ii] and [Nev], together with the nar-
rowness of the emission lines suggest that the Voorwerp
is being photoionized by the hard continuum of an ac-
tive galactic nucleus (AGN; an accreting supermassive
black hole), rather than by other processes such as star
formation or shocks (such as might be induced by a jet;
Lintott et al. 2009). Radio observations of IC 2497 re-
veal a nuclear source and a jet hotspot in the nucleus,
and a large kiloparsec-scale structure that may be a jet
(Jo´zsa et al. 2009; Rampadarath et al. 2010). The Voor-
werp lies where this jet meets the Hi reservoir and coin-
cides with a local decrement in atomic hydrogen presum-
ably due to photoionization (see Fig. 2 of ref. Jo´zsa et al.
2009). An actively accreting black hole at the centre
of IC 2497 is therefore the only plausible source of ion-
ization that can account for the emission seen from the
Voorwerp.
The light travel time from the nucleus of IC 2497 to the
Voorwerp, accounting for all possible geometries, ranges
from 45,000 to 70,000 years (Lintott et al. 2009) and so
the Voorwerp reflects the radiative output of the cen-
tral black hole of IC2497 at those times in the past. Its
large physical extent rules out a brief flare, caused for
example by the tidal disruption of a star, as the ioniz-
ing source (Komossa et al. 2004; Gezari et al. 2006). The
black hole must produce sufficient ionizing photons in or-
der to power its observed [O iii] λ5007-luminosity. This
requirement corresponds to 2 × 1045 ergs−1 between 1
and 4 Rydberg (13.6-54.4 eV), assuming isotropic emis-

2 Schawinski et al.
Fig. 1.— Ground-based optical image from WIYN of IC 2497 (top), Hanny’s Voorwerp (bottom) and a nearby companion galaxy (left).
This image is a composite of B, V and I band filters taken with the WIYN telescope in excellent ∼ 0.′′45 seeing. Since the Voorwerp is a
pure emission line object dominated by a powerful [O iii] λ5007 line, it only appears in the V band image (green). The bar in the lower-left
indicates a scale of 5′′, which at the redshift of IC 2497 corresponds to just under 5 kpc. To ionize and light up the Voorwerp, a quasar
point source in the nucleus of IC 2497 has to have a bolometric luminosity of at least Lbol ∼ 1046 ergs−1, but no point source indicating
the presence of such a luminous quasar is evident. The prominent dust lanes in the bulge of IC 2497 indicate an ongoing morphological
disturbance that may be related to the nearby galaxy to the left or to a recent merger.
sion. This likely underestimates the necessary intrin-
sic luminosity due to large amounts of dust obscura-
tion in the bulge of IC 2497, which has prominent dust
lanes (Figure 1). We calculate the required luminosity
of the quasar lighting up the Voorwerp by taking a tem-
plate spectral energy distribution (SED) for an unob-
scured quasar from Elvis et al. (1994) which the Voor-
werp is presumably seeing. We then scale this tem-
plate to match the minimum UV ionizing luminosity
needed and derive a minimum bolometric luminosity of
Lbol,past = 1.2 × 1046 ergs−1. This means IC 2497, at a
redshift of z = 0.0502 (Fisher et al. 1995), is, or has been,
the nearest luminous quasar, an extremely rare object in
the local Universe.
However, IC 2497 poses a challenge: the optical
image reveals no strong point source (Figure 1), the
nuclear spectrum shows very weak optical line emis-
sion (Lintott et al. 2009), and it also has a weak (∼
1038 ergs−1) nuclear radio source (Jo´zsa et al. 2009).
These observations are difficult to reconcile with the pres-
ence of a currently active Lbol ∼ 1046 ergs−1 quasar.
There are two possible scenarios that can account for
these apparently contradictory observations as argued by
Lintott et al. (2009): 1) the quasar in IC 2497 features
a novel geometry of obscuring material and is obscured
at an unprecedented level only along our line of sight,
while being virtually unobscured towards the Voorwerp;
or 2) the quasar in IC 2497 has shut down within the
last 70,000 years, while the Voorwerp remains lit up due
to the light travel time from the nucleus. If the latter
is the case, the IC 2497–Voorwerp system gives for the
first time an upper limit of the shutdown timescale of
an individual quasar central engine. In this Letter, we
present observations to distinguish these two scenarios.
2. OBSERVATIONS AND RESULTS
2.1. Archival Infrared Data
We have obtained multiple, independent observa-
tions to assess the current nuclear luminosity of IC
2497. Light from an obscured Lbol ∼ 1046 ergs−1
quasar in IC 2497 should be re-emitted at mid- and
far-infrared wavelengths. Archival IRAS observations
show that the infrared temperature of IC 2497 of
f25µm/f60µm = 0.1 is cold compared to that of nearby,
luminous highly-obscured AGN (Moshir & et al. 1990;
Risaliti et al. 1999) and IC 2497 also adheres to the
radio-far infrared correlation (Rampadarath et al. 2010).
Thus, IC 2497 does not exhibit any evidence for repro-
cessed infrared emission from an active nucleus.
2.2. Suzaku and XMM-Newton Observations
The presence of a quasar with high levels of obscuration
should still be detected in the hard X-rays (> 10 keV)
where photoelectric absorption is minimal. To this end,
we observed IC 2497 with the Suzaku X-ray space obser-
vatory for 75 kiloseconds on 2009-04-20 using both the
XIS (0.2–12 keV) and HXD/PIN (10–600 keV) detectors.
This observation was designed to be sufficiently deep to
detect a quasar with Lbol ∼ 1046 ergs−1 and an obscur-
ing column of NH = 1024 cm−2. There is no significant

The sudden death of the nearest quasar 3
detection with the XHD/PIN instrument consistent with
such a highly obscured quasar, although there are some
marginally significant counts at E > 15 keV; even if real,
these imply a 10–20 keV luminosity orders of magnitude
below the required luminosity.
We then obtained a second observation of IC 2497
with the XMM-Newton X-ray space observatory using
the EPIC-pn, MOS-1 and MOS-2 detectors on 2010-
04-19 with a total useful observing time of 11 kilosec-
onds and sensitivity between 0.1 and 7 keV. With XMM-
Newton, we detect a source at 0.1-5 keV, which can be
fit with a combination of two spectral components: a
collisionally ionized plasma (T = 0.78+0.18−0.14 keV), con-
sistent with thermal emission from a warm interstel-
lar medium in IC 2497, and an unabsorbed power law
(Γ = 2.5 ± 0.7) from a very low luminosity AGN with
L2−10 keV = 4.2×1040 ergs−1. The emission may equally
well be attributed to emission from star formation and X-
ray binaries. Neither the XMM-Newton, nor the Suzaku
XIS observations detect the Kα line feature at ∼6.4 keV
which is prominent in obscured AGN, especially the most
highly obscured systems (Ueda et al. 2007). We show the
XMM-Newton spectra in Figure 2. If the observed X-ray
power law is not due to a low-luminosity AGN, then its
radiative output must be even lower.
If we assume that all the observed emission is from
non-AGN sources, then the Suzaku data can give us an
extreme upper limit on the present-day AGN luminos-
ity. Assuming a Compton-thick AGN, the full XMM-
Newton and Suzaku data, especially the PIN data, limit
the present-day hard X-ray luminosity to L15−30 keV =
3.5× 1042 ergs−1, roughly two orders of magnitude more
luminous than the observed soft X-ray power law, but
not sufficient to ionize the Voorwerp. The interpreta-
tion of the power law seen by XMM-Newton as a low-
luminosity AGN appears to be the more likely one as
we see a low-luminosity AGN in two other wavelength
regimes: a VLBI radio core (Rampadarath et al. 2010)
and a nuclear point source visible in a Hubble Space Tele-
scope F184W image (Keel et al. in prep.) indicate that a
low-luminosity AGN consistent with the observed X-ray
power law is present in IC 2497.
The XMM-Newton detection of a power law contin-
uum is consistent with an active black hole at the centre
of IC 2497 but at a very low accretion rate. It must
also be unobscured along our line of sight, apart from
Galactic extinction (NH = 1.31×1020 cm−2). Additional
absorption does not improve the quality of the fit, and
the amount of absorption is consistent with zero. This
power-law AGN is therefore a fair probe of the current
radiative output of the central engine of IC 2497. An
extrapolation of the fit to the XMM-Newton data out to
the energies sampled by Suzaku PIN is consistent with
the marginal Suzaku PIN detection.
The hypothesis that a quasar of the required luminos-
ity is present, but sufficiently obscured along our line of
sight to elude detection at optical wavelengths is ruled
out by the Suzaku hard X-ray luminosity limit and the
lack of a Kα line at 6.4 keV. The Suzaku upper limit
implies a drop in luminosity of the quasar in IC 2497
of at least 2 orders of magnitude. The more likely sce-
nario is that the power law component of the soft X-ray
spectrum is that of the present-day low-luminosity AGN
Fig. 2.— X-ray spectrum from XMM-Newton from the EPIC-
pn (black), MOS1 (red) and MOS2 (green). The solid lines are
the combined model of a power law due to an unobscured AGN
with a present-day luminosity of L2−10 keV = 4.2 × 1040 ergs−1,
and a collisionally ionized plasma from hot, diffuse gas. Residuals
from the best-fit two-component model (see text) are shown in the
bottom panel. Extrapolated to hard X-rays, the fit to the power
law is consistent with the marginal PIN counts at ∼15 keV.
state of the central engine. Using the ionizing quasar
SED template scaled to the luminosity required by the
Voorwerp, the expected X-ray luminosity in this energy
band would be L2−10 keV = 8 × 1044 ergs−1, while we
only detect 4.2 × 1040 ergs−1, a discrepancy of over 4
orders magnitude.
3. DISCUSSION
The low X-ray luminosity definitively rules out the
presence of a currently active quasar in IC2497, and we
therefore conclude that the galaxy’s central engine has
decreased its radiative output by at least 2 and more
likely by over 4 orders of magnitude since being in a
much more luminous phase within the last 70,000 years.
We have therefore for the first time constrained the shut-
down timescale of an individual quasar.
The sudden death of the quasar in IC 2497 might
be due to a sharp decrease in the fuel supply or a
change of accretion state. Rapid changes between ‘high’
(radiatively efficient) and ‘low-hard’ (radiatively ineffi-
cient) states most likely driven by instabilities in the
accretion disk have been seen in Galactic X-ray bina-
ries (XRBs) which typically have black holes of a few
solar masses (Nayakshin et al. 2000; Fender & Belloni
2004; Fender et al. 2004; Prat et al. 2010). It has been
suggested that supermassive black holes are essentially
scaled-up versions of XRBs with similar black hole accre-
tion physics (e.g. Maccarone et al. 2003; McHardy et al.
2006; Ko¨rding et al. 2006). IC 2497 may be the first
quasar where such a rapid transition between accretion
states is observed, of the kind routinely seen in XRBs.
The immediate question this analogy raises is whether
the time scale of the state change corresponds to what we
would expect from XRBs. State changes in the Galactic
XRB GRS 1915+105, with a black hole mass of 10 M⊙,
are detected on timescales of 1 hour. Scaling up linearly
to the case of IC 2497 with a 109 M⊙ black hole (esti-
mated from its bulge mass; Ha¨ring & Rix 2004) yields a

4 Schawinski et al.
timescale of 10,000 years. A more detailed calculation
taking into account the ratio of bolometric luminosity
to the Eddington luminosity (Done & Gierlin´ski 2005)
yields a timescale on the order of 10,000–100,000 years.
Both are broadly consistent with our upper limit on the
shutdown timescale.
This concordance of timescales supports the interpre-
tation of IC 2497 as a system that has transitioned from
a classical quasar in a high state to a radiatively inef-
ficient state where the bulk of the energy is dissipated
not as radiation but as either thermal or kinetic energy
(Begelman et al. 1984; Narayan & Yi 1994). The pres-
ence of a recent radio outflow (Rampadarath et al. 2010)
extending over ∼ 1000 light years (projected distance)
from the nucleus of IC 2497 also supports the hypothesis
of a change in accretion state (Narayan et al. 1995) if the
launch of the jet is associated with the state change.
However, the four orders of magnitude drop in lumi-
nosity poses a problem for a direct analogy. In XRBs,
such large luminosity changes are seen as they return to
quiescence after the (quasi-exponential) outburst decline.
Typically it takes a few days for the cooling wave to prop-
agate through to the inner disc in black hole binaries,
as seen in observations (e.g., Chen et al. 1997) and in
theoretical lightcurves from disc instability models (e.g.
Dubus et al. 2001). Taking 1 day as the transition time
scale and scaling from 10 M⊙ to 109 M⊙ using the lin-
ear scaling yields a transition time scale for the quasar
of at least 280,000 years, significantly longer that what
we see in IC 2497. A change of accretion state remains
a possible explanation for the observed luminosity drop
in IC 2497, but in that case the analogy to XRBs does
not scale linearly with the black hole mass. We therefore
conclude that the sudden death of IC 2497 is a vital clue
to how quasars accrete and shut down, but that we do
not yet understand the physics of this process.
If such a change of state in the accretion disk did oc-
cur, then it is entirely plausible that the accretion disk
may change back to a high luminosity state on a simi-
lar timescale. Future multi-wavelength monitoring of IC
2497 could reveal such a change. Since the quasar in IC
2497 shut down less than 70,000 years ago, it offers an
unobstructed view of the host galaxy of a quasar. The
close distance of IC 2497 furthermore means that we can
view this quasar host galaxy in greater detail than any
other system. As such, it is ideally suited for observa-
tionally probing the fueling of the black hole and how the
quasar phase is affecting the large-scale environment of
the host galaxy, and in particular, whether it retains any
evidence for whether the central engine was, or currently
is, injecting kinetic or thermal energy into the interstellar
medium and therefore doing feedback work.
We thank the anonymous referee for helpful com-
ments. This work is based on observations with the
XMM-Newton and Suzaku X-ray satellites and the
WIYN observatory, and was supported by NASA grants
NNX09AR22G and NXX09AV69G. Support for the work
of KS was provided by NASA through Einstein Postdoc-
toral Fellowship grant number PF9-00069 issued by the
Chandra X-ray Observatory Center, which is operated
by the Smithsonian Astrophysical Observatory for and
on behalf of NASA under contract NAS8-03060. PN ac-
knowledges the award of a Guggenheim fellowship. CJL
acknowledges support from The Leverhulme Trust and a
STFC Science and Society Fellowship. We thank Charles
Bailyn, Chris Done and Phil Hopkins for discussions and
suggestions.
This research has made use of NASA’s Astrophysics
Data System Bibliographic Services.
Facility: XMM-Newton (EPIC-pn, MOS), Suzaku (XIS,
PIN), WIYN
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