PoS(ICRC2017)1010 http://pos.sissa.it/ ∗ † G. de Wasseige [email protected] Speaker. Corresponding author: IIHE-VUB, Pleinlaan 2, 1050 Brussels, Belgium Since the end of the eightiesHomestake and experiment in in response coincidence to with a solar reported flares,solar increase solar flare in signals. the detectors Hadronic have total searched acceleration neutrino for production in flux in the in the magnetic the structures solar of atmosphere. suchand flares These leads mesons of to subsequently meson O(MeV-GeV) decay, energies. resultinggamma-ray in observations, The gamma-rays study would ofacceleration such provide process. The neutrinos, a IceCube combined Neutrino novel with Observatoryand may therefore existing window be provides sensitive a to to possibility solar to flareon the measure neutrinos the the underlying solar signal flare or physics neutrino establishcoming more flux. of stringent from We upper transient present the limits events. an originalsolar Combining search flare a dedicated events, time to this profile low research energy analysisthreshold represents neutrinos of and a IceCube, new an which approach optimized is allowing selection initially to foreseen of strongly to lower detect the TeV neutrinos. energy ∗ Copyright owned by the author(s) under the terms of the Creative Commons http://icecube.wisc.edu/collaboration/authors/icrc17_icecube c Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). 35th International Conference 10-20 July, 2017 Bexco, Busan, Korea The IceCube Collaboration E-mail: † Search for GeV neutrinos associated withflares solar with IceCube PoS(ICRC2017)1010 ]. 10 ]. In (1.1) , 2 ]. The 9 14 volume. µ µ G. de Wasseige ¯ 3 ν ν respectively. + + e e α ¯ ν ν + + − + e e −→ −→ − + µ µ ; ; ] performed several studies. Using µ µ 4 ¯ ν ν + + ] and the spin-dependent WIMP-nucleon − + 13 γ µ µ 2 introduces a new event selection lowering the 2 −→ −→ ]. J.N. Bahcall predicted that if this increase were −→ 1 1 ] and SNO [ 0 − + 3 π π π ; ; ; ]. When a neutrino interacts in the neighborhood of the X X X 11 + + + ], the IceCube collaboration has set several noteworthy lim- + − 0 12 π π π      −→ α ]. Injected downwards from the coronal acceleration region, protons can + ]), this neutrino flux extends from MeV up to a few GeV. Neutrino facilities 5 p 8 , this selection allows IceCube to be sensitive to astrophysical transient events , 4 7 or , 6 p ] as well as competitive measurements of parameters [ . 4 + 15 p where the energy thresholds are 280 MeV and 180 MeV for p-p and p- Due to their hadronic origin, solar flare neutrinos are of great interest for investigating proton Originally dedicated to observe TeV neutrinos, IceCube has demonstrated the ability to extend The IceCube Neutrino Observatory is a cubic-kilometer installed in the ice Solar flares convert magnetic energy into plasma heating and kinetic energy of charged par- 1.1 In 1988, the Homestake experiment reported an increase in the total number of neutrino events, acceleration and the subsequentstudies interactions (see e.g. in [ the chromosphere. As demonstrated in several cross section [ its sensitivity to a larger energyfirst range astrophysical by neutrinos the in use 2013 of [ DeepCore. Indeed, since the observation of the A lower energy infill, the DeepCorespacing subarray, includes between 8 its densely instrumented optical strings modules withm (7 smaller in m average versus versus 125 17 m m in in IceCube) [ the IceCube strings) and its strings (72 its on, among others, the existence of sterile neutrinos [ at the geographic South Pole between depths of 1450 m and 2450 m, completed in 2010 [ threshold of IceCube downdescribed to in Section the GeV level. Combined with a dedicated time profile analysis 2. The IceCube Neutrino Observatory: from TeV to GeV detector, the subsequent electromagnetic and/or hadronic cascadebe emit detected Cherenkov by photons one that or can several of the 5160 optical modules distributed over the 1 km sensitive to this energy regimeconstraints could on open e.g. a the new proton windowwe spectral on index, will solar as focus flare it is physics on shownthe and the in neutrino provide these IceCube new spectrum proceedings. Neutrino from In Telescope solar the and flares. following, its Section sensitivity to the high energysuch part as of solar flares. The potentialend physics of reach Section when applying this combination is described at the response, experiments such as Kamiokande [ interact with the dense plasmaEq. in the lower solar atmosphere through the processes indicated in indeed due to solar flares, it would lead to large characteristic signals in neutrino detectors [ potentially correlated with energetic solar flares [ ticles such as protons [ Search for GeV neutrinos associated with solar flares with IceCube 1. Introduction different solar flare samples andsignal analyses, seen the by experiments Homestake. were not able to confirm the potential PoS(ICRC2017)1010 ], ex- 10 s. G. de Wasseige µ 1 ± (c) Detector noise event filter (FSS). The LowUp filter has been 2 fulfill the conditions to pass the running filters [ Full-Sky-Starting time window are required to define an "event". Furthermore, s did not (b) GeV neutrino interaction , respectively, show the well-known "Ernie" event in the PeV µ ]. 1c 5 . 18 , and 17 , the main difference between TeV and GeV neutrino interactions is the , 1a 1 16 within a 2 1 while 1b filter (LowUp) and/or the (a) PeV neutrino interaction At least two hit DOMs in a next- or next-to near neighbor vertical span in a time window of As illustrated in Fig. The event selection presented here is optimized for neutrino interactions happening in the The work presented in these proceedings will demonstrate a new selection capable of ex- Low-up 1 cept for the DeepCore Filter andthe either of two additional filtersdesigned dedicated to to low-energy target neutrinos: low-energy neutrinosparts coming of the from detector the as veto Northern forfrom sky incoming all muon while directions. events, the allowing to This FSS search resultsfrom for filter the in low-energy uses neutrinos original a rate significant of reduction 1400 of Hz the to 15 number Hz of – atmospheric while muons retaining – more than 98% of signal events. DeepCore volume. A softercrease trigger the sensitivity condition to is lower neutrino implementedCoincidence energies. (HLC) in Three hit this optical subdetector modules in satisfying a order Hard to Local in- amount of light emitted in theeliminates ice. neutrinos and Putting remaining strong muons constraints with onbetween an the IceCube energy number strings exceeding of 5 (i.e. optical GeV. modules A strings72 hit distinction m with is average a spacing) made to spacing optimize of theof 125 selection causally of m) connected DeepCore and events. optical DeepCore An modules, strings upperinteraction, i.e. limit (i.e. further on the helps the with to DOMs number a select that low havecascade energy likely or events. observed A a the GeV short same neutrino track interaction physics emitting produces light a small close to the interaction vertex, resulting in a small number Figure 1: Examples of neutrino interactionsis as seen illustrated in in IceCube. A typical GeV neutrino interaction tending the sensitivity toties/experiments neutrino to define energies a around time 1 windowstudy of GeV astrophysical interest. transient as With events these down well two to as tools, GeV IceCube scales. the will use be able of to external3. facili- Selection of GeV events range and a detector-noise event (see the text for more details). collaboration has also joined theevents worldwide in multimessenger our Universe effort [ studying the highest energetic Search for GeV neutrinos associated with solar flares with IceCube the sample only contains events that PoS(ICRC2017)1010 spectrum 2 − G. de Wasseige ]. About 6 Hz ) 19 FSS and/or ] with a generic E 20 [ LowUp + ( Genie 3 6 7 10 . Passing condition ≥ DeepCore or DeepCore ≤ ≤ ≤ 1 3 Variable HLC-DOMS Passing filters in IceCube strings causally connected Trigger N in DeepCore strings shows the rate, smoothed with a low pass filter, for three periods of time 2 DOMS N HLC-DOMS HLC-DOMS N N The actual sensitivity of this event selection to astrophysical transient events depends on the Events which have hits that are causally connected are kept, while events containing many After the event selection described above, the data rate is around 0.2 Hz while more than 50% Even if this rate is still substantially larger than the expectation of atmospheric neutrinos, Besides high energy muons and neutrinos that could still contaminate the low energy event characteristics of the event classspecific framework itself. that allows IceCube In to the be next sensitive in section, the we GeV energy focus range. on solar flares, defining a occurring in 2011-2013. Even thoughthe Poissonian rate is fluctuations constant are along present, the the seasons overall and behavior the of years. non-causally connected hits are removed. Thespeed causality - between two i.e. hits is the statedconsistent if distance with their the between effective speed the of light tworate in hits of ice. detector divided Applying noise by the events, from causality the 15 condition time Hz significantly separation to reduces 0.2 the between3.2 Hz. them Rate - and is detector stability of the neutrino interactions below 5 GeV generated with estimated to occur at the mHzan level, event-stacking the analysis. selection The is sensitivity sensitiveselection depends both is to on applied. single the Fig. transient stability events of as the for detector once the event of pure noise survives the selectionsample. described It above, is being therefore the important dominant to contribution minimize of this the contribution. event pass the selection. of causally connected DOMs. A summarya of GeV-like neutrino the interaction conditions is required listed for in an Table event to be selected as sample, pure detector noise events maysimulation trigger of DeepCore noise and in pass the the detectorgers above helps caused selection. to by A estimate detector detailed the noise, potentialthermal hereafter contamination noise, of referred uncorrelated accidental to trig- radioactive as noise, "noise and events". correlated These scintillation include noise uncorrelated [ 3.1 Minimizing the contribution of pure noise events Search for GeV neutrinos associated with solar flares with IceCube Table 1: Summary ofinteraction. the conditions required for an event to be selected as a GeV-like neutrino PoS(ICRC2017)1010 ] allows 22 ]. The long 23 G. de Wasseige ]. Furthermore, 23 4 ], one can select solar flares with high probability 21 These proceedings focus on an observed event on March 7th, 2012, for which the Fermi-LAT It is also interesting to note that Fermi-LAT has been able to detect the impulsive phase in The work presented in these proceedings uses the event selection described above to search for the Fermi collaboration could realize a spectral analysis of the impulsive phase. One can then instrument was able to detect both the impulsive and long duration emissions [ duration emissions, on the contrary,spread show of a the softer gamma-ray proton emission spectralevents over of index several the (between hours. last 4 Focusing solar and on cyclewith 6) the solar therefore and flares. impulsive increases a phase the of chance bright of a neutrino detection in coincidence of pion production in order tochannel optimize through this the search decay for of neutrinos. pions,neously. gamma-rays Due Therefore, and to using neutrinos their are observations common expected from production to gamma-ray be detectors emitted such simulta- as Fermi-LAT [ some of the latest solar flare events.at These half-maximum, impulsive phases narrowing are down characterized the byanalysis a neutrino of small the search full-width gamma rays window detected to duringspectrum, a these short with few phases a minutes. reveals spectral a relatively index Moreover, hard around initial the proton 3, as well as an enhanced gamma ray yield [ one to define solar flare eventssearch. of interest as well as precise time windows for an optimal neutrino Figure 2: Detector rate usingdifferent a periods of 10 the s year smoothingunblinding in and issues 2011 an with (red), order future 2012 3 transient (yellow) low-passof searches and butterworth the using 2013 filter. the data (blue) Three same are has event0.22 shown. been selection, Hz To the (2011), omitted. prevent 0.20 absolute Hz time Even (2012) and though 0.20 there Hz (2013), are are Poissonian consistent with fluctuations, each4. the other. mean Solar flare values, application neutrinos from solar flares. As described in [ Search for GeV neutrinos associated with solar flares with IceCube PoS(ICRC2017)1010 2 G. de Wasseige ]. ]). While an exponen- 0.1026 0.1026 341404 341404 0.08654 0.08654 21 htemphtemp 25 , 3 Entries Entries Mean Mean Std Dev Std Dev 26 = 7GeV = 3GeV . max max represents the spectral index and 3 E E δ 2.5 Neutrino energy (GeV) 2 5 ], using the proton spectral index extracted from 24 ] for this particular event, one can estimate the cor- 1.5 , illustrates these numbers together with the number of 6 23 4 1 0.5 , where A is a normalisation constant, ) E 7 GeV (3 GeV). A higher cutoff value leads to a higher neutrino yield in the − 0 7 3 4 5 6 2 = − − − − − −

max

10 10 10 10 10 10 yield per injected proton injected per yield Average ν E max ( E shows the expected number of events passing the event selection described in Section H 2 δ − , where the blue (orange) points show the average neutrino yield per injected proton with 3 AE is the upper cutoff. The effect of this upper cutoff on the subsequent neutrino flux is illustrated Table These proceedings describe a new event selection that allows the IceCube telescope to be Following the method described in [ = = 3.2 and max φ d dE tially falling spectrum couldin be order present to after be this conservative on cutoff, the we expected use neutrino here flux.E a The Heaviside proton step flux function isin therefore Fig. defined as for different upper cutoff values. Fig. gamma ray observations byresponding Fermi-LAT [ numbers of neutrino interactionsthe detectable proton by spectrum IceCube. has A been potential discussed upper in cutoff several of studies (see e.g. [ δ events required for a 1–, 3–,experiment. and 5–sigma deviation IceCube from the has backgroundstrength the expectation of in potential the a signal counting to detected during findfor this a the solar brightest flare. signal solar The or flare same events procedure constrain from can the this and 24th will upper solar be cycle cutoff repeated listed using in [ the energy range targeted by the event selection described in Section 5. Summary Figure 3: Average neutrino yield perof injected proton 7 with GeV a (blue) spectral and index 3energy of range GeV 3.2 targeted and (orange). by a A the upper higher event cutoff selection cutoff presented value in leads this to work. a higher neutrinodefine yield the in optimal the time window usingin gamma-rays this with way an on energy the greater energy than rangefirst 500 where 20 MeV, the minutes focusing selection of defined the above March is 7th, sensitive. 2012 In event the as following, detected the by Fermi-LAT will be considered. Search for GeV neutrinos associated with solar flares with IceCube PoS(ICRC2017)1010 2 ]. 23 G. de Wasseige 16 ± 0.3 + Bkg 0.4 + Bkg 0.7 + Bkg ± ± ± 264 19.5 43.2 94.3 6 Expected number of events in IceCube 3 GeV 5 GeV 7 GeV , IceCube has e.g. the potential to constrain this upper cutoff using the strength 4 Bkg = No signal (2011) Value of the upper cutoff of the observed signal. sensitive to GeV neutrinos, andevents, therefore such perform low-energy as searches solar for flaresachieved astrophysical or by transient the gamma-ray use bursts. of electromagnetic observations Thissearches. to sensitivity define to the An optimal low time application energy window for2012, neutrinos to neutrino can was solar be presented. flare events, Inevents and the of framework especially interest of as to solar well the flares,spectral as bright index the the derived event optimal from Fermi-LAT the instrument of time Fermi-LAT observations, window can Marchabove the for define number 7th, selection a the of has neutrino events been expected search. to established pass Assumingillustrated as the in the a Fig. proton function of the upper cutoff of the proton spectrum. As Figure 4: Comparison of7th, the 2012 expected and number the required of number eventsexpectation of in in events a IceCube for counting a for experiment. 1–, the 3–, solar and 5–sigma flare deviation of from March background For comparison, the last line shows the background expectation. for different values ofspectral the index upper of cutoff. 3.2, averaged These and derived numbers from have observations been of obtained the March assuming 7th, a 2012 proton event [ Search for GeV neutrinos associated with solar flares with IceCube Table 2: Expected number of solar flare neutrino events passing the selection described in Section PoS(ICRC2017)1010 G. de Wasseige (2016), 071801. (2017) 30. (2006) 155. (2017), 146. (2016) 161. 92 117 26 (2012) 615. 77 908 35 (2013) 1242856. (2017), P03012. 342 12 (these proceedings). (2016). 7 JINST Science (2014) 15. , Astropart. Phys. , Phys. Rev. Lett. , Eur. Phys. J. C , Astropart.Phys. , Nucl. Phys. B (2013) 56. (2009) 2461. 787 , Astropart. Phys. et al. et al. et al. et al. et al. et al. (2009) 1071. (2014) 1. (2014) 20. 45 40 et al. (1988) 2653. 55 et al. 697 789 61 (2011) 5. (1988) 2650. (1976) 151. Collaboration, Moriond EW (2016). arXiv:1606.00681 158 61 49 (1996) 284. PoS(ICRC2017)1007 48 (2004) 045. IceCube PoS(ICRC2015)1049 , Astropart. Phys. , (2015) arXiv:1505.05837 [astro-ph.HE]. , , Astrophys. Journ. , Il Nuevo Cimento 14C (1991) 4. , Astrophys. J. , Sol.Phys. 0406 , Astropart. Phys. , Phys. Rev. Lett. et al. et al. et al. et al. et al. , Astrophys. Journ. et al. et al. et al. et al. et al. Collaboration, A. Achterberg Collaboration, M. G. Aartsen Collaboration, R. Abbasi Collaboration, M. G. Aartsen Collaboration, Collaboration, M. G. Aartsen Collaboration, M. G. Aartsen Collaboration,M. G. Aartsen Collaboration, M. G. Aartsen [astro-ph.HE]. IceCube IceCube IceCube IceCube IceCube IceCube IceCube IceCube IceCube [4] B. Aharmim [5] H.S. Hudson, Space Sci.[6] Rev. G. de Wasseige for the [7] D. Fargion, JHEP [8] G.E. Kocharov [9] [3] K.S. Hirata [2] J.N. Bahcall, Phys. Rev. Lett. [1] R. Davis, Nucl. Phys. B [21] G. de Wasseige [22] W. B. Atwood [23] M. Ajello [25] Dj. Heristchi [26] M. Ackermann [24] G. de Wasseige [19] M. Larson, Ph.D thesis,[20] University ofC. Alabama, Andreopoulos, Tuscaloosa Acta (2013). Phys. Polon. B Search for GeV neutrinos associated with solar flares with IceCube References [10] [11] [18] [17] [12] [13] [14] [15] [16] M. W. E. Smith