# Properties

 Label 961.a.923521.1 Conductor $961$ Discriminant $923521$ Mordell-Weil group $$\Z/{5}\Z$$ Sato-Tate group $\mathrm{SU}(2)\times\mathrm{SU}(2)$ $$\End(J_{\overline{\Q}}) \otimes \R$$ $$\R \times \R$$ $$\End(J_{\overline{\Q}}) \otimes \Q$$ $$\mathsf{RM}$$ $$\End(J) \otimes \Q$$ $$\mathsf{RM}$$ $$\overline{\Q}$$-simple yes $$\mathrm{GL}_2$$-type yes

# Related objects

Show commands: Magma / SageMath

This is a model for the modular curve $X_0(31)$.

## Simplified equation

 $y^2 + (x^3 + x^2 + 1)y = -5x^4 + 4x^3 + 3x^2 - 2x - 3$ (homogenize, simplify) $y^2 + (x^3 + x^2z + z^3)y = -5x^4z^2 + 4x^3z^3 + 3x^2z^4 - 2xz^5 - 3z^6$ (dehomogenize, simplify) $y^2 = x^6 + 2x^5 - 19x^4 + 18x^3 + 14x^2 - 8x - 11$ (homogenize, minimize)

sage: R.<x> = PolynomialRing(QQ); C = HyperellipticCurve(R([-3, -2, 3, 4, -5]), R([1, 0, 1, 1]));

magma: R<x> := PolynomialRing(Rationals()); C := HyperellipticCurve(R![-3, -2, 3, 4, -5], R![1, 0, 1, 1]);

sage: X = HyperellipticCurve(R([-11, -8, 14, 18, -19, 2, 1]))

magma: X,pi:= SimplifiedModel(C);

## Invariants

 Conductor: $$N$$ $$=$$ $$961$$ $$=$$ $$31^{2}$$ magma: Conductor(LSeries(C)); Factorization($1); Discriminant: $$\Delta$$ $$=$$ $$923521$$ $$=$$ $$31^{4}$$ magma: Discriminant(C); Factorization(Integers()!$1);

### G2 invariants

 $$I_2$$ $$=$$ $$4100$$ $$=$$ $$2^{2} \cdot 5^{2} \cdot 41$$ $$I_4$$ $$=$$ $$78961$$ $$=$$ $$281^{2}$$ $$I_6$$ $$=$$ $$94151689$$ $$=$$ $$94151689$$ $$I_{10}$$ $$=$$ $$118210688$$ $$=$$ $$2^{7} \cdot 31^{4}$$ $$J_2$$ $$=$$ $$1025$$ $$=$$ $$5^{2} \cdot 41$$ $$J_4$$ $$=$$ $$40486$$ $$=$$ $$2 \cdot 31 \cdot 653$$ $$J_6$$ $$=$$ $$2121888$$ $$=$$ $$2^{5} \cdot 3 \cdot 23 \cdot 31^{2}$$ $$J_8$$ $$=$$ $$133954751$$ $$=$$ $$7 \cdot 31^{2} \cdot 19913$$ $$J_{10}$$ $$=$$ $$923521$$ $$=$$ $$31^{4}$$ $$g_1$$ $$=$$ $$1131408212890625/923521$$ $$g_2$$ $$=$$ $$1406419156250/29791$$ $$g_3$$ $$=$$ $$2319780000/961$$

sage: C.igusa_clebsch_invariants(); [factor(a) for a in _]

magma: IgusaClebschInvariants(C); IgusaInvariants(C); G2Invariants(C);

## Automorphism group

 $$\mathrm{Aut}(X)$$ $$\simeq$$ $C_2$ magma: AutomorphismGroup(C); IdentifyGroup($1); $$\mathrm{Aut}(X_{\overline{\Q}})$$ $$\simeq$$$C_2$magma: AutomorphismGroup(ChangeRing(C,AlgebraicClosure(Rationals()))); IdentifyGroup($1);

## Rational points

All points: $$(1 : 0 : 0),\, (1 : -1 : 0)$$
All points: $$(1 : 0 : 0),\, (1 : -1 : 0)$$
All points: $$(1 : -1 : 0),\, (1 : 1 : 0)$$

magma: [C![1,-1,0],C![1,0,0]]; // minimal model

magma: [C![1,-1,0],C![1,1,0]]; // simplified model

Number of rational Weierstrass points: $$0$$

magma: #Roots(HyperellipticPolynomials(SimplifiedModel(C)));

This curve is locally solvable everywhere.

magma: f,h:=HyperellipticPolynomials(C); g:=4*f+h^2; HasPointsEverywhereLocally(g,2) and (#Roots(ChangeRing(g,RealField())) gt 0 or LeadingCoefficient(g) gt 0);

## Mordell-Weil group of the Jacobian

Group structure: $$\Z/{5}\Z$$

magma: MordellWeilGroupGenus2(Jacobian(C));

Generator $D_0$ Height Order
$$D_0 - (1 : -1 : 0) - (1 : 0 : 0)$$ $$x^2 - 3xz + 3z^2$$ $$=$$ $$0,$$ $$y$$ $$=$$ $$-4xz^2 + 2z^3$$ $$0$$ $$5$$
Generator $D_0$ Height Order
$$D_0 - (1 : -1 : 0) - (1 : 0 : 0)$$ $$x^2 - 3xz + 3z^2$$ $$=$$ $$0,$$ $$y$$ $$=$$ $$-4xz^2 + 2z^3$$ $$0$$ $$5$$
Generator $D_0$ Height Order
$$D_0 - (1 : -1 : 0) - (1 : 1 : 0)$$ $$x^2 - 3xz + 3z^2$$ $$=$$ $$0,$$ $$y$$ $$=$$ $$x^3 + x^2z - 8xz^2 + 5z^3$$ $$0$$ $$5$$

## BSD invariants

 Hasse-Weil conjecture: verified Analytic rank: $$0$$ Mordell-Weil rank: $$0$$ 2-Selmer rank: $$0$$ Regulator: $$1$$ Real period: $$2.246438$$ Tamagawa product: $$5$$ Torsion order: $$5$$ Leading coefficient: $$0.449287$$ Analytic order of Ш: $$1$$   (rounded) Order of Ш: square

## Local invariants

Prime ord($$N$$) ord($$\Delta$$) Tamagawa L-factor Cluster picture
$$31$$ $$2$$ $$4$$ $$5$$ $$( 1 - T )^{2}$$

## Galois representations

For primes $\ell \ge 5$ the Galois representation data has not been computed for this curve since it is not generic.

For primes $\ell \le 3$, the image of the mod-$\ell$ Galois representation is listed in the table below, whenever it is not all of $\GSp(4,\F_\ell)$.

Prime $$\ell$$ mod-$$\ell$$ image Is torsion prime?
$$2$$ 2.120.2 no
$$3$$ 3.72.2 no

## Sato-Tate group

 $$\mathrm{ST}$$ $$\simeq$$ $\mathrm{SU}(2)\times\mathrm{SU}(2)$ $$\mathrm{ST}^0$$ $$\simeq$$ $$\mathrm{SU}(2)\times\mathrm{SU}(2)$$

## Decomposition of the Jacobian

Simple over $$\overline{\Q}$$

magma: HeuristicDecompositionFactors(C);

## Endomorphisms of the Jacobian

Of $$\GL_2$$-type over $$\Q$$

Endomorphism ring over $$\Q$$:

 $$\End (J_{})$$ $$\simeq$$ $$\Z [\frac{1 + \sqrt{5}}{2}]$$ $$\End (J_{}) \otimes \Q$$ $$\simeq$$ $$\Q(\sqrt{5})$$ $$\End (J_{}) \otimes \R$$ $$\simeq$$ $$\R \times \R$$

All $$\overline{\Q}$$-endomorphisms of the Jacobian are defined over $$\Q$$.

magma: //Please install CHIMP (https://github.com/edgarcosta/CHIMP) if you want to run this code

magma: HeuristicIsGL2(C); HeuristicEndomorphismDescription(C); HeuristicEndomorphismFieldOfDefinition(C);

magma: HeuristicIsGL2(C : Geometric := true); HeuristicEndomorphismDescription(C : Geometric := true); HeuristicEndomorphismLatticeDescription(C);