J/MNRAS/448/2210 Swift follow-up of IceCube triggers (Evans+, 2015)
Swift follow-up of IceCube triggers, and implications for the Advanced-LIGO era.
Evans P.A., Osborne J.P., Kennea J.A., Smith M., Palmer D.M., Gehrels N.,
Gelbord J.M., Homeier A., Voge M., Strotjohann N.L., Cowen D.F., Boser S.,
Kowalski M., Stasik A.
<Mon. Not. R. Astron. Soc., 448, 2210-2223 (2015)>
=2015MNRAS.448.2210E 2015MNRAS.448.2210E (SIMBAD/NED BibCode)
ADC_Keywords: Gamma rays - X-ray sources
Keywords: gravitational waves - neutrinos - methods: observational -
gamma-ray burst: general - X-rays: general
Abstract:
Between 2011 March and 2014 August Swift responded to 20 triggers from
the IceCube neutrino observatory, observing the IceCube 50 percent
confidence error circle in X-rays, typically within 5h of the trigger.
No confirmed counterpart has been detected. We describe the Swift
follow-up strategy and data analysis and present the results of the
campaign. We discuss the challenges of distinguishing the X-ray
counterpart to a neutrino trigger from serendipitous uncatalogued
X-ray sources in the error circle, and consider the implications of
our results for future strategies for multimessenger astronomy, with
particular reference to the follow-up of gravitational wave triggers
from the advanced-era detectors.
Description:
Following IceCube triggers, high-priority Target of Opportunity (ToO)
requests were submitted to Swift. Due to the efficient and flexible
operation of Swift, observations were able to begin rapidly once the
ToO was received: the median time from IceCube trigger to the first
Swift observation was 1.8h.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 41 20 Details of the 20 IceCube triggers followed up
by Swift as of 2014 September 03
table2.dat 112 109 Sources detected in the XRT follow-up of the
IceCube triggers
table3.dat 67 47 Details of the X-ray sources with spectra
table4.dat 87 30 Details of the X-ray sources with catalogue
matches
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Trigger IceCube Trigger number
4- 6 F3.1 deg eRad Error radius (50% confidence)
8- 17 A10 "YYYY-MM-DD" Obs.date Trigger date
19- 26 A8 "h:m:s" Obs.time Trigger time
28- 31 F4.1 h Delay Time between the possible neutrino event
detected by IceCube and the start of
the first observation with the Swift-XRT
33- 41 A9 --- Type Tiling type (Manual or Automatic)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Trigger IceCube trigger field number
4- 5 I2 --- Source Source number, within the trigger field
6 A1 --- n_Source [j] Note for no XRT spectral fit
available (1)
8- 9 I2 h RAh Right ascension (J2000)
11- 12 I2 min RAm Right ascension (J2000)
14- 17 F4.1 s RAs Right ascension (J2000)
19 A1 --- DE- Declination sign (J2000)
20- 21 I2 deg DEd Declination (J2000)
23- 24 I2 arcmin DEm Declination (J2000)
26- 27 I2 arcsec DEs Declination (J2000)
29- 32 F4.1 arcsec e_Pos Position error radius, 90% confidence
33 A1 --- n_Pos [*i] Note on position (1)
36 A1 --- Flag [GPR] Flag (2)
38- 41 F4.1 ks ExpTime Exposure time
43- 45 I3 ct Count Number of counts found in the region used
to detect the source
47- 50 F4.1 ct CountExp Number expected from the background
52- 59 F8.3 10-16W/m2 Flux Observed (i.e. absorbed) flux. For objects
with more than one light-curve bin,
peak observed flux, in 0.3-10keV band
61- 67 F7.3 10-16W/m2 E_Flux Error on Flux (upper value)
69- 75 F7.3 10-16W/m2 e_Flux Error on Flux (lower value)
76 A1 --- n_Flux [k] Note for no XRT light curve was
available (1)
78- 82 F5.2 10-16W/m2 FluxM ? For objects with more than one
light-curve bin, mean observed flux
84- 87 F4.2 10-16W/m2 e_FluxM ? rms uncertainty on FluxM
91- 95 F5.1 --- FluxUL ?=- Upper limit for 0.3-10keV band flux,
from the RASS unless otherwise
indicated (3)
96 A1 --- n_FluxUL [l] Note for a very hard source (1)
98-102 F5.2 --- Nseren Number of sources at least as bright as this
one, expected in the XRT field of view
(see Section 4.2 for details)
104-110 F7.5 --- Pconst ? Probability that the source is constant,
from a chi2 test, only available if the
light curve contained at least two bins
112 A1 --- Cat? [Y] Whether a catalogued source was found
which matched this object; details are
given in Table 4.
--------------------------------------------------------------------------------
Note (1): Notes as follows:
j = No XRT spectral fit was available, generic AGN spectrum assumed
* = position enhanced by UVOT astrometry
i = Position derived from XRT-2MASS astrometry
k = no XRT light curve was available: the brightness was estimated by the
source detection routine
l = this was a very hard source to which ROSAT was insensitive, therefore
an RASS limit is uninformative
Note (2): flag (see text for details) as follows:
G = Good
R = Reasonable
P = Poor
Note (3): If no value is given, this is because the source is a known X-ray
emitter, so an upper limit is unnecessary.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Trigger IceCube trigger field number
4- 5 I2 --- Source Source number, within the trigger field
7- 12 F6.2 10+20cm-2 NHG Galactic absorption value, taken from
Willingale et al. (2013MNRAS.431..394W 2013MNRAS.431..394W)
14 A1 --- l_NHi Limit flag on NHi
15- 21 F7.1 10+20cm-2 NHi Intrinsic absorption, fitted to the spectrum
23- 27 I5 10+20cm-2 E_NHi ? Error on NHi (upper value)
29- 35 F7.1 10+20cm-2 e_NHi ? Error on NHi (lower value)
37 A1 --- l_Index Limit flag in Index
38- 42 F5.2 --- Index ? Photon index
44- 48 F5.2 --- E_Index ? Error on Index (upper value)
50- 53 F4.2 --- e_Index ? Error on Index (lower value)
55 A1 --- n_Index [e] e: Photon index was unconstrained
57- 62 F6.1 10-14W/m2 ECF Conversion from XRT measured count rate to
0.3-10keV observed flux
64- 67 F4.2 --- PSPC Conversion from XRT measured count rate to
that expected in the ROSAT PSPC
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Trigger IceCube trigger field number
4 I1 --- Source Source number within the trigger field
6- 31 A26 --- Simbad Simbad match source name
33- 35 F3.1 arcsec DS ? Distance to Simbad match
38- 60 A23 --- X-ray X-ray match source name
62- 65 F4.1 arcsec DX ? Distance to X-ray match
68- 73 F6.3 10-16W/m2 FX ? X-ray 0.3-10keV flux (1)
75- 80 F6.3 10-16W/m2 E_FX ? Error on FX (upper value)
82- 87 F6.3 10-16W/m2 e_FX ? Error on FX (lower value)
--------------------------------------------------------------------------------
Note (1): For ROSAT objects, this is the catalogued count rate, converted to
0.3-10keV flux using the conversion from Table 2; for other sources it is the
catalogued flux, which is already in the 0.3-10keV band (1SXPS sources) or
the similar 0.2-12keV band (XMM sources).
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 04-Sep-2015