An Interacting Molecular Cloud Scenario for Production of Gamma

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Rossi the by discovered was eua[,7.Tesz fteA 13.-65i -asis x-rays in J1838.0-0655 J1837 AX HESS the of the size than The smaller 7]. [6, nebula atce ntesronigmdu.Teoii fGeV-TeV of J1837 MAGIC origin from The rays medium. gamma surrounding ener high the of in diffusion particles the as interpreted generally are which bevdgmary ietyfo ESJ1837 HESS the from cos- explain directly to same required gamma-rays the is observed which with spectrum Secondly, production with ray rays mic matter. cosmic (proton) accelerated ambient SNR the PWN/ the of interactions nteliterature. the in h pcrlbhvo fosre am-asfo h HESS the whether from examine J1837 gamma-rays to observed of like behavior would spectral we the First, follows: as are work ossetyepanteosre MSDfo h sources the can from one SED J1837 whether EM MAGIC explore observed to the explain like consistently would we G24.7+0.6, SNR ntevcnt fPNHS J1837 HESS PWN of vicinity the in fcsi-a-luiae lu neatn ihtePWN the with J1837 interacting HESS cloud cosmic-ray-illuminated of rnsfo h W/N n urudn oeua clouds molecular surrounding and esti neu- PWN/SNR numerical and the the gamma-rays from 3, produced trinos hadronically sect. of In fluxes section. mated same the in estimated ore n usqetysuyterdtcinlikelihood observatories. neutrino detection present/upcoming their state the study the subsequently all from and fluxes sources neutrino corresponding the termine n usqetymse ftergosudrtesuyas- study the under regions J1835 the MAGIC distributions suming of gas masses The subsequently PWN/SNR. and the molecular with the interacting and PWN/SNR cloud the from gamma- fluxes the neutrino evaluating and for ray methodology the describe shall we te w ore,MGCJ1835 MAGIC sources, two other ne h icmtne,temi betvso h present the of objectives main the circumstances, the Under h lno h ae stefloig ntenx section, next the In following: the is paper the of plan The 37 − rilsi h N 2.+./PNHESS PWN G24.7+0.6/ SNR the in articles − 6 n N 2.+. a eepandb hadronic by explained be can G24.7+0.6 SNR and 069 hl ute eosrt htteobserved the that demonstrate further shall esalso htteosre gamma-rays observed the that show shall we tne ore nteglci ln nthe in plane galactic the in sources xtended 6 hudb eetdb cCb Gen-2 IceCube by detected be should 069 rytlsoe.Tesuyo e neutrino TeV of study The telescopes. -ray mary n etio rmMAGIC from neutrinos and amma-rays J1837 S t egl iiui741,India 734013, Siliguri Bengal, rth − − 6/N 2.+..W ol iet de- to like would We G24.7+0.6. 069/SNR − † 073 7 n AI J1835 MAGIC and 073 − 6 a eetderirb the by earlier detected was 069 − − 6,adMGCJ1837 MAGIC and 069, 6 sitrrtda usrwind pulsar a as interpreted is 069 − − 6 bevdi am rays gamma in observed 069 6 n MAGIC and 069 − − 7 ss a o discussed not far so is 073 7.N such No 073. wycosmic- away − 6/N 2.+. are G24.7+0.6 069/SNR − 6.We 069. − 6 ihascenario a with 069 − 7 located 073 − 6 and 069 es, gy by at d - 2 over the GeV to TeV energy range along with the observations. density of finding a cosmic ray particle at a given radius A The findings of the present work will be discussed in Sect. 4 from a PWN/SNR for an impulsive injection spectrum, after and we shall conclude finally in the same section. including the energy loss due to hadronic ??−interaction of cosmic rays in PWN/SNR, can be written as [14, 18, 19]

1 II. THE GAMMA RAYS AND NEUTRINOS PRODUCTION %( ,A,C) = exp(−( U − 1)C/g − (A/A )2) (4) ? 3/2 3 ? ? 38 5 METHODOLOGY c A38 5

where C denotes the age of the supernova explosion/PWN, The production spectrum of cosmic rays at PWN/SNR can g = = 2:f stands for represents the cosmic ray en- be represented by a power law and is given by ?? ?? ergy loss time-scale due to hadromic interaction of cos- 3= ? = −U mic rays with ambient matter of the PWN/SNR, : ∼ 0.45 ? . (1) 3 ? denotes the inelasticity of the interaction, and f?? [9] being the interaction cross-section [19]. Here, A38 5 = where U is the spectral index, is the energy of the cos- ? 2 C[exp(CX/g )− 1]/[CX/g ] is the radius of the sphere mic rays. The normalization constant is related with the ?? ?? up to which the cosmic ray particles have time to travel after supernova explosion energy via the relation [8] p B= their injection [19]. Therefore, the intensity of cosmic rays at ?,<0G 3=? a distance A from the source can be written as [10] bB= = ? 3 ? (2) ¹ 3 ? ′ ?,<8= 3=? 3=? (A, C) = %( ?,A,C) (5) where b denotes the efficiency of supernova explosion energy 3 ? 3 ? into cosmic rays, ?,<8= and ?,<0G represents the minimum and maximum energies of accelerated cosmic ray protons. where it is assumed that cosmic rays are diffusing from a point The high energy gamma-ray flux from the PWN/SNR can source. be explainedby the interactionof the shock acceleratedcosmic To explain the MAGIC collaboration observed high energy rays with the ambient matter (protons) of density = . Such gamma-rays from the source MAGIC J1835−069 and MAGIC interaction will produce gamma-rays and neutrinos after sub- J1837−073, we consider a dense molecular cloud at the center sequent decay of neutral and charged pions respectively along of this source. The cloud is continuously illuminated by run- with the other secondary particles. Here we follow Banik & away relativistic cosmic ray particles accelerated at the nearby Bhadra (2017) [8] to estimate the differential flux of high en- SNR G24.7+0.6 or the PWN HESS J1837−069. We follow ergy gamma rays reaching the Earth from the SNR G24.7+0.6. Banik & Bhadra (2017) [8] and Banik & Bhadra (2018) [10] The corresponding flux of high energy neutrinos reaching the to find out the differential flux of high energy gamma rays Earth from the direction of the SNR can be written as and neutrinos reaching the Earth from the source MAGIC 3Φ 1 J1835−069 and MAGIC J1837−073 after their production in a ( ) = & ?? ( ) (3) a 2 a a the interaction of runaway relativistic cosmic ray particles with 3a 4c3 molecular clouds. ?? where &a (a) represents the resulting neutrino emissivity Since our objective is to examine whether the observed which can be obtained by following [9, 10] and 3 denotes the gamma raysfrom MAGICJ1835−069 and MAGIC J1837−073 distance between the PWN/SNR and the Earth. are correlated with the two known high energy gamma rays After escaped away from the PWN/SNR, the accelerated SNR/PWN of nearby regions (SNR G24.7+0.6 and HESS cosmic ray protons diffuse in the interstellar medium with a J1837−069),weexcludetheleptonicoriginscenarioofgamma = ? X rays from SNR G24.7+0.6 and HESS J1837−069. The decay diffusion coefficient given by [11] 0 ( 104+ ) where 0 represents the diffusion coefficient of accelerated protons of charged pions produced in pp interactions at the molecular at 10 GeV energy (∼ 1028 cm2s−1 in our Galactic medium) cloud region will finally lead to electrons and positrons along and X indicates a constant having value between 0.3 to 0.7 with the neutrinos. The so produced electrons will give syn- [12, 13]. However, a slow diffusion has been inferred in the chrotron photons while traveling through the magnetic field of dense gaseous medium of molecular clouds [14, 15]. The the molecular cloud. However, the density of soft photons in measurement of Boron to Carbon Flux Ratio in Cosmic Rays the cloud region (synchrotron photons) will be low because of over the rigidity extent of 1.9 GV to 2.6 TV by the Alpha the weak magnetic field of the clouds. As a result, the inverse Magnetic Spectrometer (AMS-02) on the International Space Compton process is not significant in the present scenario. Station found that X is around 0.33 [16]. Becker et al. (2016) [17] have recently demonstrated that the cosmic ray budget can be likened well for a diffusion coefficient that is close A. Gas density map around SNR G24.7+0.6/PWN HESS to ∝ 0.3 by studying 21 SNRs, those are well-studied J1837−069 from radio wavelengths up to gamma-ray energies. On the other hand, if cosmic rays originated at SNRs of the galaxy, The gas distribution map of the regions, particularly in a more powerful diffusion with X = 0.5 cannot generate the the locations of SNR G24.7+0.6, PWN HESS J1837−069, observed cosmic ray energy spectrum especially at the high- MAGIC J1835−069, and MAGIC J1837−073 is studied be- energy(TeV) componentof the spectrum[17]. The probability low considering that either MAGIC J1835−069, and MAGIC 3

1.0 = 1 − 0 emission from the carbon monoxide (CO) composite 1.0° survey [20]. We evaluate the column density of molecular hy- 0.9 = 0.8° drogen by assuming a linear relationship #2 -$ × ,$,

0.8 where ,$ represent the velocity-integrated brightness tem- 0.6°

G24.7+0.6 perature of CO 2.6-mm line [21, 22]. Here, the conversion 20 −2 −1 −1 0.7 factor, -$ is assumed to be 3 × 10 cm K km s 0.4° MAGIC J1835-069 which is consistent with the suggested conversion factor of 0.6 20 −2 −1 −1 0.2° -$ ≈ (2 − 4) × 10 cm K km s from diﬀerent ob-

0.5 servations for the molecular clouds very near to galactic plane 0.0° [20, 23]. We use the circular rotation model for the milky-way 0.4 Galaxy as given in Ranasinghe & Leahy (2018) [24] and the MAGIC J1837-073 -0.2° rotational curve data for gas velocities at diﬀerent Galacto-

0.3 (cm density Column

Galactic Latitude (degree) Latitude Galactic -0.4° centric distance [25] to correlate measured radial velocity of 0.2 gases with kinematic distance. We obtained a radial velocity −1 -0.6° of the molecular hydrogen gas about 88 km s and 31.2 km 0.1 −1 25.8° 25.6° 25.4° 25.2° 25.0° 24.8° 24.6° 24.4° 24.2° s which corresponds to 6.6 kpc and 3.5 kpc distance from Galactic Longitude (degree) us respectively. Therefore we choose a radial velocity range of E = 78 − 98kms−1 (or E = 21 − 41kms−1) to be integrated 1e22 0.8° 1.8 to determine the column density of molecular hydrogen at a distance of about 6.6 Kpc (or 3.5 Kpc) and obtained column 1.6 0.6° density map of gases are shown in the Fig. 1.

1.4 We obtain the column density of HII from the Planck ob-

0.4° ) MAGIC J1835-069 served free-free emission at 30 GeV frequency [26]. First, 1.2 0.2° we use the conversion factor at 30 GHz as given in table 3 of Planck Collaboration X 2016 [26] to convert the measured 1.0 0.0° brightness temperature into free−free intensity (a ). Then we

HESS J1837-069 0.8 follow the equation (5) in Sodroski et al. (1997) [27] to trans- MAGIC J1837-073 -0.2° form the free−free intensity into column density. To calculate 0.6 the H II columndensity, we adoptedan electrontemperatureof -0.4° Column density (cm density Column

Galactic Latitude (degree) Latitude Galactic )4 = 8000 K and the eﬀective density of electrons of =4 = 10 0.4 −3 -0.6° cm [27].

0.2 The column density of HI in the aforementioned regions is -0.8° estimated under the consideration of the optically thin limit 25.8° 25.6° 25.4° 25.2° 25.0° 24.8° 24.6° 24.4° 24.2° Galactic Longitude (degree) [21, 28] from the data cube of Galactic HI 4c survey (HI4PI) [29]. To evaluate gas column density distributions of HI, we integrated the gases over the radial velocities E = 78 − 98 km FIG. 1. 2 column density obtained from the carbon monoxide (CO) s−1 for 6.6 kpc and E = 21 − 41 km s−1 for 3.5 kpc. composite survey. Top: 2 column density of gas content integrated over the velocity interval from 21 to 41 km s−1 which corresponds to The total mass within a molecular cloud/source has been estimated from the expression [7] 3.5 kpc. Bottom: 2 column density of gas content integrated over the velocity interval from 78 to 98 km s−1 which corresponds to 6.6 " = < # 32 kpc. 8 0=6

where < represents the mass of the hydrogen atom, #8 is the column density of hydrogen in ith phase (8 ≡ 2,, ), J1837−073are at the vicinity of PWN HESS J1837−069or of 0=6 denotes to the angular area, and 3 indicates the distance SNR G24.7+0.6. of the molecular cloud/source. The interstellar molecular clouds are a complex mixture of The total mass of hydrogen gas content of the sources SNR gas at certain velocities. The major constituent of molecular G24.7+0.6 (at 3.5 kpc), HESS J1837−069 (at 6.6 kpc) and cloudsis hydrogenwhich may remainin three diﬀerentphases, two possible associated sources, i.e MAGIC J1835−069 and the neutral atomic hydrogen (HI), the ionized hydrogen (HII), MAGIC J1837−073 either at 3.5 kpc or 6.6 kpc are shown in and the molecular hydrogen (H2). The cold H2 is not directly Table I and Table II respectively. observable in emission. Carbon monoxide (CO) is widely used as tracer for H2, the intensity of rotational transition of CO relates with the abundance of H2. The column density of III. RESULTS AND DISCUSSION atomic hydrogen can be estimated straightway from the 21 cm radio frequency transition between the two hyperﬁne levels of Beforethe reportbytheMAGIC collaboration,Katsutaet al. the ground state of HI. The regions of HII is characterized by (2017) [21] carried out a study of the complex region around thermal free-free radiation and recombination lines. the SNR G24.7+0.6 with the Fermi-LAT telescope and found 12 To estimate the column density for H2, we take data for CO GeV gamma-ray emission from two elliptical extended regions 4

−8 TABLE I. The mass of the gas content in the sources at 3.5 kpc. 10 SNR G24.7+0.6 Fermi-LAT Mass of the gas content in M⊙ for CTA-1000 hr sensitivity −9 Source H2 HI HII 10 Magic-31 h sensitivity SNR G24.7+0.6 2.5 × 104 1.5 × 104 1.3 × 104 ) MAGIC J1835−069 2.3 × 104 1.1 × 104 1.2 × 104 -1 −10

.s 10 MAGIC J1837−073 1.2 × 104 4.1 × 103 5.5 × 103 -2

10−11 ) in erg.cm

TABLE II. The mass of the gas content in the sources at 6.6 kpc. ∈ ( φ ∈ d d − Mass of the gas content in M⊙ for 2 12

∈ 10

Source H2 HI HII

5 4 4 − HESS J1837−069 1.9 × 10 3.8 × 10 5.6 × 10 10 13 MAGIC J1835−069 1.1 × 105 3.7 × 104 4.3 × 104 MAGIC J1837−073 2 × 105 1.5 × 104 1.9 × 104 10−14 105 106 107 108 109 1010 1011 1012 1013 1014 log (∈) in eV G25A and G25B, each composed of three components. Note 10 that, the emission from the G25A1 component is coincident with the new source MAGIC J1835−069 detected by MAGIC [1]. In addition, throughX-ray observations of the region with FIG. 2. The estimated differential energy spectrum of gamma-rays XMM−Newton [21] found a young massive OB association/ reaching the Earth from the SNR G24.7+0.6. The red dotted line cluster, G25.18+0.26 which is proposed to be associated with represents the gamma-ray flux produced due to interaction of SNR accelerated cosmic rays with the ambient matter of the SNR. The gray the extended GeV emissions (G25A and G25B). According dotted line denotes the background gamma ray flux from the SNR due to the MAGIC collaboration the emission detected at VHE to interaction the cosmic rays galactic background with SNR material. with MAGIC is unlikely to be correlated with the OB associa- The black continuous line represents the estimated overall differential tion/ cluster G25.18+0.26 detected in X-rays as MAGIC only EM SED from the SNR G24.7+0.6. The blue dash-double-dotted and detects emission from the G25A1 component [1]. As men- brown dash-single-dotted lines represent the detection sensitivity of tioned above we have estimated high energy gamma rays to the CTA detector for 1000 hours and the MAGIC detector for 31 hour, explain the observed gamma-ray spectrum from the sources, respectively. SNR G24.7+0.6 and HESS J1837−069 in the hadronic interaction of cosmic rays with ambient matter. We have also investigated below the observed gamma-ray spectrum of the distance of the SNR, the size of the SNR has been estimated sources, MAGIC J1835−069and MAGIC J1837−073in terms to be (30.5 ± 1.7)×(15.3 ± 0.9) pc [24] and therefore mean of the hadronic interaction of cosmic rays with giant molecu- radius of the SNR will be ∼ 11.45 pc. The mean radius in the lar clouds at the centre of these sources which are illuminated 1420 MHz radio continuum image can be considered as the by the accelerated cosmic rays either from SNR G24.7+0.6 or shock wave radius '. Here we apply a basic Sedov model[37] HESS J1837−069. The estimation of gamma ray flux along and the shock wave radius in the Sedov stage can be written as with observed data and consequently corresponding predicted 1/5 highenergyneutrinofluxesfromthe said sourcesare discussed = B= 2/5 ' 12.9 C4 ?2 bellow. = −3 where = is the ambient medium (proton) density in cm units, B= is the supernova explosion energy in units of 0.75 × A. SNR G24.7+0.6 51 4 10 erg and C4 = C/10 is the age of the SNR in units of 104 year. For an age of the SNR about C ∼ 2.09 × 104 year The SNR G24.7+0.6 is a radio and gamma-ray supernova and shock wave radius ' = 11.45 pc, we can adopt a typical 51 remnant advancing in a dense medium [1, 30–34]. A recent supernova explosion energy of B= = 1.8 × 10 erg and an −3 study based on analysis of the 1420 MHz radio continuum ambient matter density of the SNR of = = 19 cm in order data, H I-line absorption spectra, and H I channel maps which to explain observed gamma-rays from the SNR G24.7+0.6. is obtained from the VLA (Very Large Array) Galactic Plane Here we have explored whether the observed high energy Survey (VGPS) [35], suggests a new distance about ∼ 3.5 ± gamma-ray spectrum from the SNR G24.7+0.6 can be inter- 0.2 kpc of the SNR from us [24]. Using the new distance (3) preted through hadronic interactions of cosmic rays (mainly measurement of the SNR [24], we have estimated the age of protons) accelerated by the SNR with the ambient (proton) the SNR to be C = 2.09 × 104 year from (32 − C relation as matter. The primarycosmic-ray productionspectrum has been given in [36] where ( (1 I) = 20 H is the observed flux obtained assuming a typical supernova explosion energy of 51 density from the SNR at 1 GHz frequency [30]. Using this B= = 1.8 × 10 erg with a spectral index of U = −2.2 and 5

−8 10 10−8 Fermi-LAT (G25A1) Fermi-LAT MAGIC J1835-069 MAGIC-J1837-073 MAGIC MAGIC −9 10 10−9 ) )

-1 − 10 -1 −10

.s 10

.s 10 -2 -2

−11 10 10−11 ) in erg.cm ) in erg.cm ∈ ∈ ( ( φ ∈ φ ∈ d d d d

− 2 12 − 10 2 12 ∈ 10 ∈

− 10 13 10−13

10−14 −14 5 6 8 9 10 13 10 10 10 107 10 10 10 1011 1012 10 1014 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 log (∈) in eV log (∈) in eV 10 10

FIG. 3. Left: The estimated gamma-ray flux reaching the Earth from the MAGIC J1835−069. The red dotted line represents the corresponding gamma-ray flux produced due to interaction of SNR accelerated cosmic rays with the molecular cloud. The gray dotted line denotes the corresponding background gamma-ray flux from MAGIC J1835−069 produced due to interaction the Cosmic rays galactic background with molecular cloud. The black continuous line represents the estimated overall differential EM SED from the MAGIC J1835−069. Right: The estimated gamma-ray flux reaching the Earth from the MAGIC J1837−073. The red dotted line represents the corresponding gamma-ray flux produced due to interaction of SNR accelerated cosmic rays with the molecular cloud. The gray dotted line denotes the corresponding background gamma-ray flux from MAGIC J1835−073 produced due to interaction the Cosmic rays galactic background with molecular cloud. The black continuous line represents the estimated overall differential EM SED from the MAGIC J1835−073. we have considered an ambient matter density of the SNR of explosion. Here we use our estimated mass of gas content −3 4 = = 19 cm as mentioned above in order to match the ob- of the SNR of ∼ 5.3 × 10 M⊙ to estimate the background served gamma-rayspectrum. We have foundthat a ∼ 10% effi- gamma-ray flux. The Model fitting parameters for observed ciency of conversion of supernova explosion energy to cosmic gamma-rays from SNR G24.7+0.6 are shown in Table III. ray (proton)energycan explainwell the observedexperimental Because of the low value of maximum energy attainable data. The estimated differential gamma-ray flux reaching the by cosmic rays in the source, the SNR G24.7+0.6 should not Earth from the SNR is displayed in the Fig. 2 along with the generate neutrinos above 1 TeV energies. observations. The MAGIC detector sensitivity for 31 hours of observation with the medium zenith angle (30◦ − 45◦) has been obtained from the MAGIC detector sensitivity for 50 MAGIC J1835−069 hours as given in [38] by assuming 1/observational-time de- pendency of the sensitivity for short observation times [38]. The gamma-ray source MAGIC J1835−069 has been de- The non-detection of gamma-rays from the SNR G24.7+0.6 tected with a peak significance of 11f and resolved from SNR by MAGIC observatory restricts the maximum energy ?,<0G G24.7+0.6 at a level of 13f for the first time [1]. Its gamma- attainable by a cosmic ray proton in the SNR shock to 1 TeV. ray spectrum is well-represented by a power-law function with Such a choice of maximum energy of cosmic rays leads our a spectral photon index of 2.74 ± 0.08 [1]. The source posi- estimation of gamma-ray flux compatible with the Fermi-LAT tions between two extended sources detected above 10 GeV observation and non-detection by the MAGIC detector (con- by Fermi-LAT, one of which is FGES J1836.5−0652 and the sidering sensitivity of 31 h for detection of a point source with otheris FGES J1834.1−0706,which are associated with HESS 5f significance) as shown in the figure. Future large-area J1837−069 and SNR G24.7+0.6 respectively. The centre of telescopes like CTA [39] and LHAASO [40], which have un- MAGIC J1835−069 is located at \ = 0.34◦ away with respect precedented sensitivity up to 100 TeV energies, should be able to the center of the radio SNR G24.7+0.6. MAGIC collab- to identify the maximum attainable energy up to which cosmic oration suggested that the detected gamma-ray emission can rays can accelerate in the supernova remnant. We have also be explained as the result of proton−proton interaction be- included the effect of background gamma-ray flux produced tween the cosmic rays accelerated by SNRs and the CO-rich due to the interaction of diffuse cosmic rays in the galaxy with surrounding [1]. the matter spread over by the progenitor star after a supernova To explain the observed high gamma-ray spectrum from 6 the unknown source MAGIC J1835−069, we have consid- TABLE III. Model fitting parameters for observed gamma-rays and ered MAGIC J1835−069 as a giant molecular cloud that is predicted neutrino flux from SNR G24.7+0.6 and as well as HESS illuminated by the runaway cosmic rays accelerated in the J1837−069. SNR G24.7+0.6. Here we have taken the distance of MAGIC J1835−069 from the SNR G24.7+0.6 as A = 30 pc follow- Parameters SNR G24.7+0.6 HESS J1837−069 ing the MAGIC observation. Here we take the mass of the 3 (in kpc) 3.5 6.6 4 51 51 molecular cloud MAGIC J1835−069 4.6 × 10 M⊙ which is B= (in erg) 1.8 × 10 3 × 10 ′ estimated considering the source distance at 3.5 kpc to explain ?,<0G (in TeV) 1 70 gamma-ray observations. b 10% 10% The high energy cosmic rays accelerated in a DSA mech- U −2.2 −1.9 −3 anism at the shock front of the SNR G24.7+0.6 may escape = (in cm ) 19 8.7 4 4 and finally interact hadronically with the matter (dominantly C (inyr) 2.09 × 10 2.3 × 10 protons) of molecular cloud MAGIC J1835−069 after a dif- fusive propagation over a distance of A. Consequently, such hadronicinteraction will produce high energygamma-raysand the order of 1051 ergs which satisfies the required energy bud- neutrinos from the molecular cloud after subsequent decays of get to interpret the observedradiations in hadronicinteractions neutral and charged pions. The estimated differential gamma- of so accelerated cosmic rays. A fraction of rotational energy ray flux reaching the Earth from MAGIC J1835−069 is shown released during slowing down of pulsar can be assumed to in the left-hand panel of Fig. 3 along with the observations. accelerate cosmic ray protons extracted from the surface of = 27 2 Here we have adopted a diffusion constant of 0 10 cm the neutron star [44–46]. The accelerated primary cosmic −1 s with X = 0.33 for cosmic rays. Our findings suggest rays may interact with the ambient medium and produce high that the observed GeV-TeV gamma-rays from the location of energy gamma-rays and neutrinos. The primary cosmic-ray MAGIC J1835−069 can not be interpreted by the presented production spectrum has inferred by assuming released rota- 51 model for any reasonable fitting parameters. The present anal- tional energy of A>C = 3 × 10 erg with a spectral index of ysis thus does not support the hypothesis of possible associa- U = −1.9 using Eq. 2. Here, we consider an ambient matter − −3 tion of the unknown source MAGIC J1835 069 with the SNR density of the nebula of = = 8.7 cm to meet the observed G24.7+0.6. The possible correlation of MAGIC J1835−069 gamma-ray spectrum. We notice that the efficiency of con- with HESS J1837−069 is examined below. version of rotational energy to cosmic ray energy of b = 10% for primary cosmic ray protons can explain well the observed data. MAGIC J1837−073 The expected differentialgamma-rayflux reachingthe Earth from the PWN has presented in Fig. 4 along with the obser- The detailed production model for GeV-TeV gamma-rays vations. We find that this hadronic model can also explain from MAGIC J1837-073 (3FGL J1837.6-0717 [41]) is not the observed SED from the source considering the maximum available in the literature yet. An analysis similar to the energy attainable by a cosmic ray proton in the PWN to be MAGIC J1835−069 as reported above suggests that this un- ?,<0G = 70 TeV. As shown in Fig. 4, future telescopes like known TeV source is not associated with the SNR G24.7+0.6. e−ASTROGAM [47], CTA [39] and LHAASO [40], which The estimated differential gamma-ray flux reaching the Earth have higher sensitivity than the present generation gamma ray from MAGIC J1837−073 is shown in the right-hand panel of telescopes, should able to detect the EM SED of the source Fig. 3 along with the observationswhere we adopt the distance in a wide energy band and hence can help to identify the true of MAGIC J1835−073 from the SNR G24.7+0.6 to be A = 65 physical model that leads to its EM emission. We have also 27 2 −1 pc and a diffusion constant of 0 = 3 × 10 cm s with considered the effect of background gamma-ray flux produced X = 0.33 for cosmic rays. Here we take the mass of the molec- due to the interaction of galactic diffuse cosmic rays with the 4 ular cloud as ∼ 2.2 × 10 M⊙ which is estimated as stated matter of the PWN. The mass of the gas content for the source 5 above considering cloud distance of 3.5 kpc. is foundout to be ∼ 2.8 × 10 M⊙ which is adopted to explain the observed gamma-ray spectrum. Along with the EM SED matching by modeling, we have also reproduced the observed B. HESS J1837−069 integral gamma-ray flux above 200 GeV from the source as reported in [2] in order to precise determination of cosmic ray The H.E.S.S. Galactic Plane Survey (HGPS; [42]) in this re- production spectral index U and also the maximum attainable gion above 500 GeV shows a large and bright source, dubbed energy <0G. HESS J1837−069 [2, 43]. The source HESS J1837−069 We have also determined the neutrino flux originated due is found to be associated with a spin-down pulsar PSR to the decay of charged pions produced in the hadronic inter- J1838−065 of characteristic age C ≈ 2.3 × 104 year, surface action of cosmic rays accelerated by HESS J1837−069 with 12 dipole magnetic field B ≈ 1.9 × 10 G and pulsation period the ambient matter (proton). The expected all flavor neutrino %C ≈ 70.5 ms [5]. Using the relation given in [44, 45], we find flux reaching at the Earth from the source is shown in the that the initial period of the pulsar was about few millisecond right-hand panel of Fig. 4. We have estimated the expected only and therefore initial rotation energy of the pulsar was of muon-neutrino events in the IceCube detector from the PWN 7

− 10 8 10−8 HESS J1837-069 Fermi-LAT HESS J1837-069 IceCube-Gen2 (10 yr, δ = 0) HESS CTA-1000 hr sensitivity −9 −9 10 LHAASO-1 yr sensitivity 10 e-ASTROGAM-1 yr sensitivity ) ) -1

− -1 10 10 10−10 .s .s -2 -2

10−11 10−11 ) in erg.cm ) in erg.cm ∈ ∈ ( ( φ φ ∈ ∈ d d d d

2 −12 2 −12 ∈ 10 ∈ 10

10−13 10−13

10−14 10−14 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 log (∈) in eV log (∈) in eV 10 10

FIG. 4. Left: The estimated differential energy spectrum of gamma-rays reaching the Earth from the PWN HESS J1837−069. The red dotted line represents the gamma-ray flux produced due to the interaction of SNR accelerated cosmic rays with the ambient matter of the PWN. The gray dotted line denotes the background gamma-ray flux from the PWN due to interaction of the Cosmic rays galactic background with PWN material. The black continuous line represents the estimated overall differential EM SED from the PWN. The blue dash-double-dotted, brown dash-single-dotted, and green dash-triple-dotted lines represent the detection sensitivity of the CTA detector for 1000 hours, the LHAASO detector for one year, and e−ASTROGAM for one year, respectively. Right: The estimated neutrino flux reaching the Earth from the PWN HESS J1837−069. The red dotted line represents the corresponding all flavor neutrino flux produced due to the interaction of SNR accelerated cosmic rays with the molecular cloud. The gray dotted line denotes the corresponding background of all flavor neutrino flux from PWN HESS J1837−069 produced due to interaction of the cosmic rays galactic background with a molecular cloud. The black continuous line represents the estimated overall differential of all flavor neutrino flux from the PWN. Here blue long-dashed line indicates the sensitivity of IceCube-Gen2 to detect the neutrino flux from a point source at the celestial equator with an average significance of 5f after 10 years of observations

= 5 following [48] and it is found out to be #a` ∼ 1 event in one considered as "2; 1.9 × 10 M⊙ (estimated for a distance of year of observations above 1 TeV energies. We found that the 6.6 kpc). The estimated differential gamma-ray flux reaching estimated all flavor neutrino flux around 1 TeV energies is well the Earth from MAGIC J1835−069 produced in hadronic in- within the reach of the sensitivity of IceCube-Gen2, a future teraction of these runaway cosmic rays with molecular cloud extension of IceCube detector [49]. materials (protons) is shown in the Fig. 5 along with the observations. Our findings suggest that MAGIC J1835−069 is also unlikely to be associated with HESS J1837−069. MAGIC J1835−069

The projected distance of the gamma-ray source MAGIC MAGIC J1837−073 J1835−069 from the pulsar associated with HESS J1837−069 (for a distance of 6.6 kpc) is reported to be more than ∼ 65 pc. The energy density of escaped accelerated cosmic rays As discussed above, it is unlikely that MAGIC J1835−069 is at the position of MAGIC J1837−073 coming from HESS correlated with SNR G24.7+0.6. Here we have explored the J1837−069 can be obtained from Eq. 5 where we consider a 27 2 −1 possibility of molecular cloud origin of the observed gamma diffusion constant of 0 = 2 × 10 cm s with X = 0.33 for rays from MAGIC J1835−069, associated with the source cosmic rays. The distance of the molecular cloud from HESS HESS J1837−069. The energy density of runaway acceler- J1837−069and mass of the cloud are adopted to be 38 pc and 5 ated cosmic raysat the location of MAGIC J1835−069coming "2; = 2.3 × 10 M⊙ respectively. The estimated differential from HESS J1837−069 can be obtained from Eq. 5 consis- gamma-ray flux reaching the Earth from MAGIC J1837−073 tently where we have adopted the age of HESS J1837−069 to created in hadronic interaction of these runaway cosmic rays 4 27 be C = 2.3×10 years [5], a diffusion constantof 0 = 2×10 with molecular cloud materials (protons) is shown in the left cm2 s−1 with X = 0.33 for cosmic rays. The distance of the panel of Fig. 6 along with the Fermi-LAT and MAGIC ob- molecular cloud from HESS J1837−069is taken as 65 pc fol- servations. Our findings suggest that MAGIC J1835−073 is lowing the MAGIC observation and the mass of the cloud is likely to be associated with HESS J1837−069. 8

− 10 8 G24.7+0.6 can be interpreted in terms of hadronic interaction MAGIC J1835-069 Fermi-LAT (G25A1) oftheSNRacceleratedcosmicrayswiththeambientmatterbut MAGIC the non-detection of TeV gamma rays from the source restricts − 10 9 CTA-1000 hr sensitivity the maximum energy attainable by a cosmic ray particle in LHAASO-1 yr sensitivity e-ASTROGAM-1 yr sensitivity the source to just 1.3 TeV. Consequently, there will be no TeV )

-1 −10 neutrinos from the source.

.s 10

-2 ii) The present analysis suggests that the GeV-TeV emission of HESS J1837−069 can well be described by hadronic inter- − action of the PWN accelerated cosmic rays with the ambient 10 11 matter. The maximum energy attainable by a cosmic ray pro- ) in erg.cm ∈ (

φ ∈ toninthesourceturnsouttobe70TeVwhichcanbeveriﬁedin d d − 2 12 the future by the upcomingCTA and LHAASO detectors. The

∈ 10 estimated all flavor neutrino flux above 1 TeV energy is found to be well within the reach of the sensitivity of IceCube-Gen2, − 10 13 a future extension of IceCube detector. iii) The newly detected source MAGIC J1835−069 is unlikely to be a cosmic ray illuminated molecular cloud. The 10−14 105 106 107 108 109 1010 1011 1012 1013 1014 1015 1016 present analysis shows that the runway cosmic rays either from the SNR G24.7+0.6 or the PWN HESS J1837−069 fall log (∈) in eV 10 short to reproduce the observed TeV emission from MAGIC J1835−069 by interacting with molecular cloud at the location of MAGIC J1835−069. Instead of considering the SNR FIG. 5. Same as in left-hand panel Fig. 4 but from MAGIC J1835−069 G24.7+0.6 and MAGIC J1835−069 as a resolved separate which is investigated to be a molecular cloud associated with HESS sources recently Sun et al. [7] have considered the gamma J1837−069. ray emission from the two sources together (over an extended region) and described the observed GeV-TeV gamma rays from theregion containing SNRG24.7+0.6and MAGICJ1835−069 We have also estimated the neutrino flux originated due to by hadronic interaction of cosmic rays with ambient mat- the decay of charged pions created in the hadronic interac- ter (cloud). Since the MAGIC telescope resolved MAGIC tion of cosmic rays accelerated by HESS J1837−069 with the J1835−069 from the SNR G24.7+0.6 with high significance molecular cloud. The expected all flavor neutrino flux reach- we have here treated the stated sources separately. It may hap- ing at the Earth from the source is shown in the right-hand pen that MAGIC J1835−069 is the major part of the ejecta of panel of Fig. 6. We have estimated the corresponding ex- supernova explosion that leads to G24.7+0.6. pected muon-neutrino events in the IceCube detector from the iv) The newly detected TeV gamma ray source MAGIC SNR following[48] and it is foundout to be # = 0.21 events a` J1837−073 appears to be associated with the PWN HESS in 1 year of observations above 1 TeV energies. We found that J1837−069. The gamma ray emission from MAGIC the estimated all flavor neutrino flux around 1 TeV energies J1837−073 can well be interpreted by hadronic interactions of may be detected by IceCube-Gen2 [49]. runway cosmic rays from HESS J1837−069 with the molecular cloud at the location of MAGIC J1837−073. The flux of TeV neutrinos from the source is, however, too small to be IV. CONCLUSION detected by the present or any upcoming neutrino telescope.

On the basis of our present analysis we conclude the follow- ings: ACKNOWLEDGEMENTS i) The Fermi-LAT has detected the SNR G24.7+0.6 in the GeV energy range but the MAGIC telescope did not detect The authors would like to thank an anonymous reviewer any TeV gamma rays from the source, instead they found a for insightful comments and useful suggestions that helped us new TeV source, the MAGIC J1835−069, in the neighborhood to improve the manuscript. AB acknowledges the ﬁnancial of the SNR G24.7+0.6 resolving it from SNR G24.7+0.6 at a support from SERB (DST), Govt. of India vide approval level of 13f. TheobservedgammarayemissionfromtheSNR number CRG/2019/004944.

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−8 10−8 10

MAGIC J1837-073 Fermi-LAT MAGIC J1837-073 IceCube-Gen2 (10 yr, δ = 0) MAGIC CTA-1000 hr sensitivity −9 −9 10 LHAASO-1 yr sensitivity 10 e-ASTROGAM-1 yr sensitivity ) ) -1 − -1 −10 10 10

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FIG. 6. Same as in Fig. 4 but for MAGIC J1837−073 which is investigated to be a molecular cloud associated with HESS J1837−069.

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