2Q. How many transients in 1 deg ?

IceCube event

2
Q. How many transients in 1 deg ?

IceCube event

Op=cal 20 mag survey (1m telescope)magmagMt
Type Ia SNtΔt

NΔt ~ 20 days, Mabs = -19 mag (1043 erg s-1)=> dmax ~ 800 Mpc (zmax~0.18)
N ~ R V Δt fΩ ~ (0.3 x 10-4 Mpc-3 yr-1) x (4π/3) (800 Mpc)3x (0.05 yr) x (1 deg2/40,000)~ 0.1zzmax

Op=cal 20 mag survey (1m telescope)
N ⇠ RVtf⌦ ⇠ 5 ⇥ 104✓R10 4 Mpc 3 yr 1◆✓d100 Mpc◆3 ✓t
20 days◆✓⌦1 deg2◆TypeMabsΔt

R(Mpc-3 yr-1)

dmax
(Mpc)

zmax

N (deg-2)

Ia-19

200.3 x 10-48000.170.1

Type II(H-rich)

-17

50

0.7 x 10-4300

0.070.02

Type Ibc(H-free)-17200.2 x 10-4300

0.070.002

Type IIn(CSM rich)

-19

50

0.1 x 10-48000.170.05

Hypernova-18

200.01 x 10-4400

0.090.0005

Op=cal 20 mag survey (1m telescope)
For core-collapse SNe: z ~ 0.1IceCube event

Op=cal 25 mag survey (8m telescope)
N ⇠ RVtf⌦ ⇠ 5 ⇥ 104✓

R
10 4 Mpc 3 yr 1◆✓d100 Mpc◆3 ✓t
20 days◆✓⌦
1 deg2◆TypeMabsΔt

R(Mpc-3 yr-1)

dmax
(Mpc)

zmax

N (deg-2)

Ia

-19

20

0.3 x 10-4

7000

150

Type II(H-rich)

-17

50

0.7 x 10-4

2000

0.4

10Type Ibc(H-free)-1720

0.2 x 10-4

2000

0.4

1

Type IIn(CSM rich)-1950

0.1 x 10-47000

120

Hypernova-18

200.01 x 10-4

4000

0.70.3

Op=cal 25 mag survey (8m telescope)
For core-collapse SNe: z ~ 0.5

IceCube event

SN Typing is not easy only by images (needs color, spectrum)Op=cal (transient)
N (deg-2)
102
101
100

Type Ia (z<1)
Type IIn (z<1)
Type II (z<0.4)Type Ibc (z<0.4)
Hypernova (z<0.7)

10-1Type Ia (z<0.2)

10-2

CCSN (z<0.1)
sensi=vity
25 mag

20 mag

Radio (transient)

Astrophysical Journal, 818:105 (27pp), 2016 February 20~ 5 ﬂat spectrum source(persistent)

MoolMooley+2016
gure 22. Top: the phase space of slow extragalactic transients. The panel shows the upper limits to the transient rates from previous
radio surveys (coloredX-ray (persistent + transient)
N (deg-2)

2102
101
Un-cataloged
100
10-1

Cataloged
Variable

Sakamoto-san’s talkSerino-san’s talk
7 x 0.15 deg2

Evans et al.

results from both the IceCube (Abbasi et al. 2011, 2012)
and ANTARES (Adrián-Martı́nez et al. 2013) observatories.
Similarly, gravitational waves are expected to arise from a
range of phenomena, particularly the merger of two neutronstars in a short GRB. Targeted searches for gravitational
waves from short GRBs have also, so far, failed to produce
any detections (e.g. Abadie et al. 2010b).
Eﬀort has also been expended to search for EM counterparts to non-EM triggers. Because EM facilities tend tohave narrow fields of view, the likelihood of a non-EM trigger being contemporaneously observed by an EM telescopeare very low, therefore the EM data have to be collected after the non-EM trigger. The error regions from neutrino or
gravitational wave facilities are on the scale of degrees, thusit often requires multiple pointings to collect the necessary
EM data. It is also not clear when is the optimal time tosearch for the counterpart, as the relative timescales of EM
and non-EM radiation depends on the physical source of theemission. For example, for supernovae the neutrino signal
precedes the EM signal by many days. An optimal followup facility would, therefore, have a large (ideally all-sky)field of view, and high level of sensitivity. Due to the highrate of transient events in the universe, multiwavelength capabilities are also desirable, for example to help distinguishrapidly between GRBs and flare stars.
The Swift satellite (Gehrels et al. 2004) arguably provides the best existing facility for the EM follow up of nonEM triggers, at least in X-rays. Although the X-ray telescope(XRT; Burrows et al. 2005) has only a modest field of view
(radius ∼ 0.2◦ ), the Swift spacecraft is capable of rapid slewing, and has the ability to ‘tile’ regions on the sky, so as tocover a large error region in a single spacecraft orbit. TheXRT is sensitive to 5×10−13 erg cm −2 s−1 in 1 ks (0.3–10keV), and can localise sources to a 90% confidence radiusof 3.5 arcsec (improving to 1.4 arcsec for brighter sources;
Goad et al. 2007; Evans et al. 2009).
Evans et al. (2012) reported on Swift follow up of
two gravitational wave triggers from the LIGO-Virgo(Abbott et al. 2009; Accadia et al. 2012) facilities. No Xray counterpart to the gravitational triggers could be found,and indeed it transpired that neither of the gravitational
wave triggers was in fact real (one was a subthreshold noise
event, the other an artificial signal introduced to the data
as a blind test of the detection algorithms). In this work,
we report on the search with Swift-XRT for X-ray counterparts to 20 neutrino-doublet triggers from the IceCube
facility (Achterberg et al. 2006), and discuss the challenges
related to idenfitying the EM counterpart. A neutrino doublet (or multiplet) was defined as two or more neutrinos
detected within 100 s of each other, and with an angularseparation of at most 3.5◦ ; more details about this is given
in a companion paper (Aartsen et al., in preparation).
The Swift follow-up observations began as soon as possible after the neutrino trigger, implicitly assuming that
the X-ray emission from the astrophysical neutrino source
is temporally coincident with (or only a few hours after)
the neutrino emission. We consider two ways of identifying
the X-ray counterpart: by its brightness compared to reference catalogues, or by its temporal variability (in particular,
whether it shows signs of fading, as may be expected following some form of outburst).
We did not set the threshold at which Swift will re-109 sources(16 cataloged)for 20 IceCube events
Figure 1. An example exposure map of a 7-tile Swift-XRT observation of an IceCube trigger. This observation was taken withthe on-board tiling, so the exposure in each field has been built up
over multiple spacecraft orbits; the pointing is slightly diﬀerent
on each orbit, hence the blurring round the edges of the fields.
The black lines and dots are the bad columns and pixels on theCCD.

spond to a neutrino trigger based on theoretical predictionsof neutrino flux (which are highly uncertain due to the lackof observational constraint), instead we set it such that IceCube would be expected to produce roughly six spurious(i.e. non-astrophysical) triggers per year, which represents acompromise between sensitivity to astrophysical neutrinos,
and the value of Swift’s observing time. The companion paper (Aartsen et al., in preparation) will discuss the expected
rate of doublet triggers from the background and from astrophysical objects, and consider the lack of neutrino triplets
during this experiment.
This paper is organised as follows. In Section 2 we describe the follow-up observing strategy employed by Swift,
and in Section 3 we overview the data analysis techniques. InSection 4 we consider the sources detected, and attempt toidentify if either of these is likely to be the counterpart to theneutrino trigger, which we expect to be a source undergoingsome form of outburst. Finally, in Section 5 we consider theimplications of our findings for future EM follow-up of nonEM triggers, in particular, the expected gravitational wave
triggers from the Advanced LIGO-VIRGO facility.
Throughout the paper we have assumed a cosmology
with H0 = 71 km s−1 Mpc−1 , Ωm = 0.27, Ωvac = 0.73.
Unless otherwise stated, all quoted errors are at the 90%
confidence level, and upper limits at the 3-σ (=99.7%) confidence level.

2

SWIFT ’S OBSERVING STRATEGY

Following IceCube triggers, high-priority Target of Opportunity (ToO) requests were submitted to Swift. Due to thec 2015 RAS, MNRAS 000, 1–18
⃝10-2

Transient
Swid (=ling)MAXI

sensi=vity

F = 10-12 erg s-1 cm-2

F = 10-9 erg s-1 cm-2

High-E gamma-ray (persistent)
Tanaka-san’s talkN (deg-2)

3FGL: ~3000 sources

102
101
100
10-1

3FGLAGN

10-2
sensi=vity
Fermi/LATVery high-E gamma-ray (persistent)
Hayashida-san’s talkN (deg-2)~200 sources(all sky)

102
101
100
10-1
10-2
「ソース様」MAGIC/HESS/VERITAS

sensi=vity

Discussion••

Contamina=on strongly depends on sensi=vity•Source luminosity•

Distance

Radio/X-ray/Gamma-ray transient••< 1 deg-2 @ current sensi=vity

Op=cal transient•~0.1 deg-2 @ 20 mag (core-collapse SN, z < 0.1)•~50 deg-2 @ 25 mag (core-collapse SN, z < 0.4)•=> 0.1 deg localiza=on is desired